Question 193: "Karl, I have a Nick Ziroli 100" wingspan SBD-Dauntless. I would like to put the Robart 7 cylinder R780 radial engine in it. What is your opinion? Thanks Chuck."
Karl: "Chuck, I couldn't think of a better engine than that one. Of course, depending on the size of the firewall/ cowling, you may or may not get away with the 215cc gas radial from RC Showcase. That one has 13 hp, is larger and heavier I suspect. The R780 will allow you to add many more scale goodies to the plane with out sacrificing performance. With 10 hp available it will get the job done for sure. It can handle up to a 32 inch prop, and is very reliable. I have it on good authority that the guys at Robart Engineering make regular upgrades to the radial that they try to incorporate into each engine, and can retrofit any existing engine should the guy want to. That is good product support if you ask me. The Dauntless is a good plane, and has plenty of documentation sources for them. Detail & Scale has magazines that do walk-arounds and history on them in combat. They are available at most hobby stores. Good luck with the build, send us some pictures of your progress, ok? Thanks, Karl"
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Question 194: "I am considering the use of the Saito 100Ti "V" Twin in a scratch built plane that will have a 72" span and target weight of 10 - 11 pounds. I haven't been able to find much information on this engine other than "sales hype". What little I have been told is that it sounds wierd ... and ... that it requires the use of an on board glow driver. Have you seen or heard anything about this engine? Any video or sound clips available? Anyone with good reliable performance information?
Thanks in advance for your help, Kevin"
Karl: "Hi Kevin and thanks for the question. To begin with, this may seem a bit blind, but I would be willing to say that anything coming from the Saito line is indeed a good thing. Which is to say the products (speaking here in the context of 4-stroke glow engines) are very reliable, rarely need repairs and make consistently good power. The 100 Ti twin is a good engine for planes in that weight range. The "wierd" sound spoken of is the unique putt-putt of a 4-stroke Saito. At a local airfield near my house there are several planes from trainers to warbirds that have Saito's for power and they are truly a neat sound. I have seen guys use only a slight push of the prop before it lights and it stays lit. Never seen one stall in flight yet. A while back you could go to www.saitoengines.com and see the whole line easily. Now if you enter that web address it takes you to Horizon Hobby and I have found this is much more inconvenient for research. No longer can you go "straight to the horse's mouth" for facts. However, the articles linked to the pages there are fairly well done and have different kinds of facts contained in them. Not a bad source for information, really. The use of the onboard glow-driver is necessary for multi-cylinder engines, not for singles. The driver helps keep the plugs hot while idling for taxiing, adjustments, what have you. In radials it is mandatory since you don't want the lower cylinders to load up, foul the plugs and cause a stall. Bad news. Try going to Saito's link site and see if they have a link yet to a video. If you buy one, you won't regret it. Hope this helps, Karl "
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Question 195: "Hi Karl. I'm building a TF giant scale P47 and considering the Supertigre G4500. The cost of the engine looks appealing, however, it looks like any benifit there may be lost quickly to the higher price of glow fuel vs gasoline. In researching it seems the most popular engine for this app is the G62. I guess my question is two part; First do you have any experiance/opinion of the ST G4500 and second am I being foolish to consider it for the reason of economy? Thanks in advance for any input you can give me, Tom"
Karl: "Thanks for the question, Tom. It doesn't sound as though you are sold on the Supertigre unit or the Zenoah unit. First, not only will the G62 be a good choice, but you can also buy a belt-driven gear reduction unit for the prop so you can fly a scale-sized prop in four blades as the P-47 flew in full-scale. If you really want scale operation with the looks, try installing a Constant Speed Prop, both of these systems are available from www.warbirdpropdrives.com and have been proven in many tests. This type of setup will allow you to maximize the power, performance and efficiency of any of the 2-stroke gassers from Zenoah, Quadra, ZDZ, etc. I like the P-47 but not as well as the Corsair, but you might even consider radial power. Saito and Techno Power make good ones, as does Robart. The Zenoah line is proven, reliable and fairly cost-effective when properly maintained. You might find that the Saito FR450R3D is the ideal engine. Sure, it costs more than the Zenoah offering but it runs smoother by design, looks much cooler and sounds better since it is a four-stroker. As for fuel costs, where I am, gas is still over $2.75 a gallon, and even when you figure in fuel-efficiency the costs may actually be a wash. See, glow fuel has lubricant in it already, for the engine internals. Gas needs to have it mixed before use, another cost. Talk to some buddies at your local airfield or hobby store, gather opinions, whatever, and do the math to see which one is suited for your particular needs. Bottom line will be what engine you really would like to use in the Jug. All things aside, that's really all it comes to. Hope this helps. Karl"
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Question 196: "I love your site, I appreciate your efforts. Here is my dilema. I bought this 1/4 Barth/proctor Waco and cant seem to find a perfect radial I can afford that will do the plane justice powerwise and also lookswise. The plane is suppose to finish around 25 pounds. I would love to know what you suggest in a radial. I have been told the Seidel 7 cylinder but they are $3000 U.S. and difficult to get, the OS FR5-300 is $1400 but I am not sure if it will be enough power. Saito makes a 3 cylinder 450 but it looks too techno-ish. In the forum RC-Universe.com I was told to put a 22x8 prop on and this should increase the static pound thrust to 32 pounds, but I dont know where this info comes from. My cowl is 10 inches wide and the manufacturer suggested a Laser 240 twin british engine. I prefer a 5 or 7 cylinder radial. Although I wont be doing insane stunts I would like to fly a few basic ones. Thanks.....Henry"
Karl: "Henry those are good questions and reflects the fact you have been doing some homework. In my humble opinion, it is flat out silly to put a large single or twin 2-stroke on the front of a 1/4 scale bipe----or any size bipe for that matter! The Saito 5 cylinder will not have enough power, you are right about that. Techno-Power has a 9 cylinder radial that looks real great but it too doesn' t have the UMPH! The Robart radial is perhaps the best glow radial out there---again, in my humble opinion---but you get one phenomenal powerplant for $4,000. Cactus Aviation offers a 5 cylinder gas radial that is nearly 16 CID and has 20 horse power. I think that is too much for this plane. Perhaps the one that is the best suited is the RCS 215 cc gas radial from RC Showcase. They have links on their site for video and audio of this engine running. It is perfect for 1/4 scale bipes, trainers, Golden Era planes, etc. It sells for $2,950 plus shipping, prop hub adapter is $22 more. Now, according to what you were telling me about your desires, needs, etc. this engine is perfect for you. The only thing is the cost. Maybe you didn't want to spend that kind of money. The RCS engine even has more manageable power at 13 or 13.5 hp. It will look perfect on the front of that plane, sound perfect and fly the same. You can even get away with a large, 2-blade ground-adjustable-pitch prop from Solo Props to make it close to the perfect flyer. Keep us posted on your choice and progress. Thanks again. Karl"
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Question 197: "Karl, I have a Zenoah G-62 that I am looking to put into a Ziroli Corsair. I have a Byron 3 blade prop, the problem is the bolt from the propeller is smaller that the engine hub. How can I make this two components compatible?Thanks for your help. Micheal"
Karl: "Hi Michael, thanks for visiting our site. The crank threads for this engine are metric, 10x1.25. The length of the crank output shaft will accomodate prop thicknesses from .50 inches to 1.25, according to the drawings. If you are satisfied with the fit of the prop--which is to say that when you slide it onto the prop shaft do you have to push firmly or lightly to fully seat it? Does it have lateral play, which is side-to-side play on the shaft. If it does, then the inside diameter of the prop is too large for the shaft. Remember, on the engine the prop mount should have a serrated rear mount flange and serrated front mount flange to grip the prop hub as you tighten the nut on the prop shaft. If you are talking about the prop retaining nut being too small this is perplexing to me since the engine should have come with the correct nut on it. If the nut is incorrect, you need to find the nut of those metric dimensions so you don't have a problem with prop retention. If you are speaking about the inside diameter of the hole in the prop, that fits over the shaft, then use a digital micrometer ( I use one of those because they are super-accurate and don't waste your time with conversions and calculations that comes with a regular type of micrometer). Using the mic, you measure the shaft diameter and drill the hole in the prop to the appropriate diameter, testing after each drilling if you find you have to change bit sizes, going up in size, until you are satisfied with the fit. If you have access to a bench-drill press, this would be ideal since you will then be able to set the prop flat and drill true to the center line so you don't have wobbling of the prop during running. I hope this helps, Michael. Thanks, Karl"
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Question 198: "I have two of the Top Flight Giant Scale Corsairs with G62's on them. Does anyone make a scale 3 Blade prop for this configuration?"
Karl: "Hi Kent, as a matter of fact, go to www.soloprops.com and see for yourself. They have done some amazing things for giant scale, flying props that are a far cry from the toothpick variety. You can even try www.warbirdpropdrives.com and see what they have to offer in constant-speed props and gear-reduction for narrow-cowl planes. Good question, thanks for visiting our site. Karl"
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Question 199: "Hi Karl, I'm building a J. Bates B-26 and trying to come up with the best engine-prop combination. The B-26 will come in at around 35lbs. I like the Saito 180 and I also like the Solo props 4 blade props. Is the Saito enough engine for both the B-26 and the 4 blade prop? thanks, Ray. "
Karl: "Hi Ray, thanks for your patience. Here is what I have to say about this engine choice. I think the Saito engines are a good choice. They can handle a 16-inch diameter prop with ease, and sound real cool. Another choice, which is somewhat unorthodox is the Saito FA200 Ti inline twin. They are around $750 a piece and have 3 hp each. The prop range goes from 16" to 18" and does real well on 15-30% synthetic fuel. Some guys use heli fuel as the mix seems to be able to make more power for their airplanes. Fuel choice is up to you, though. I don't remember if the B26 came with 3 or 4 bladed props, but in my opinion, considering the weight of the plane, and engines, you may do better to get some Solo 3-bladers and make prop adjustments for scale flight. I totally agree that the 4-blade Solo's are beautiful, but then you may be asking too much of those engines with the load you put on them. There are larger engine choices too, you just have to spec them out to see how compatible they are with that airframe. Thanks for visiting our site and I hope we helped. Karl"
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Question 200: "Dear Karl Building a Pica P5 1/5th scale, My Question is would an OS BGX 35cc, swinging an 18x10 be enough power for the plane with a weight of 22lbs. Using Robart retracts, and the Finnish will be monokote for simplicity and weight. The BGX produces 4.1 HP. and I have the engine, now I have considered the Moki 210 but that would mean buying an engine, for the sake of 5.0 HP Using a glow engine will give me the best power to weight performance as aposed to using Gas, which I have noticed a lot of these ARF Top flight, mustangs are using. Thanks William"
Karl: "Hi William. It is true that the majority of engines in ARF's of nearly any variety are glow engines. They are reasonably affordable, plentiful and you have a large number of choices available. You stated that your Pica P51 will come in around 22 lbs. You have allowed a choice between a Moki and an OS. If it were me, between those two I would choose the OS. But consider a G-38 from Zenoah. It too will swing an 18x10 prop with no problem, and since it burns regular gas it will be cleaner and kinder to your airplane's finish than glow fuel residue. In my opinion, gas engines are easier to tune, keep tuned and maintain than glow. You can even burn Coleman fuel in most of them, which is even cleaner, even in emissions. The plane I am working on is also 1/5 scale but was radial-powered in full-size form. The only radial that fits this size kit is a glow-fuel radial. There are lots of good gas radials, but too large. When I set about setting the spec's for the project, a radial engine was a must. I will have to deal with the glow fuel residue issue later I suppose. So, we know there are lots of choices with just as many consequences. If you go with the OS engine and are concerned about power, try going to an 18x12 prop just to be on the safe side. You won' t load the engine that much nor will performance suffer either. If you go with gas, the G-38 will be fine. It only costs $300. 00 as well. That will help the pocketbook, eh? Hope this helps, William. Karl"
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Question 201: "Hi Karl, I need to know ONE thing in your opinion what is the best radial engine out there. Who is the best manufacture of Radial Engines. I am looking for the best quality that I can get. Thanks for your time. Carl"
Karl: "Wow, Carl, that is a loaded question for sure. I have pondered this question for days. The difficulty experienced in assessing the answer is proportional to the quality of virtually all the radials offered, be them gas or glow. I decided to break it down into two categories; value, and quality. I am in no way attempting to hint that value is independent of quality or vice versa. Quite the contrary, you will find that the better quality a product is, often the better value it is. That said, let me define the criteria for quality.
The engine has to be made of high-quality, state-of-the-art metals and other materials. It should have aluminum in appropriate areas for weight, and relatively lower cost to manipulate. It should use high-grade steel again, where appropriate. If a chrome-moly alloy is employed, where and how much. How are things like the crankcase, cylinder head flow design, cooling capacity of the fins, lubrication system? In the ignition system, it should be simple, very reliable and trouble-free to check and operate. This includes glow-drivers as well as electronic ignition modules and all related ignition hardware. Are all the parts easily repaired or replaced? Do you have to wait six months for the manufacturer to make all materials to order or did they think ahead and build a practical number of replacement parts?
One of the last things is customer service. If you have a problem, are they willing to help with shipping if they ask for the engine back? If it is just parts, do they make it easy to return damaged or causal parts to them? Lastly, what is the service record like for people who have any of the engines you ask about? Do they have a dozen, two, a hundred flights on an engine or do they have to have it serviced once a month? This last category is perhaps, in my humble opinion, the best gauge for quality since before you make the plunge and put down hundreds or even thousands of dollars on a radial engine, you can ask people who fly them.
On value Carl, likely some will be redundant here because when you buy a radial engine, you want it to install well, not break, leak profusely, or otherwise fail to function normally. If at any time you have a problem, how much hassle the manufacturer puts you through before it is back to you in perfect condition is often the strongest indicator of value. Service records are a big deal, Carl. You don't want a lemon, so even with the advent of the internet, the net usually is a sales tool, and you still will need to ask people who fly the different ones. What the value category boils down to is how much bang-for-the-buck do you get? That is true in virtually all areas of our economy and industry in the country. Think of it this way, Carl, I find this helps me from time to time. Say you go to an auto auction. You have been looking for a particular vehicle for a while and just haven't found the one at the right price. At this auction are vehicles that are law-enforcement impounds, repo'd for non-payment, etc. All of the cars are in very good condition with low miles. Say the vehicle you search for is a used Expedition. At any used lot they go from between $9,999 and $15,000. The one you want is a 4x4 XLT. You find one at this auction for sale for $7,500 and it has lower miles than all the ones you saw at the lots. Plus it has added DVD player and screens for the kids. No strings attached, simple price, is that value? Of course it is.
Here's what the choices boil down to for me, Carl. A large portion of the RC hobby, especially warbirds, builds ARF's or kits around 1/6 scale. A slightly smaller portion build 1/5 scale, which is larger. And a real small portion build giant scale like 1/4 scale or some figure in between due to enlarged plans for the plane of choice. In the 1/6 scale arena we have the engines by Saito, TechnoPower, OS. TechnoPower, I think, has the higher number of offerings in different cylinder numbers and displacements. Next is Saito. You can't hardly beat them for reliability, Carl. Saito has at least four radials from small 3 cylinder, to a mid-sized three, a 5-cylinder and a honkin' large 3 cylinder. These are all glow engines. The choices in 1/5 scale are now joined by some gas engines and at least one larger glow engine from Robart. Going larger than that and we see a gas radial offered by RC Showcase, Cactus Aviation and one through Desert Aircraft. Go to their respective websites to see the links. For 1/6 scale, Carl, I think Saito is the best line to look at; for 1/5 scale, Robart wins my vote; and for larger than that, I think I really like the practicality of the RCS radial.
I decided to answer this way since you didn't have an aircraft in mind that you told me you were building or buying. I decided to hit as many of the scales as possible so hopefully you will have sufficient information. I am going to go out on a limb here though and admit to doing some speculating. Given the popularity, decreasing entry costs, abundance of scale details and features not only in ARF but kit form, I would say that interest in the 1/5 scale arena is growing by leaps and bounds. When you combine what I said about the 1/5 scale engines, in my opinion the best quality is the Robart engine. If all these engine manufacturers want to send me a copy of each of their engines I would be happy to do testing and make it more scientific and less speculative. Even though you may think I waffled the answer, just think of how high-quality all of these powerplants are. It is really difficult to look at all of them and determine THE best since so many are designed for different planes, scales, etc. Carl, this was a really long answer to a very tough question. I hope I answered it to your satisfaction. Let me know which one you buy, okay? Just contact me through this site. Thanks, Karl"
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Question 202: "Karl, Ive been reading with quite a bit of enthusiasm the questions and answers posted on your site. Im particularly interested in a radial engine application for a project Im working on right now, a 33% Bucker Jungmeister. Based on your recommendations to other individuals, I fear that you may laugh at my engine choice for my project as being way underpowered. The plans are from Model Airplane News, designed by Gary Allen (he competed with this plane at Top Gun in 2004). Mr. Allen recommends a Zenoah G-45 for scale flight. That big 10 open cowl just begs for a radial engine to be proudly displayed up front. I purchased the SAITO 325 R5D 5 cylinder radial for this project. The physical fit is just perfect in the cowl (although I wish it was 7 cylinders instead of 5). The engine is rated at 3.25 ci with 3.8 hp while the Zenoah G-45 is 2.74 ci with 3.3 hp. I base my powerplant choice partly on Mr. Allens power recommendations, but Ive been convinced by the article published in Model Airplane News, March 1998, pg 60-62, that for true scale flight characteristics of our models, we should pay closer attention to the full scale power to weight ratio of our subject.
The subject: Bucker Jungmeister Bu-133C, Weight: 1,290 lbs fully loaded, Powerplant: 160 hp Siemens Sh 14A-4 seven cylinder radial, power to weight ratio: 1:8.06 The model: 33% Bu-133C, Estimated final weight: 23-25 lbs According to the article by Mr. Greg Hahn, a well known and successful Top Gun scale competitor, if we look at any aircraft made, there tends to be a relatively constant power to weight ratio. WW II fighter aircraft tend to have a 1:8 ratio, while bombers and other heavy aircraft tend to run around 1:10. Its true, if you look up the physical properties of any of the WW II aircraft, they will fall very close to these power to weight ratios, everything from the light weight (relatively) Spitfire to the B-17 bombers are right on the money. We know from his Top Gun experience that Mr. Allens Jungmeister flies very scale with excellent flight characteristics using a Zenoah G-45 engine, and his all up weight was around 23-24 pounds for a 1:8 ratio.
Applying this ratio to my project, assuming Im building a little heavier, around 25 lbs, and using the 3.8 hp Saito 5 cyl, I have a ratio of 1:6.58. This should provide me with plenty of power to move this airplane around in a scale fashion and slightly beyond. What Im trying to get at here is, perhaps we tend to overpower our models quite a bit to attain unlimited vertical performance in aircraft that shouldnt have vertical. In particular, I noted your recommendation of the RCS 215 (13.5 hp) engine for a 25 lb Waco, or even the Robart radial (10 hp). Perhaps my thinking is flawed, but Im sure that most individuals will try to have a scale flying aircraft when the build a Waco, or as in my case a Jungmeister, maybe with a little power to spare. My model will come in around 25 lbs, and I cant imagine shoving a 13.5 hp or even a 10 hp powerplant up front. I an interested in your opinion on this subject and if you havent read it, I highly recommend Mr. Greg Hahns article as a reference (Im attaching a copy of this article in PDF, Adobe Acrobat, format for your review). This discussion was partly spurred on by a revival of this discussion in this months (February 2006) issue of Model Airplane News, pg 86-88. I look forward to your feedback and your suggestions for a radial engine for my Jungmeister. Regards, Mark"
Karl: "Thanks for the excellent questions, Mark. I appreciate your studious research into the oft-overlooked or at least slightly underrated issue of power-to-weight. Within reason, theoretically, you can put nearly any engine you want on the front of a plane and get it to fly. But, true to life, physics, what have you, a change in one thing begets the necessity for a proportional change in something else. Aircraft designers try to see a plane from as many angles as possible both geometrically and utility. What will the plane be used for, what altitudes will it see? What speeds? What kind of loads (payload)? That's why it takes so long, because so much of the design is based on theory. After all, who knew that a B-17 would be able to have an elevator shot off, two engines fall off and still be airworthy? Did engineers plan that? Well, I like to think they sat and tried to think of worst-case-scenarios, but reality is a whole different ball game, pal. They couldn' t possibly account for the skills and expertise of the pilot or flight crews as they fought to maintain trim in a battle-damaged plane so the designers had to build it as rugged and balanced as possible to make it easier for the men who used them and whose lives depended on them.
Ah yes, radials. In your research you didn't mention the O.S. FR5-300. It's rated at 4.0 hp., can handle up to a 22" prop and will still look scale in front. It weighs something like 96 ounces, so it really doesn't add much weight either. In my opinion here, Mark, you will find it necessary at times, to use more throttle to get out of a potentially disasterous situation than what you may be used to. In the world of muscle-cars and hot-rods, the mantra goes like this "..you can't beat cubic inches..." . In RC, when you have a plane that you want to fly scale, it usually is okay to use an engine that is slightly more powerful than what a perfect mathematical equation would tell you. Of course, the kit builder/manufacturer has engine parameters and for good reason. However, if the manufacturer says the range is between 2.5 and 3.5 hp, installing a 4.0 hp won't kill the frame, you will just have to pay attention to the integrity of the frame and balance. Besides, radials run smoother than one-lungers any day of the week due to their design. A single will shake the frame because it only has one cylinder to balance, which is done by weights. In a radial, there are multi-cylinders to balance in rotation, so it is smoother. Look into a prop with this outfit: www.soloprops.com and pick one. They are cool. Good luck on the Bucker and let us know how it turns out, okay? Karl"
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Question 203: "Hi Karl Im planning on building a Wendell Hostetler 40% Gee Bee Z this winter (already have the wood cut by Precision Cut Kits). The estimated final weight of this bird is around 35-40 lbs, and Mr. Hostetler recommends a 6-8 ci engine. I was considering using a 3W 14B2F for this project, but in further research, I wonder if the RCS 215 with 13.5 hp might not be a better choice. By my calculations using a power to weight ratio, this bird requires about 13 hp for scale flight. The Gee Bee Z has a short nose, so the extra weight of the RCS radial will probably come in handy for balancing (rather have engine weight than lead). Id appreciate your opinion on this subject and whether the RCS 215 wouldnt be too much for this Gee Bee (besides, the large open round cowl really needs a nice radial up front love those radials). Regards, Mark "
Karl: "Thanks for visiting our site, Mark. There are a few choices you have in radials. RC Showcase has two they offer, one is the 215 cc gasser, and a larger version at 400 cc. Let's start from square one first. Your intial engine choice was the 3W 140B2F twin. It is a little less than 7 1/2 lbs., is slightly more than 7" long and develops 13.5 hp. It will easily swing a 32-inch prop. Your all-up weight you project is 35-40lbs. The RCS 215 weighs in at a hefty 12.2 lbs and has 13.5 hp. It is nearly 8-inches long. As you know, engine length is measured from the mount where it contacts the firewall, to the rear flange of the prop hub. That said, you will have to ensure you have sufficient weight behind this engine to balance the CG. Worst case scenario you'll have to build the fuse heavier rather than add lead. So, you might use 1/4 light ply formers all the way from stem to stern, and perhaps beef up critical areas in the saddle and rear stab mount areas. Or, you can build per plans and add lead. Truth be known, you still may not need any weight due to the short cowl. In this man's humble opinion, this kit is begging for a radial engine. Now, I don't know what the cowl diameter is with this kit in this scale, but you may want to consider also the Robart radial. It has 10 hp, but is less than 10 inches in diameter so it may even look under sized in the cowl of the Gee Bee. Other things to consider are prop choices. I strongly recommend paying a visit to this site: www.soloprops.com and ask questions about props. They are made of maple, CNC machined then finish-sanded by hand. They have three blade config's according to them. You can have them painted flat black or natural wood with a good aerospace varnish applied. Beautiful works. Another to look at is www.warbirdpropdrives.com . They have a constant-speed prop drive system they've been working on for more than a year now. It is functional and has moved their test-bed plane to scale speeds in excess of 300 mph. Cool stuff. The reason I mention these is because you can't always bank on engine power to move an airplane. Of course, it nearly goes without saying that the closer you get to obtaining scale power-to-weight ratios, the more scale your plane will fly. In short, what you may lack in engine you can at least partly compensate for in prop. The SoloProp units are ground-adjustable-pitch, which means you set one pitch, fly the bird to see how she does, then land and readjust if needed. If my mind serves me right, the hubs adjust from 4 or 6-pitch up to 24. Huge possibilities there. I need to qualify something first, with Warbird Propdrives. Their research and development mainly has targeted planes such as P-51's, Spitfires, basically narrow-cowled and water-cooled planes. Their constant-speed prop was also developed to be used with their design of a belt-driven gear reduction for those types of planes since the prop shaft needs to be hollow to accomodate the rods and controls for the CS prop. I dialogued with the guy who runs the operation, several months ago and he was just then trying to problem-solve a set-up for radial engines to see if that was possible. In RC, it's dangerous to have a hollow prop shaft right into the crankcase. Now, they might have done it that way in real life, aka full-scale, but in those planes, if you had a prop hub failure you could at least ditch or bail. With these planes, they could careen into a crowd and kill someone. No body wants that. Talk to Warbird Propdrives and see how they are coming along with their ideas. Hope this helps. Karl"
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Question 204: "Hi Karl: Like many others I to would like some advice on radial engines. I am building a Top-Flight F4U Corsair Giant Scale and would like any ideas you can offer me. I am building this plane with all the bells and whistles, more for looks and functionality than flight, although I still want it to fly when I am done. I have been to several web-sites doing research on radial engines but cant seem to find what I am looking for. The RCS 215-Radial, gas, would be perfect but it will not fit the cowl. Are there any other gas radials out there or am I stuck with the nitro radials. Crazy thought, can you modify two single row radials and combine them to make one double row radial? A little bit of info on me. My main enjoyment and interest is custom building any R/C vehicle and my current project is the F4U Corsair. I am currently working on all the working custom features and would like to purchase a radial engine soon. I would like to install an exhaust that comes out the bottom like the real thing. Cooling should not be a problem since I am installing functional cowl flaps with a heat sensor. I would very much appreciate any advice or ideas you can offer to help make my project a success. Ill send you pictures when Im done, its going to look awesome. Thank you very much. Joe"
Karl: "Thanks for the questions, Joe and happy New Year to you and yours. First, I am glad you have chosen the right engine for the Corsair. Second, I think this will be somewhat bad news, but there are, to my knowledge, no gas radials of the right size to fit the cowl of the 1/5 scale F4U. Perhaps the best choice is the Robart R780 glow radial. Go to www.robart.com to get to the link to see this beaut. Another choice might be the Saito FR 450-3 rd engine. It is a large 3-cylinder glow radial. It has less than 10 hp so if you are planning to add scale goodies, be prepared to deal with the added weight. It would be seriously cost-prohibitive to graft a second row of cylinders together to make a two-row. You would be opening up a can of worms of gargantuan proportions. You have to then deal with crank timing, damping second-order crank vibrations, the list goes on. Just to give you an idea, when Pratt and Whitney was developing the famed R2800 radial, it took them no less than 4 years (1938-1942) to develop the crank and reciprocating assembly just so it would last a full test-session without blowing up! Cool idea, really, but unless you have REAL deep pockets, better leave that one to the pro's, pal. Obviously cooling is a big deal on any engine. When you have a radial, the space between and around the cylinders becomes potential heat pockets and can lead to engine failure. For the cowled engines, some guys in RC who use a radial will build baffles to go inside the cowling and fit between each cylinder to direct the air through the "open space" or "dead area". In addition, wherever the metal baffle contacts the cylinder head it also acts as a heat-sink that absorbs some of the heat and when the baffle contacts the air it cools. It's a really simple approach but is mostly needed on single-row 3- and 5-cylinder radials. In my opinion based on research and visual study, having seven or nine cylinders helps decrease the dead space and facilitates the air movement across the heads, thereby carrying heat away. The critical thing is to allow sufficient space at the rear to exit the air without causing an "air dam" inside the cowl which will lead to over heating and...well, you get the picture. Keep in mind when things get hot, they expand. Cowl flaps are a good idea.
Other than that, you have done much of the work yourself so it shouldn't take you long to decide on a powerplant to suit you. Hope this helps, Joe. Karl"
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Question 205: "Karl, I've been bitten by the bug again. A couple questions on engines for a Beechcraft D17S Staggerwing in military dress.I am planning on a scratch build of 1/6 scale. The plans call for a 0.60 to 0.80 engine, The bird will be 64" ws. I don't have the plans in hand just now, but it looks as if at 1/6 scale, the cowling will cover an 8" radial. Just the right size for the P&W R-985 I would like to make to power it. That engine is "approximately 8" diameter. The rub comes in with the prop though. For 1/6 scale, I need a 16.5" prop, but the engine "turns a 20 prop". My first question is, does the engine need the weight(flywheel) of the 20 Inch, or will the 16.5" do. If weight is needed how about a solid aluminum prop vs wood? Second is the weight. I am guessing that this engine is going to be somewhat heaver, probably a lot, than a single stroke glow. Any ideas other than loading radio and such as far aft as possible to maintain CG and still not exceed the wing loading? Don "
Karl: "Good questions, Don, thank you for paying us a visit. Merry Christmas, by the way! You might be interested in the 9cylinder radial by TechnoPower in Santa Ana, CA. I believe the diameter is okay to fit the cowl, and with a 64" w/s you are likely looking at a weight of around 15 lbs or less, depending on scale details, etc. TechnoPower's 9 cylinder is a nice-looking unit that could easily replicate a Jacobs or R-985 of early production. It has 2.5 hp and weighs 22 lbs ready to fly. Here is where it gets interesting. I don't have my AMA rule book accessible but I believe in it they expressly prohibit using metal props of any kind, for obvious reasons. Addressing the diameter issue of the prop, you should check out www.soloprops.com and see their products. They are state-of-the-art for sure. You can get a prop as small as 16-inch diameter up to 32 inches. They have 2, 3, and 4-blade hub and prop kits available. They are ground-adjustable-pitch, (GAP) which means after you complete the bird and take it flying, you don't have to bring 5 or 6 different props along to get optimum performance. Using the instruction manual provided with each hub and prop assembly, you can maximize the prop adjustment between flights for aircraft weight, wind and other climate conditions, desired flight characteristics; eg. slow-flight, fast-flight, anywhere in between. At least in theory, you can use a prop to make up for some of what the engine lacks, within reason. Conversely, you can have a more-than-adequate engine and use the prop and throttle to control its flight. Thanks again for the questions, Don. Hope this helps. Karl"
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Question 206: "Hello. I have bought a Sist Fw-190 A8 and thinking of using a ASP (Magnum, ASP, SC) 400XL Radial engine in it for scale sound and look. Do you think this will work or is it to small for this plane. Do have any experience on this engine or similar choices? What would you recomend?"
Karl: "Hello, Thomas! Isn't the Web a cool thing? Where else or how else can you communicate with someone on the other side of the globe? Ten years ago I would never have thought I would be conversing with people from around the world!
The ASP radial looks alot like the O.S.radial offered here in the U.S. It is common for the same engine to have different names or model numbers due to where they are sold, state-side or over seas. So, assuming it is an OS, it has 4 hp and may be ok for a plane up to, 15-18 lbs. If yours will weigh more, then I recommend the Saito FR 450 radial which is a 3-cylinder but has more power due to larger displacement. The FR 450 sells for just under a grand, at least here in the US, and is one of Saito's best-sellers. You always want to have a little more power on tap than specified because you never know when you'll need it. Hope this helps you. Karl"
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Question 207: "Dear Karl, I have a G-45 Zenoah engine that is blowing too much oil down the side of the plane. I'm using one 8-oz. can of Lawn Boy, 2-cycle ashless oil mixed with one gallon of fuel. I need to know what the correct mixture is for the oil and gas for this engine. I bought the plane second-hand and have no instruction manual to go by. Any help you could provide would be greatly appreciated! Thank you,
Karl: "Thanks for the question. The Zenoah line uses a 50:1 mix ratio in their engines. Doing it your way, you were mixing only 16 ounces of fuel to 1 ounce of oil, which is extremely rich and is the direct cause of your concern. There are 128 ounces in a gallon of liquid. When doing the math, you need only 2.56 ounces of oil to one gallon of fuel to obtain a 50:1 ratio such as that prescribed by Zenoah. Some people try to use castor oil, but I think that the oil offered by Amsoil will do better. Amsoil has one of the best lines of synthetic engine lubricants that I have ever seen. I have personally seen a diesel engine with over 300-thousand miles and it never had a teardown! For the repair I had to do on that I was able to see some of the internals and they looked brand-new. Amsoil is a good choice. So, in short, change the spark plug, clean the oil residue and remix the fuel then take another stab at it. Let us know how it turns out, okay? Hope this helps. Karl"
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Question 208: "hi karl, i have a new super tiger 90 engine and it is placed almost upside down (as in most warbirds i think). so my questions is how many tanks does it need for break in? and how do i set it up properly? i have started the engine a few times, and set it to idle and the engine works fine but only when it is straight. it does not work when the plane stands on its wheels(engine upside down) why does this happening? thank you very much for your help..
Karl: "Thanks for the question, Erez. It usually takes at least a tank or two to adequately break-in the powerplant. Make sure your tank is not lower than the engine when you run it setting on the wheels. You will need a Cline-style pump or something similar to run exhaust gas pressure to the tank so it will siphon fuel, not air, as the tank emptys. On your engine's exhaust pipe there should be a pressure port, or nipple, to which you attach the fuel line. The other end connects to the tank cork (the rubber plug). When you get it to running at idle, on the wheels, you can then make some adjustments to the idle mix, and the high-end setting. In each case you want as little smoke as possible. Nitro will always have some smoke, so don't worry. It is not a gas engine so emissions concerns as we know them go out the window. We just have to adjust our own understanding about emissions. Idle quality should be reasonably steady with smoothe off-idle response. It should stay the same rpm, in general, even though it may sound like it is searching for a steady rpm. Once it warms up, move the throttle manually but smoothly to part throttle and monitor the head-temp. In a glow engine the head temperature is perhaps the biggest measure of proper fuel/air mix. The higher the temp, the leaner it is running; the lower the temp, the richer. You should even test yourself by getting together with another RC-er who can give you pointers or corrections, if necessary. If you have anymore questions, don't hesitate to write me here, pal. Thanks for the
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Question 209: "Karl, My son is building his first warbird, Top-Flite P51 Gold edition kit. He was informed by his flight instructor that 4 blade props are just for static display. Do they make 4 blade props that small, for a .75 motor, and if they do what Mfg.'s are out there? He would love to keep the "Real Look" to his airplane. Thanks "
Karl: "Hi John. It is true that for smaller scale birds that are 1/6 scale or smaller it is more difficult to find a scale, flying four-blade for the planes that had them originally. If you want, try looking into what Solo Props has. They do have a scale 40-blade hub and blades as small as 16-inches in diameter. Another option would be to go to the following sites, as I've written them and follow the links for propellors. Thanks for the question, John." www.cactusaviation.com, www.desertaircraft.com, www.rcshowcase.com.
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Question 210: "I am starting on two Ziroli Corsairs, one for my uncle, and one for myself. We have just got back into the hobby about a year ago after a 15 year break. My question is on a limited budget what would be a good engine for these warbirds? We would like reserve power for when we may need it or just want to cut up the sky, and we also would like twins that will fit inside the cowl without butchering it up. Thanks for your time. Bryan "
Karl: "Brian, in this man's humble opinion you should install the Saito 450 R-3 glow radials. They will have good power. Up front though, you didn't say what size they are. I was assuming 1/5 scale, which for Ziroli is the 98-inch span version. That is a beaut, no doubt about it. If they are smaller, you can still use Saito's 5-cylinder radials for a really cool sound, a unique look, good performance, cool sound, good reliability, and did I mention cool sound? If you are building a Corsair of a good size, then always put a radial in it, that's my opinion. Thanks for the question, Brian. Karl"
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Question 211: "Karl: Enjoy your column. What is you opinion on dual tanks? Due to space concerns, I am considering using a dual (24 Oz.) tank set-up for a Ziroili 1/6 Skyraider powered with a Q75. Any thoughts or comments would be appreciated. Thanks, Don."
Karl: "Hi Don, cool choice for a plane. The Skyraider came in just at the tail end of WW II but according to my research, did not see action in that war. Instead, it was hugely useful in Korea and Viet Nam in the CAS role. Somewhat of an unsung warbird hero, I think. The 1/6 scale is sometimes a tough one in which to garner any scale details and still have a reasonably airworthy weight, due to the size. Of course, a 1/6 scale B-17 is much larger than a 1/6 scale fighter plane, to be sure, so let's keep things in perspective. The size is an ussue here, mostly for the reasons of power-to-weight ratios. Many warbird builders have successfully installed dual tanks, especially for multi-engine applications, but not so often for singles. Here is what you need to consider-1) how will you control the fuel flow to the engine? You have one engine and two sources for fuel. You can't take from one tank then the other due to major trim issues then. 2) The weight of all that fuel added will wreak
havoc on the CG as well, so locating the tanks in suitable locations will definitely be a challenge. You will likely then have extra plumbing to install, some kind of flow meter/controller/restrictor, etc. The Q75 is a good one for power in this size plane, but it's still a one-lunger and can't be THAT thirsty! It may be possible to use a central fuel tanks that collects the fuel from the tanks, utilizing a check-ball from each tank that only allows fuel IN. The central one will only fill up so much, since you should vent the system at the tanks (I'm assuming you are planning wing-tanks, eh?) The engine can then draw the fuel from the central bladder, and perhaps with occasional wing-wagging in flight you can slosh fuel to help keep trim requirements to a minimum. If you do it this way, the pressure-port on the exhaust system will have to be plumbed to the wing tanks, not the central one. You don't want the air in the central bladder, you want the fuel to draw into the engine and empty the wing tanks, then to the center one, like a real one might. In theory, Don, this is totally possible. When I say this next thing, I only mean it as brain fodder when you are problem-solving, not to be sarcastic, but scientists THEORETICALLY have been able to prove we can live on Mars too. As with many things, there is theory, and there is reality. If you have enough engine power, a good prop, and patience, you may just be able to make this happen. Expect as well to have some extra money available because, if you actually produce a design, test it, the results may be---well, you get the picture. I would be interested, as would countless others, to hear about your progress, with pictures, so what works for you might work for another. Great question, hope this helps. Karl"
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Question 212: "karl, I hae a RCV 90 engine that I wan t to use in a Wing Hellcat. As usual we want to use a scale prop and that is the reason for the RCV90. I found a company called Solo Props which make scale shaped and sized propsfor our hobby. The claim that this rcv 90 will turn the 15" prop just fine. My question to you is have you used RCV engines, what effect can this size prop have on our models in flight and on take off and landiing and what is the break-in period like or consist of. I reviewed al your responses and noticedyou have no questions on the RCV engines...so maybe this will be a change for you. Anthony"
Karl: "Thanks for the question, Anthony, I actually do get a couple questions about RCV stuff. I don't know anyone locally that has one. Which is to say, there could be many, I just don't know them yet. I have studied the RCV design and it is quite revolutionary, pardon the pun. It is still a four-stroke engine but utilizes a rotating sleeved cylinder to work as valving. Pretty cool, really. This means it can have a more compact design, make at least as much power, and it would appear to me, less vibration. All of these things are good in and of themselves. In this wonderful world of RC warbirds, however, most may still opt for the tried-and-true 2-stroke or 4-stroke glow engine. In most cases in life, usually what is little understood is least accepted. Based on the information I was able to peruse, it should be no problem to swing a 15" prop with the 90. Solo Props has one of the best operations going, when it comes to replicating flying, scale warbird or vintage propellors. I love their craftsmanship and good eye for problem-solving complicated design issues in a way that stays pretty faithful to their full-sized counterparts.
RCV engines are relatively new on the U.S scene but are rapidly gaining popularity so given the fact I like the design solution they have, I think it is a good powerplant. Good luck, hope this helps. Karl"
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Question 213: "Karl, I am in process of building TF T-34 mentor. I am considering putting in it 90 size engine I am now debating between the ST and the OS 90 version. It is very hard to me to decide between the two. Can you advice which is the best. Best Regards, Ronen"
Karl: "Thanks for the question, Ronan. In my opinion you should also look at a Saito 90 or 100 to install. The O.S. line is also good, but I really like the Saito's.
They look real nice, balanced, and sound awesome! If it were me, I would use the Saito 90 4-stroke. Cool engine. Perfect. Thanks for paying us a visit. Karl"
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Question 214: "hi im building a 40%waco and im looking at the rcs 400 radial do you know any thing about this eng. thanks, vern"
Karl: "Well, Vern, you have chosen an absolutely fabulous engine for that plane. Basically the 400 is a larger version of the 215cc gas radial. The 215 costs less, has 20 hp and may be better on the weight issue of the plane. Both engines are superb for giant-scale, radial-powered planes. They should be perfect for planes of 1/4 scale or bigger. Of course, you make them much bigger and you start thinking about a live pilot----let's leave that one lie, okay? You can learn alot about them by going to the site www.rcshowcase.com and they have both engines and tech info provided. If I had the money and the time I would be installing one of these baby's in a project suitable for such a piece. They both use a gas/oil blend, which is different to me since I thought they both had dry-sump oiling. Guess that's what I get for thinking. They both have computerized ignition so it is virtually trouble-free. I have yet to hear from anyone using an engine with electronic ignition, that the ignition system failed. They are pretty reliable, to be sure. They start easy, run like a dream from listening to their audio and watching the video. At my local flying fields I haven't seen anyone with one of those, yet. Hope this helps you and thanks for visiting our site. Karl"
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Question 215: " Hi. I've been researching engines lately with the hopes of building one myself, and I was hoping you could tell me the maximum Horsepower:Liter figure that has been attained in a naturally aspirated engine. I've heard of some RC engines getting 750hp/liter, could you tell me which ones do this, and if there are more efficient ones out there? -Charlie"
Karl: "For me, Charlie, that is a little difficult to answer. See, in RC, most engines' power output is measured, rated, what have you, based on what size prop it can swing, and the max suggested weight of airplane it can positively get off the ground. So it figures that if a .90 size engine can fly up to a 18lb plane, for example, it has pretty good horsepower. So, that's a little of an exaggeration. Take the Robart R780 7-cylinder radial engine. It is rated at 10
horsepower, and displaces 7.8 c.i. It figures to more than one horsepower per inch displacement, and that is usually good. It should fly up to a 30 lb model
pretty well, provided you select the right prop. I'm not sure you will find very accurate statistics either, on the power output of RC engines, across the board. For the most part, Saito doesn't state the power rating, just the prop potential, and plane weight. There are some formulas out there and test
equipment that will let you calculate those numbers but I have no clue what they are, to be honest. RC Showcase, Robart, and Cactus Aviation all DO tell
you what the power of their engine offerings are, but that's about it. If you are looking to build your own, do alot of research, make sure you have the engineering infrastructure in place to help your ideas and designs materialize. One place I know of where you can order castings of an entire engine to machine and assemble yourself is here, at www.quarterscalemerlin.com. They have a 1/4 scale V-12 Merlin that is stunning. They make all the castings, but like I said, you have to find your own machine shop, and spend hours studying the drawings and instructions. That project is not for a novice, to be
I hope you don't think I waffled the question, it is a different type of question than I'm used to. I just felt the best I could do was share from my own experience of research, design, obervation, etc. Thanks for visiting us. Karl"
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Question 216: "Hi I'm new to the warbirds and do a lot of reading trying to catch-up on RC Universe and saw your link. I have read through your site and have at least one question. I like Corsairs. They have a crazy power ratio and huge prop. Me being a power junky*; I bought a Top Flight 60 Corsair kit. The kit says a 4 stroke from 90-1.20 so naturally I found a YS 110 and a RCV 1.20 to swing a Master Airscrew 16 X 8, 3-blade prop. These are big items and my question is about -- Torque roll, Which engine could be a problem, And how to compensate for power. (maybe this is also a building question
now I think about it.) I have drag raced frequently so I know about setting-up drivetrains and instant center, but this plane only has wings... Karl any direction is good from here, I haven't bought anything but the kit and retracts so far. I'm after a gutzy huge sounding plane to mimic the real deal going overhead. I would even fabricate open split headers to both sides like the full size if needed. (*I built a BBC 496 from scatch. mech roller Dart single plane Demon 850 to put into something for car shows-- thats where my head's at)
Thank you for an answer and for the wonderful site and Jacks flying advisor. I have gleaned so much experience from this site it's ncredible!!!! Paul"
Karl: "Thanks for the question, Paul. Actually, many questions. At least issues. Onward. Torque roll is inherent in all airplanes with engines and propellors, unfortunately. Torque roll is a byproduct of the engines' rpm. More to the point, the opposing inertial rotation that is generated by the rotating mass of the internal engine components. That said, let me use an oft-quoted segment of Physics, 101 by saying- "for every action, there is an equal and opposite re-action..." I believe it was Sir Isaac Newton who said that. I might be wrong, however. As a drag racer Paul, you are then all-too-familiar with watching the chassis twist and feeling the car launch, and knowing that the harder you set back in the seat without making tire smoke, the better the car has hooked up. What no one really sees is the unfathomable toll this takes on the equipment-stressed welds, stretched bolts, broken brackets, twisted or broken axles. All these are the outward signs and results of the power and torque applied in a drag race car. In an airplane, the engine produces a reactionary torque twist in the opposite direction of propellor turn. If you were to fly the plane at part-throttle at eye level as you make a pass down the runway, then slam it to full throttle you would likely see severe reaction and uncontrolled flight characteristics. In a race car you use roll cages, track bars, shocks, aerodynamic enhance-ments, etc, to stabilize the car at speed and for initial take-off. In a plane, that's what we use the flight control surfaces for, for stabilizing the plane as we make it do what it was designed to do. Jack Devine really explains it the best in his Tech article, that covers this very issue--more to the point, how to avoid its pitfalls so you can enjoy flying longer. About the engine choice----Perhaps the RCV is the best one of the ones you mentioned, but look into the Saito engines to see if a smaller radial won't work, or a large single. Go to www.technopower.com and see their small glow-fuel radials. Way cool! I think the Saito sounds better and will be easier to build a custom exhaust for, if that floats your boat. The thing is about RC engines, most of them are 2-stroke glow engines. Some are 4-stroke but most do not have multiple cylinders. You'll only see multiples on 1/5 and larger planes, as a loose rule of thumb. If you use a radial, you can build a custom exhaust for that and it will sound totally unique for sure. Just keep a level head, Paul. There is alot to learn in this hobby and we here at RC Warbirds like to think that this may perhaps be the best place on the web to learn. Not to discredit the other establishments, because they too, have done their homework----I'm just saying. Hoep this helps, glad to be able to count you on the rolls in this rapidly-growing hobby. Keep us updated and feel free to askany of us here any question you have. Karl"
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