Please email Karl your questions by clicking "Contact Us". Please label your email "Karl: Question".

Some questions and answers will be posted in this section.

Page 2: Questions 73-96, click on links or browse page.
Q73 Four blade prop for a 3W 150 inline twin ? Q85 Thunder Tiger .91 4 stroke adjustments ?
Q74 RCS 215 radial cooling ideas ? Q86 18 cylinder radial ?
Q75 G-26 throttle linkage ? Q87 St. 3250's converted to diesel ?
Q76 Engine for Vailly Huricane ? Q88 Twin Saito 450r's for Widgeon ?
Q77 O.S Gemini for Top Flite P-47? Q89 Plane for Technopower radial ?
Q78 What four cycle for the TF P-47? Q90 Fueling valve location ?
Q79 Breaking in an OS 50 ? Q91 TF P-51 w/ US 41 engine prop selection ?
Q80 Don Smith A-26 engine choice ? Q92 Engines for 3W Tigercat ?
Q81 Engine mounting questions ? Q93 Gas engine for Top Flite P-47 ?
Q82 T-28 engine choice ? Q94 Functional scale exhaust for P-51 ?
Q83 DA-50 for 80" ME 109 ? Q95 Radial selection ?
Q84 Engine vibration loosens intake ? Q96 Scale four blade for P-51 ?

Question 73: "I am building a 3W P-51 Mustang 1/4 scale with an inline 3W 150 twin...is there a four blade prop available for this size engine and airplane. Thanks, Richard "

Karl: "Hi Richard, I was chuckling as I read your question because it so happens that I and a few other folks lately have been discussing this very issue and the why-not's of it all. To answer directly, no, there is no 4-blade of suitable size for a 1/4 scale warbird. Now, because of the needs stemming from research for my own project, this has led to me designing and building a 3 and 4-blade hub and prop system for 1/5 scale and larger planes, with emphasis on 4-stroke power since most of the 2 strokes wind too high. So, if it were up to me, I'd tell ya to talk to me about the need but alas, there is nothing concrete yet so I can't tell about it. The main reason is the typical engines used for larger birds need to be at or above 3,000 rpm to be of any use for thrust. A scale 3 or 4-blade system has too much mass or inertia for that rpm and likely would either hinder the power production or destroy the engine and prop altogether. That's why a 4-stroke engine is better suited for this kind of propulsion system, the rpm is lower. A typical 2-stroke idle speed is usually well above 1000 rpm and makes power past 10,000 rpm. A 4-stroke idles around 700-800 and makes power through a lower rpm range. I know you didn't ask about engines but I have to tell you about this project in California, if you haven't already heard. The website is www.quarterscalemerlin.com and it is the most astounding example of r/c powerplant design I have ever seen. The plane you have chosen is a great one and you should have alot of fun building it and flying it. Hope this helps you, Richard. Karl."

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Question 74: "Karl, I too have a Mackay FW190 with an RCS215 Radial, she runs great but I've already fried a piston and RCS charged $800.00 to repair it once. I flew it a second time and it apparently overheated again and on flight #2 I deadsticked it and the gear stayed stuck again so it was a deadstick belly-landing, but never even scratched the plane. I getting more experience with no power and gear landings than I'd like, and I'd like to make a power on landing one day, so its come to my attention that there's obviously a cooling issue, not to mention that I had a rocker arm hitting the cowl, how much exit air do I need? I'd like to keep from hacking this plane up. Currently all I have for exits are the 2 muffler exits on each side of the cowl, I also have very little air going into the fuse..I have two 1/2" penetrations in the firewall for plug wires and a little seepage from the canopy.. should I put a scoop under the fuse to direct cool air to the carb? and should I cut out a big exit with a diverter plate ahead of the cut out to draw air out of the cowl? and should I baffle the heads or just make a big exit? please advise, I'm tired of deadstick bellylandings. Rick, (BAGOSTIX)"

Karl: "Wow, Rick, you are having an expensive go at dialing this radial in aren't you ? The first thing you need to check and change if necessary is modify the amount of fiberglass on the cowl just as it takes the turn to the inside to the engine. If there is a significant ledge it needs to be removed so air can effectively move around it and to the heads. The second area is of course the exits. This can be tricky since if you have an "equal" flow comparing entering and exiting air, there will be too much dead air in the cowl and it still won't cool well. The exits have to be slightly larger than the entrance to create some pressure and flow around the heads. On a full-size FW 190 I think the cowl has flaps for cooling although I can't say I've seen a builder add them open. It may help to richen the air/fuel mix a tad to compensate for heat. If it's running fatter it will be cooler. Don't go too much obviously 'cause it will smoke and run like you-know-what. I've seen some of these FW 190's and the Mackay offering is quite good. But the cowl entrance of air and the exits have to be modified. Consider the fact that most rc'ers use a gas or glow 2-stroke of considerably less size, so the cowl and its exits are sufficient for those types of engines. For my project of an F4U Corsair I will be using the Robart engine, but will be adding functional cowl flaps to help preserve the life of this most expensive piece of art. Hope this helps save you another engine, Rick. Thanks, Karl. "

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Question 75: "G'day Karl, I have trolled through the historical questions just in case my questions was a repeat... I have recently purchased a G-26 for use in a 1/7th Corsair. Whilst the install is going well I have only come up with some average ideas on how to connect the throttle linkage to the carby. Since the throttle arm movement is essentially perpendicular to the firewall, is there a sure-fire way to connect up a slop free linkage. I'm out of ideas, maybe your extensive experience might be able to show a newbie the way!! cheers Justin"

Karl: "G'day Justin and thanks for visiting our site. The g-26 is good one for smallish planes--should be relatively trouble-free. Now, if you have the straight-style intake which has a side entrance for the air, then the throttle linkage will be as you say, perpendicular to the firewall and you will then have to devise a belcrank that changes the fore-and-aft motion from the servo to side-side to operate the throttle. If you purchased the optional bent intake pipe, the throttle will be parallel and perhaps easier. As for the linkage, try using a heavier gauge piano wire or something like what we use on rear vert stab and horiz stab operation with actuator rods within a 'glass housing to reduce flex. There will be some play in the whole shebang just because you don't want anything to bind. If it does......I think you get the picture. You know, the Corsair actually came with a radial--the New Zealand Air Force bought several during WW II---you might, for kicks and giggles, look at the offerings by these folks: www.technopowerengines.com , or www.saitoengines.com , or www.osengines.com . All of these have radials to offer, and you just might be inspired--------! Thanks, Karl."

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Question 76: "Karl I'm in the process of selecting an engine for a 92" Vailly Hurricane, projected weight about 26lbs. I currently have a 88" Pica Spitfire with a G62, spinning a 22x8 3 blade Zinger prop. That engine/prop combo flies the Spitfire well, but I'd like to get something that fits within the cowling a bit better. I'm considering either the Brison Revolution 52cc, which is so new nobody has reviewed it yet, or maybe the 3W 50, if I can find a six bolt to one bolt adapter, which also will serve as a prop shaft extension, in order to go to single prop holes and move the cylinder head back a bit. Have you heard any good/bad things about the new R-50 Brison "Revolution" 52? Any feedback on the choice of the 3W50? And lastly, do you know who makes the prop extension/adapter for the 3W? Thanks in advance, Sam"

Karl: "Thanks for the question, Sam. I appologize though, for taking so long to answer. No excuses. Laziness, maybe. Anyway, the G62 is still a good choice, the 3W50 is a flat twin, isn't it? I can't remember off the top of my head. The only company I know of at this time that makes an engine to fit narrow cowls is the Saito deep-vee twin, the 200 ti. It only has 2 hp though and may not be enough for the Vailly. I have not heard about the Brison R-50. Even the awesome looking Laser engines have a 90-degree v-twin or large v-4. They would be too wide for the cowl. As for the prop extension, you would have to take that up with the 3W engine folks to see what they offer. If all else fails, make one. Hope this helps. Karl. "

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Question 77: "Hi Karl I am building Top Flite's P-47 Thunderbolt Gold edition (wingspan 1600 mm) and planning to power it with the OS FT-160 Gemini that have bought already and currently running it in on the bench. However, I am worried a little about overpowering the plane with this engine. On the bench FT-160 gives me 9,600 rpm with a Master Airscrew 16x6 prop. My questions, if you could please answer them are: Are 9,600 rpm on the ground too much for FT-160? Do you suggest 16x8 instead? (I do not have the clearance for bigger diameters) Am I going to face problems (too fast landing speed) landing the plane (approx. 4,8 kg) with the MA 16x6 or even 16x8 prop idling at 2,000 rpm? Thanks in advance for your kind reply. Stelios"

Karl: "Good question, Stelios. I don't think the FT 160 is spinning too fast at 9,600 rpm. The spec's for it are 2.0 hp at 10,000 rpm. I don't know what 4.8kg converts to in standard measure, but it sounds like maybe12-15 lbs. If that is the case, you have a couple of options for this plane that you might want to consider. The first thing is look into the different radial engines from www.technopowerengines.com They have 5,7, and 9-cylinder units that are fantastic. They all should fit in the cowl easily. The other item is flaps. If you are concerned about landing approach speed, install flaps on this bird. Not only will it look really cool, but they are totally functional for controlling landings. They will assist with take-offs as well, but usually you won't need them for take-offs. The prop choices sound good as well. Since the cost isn't REAL big, it won't be a big deal to have a couple on hand to try and see what gives you the best flight characteristics. Hope this helps. Karl."

Editors Note: The TopFlite P-47 requires a 60 to 90 two stroke engine so the Gemini might be ok if there is not a balance problem. I always say stick the biggest engine you can use with out making the plane nose heavy. Use a bigger engine and you can use a bigger prop, maybe a large 3 or 4 blade. Not sure how much you can lug the Gemini down but some bench running with different props might help you find one that will work just fine. I use 15/8 Graupner 3 blades on my Saito 150's for example, they turn only 5200 rpm but seem to like it.

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Question 78: "Karl, Santa left a TF Gold Edition 1/8 Scale P-47 Thunderbolt under the tree last year. This year I'm thinking about asking him for a compatible engine. The review I read used the SuperTigre G75 and had favorable comments about that. I'm thinking about going the 4-stroke route. And since I've now learned that Santa does indeed deal in big-boy toys, I'm wondering about using one of those Saito flat twin-cylinder engines. They have a 90 size and a 100 size twin that will fit in the cowl. The HP output is 1.4 and 1.6 respectively and they both will swing a 13x8 and 14x6 prop. My desire is to have 4 stroke sound combined with scale performance. Without asking you to endorse one product over another, I've got a few generic questions on the subject that I'd like your input on: 1. Do you think the power output is adequate for the P-47 kit? 2. Are you aware of anyone's attempt to use one of these engines on the 1/8 scale kit? 3. Do you think overheating will be a problem?4. Do you have an opinion on the subject that you'd like to share? In talking with members of my club, the majority opinion so far is that I should use the 120 size 4-stroke for this kit. Thanks for your assistance. I would really appreciate any ideas you can send my way. Regards, Mark"

Karl: "Good series of questions, Mark and welcome to our site. The kit sounds cool. The guys that flew these birds in WW II affectionately called them "jugs". You are wise to select a 4-stroke for power. They can't be beat for sound and scale appearance, depending on the plane. I tend to "endorse" which ever product seems to fit the situation of the person asking the question. At this point I can't say that I have any "loyalty" so not to worry about that. One thing I try to do when someone sends us a question is at least offer some insight that might seem outside the box, in the hopes that the asker can likely gain from asking a good question ( there really are no bad questions, here...) and have an even better modeling experience. That said, have you considered the Saito FA 170 R3 radial? According to my sources, if the cowl on your Jug is at least 8 1/4" in diameter, this may be the engine for you. Rated at 2.0 hp and having a very comfortable rpm range, the engine can handle many selections of prop dimensions. The sound is cool, the price is not too high--for what you get-- and safe to say you will have a P47 that will turn heads whenever it takes to the air. Radial power. Makes me want to cry thinking about it. haha."

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Question 79: "Hi Karl, I got a OS 50sx ring, my friends tell me to break in the engine is way and that way, and don't go by what the manual say to do, maybe my friend are from the old school...lol they tell me to run it rich at full throttle, for at lease 2 tanks full, and I should be ready to fly? and should I use a prop that I'm going to fly with, or use an other prop for breaking in? I'm putting it in a VQ zero, and would like to put a 3 blade prop on it, what size should I use? Thank Dennis"

Karl: "Thanks for the question, Dennis. I'll start with the questions in order and do my best to help you out here. First, if it were me breaking in an engine, I'd run at least 4 tanks of fuel through it so I can make sure the ring has seated and the cylinder is sealed well. You want to observe the throttle response as you slowly move towards wide-open-throttle (wot). If a glow engine blows smoke and seems to have no power, you've cooked it. If it builds rpm well and smokes slightly, you are in the ballpark. Of course, if it smokes alot, you will have to change glow plugs since they foul with too much fuel. Make sure the glow plug is correct for the fuel and engine. The last test to do toward the last tank or two is how it responds to rapid throttle movement. Snap it open then closed, check the exhaust and listen for an engine miss and idle return conditions. If it does these well, you should have it fairly well dialed. Just don't forget to regularly recheck things. Climate has alot to do with performance.

It is a good idea to do the bench run-ins with the prop you plan to use, so the fuel settings can be reasonably accurate for the load. The prop only puts part of a load on the engine when you are testing. The rest of the load comes from the plane, gravity, etc. My research has shown me that the engine is likely a good choice. As far as props go, the engine recommendations are 10x8 and 11x7. If you dare to try, look into an 11x8 and a 12x7. All these sizes should be readily available in 3-blade form. APC and MasterAirscrew each make props that will look good. Keep in mind that the larger the prop, the more load on the engine and more adjustments you will have to make at the field before flight. Here is a simple rule---the larger the diameter, the less the pitch has to be. Vice versa is true to an extent. I don't think it will fly with a 6-inch prop, savvy? Hope this helps and we here at RC Warbirds hope you had a great Chistmas. Happy New Year. Karl."

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Question 80: "Hey Karl, First of all, thanks for giving of your time and helping out the rest of us. I am building a Don Smith 105" A-26 and am struggling between using G26's vs. Ryobi 31cc conversion from Jag Engines. I am trying to keep the cost down as it is getting expensive in a hurry. My main concern is reliability of the Ryobi engine. I have heard from some that they are quite reliable and others totally pan them. Any thoughts on this? Thanks again for the service..........Doug"

Karl: "Thanks for the question, Doug. Hope you and yours had a great Christmas. I have not heard anything about Ryobi engines for scale planes, but if we are talking about a weed-eater conversion, may advise is, DO NOT. The G26 is a popular, well-established engine for RC stuff. They are quality, make no mistake. If you are willing to think a little bit oustide the proverbial box, consider Saito's FA 90 R 3 D radial. It has the proper displacement, good power and is still a right size for finding a quality 3 or 4-blade prop to fly it with. There is nothing like the sound of a radial, pal. Your Don Smith A 26 will look and sound great with this. They run $ 700.00 but what will you spend in trying to make a different one fit, dial it in, get the right prop, conversion kits, etc. I believe that in the Saito engine you have one that fits, has power and all you have to do is add the prop. Just think about it. Hope this helps. Karl. "

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Question 81: "Hi, Karl. First of all, Happy New Year to you and yours. I'm hoping that the new year brings new, interesting (and less expensive) things for the R/C world. My question is about where to position the engine on the motor mount in relation to distance from the firewall and the front of the motor mount. Does it make any difference, other than with the balancing of the model? I ask, because I have a motor mount for an OS .60 size engine and miss drilled the holes on one side of the motor mount. What effect, again aside from balance would I get if I relocated the engine, forward or backwards on the same motor mount and drilled four new holes? How will this effect the strength and vibration qualities of the mount, etc? Also, a friend gave me an old plane of his and I found that the motor mount bolts were smaller than the motor mount bolt holes in the engine being used, but fit the holes perfectly that were drilled into the motor mount. It didn't appear to effect the engine performance, as he has been flying this plane with the same set up for a couple of years, now. I would feel better if I replaced the bolts with bolts that fit the engine mount holes and redrilled the motor mount holes, even though the engine didn't have any problems with this set up before. What do you think? Bob, Giebelstadt, Germany"

Karl: "Good question, Bob. Frohliche Veihnachten und Frohe Neu Jahre! I hope my German is not too embarassing. I haven't been immersed in it for 20 years or so. Are you serving this great nation in the Military? If so, I salute you and say thank you for your service. I live in a free country here because of you and others before you who have paid a heavy price. To answer the question, the distance of the engine from the firewall is important, but not written in stone. That's why we have lead! haha. The first thing to consider is the cowl---will I have to shorten or lengthen it to accomodate the engine location? It will always affect the CG of the plane, to be sure. A general physics rule of thumb is the farther away from the mount you hang the engine, the more vibration and unsteady it becomes. Think of a forklift--if you attempt to lift a thing too far out on the forks, what happens? The closer you mount it to the firewall, the more stable it will be. It is a good idea---I think---to loctite the mount bolts so they don't vibrate loose. Cheap insurance, eh? Lastly, be reasonable about the location of the holes. If relocating the engine fore or aft only amounts to 1/4" or so, then you likely won't have to compensate much on the weight, even though it will change the CG. Hope this helps, Bob. Happy flying. Karl. "

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Question 82: "Karl, I suppose the T-28 will qualify as a warbird.....I saw some in 'Nam with guns on them......anyway I building a Pica 1/5 scale T-28 as my first scale airplane and I am having a fit trying to decide the right engine to install. I think the airplane with cockpit kit will come out about 12-13 lbs. The full size had a nice R 2800 installed what would you suggest? Thanks for your help.

Karl: "Thanks for the question, RIchard. I am going to be unappologetic in only recommending a radial for power for your plane. The T-28 is a great warbird. It was also used as a trainer and some did see service in 'Nam, along with some Douglass Skyraiders and AT-6's. Since the jet age had been well-stablished by that time, it was only a matter of time before air wars would not use propellor (piston) driven airplanes. Due to the size and weight of the plane, you have several choices. I'll just give you some suggestions and you can look into them. Saito's choices are as follows: FA 325 R5D 5-cylinder radial, rated at 3.8 hp.; then there's the FA 450 R3D 3-cyliner radial rated at 7 hp. O.S. Engines has the FR5 300 5-cylinder radial rated at 4.0 hp.; TechnoPower Engines has 5,7, and 9 cylinder radials sized from 1.35 cid to 4.0 cid. Horsepower of the largest--the 9-cylinder 1/5 scale--is around 4-5 hp. All of these have excellent reliability and unsurpassed scale influence. There is nothing quite like a large-scale warbird with an authentic radial engine for power. I don't mean to imply the usual choices are not good, such as any of the suitable Zenoah line or ZDZ or Husky. These are good, but if you are looking for a stunning, high impact airplane then go with the radial. I hope this helps and have fun building the T 28. Give us an update later, ok? Thanks. Karl. "

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Question 83: "Hi Karl - I am planning on building a Me109 from the Meister Scale kits. The only gas motor I have is a DA50. To me, it seems too much for the 80" version and not enough for the 104". I don't want to buy another engine just for this plane. I'd appreciate your ideas on this. Thanks! Darryl"

Karl: "Hi Daryyl and thanks for the question. I have a few thoughts on this so bear with me for a bit. First, I was trying to find a solution within the confines of your desire not to buy another engine. What I came up with isn't real strong so I'll make those suggestions and then some others using different powerplants. Using the DA 50 on the 84-incher ensures you will have to add ballast behind the CG, you likely will have to use less prop and the stability at low speeds would possibly have something to be desired since you are already at low throttle or idle when landing, couple that with less prop and you can see a problem developing. Using this engine in the 102-incher means less ballast, but more prop and likely could result in higher wear in the engine. You can only play with the prop option so much because a 2-stroke's power band is high so loading the engine with a big plane and prop is not good physics, eh? So, let me share these others. The REAL downside to these will possibly be having to hog out part of the cowl to fit the engines. So stop here if you know that definitely is not a consideration. Onward. For the 84" one you could look into a large four cylce. What you might lack in power you can compensate a little in the prop, but to a lesser degree than the DA 50. All of these are glow engines but are 4-strokers. I don't know why there aren't more gas engines available that are smaller and 4-strokes. There are gas radials and gas 2-strokers but not very many offerings that I have found for 1/5 scale or smaller. There is the other thing regarding cowlings. There are more options available for planes where the full-size ones came with a radial than for the narrow-cowl planes such as Mustangs, P-38's, Messerschmit's, etc. Saito has an awesome deep-vee twin 4-stroker for narrow cowl planes but I think it is too small for yours. If it helps, try to see your plane in person with the different engine combos installed and when you see one that hits you good, ask questions. Can't hurt. I'm sorry if this doesn't help much but I hope so. Thanks, Karl."

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Question 84: "Karl i have a problem keeping the rotator intake on the engine.vibration its held on by 2 10/24 alen screws locktight /epoxy/threadlock all dont work. can you help"

Karl: "Well, Mr. Bradlow, this is a different sort of problem, for sure. I don't know too much about Poulan engines beyond their original intended use for chainsaws, line trimmers, etc. There are a few variations of intake for 2-strokes---one is reed valves, rotary valves and carb's. Rotary's work alot like the 2-strokes built on-purpose for RC planes. Most are attached by 2-to-4 screws or a clamp around the carb base. From what I can tell from your problem, it shouldn't be unique to RC engines, since all engines have vibrations inherent, and there is not the luxury for utilizing large fasteners. In this case, try drilling and tapping the holes one size larger, and continue using thread- locker or other suitable adhesive. The added size of the screws should help with the clamping forces necessary to accomplish sufficient holding power. The other thing you might try is balancing the engine assembly. This would mean balancing the crank, rod and piston together since those are the moving parts, stands to reason that they should be as vibration-free as possible. Hope this helps. Happy flying, Karl."

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Question 85: "Hey Karl, just slammed my TF P-47 down hard on the runway yesterday after my Thunder Tiger .91 four stroke cut out. Almost had it down with ½ flaps…this is my first 4 stroke engine and I’m having difficulties getting it “just right”. Is the only way to really tell if it is where is should be is by measuring RPM’s?Thanks, Pat"

Karl: "This is a good question, thanks Pat. Let me say there are a few things at play here to consider. One, the type of fuel. Two, the amount of cooling of the engine in the cowl. Three, the heat range of glow plug you have in it. From what I have learned, most engine manufacturers recommend using around 3-4 tanks of fuel to break in the powerplant. I know people in RC that run no fewer than 5 tanks---and they have far fewer problems. Getting the mix correct at idle is crucial. It has to maintain a steady idle rpm, an appropriately corresponding amount of smoke and even temperature at the center of the head, measured where the glowplug screws in. Glow plugs for these are alot like cars---you can get a different heat range glow plug based on fuel, head cooling, mixture and of course the operating conditions the plane will see. Too hot of a plug and it will detonate too much and likely burn out the glow plug. Too cool and it will likely load up under most conditions. Make sure ALL of the carb is sealed--tight to the engine, no air leaks in the fuel line and proper diameter of fuel line are all---mondo-importante---, get it? This is the base at which to start otherwise all carb adjustments are useless. I hope the plane wasn't destroyed, Pat. Hope this helps. Karl. "

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Question 86: "Hi Karl, I really enjoy your unconventional advice and your challenge to " think outside the box". About the time you mentioned the 1/4 scale merlin in one of your responses I was inspired to look into a radial alternative as I am a corsair fan. I soon found a set of plans for a 1/5 scale 18 cylinder radial which I purchased. The engine is not designed for R/C flight but I am hoping with some modification it might. It's heavy but I think there is considerable weight to be saved and the diameter reduced to fit a smaller cowl. It runs on gas with an idle of 400rpm with a maximum of 2500rpm according to the designers specs. My question is, with 15.9 cu.in. and 2500rpm, will this engine make enough power to turn a 30" prop and enough thrust to fly? Previously you mentioned a 1/4 scale plane needed 3000rpm+ for adequate thrust. I guess only thorough testing on an engine stand will tell. This project may not be practical, but if it proves to be impossible to fly, I'd still like to mount it in a model and taxi up a storm!( and I won't have to worry about crashing it) Thanks for your interest, Al."

Karl: "Thanks for the question, Mr. Peters. After several long moments contemplating what a 1/5 scale 18-cylinder radial must look like, I discovered it is possible to be comatose and still concious!!! Just think of the possibilities,....an 18 cylinder scale radial!!! Robart has a seven cylinder radial making 10 hp and has a prop range of 24x8 to 32x10. RCS has a 215cc gas radial that swings a 32" prop effortlessly. Safe to say that with nearly 16 cubes and 18 cylinders on gas you should be able to handle close to a 36" prop. Now, here are some insights ( gained while I was in this aforementioned coma...) Coleman fuel burns cooler, cleaner and better than gas and does not harm the engine. It, too, is a petroleum distillate. If reasonably accurate performance numbers were available, we would surely see a comparative mountain of torque from this big unit relative to glow engines, and this translates to better prop capabilities. ALWAYS bench-test an unproven and/or unfamiliar powerplant. Test it with Coleman fuel (white gas) and regular gas. Test it in all recommended rpm ranges. You might go through $$$ of fuel, but at what cost is the alternative? $$$$$$$. You could have a hay day designing and building a 1/4 scale F4U Corsair and use this engine. Yeah, the engine might be heavy but the better alternative to adding lots of weight to the plane is, build a bigger one! The possibilities are really trendsetting. What about an airframe that uses aluminum to mount the engine that is built back into the conventional wood airframe? What about a simplified all aluminum frame?You want help designing one? Let me know. Lastly, how can I get to view these same plans of this engine as you ? Does this company have a website? Send me an e-mail here and let me know. Thanks again for the question and hope this latest project comes to fruition. Karl."

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Question 87: "Karl, I plan to convert two ST 3250's to diesel, using Davis Diesel heads, and put them in my new twin warbird. The obvious reasons are low fuel consumption, no electrial shielding to deal with, and high torque. Do you have any thoughts about the conversion, and any issues that I should look out for? Thanks, Lee."

Karl: "This is a good question, Lee. I am not very familiar with the Davis Diesel conversions but have read an article in an RC magazine last summer that detailed the typical conversion and it sounded pretty promising. I personally don't know anyone that has this installed on their engine, however. I can tell you from this perspective that diesel always outdoes gas in fuel efficiency and power, due to the nature of compression and combustion unique to the diesel. That's why it takes a diesel engine so much longer to warm up than a gas engine---the diesel uses the heat much more effectively. As long as your engine is one that Davis Diesel has a kit for, you should have no trouble with it, just get used to different tuning approach. Thanks, Karl. "

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Question 88: "Hey Karl, I have now read every line published at your site. The questions and answers are almost addicting; you can't stop at one (or even a dozen). Thanks for all your hard work and the help you, and all the guys at RCWarbirds give. I have several questions I would greatly appreciate some help with. First, a little outline of the project. I am building a 1/4 scale Widgeon G44a. The last one ever certified by the FAA. It is in fact, the same plane used on the TV series "Fantasy Island". This particular plane was modified with two Lycomming 680R engines. The cowl ID will be 11.5", with the inside lip/cheek ID of 7.625". I plan on using twin Saito 450r engines. I will be flying a 21"x7-10 pitch, 3 bladed prop. I was hoping you could give me an idea if this combination would pull a 45-50lb. plane off the water and fly it with enough authority to get me out of trouble with an engine out situation. I plan on using all of the Twinmans advice on setup and trimming the engines, and I also plan on tying the throttles to the rudder for help turning on water, land, and air. Also, is there a way to plot the throttles using a JR radio, say a 388s or 8103 instead of a Futaba. I really like JR radios and Hitec servos. Last question: I need to replicate the Lycomming 680R in front of the Satios and I'm not sure how to do that with a good dummy engine with out jeopardizing the temperature of the Saitos. Any help you can give would really be appreciated.

Karl: "Ha-ha-ha, Jack, now you know how I got hooked over a year ago!! Anyway, welcome. Onward. I have a couple of things to say about that. First, When you have an air-cooled radial you do NOT want to shroud the air flow from going across the heads. When you have a one-lunger that is air-cooled, you can get away with putting a dummy in front because all you have to do is cut out a portion from in front of the engine so the air can get to it. When you have multiple cylinders, you want all the airflow you can get so I would not recommend putting a dummy in front of the radials. The second thing I want to say is perhaps looking into the radial offerings from TechnoPower Engines in Santa Ana, CA. I believe the power is good enough, they will swing the props of the size you called out in your question, and you won't have to worry about a dummy. Third, I would recommend going with the higher pitch props soas to lessen the load on the engines--maximum thrust potential for the rpm range. This will likely affect carb tuning, etc., so bench-test the combination first before you bolt them to the plane. Fourth, when you are asking Mr. Lumpkin (Twinman) about the trim issues and such, ask about the radio deal as well. It is my understanding that on twin-engine planes the engines rotate contra to each other so as to minimize yaw rates. If this is true, then getting twin radials to operate this way could get interesting. Think about it, if full-size F4U Corsairs had to have fullright rudder on take off to counter torque from the powerful R2800 engine, you can get the idea of how it will affect your Widgeon. I will finish by kind of shrugging this response that if you REALLY have settled on the Saito radials---which is an excellent choice by the way----then you might just have to deal with seeing only three cylinders through the cowl. If you are set on the cosmetic or aesthetic appeal of the dummy, then you are going to have to make some decisions, which I may not be able to help you with. Any way, this sounds like a fun project. I was a lad when Fantasy Island was a hit. Probably two lines from that show will go down in show-biz history are "Welcome, to Fantasy Island", and "De plane, Boss, de plane!!!" Happy flying, pal. Karl. "

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Question 89: "Hi, Do you have any suggestions for a Technopower 9. 3.5 cu. in.- approx. 4lbs.-8.75 in. across. I am thinking two wings and a tail wheel- you know. Any ideas? Also do you know a source for a bucker jungmann? (kit or arf)"

Karl: "Hello, Cheri and Peter, welcome to the site and thanks for the question. The Technopower engine is a real work of art for RC planes. You can put one in any bipe kit that originally came with the radial, so there are several choices. A Stearman trainer is probably the most popular for round-engine-powered craft. You might even consider a PBY like the ones used in WW II for recon missions or transport of officers, etc. Since my interest is in WW II warbirds, my knowledge at this point is somewhat limited about earlier planes such as bipes or non-warbird stuff. The PBY makes a neat project and you can build them just for water or with retracts for land use. As to the other, I have NEVER heard of a Bucker Jungman, pal. I'm afraid you're on your own there unless one of our other advisors happens to know about it. Try our Historical Advisor, Lt.Col. Monroe Williams. Thanks for the questions, hope I was able to help. Karl."

Editors Note: Bucker Jungman was a bi-plane German trainer and some were dressed in military paint schemes. I have an old Pilot kit and they fly very well. Pilot does not make these anymore but try searching google or post this question on RCU and see what turns up.

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Question 90: "Hi Karl, Should a fueling valve be placed on the same centreline or axis as an engines carb along the fuselage, or as long as the tanks relationship to the carb is ok does it not really matter where the position of the valve is? Cheers Chris"

Karl: "Thanks for the question, Chris, and nice to hear from someone from across the pond, pal. The main thing to keep in mind is not to get the fueling port too far from the tank, for venting reasons. During aerobatics or some other type of harsh maneuver the fuel will slosh around and proportionately so will the air in the tank. Since there is also a vent hose at the fueler, this tube has air in it for a reason. If you make the tube a figurative million yards long, it takes much longer for the exchange to happen and getting a vapor lock or spillage can occur. I would say, for most 1/5 scale planes ( I choose that size because it is a popular one....) you shouldn't go more than 12 inches from the tank with the filler. As to the location, there may be other schools of thought out there, but personally I think it really doesn't matter where the fueling port is, as long as the tank is in the best location that the fuse allows, and the fueler is above the tank well enough to vent as you fill. I have learned that keeping the tank as low in the fuse as possible is best so the CG doesn't change so much, and not too far from the engine. As you know, having the former between the engine and tank is standard. There's a reason they call it a "firewall", haha. There is one type of fuel pump called a Kline pump, which keeps the tank pressurized to maintain fuel to the engine at nearly all attitudes. There are other systems, so check them out. Hope this helps, Chris. Karl"

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Question 91: " am putting a us 41cc on my top flite p-51 arf.can you recommend a proper sized prop for me? I like the master airscrew classic series. thanks Mike"

Karl: "Thanks for the question, Mike. There are a couple of things to consider first. Many RC'ers with warbirds strive for authentic appearance as much as possible, including when flying. So let's start with the big picture and say you want a scale-sized 4-blade since the P51's came with them. It is possible to find one by either Master Airscrew or APC or FUCHS but when the full-size prop is at least 12 feet in diameter, the 1/5 scale size is nearly 2 1/2 feet across. It may not look bad on your 1/5 scale Top Flite, but flying with it likely will be another matter. Or else you can make one yourself or have someone make it for you, assuming they know what they are doing in airfoil design. Out of the question? Okay, so let's go down a little bit and say you can settle for a 3-blade even though it isn't scale. Fine. Master Airscrew does make a handsome batch of props in their Classic series and there I agree with you. APC also has 3 blade offerings and I think 4-blades but smaller diameter. You are looking at all-up weight of shy of 20 lbs so you don't have to have a lot of pitch in the prop, unless---to a degree---you have a steeper pitch so rpm's will be lower. Up to you. The props I mentioned are arguably the best out there. Lastly you can always stay with a 2-blade and have up to maybe a 16-18 pitch. Personally, I think the 2-blades on these babies makes them look awkward. But, that's just me. As you can see, many choices. That's why we have a free enterprise system and that is good for all of us as far as choices. Happy flying. Karl."

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Question 92: "Hi Karl: I am getting a 3W Tigercat. I need engines. Bobby said that the new 3W-50 would fly this plane nicely. Than another guy said I should go with the DA-50, yet another said the qudra 75. And last said go with the GT-80. I would like the GT80, but I hear the 445 was a great engine and I hear the new one is a problem child. I do not have a lot to spend on a big twin motor's. HELP please.
Thank you, David"

Karl: "Thanks for the question, Dave, AND the extra help. Based on what you told me of the plane, and the experience/research factor on my end, here's what I can tell you. The engine choices are many, ranging in price from $509.00 to $2,300.00 and go from typical, popular one-lunger 2-strokes to radials. The strange thing is, though that the radials don't cost all that much more than some of the high-end 2-stroke gassers you mentioned in the question. The horsepower ratings are very close, from 3.8 to 5.8. I will unapologetically recommend putting radials in it for many reasons 1) the Tigercat came with them originally, 2) they will look really cool 3) they'll sound cool 4) I think they will be easier on the airframe due to more control of vibrations, etc. Since this plane is well over 100" in span, you are probably looking at a plane over 20 lbs easy. This will mandate bigger engines. If you go with radials, I think the best choice might be the one from O.S. Engines. More power and less money than the Saito one, MUCH less than the Technopower one, and all the radials are more authentic than non-radials. Of the non-radial selection, I would probably go with the 3W 50i since for only $20 more than the 42i, you get a whopping 1 more horsepower! More bang for the buck, ya know? Hope this helps and I'm sorry for the delay in getting your question answered. Happy flying, Karl."

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Question 93: "Hi Karl, I have a TOP FLITE GIANT SCALE P47 (85" WS). It is ready for covering & weighs 17 lbs w/retracts installed. What Gas engine (MANUFACTURER/SIZE) would you use in this plane? This is my first WARBIRD & any info is much appreciated"

Karl: "Roy, you picked an awesome warbird for your first one. The "jug", as they were affectionately known in WW II, could take a real beating in combat and still fly their pilots home. I recently read a story of a Lt.Col. in the E.T.O. who flew one and one other pilot in his squadron actually was flying so low...(there really is a tie-in here to your question, bear with me....)....during a strafing mission, he hit a chimney on a house! Now, this plane was fitted (here is the tie-in...) with the Pratt and Whitney R2800 with water injection, an absolute powerhouse and rugged as all getout. So let me say, if you want to do the bird justice, look into some of the radial offerings. Sorry if I appear shamelessly pursuading you another way. There are many engines to choose from that are gassers and one-lunger 2-strokes. Not that that is bad of course, because there are alot of flyers out there who will swear by them. Zenoah, Quadra, ZDZ, all have great engines. The size IS important here because of the possibility of over-powering the plane. It only weighs 17 lbs so far, so don't get too aggressive. There is an awesome radial offered by Robart, which will fit in the cowl but is too much power. Saito, O.S. and TechoPower all have 4-stroke, glow fuel radials. These are real pieces of art that are also useable for flying. Check out the websites. Let me know if you don't have their websites and I'll give'em to you. Thanks for the question and let us know how the maiden flight goes. Karl."

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Question 94: "Karl, I want to add functional scale exhaust stacks to a 1/4 scale P-51. Can you help with a suggesstion or two? Jeff"

Karl: "Hello, Jeff. This can be tricky, but the results can be well worth bragging about. If you have an opposed twin, or the Saito shallow vee twin for narrow cowl engines, this could be real neat. If you have the usual single cylinder glow fuel or gasser like a ZDZ or Zenoah, etc, there will be a little more work involved. Probably the easiest way to do this is to take some tubing of the appropriate scale diameter and make several slight bends and cut the bends off. These will serve as the outlets you see sticking out of the cowl. Next you take another length of tubing, slightly larger in diameter, and fashion the tube to fit from the engine to the cowling where the exits would be. Taper the end ever so slightly as it gets further back, to maintain pressure. Once you have the right angle of the main tube, postitioned safely away from the inside of the cowl, you need to bolt it to the engine in place, and make six marks on the main tube (scribing works best...) where the exits will be. Using a Dremel or equivalent, grind out the holes for the exits and begin soldering them in place, being careful not to overheat the adjacent exit that you have just installed. Proceed until all six on a side are done and ditto on the other side. Now, this likely will be time consuming so here is another suggestion. Go to this site www.quarterscalemerlin.com and look at their masterpiece of an engine. They have designed and built a running 1/4 scale water-cooled V-12, supercharger available. See if you can get a set of the stacks from them and modify to your needs. Functional stuff like this always adds to the uniqueness of a plane. Hope yours turns out nice. Thanks again. Karl. "

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Question 95: "Karl, I am planning a project to scratch build a Beachcraft Staggerwing to scale and would like to put a “real” radial engine in it. I can afford either of these two engines, the OS FR-300 or the Saito FA 325, they are both around $1,400. Both are five cylinder radials. Which if either is the “better” engine and or is there something else out there in that price range I should consider. Thanks for any help you can give me!"

Karl: "Good question, Gary and thanks for visiting our site. Pretty cool, huh? The Beechcraft staggerwing is a cool one, no doubt about it. I have a couple of questions to ask, you can think on them and incorporate what you find out or respond here, doesn't matter. First, what size are you aiming for? Scale is relative so deciding on what wingspan, type of construction such as traditional built-up wood, frame and cloth covering, etc. You get the picture. What type of features will you have, air brakes? flaps? functional cowl flaps? (personally, I think cowl flaps are a MUST for radial engine choices in RC.), all of these things will deterimine the all-up weight. There are several radials out there, the other outfit that has radials in this range is TechnoPower Engines. They have 5, 7, and 9 cylinder offerings that are spectacular. They are all less than 6 hp though, so you might want to do a little research first. Ask for a gentleman there by the name of Marc Linville, he has all the scoop.
Next, have you considered finding a suitable engine, determine the size and scale the plane around that? Just in case you are curious, go to www.rcshowcase.com and look at the 5 cylinder gas radial they have. They even have a loop audio of the engine at idle, to help you. It is less than 2x the cost of the ones you asked about, and they too are good ones, so you may still stay with those, I realize. Lastly, for the most expensive see Robart's 7 cylinder glow fuel one. Wow. Hope this helps. Thanks, Karl"

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Question 96: "Hi Karl im building a balsa usa p51 im putting a saito200ti in it. I want a scale looking 4 blade propeller for it. Do you have any suggestions? thanks "

Karl: "Great question, Mandy. I will try to answer this well without disclosing too much of the details of the project I have been working on for a year. First, if you are looking for a scale 4-blade to fly with, I'm afraid you are out of luck. I have done lots of research on this very subject because of the project plane I am planning to build. The plane of my choice is a 1/5 scale F4U Corsair. After more research about engines, I finally made what I think is the right choice and this led to me looking into props. Due to engine loads, rpm's and so on, no one I spoke with recommended a scale, flying prop. It's a bad thing when the tips exceed the speed of sound---bad things happen. There are many things to consider, I believe, as to whether or not a prop system like this is practical. I believe I have found a good solution but the first version isn't done yet. After nearly a year of research I decided to make my own. My plan is for a scale, flying 3 and 4 blade prop, adjustable pitch and interchangeable blades. Right now I have only four made of maple. My design won't work with several engines due to high rpm ranges, but it will work on others.

If you are looking for a static four-blade, check out Century Jet or APC (sorry, maybe it's ACP...brain fade...). The plane you chose is a great one and the engine is real cool. The latest issue of RC Modeler, ?I think, has an article on this very plane and engine. It might be in the other popular RC magazine, whose name escapes me. Anyway, I hope this helps. It really sounds like I waffled on the answer by shamelessly talking about "my" project.Anyway, hope the plane turns out well and you get to enjoy it for a long time. Karl."

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