Question 73: "Hey George I am building a g&p sales 81inch albatross and I was wondering what engines you would recommend? I was looking at 2 os 70 surpass four stroke with pump or 2 os 70 four stroke with out a pump. Do you think they would have enough power and reliability? What engines would recommend for both reliability and power of any engine? Thanks, Brandon from Minnesota"
Twinman: "Hi Brandon, Which engine is best is the biggest can of worms in the world. And everyone has an answer. OS has a very good reputation. I do not normally use four strokes as I am usually after the maximum power. ( Never mind that I always warn others not to go for maximum power)I recently bought or traded into a Fokker 27 at 120" and two Magnum 91 four strokes. I have never used these engines, but I must say that I am impressed. Easy to start, and good power for such a large plane. The sound or two four strokes is MUCH Better than my usual two stroke fare. Am running YS 20% due to the large size of the plane, but, while it will not loop, they are doing a good job.
Pump or not? Depends upon how close you can get the fuel tanks. If close, no problem either way. If far, use pumps for best dependability. Note Perry makes an oscillating pump for four strokes. Now, how are you going to mount the engines? If inverted, really consider on board glow. Good Luck and send pictures, Twinman"
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Question 74: "Hi George, I wish to complement you for your very interesting articles about twins. I learn a lot from them. I am building a Don Smith 126" A 26 Invader, and have purchased two 3W 24 engines to power it. It seems to be coming out fairly light, however I am beginning to have doubts about the size of the engines. I really think that it will be underpowered. I would like to use these engines as they will not stick out of the cowls, however I would appreciate your opinion. Thanks and regards, Joseph"
Twinman: "Hi Mr. Attard, I took the position a long time ago, if I have not done it, don't tell someone else how to do it. I too would worry about that power amount. OK, here is as close as I can get. The silver P-38 shown here at rcwarbirds in the fighter and P-38 section weighs 29 pounds or 13.2 Kg for our European buddies, It has two Super Tiger 2500's which are about the same size as what you propose. Here is the problem. I am running 18x6 props at 8000 rpm....ok so it has larger carbsbig mufflers, and Perry Fuel pump. I fly off of a concrete runway. While the plane flies well and will do a loop, with planning, I personally consider it slightly underpowered. It would really have a long take off roll on grass. If you cannot get the above rpm, out of the 3W 24 engines, I would really be concerned. I have flown the VQ A-26 under powered and it is not fun at all, to need full throttle to stay in the air and be a heart beat away from a snap roll in a turn. I have also flown it with good power and was a lot of fun with the engines at 30-50% for normal flight.
Go to the P-38 picture section and about half way down, there is a P-38 flying with your engines. Maybe rcwarbirds can contact him for his impression, but your plane is bigger. Gas engines are reliable, but they can fail. With this combination, I would really worry about any chance to fly it down safely on one engine. While I have not directly answered your question, and I must apologize for that, I hope this helps. I do understand the concern for the engine not sticking out. Send pictures when you finish and let us know how you went for power. Twinman"
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Question 75: "George: I appreciate your assessment and comparison of the KMP and VQ P-38s. Do you have a flight assessment of the KMP P38? I also would like your opinion on engines for the KMP p-38. I would like to use four strokes and go a little large on the cubes so as to get a more realistic sound. I am thinking that larger engines and props would produce the desired thrust and speeds, at lower RPMS than would be necessary with smaller engines. I am thinking about 91 FS for the KMP P-38. I realize there is a weight penalty and going full throttle could be a disaster. What is your opinion? Thanks Eric"
Twinman: "Hi Eric, I really cannot help with actual flight experience with the KMP. The local one I took the pictures of, is still not ready. Can't wait to fly together!! I have now owned five P-38's ( yes, I need a life) My current is the VQ with ST 90's two strokes and that is way over kill on power. My Aerotech at approx the same weight, and 78" wing span used two ST 60's two strokes and had all the power you could want. Several of the guys I have corresponded with are going to use Saito 100's and three blade props. I am using the three blade Master 13x8's and they really look great.......to me.
The power of the engines you are proposing sounds great, but not as great as the sound they will make in the air!!!
While I do not recommend over powering twins, as you can get into trouble there too. Having flown underpowered twins and the Wing Mfg P-38 underpowered, do not do that. The plane will tip stall and require a scary amount of runway to get off. Flying an underpowered twin is not fun and really makes the worry of engine failure worse.
You did not say if you plan to fly off of concrete or grass. The extra power of the engines will be of benefit in either case, but almost a necessity from grass. The high wing loading of the P-38, and the smaller ones are worse, make high take off speeds necessary.
My two cents. If you are doing this to be able to fly the P-38 on one engine........don't even think about it!! An inverted flat spin is a heart beat away.
Consider, Strongly, on board glow, as I assume that you are talking about inverted engines. Burn into your mind, reliability for the engines. Do not worry about full throttle. Use it for take off and get as much ground speed as possible before take off. These engines will also get you up faster to a safer altitude. I am using every ounce of power my 90 two strokes can provide, to gain safe altitude, then power back to less than half throttle for flight.
I, personally do not like the KMP elevator control. I would really suggest using two separate servos, one in each boom, for the elevator. The Wing Mfg P-38 used one elevator servo and the elevator fluttered at high speed. Yes, the control was at one end, but still, you will get better control if you connect at each end of the elevator.
As you are going to use extra power, and let's be honest, you will use it at least once!! Consider to pin the horizontal stabilizer to the booms. That is a very high stress area for glue only, in my opinion.
Check all the glue joints, yours and theirs.
The next comment is not being critical in any way. The firewalls on the KMP are one half the thickness of the VQ. Look if you feel any additional beefing up is necessary with larger engines. You will sleep better the night before the maiden flight!!! In this legal eagle world, I do have to remind you that the manufacturer does not recommend these size engines.......neither does VQ!! Now with the disclaimer out of the way,,,,,,,,,GO HAVE A BLAST!!!!! and wow the local "Single Pilots" at the local field. Twinman PS Send pictures!!!!!!!!"
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Question 76: "I have an P 82 mustang from dynoflight kit. I put two k&b 45 sportster engines on it and I made one counter rotate. Does this have any effect on the performance?"
Twinman: "Hi, I do not think that it hurts at all and the take off's will be a bit easier. Is it necessary? Not really, but looks cool. A bit of a pain to start. Good Luck, Twinman"
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Question 77: "I am new to the multi engine scene so I am writing for your blessings on engine choice. For the 120" Wescraft B-17 I have gone with YS 63's (mainly for their pressurized fuel system and reliability) For the 101" Ziroli B-25 and the Ziroli P-61 I have gone with the RC Showcase 180 F . Any thoughts or recommendations on these selections. Thanks Glenn"
Twinman: "Hi Glenn, The engine selection sound great. I have not flown those birds, but above all, Remember reliability is the life blood to long multi engine life. Good Luck and send pictures, Twinman"
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Question 78: "Twinman, I have the pleasure of training new pilots with the simple trainer style aircraft, and my third lesson to them is rudder usage!!!!!! My motto is: use the rudder, it's not just there to place decals on! Before a student gets the boot out of the nest I make sure they correctly use the rudder in the turns, on takeoffs/approaches and on the ground. With complete knowledge of rudder control I still take your lessons (learned the hard way by the sound of it) to heart and have decided to build a trainer style
aircraft to learn the do's and don'ts of twin aircraft. My ultimate goal is to build a P-38, but after much research and listening
to your "squeaky soapbox", I have decided to build a "trainer" version first. I have an old style ugly stick 60 size kit that I am going to bash together to make my first twin. I am planning on simply cutting out a second set of wood parts to make the other fuse. I planned on modifying the wing to achieve the longer wing and building the center pod of the airframe as a whole with only detachable wing tips. I have a couple of questions, how do you calculate the distance between the fuses? I realize that the closer together you put them the more stable they are, but I want to be sure this plane battle test me for the P-38 kit that I want. I was also thinking twin Satio 1.00 four stokes with on-board glow for power (thinking I could use them in the VQ P-38 kit when I'm ready). Should I use the gyro's now, or should I wait and just use them on P-38 kit? Any advice would be appreciated. Thanks, Bill"
Twinman: "Hi Bill, My original test bed was a bashed 60 size stick and still fly the twin fuse version.....kind of a 100' standoff scale F-82. My wing is 88" long. Actually, I did plan to make this plane the Stand Off scale P-38, as you are going to do, but got lazy and left out the center section. This is the most fun plane I own and fully aerobatic. Engine out is great and easy to handle. It will look like a P-38 but due to the wing loading, will not fly that way. This is too light, large booms and large rudders. For now, don't change this and you will have a blast. Now, if you get to where you feel better about it, you can gently add weight to increase the wing loading. I am flying twin ST 90's on mine, so you have no problems with your proposal. I would reinforce the wing with carbon fiber above and below the wing. The loads on the standard wing is higher, and a little extra insurance is good. Watch out for the junction at the fuse and tail. Have seen several cracks there with long use.
Gyros, you will not need them as long as you are really into the rudder mode as you teach. Few fliers do this and few progress because of it. You will eventually have an engine out or you can program to control one engine to get the feel without the unexpected out that causes the heart to race. Now, once you get the hang of the plane, you can insert gyros to get a better feel, but I would wait until you begin to add weight. Enjoy it and you will with that power. Now, for prop spacing. Set the engines up away from the center pod to allow prop spacing for whatever prop you plan to use on these engines and add 1/4 inch. Fantastic idea!! You must send pictures. Twinman"
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Question 79: "I just bought at a garage sale several old model rc kits. I thought I might inspire my brother in Phoenix who worked for Sperry making auto pilots for aircraft and has his pilots license, to have some fun with his grand children. Now I see they are older and may or may not have all the parts. Do I dare send it on. The plans seem to be there and just wondering if I have an inspiration for the brother who has everything or if it is actually a can of worms and I should use the balsa for sculpture?Perplexed in Carmichael, CA Sue"
Twinman: "Hi Sue, Never throw away rc kits!!!!!!!! Arrrggg!!!!!! Seriously, those kits are worth something to some modeler. You can sell, if nothing else, on our sister website at rcuniverse.com. The skymaster is very popular right now, as are amphibious planes, so they in particular has value. Good Luck and Happy New Year, Twinman "
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Question 80: "Hi Twinman, Sorry to hear about your recent accident with your P-38. I am just about to start construction of a 81" OV-10. To make it easier to transport and assemble I am thinking of constructing the wing so I can remove the wingtips, outside of the booms. Have you any advice on constructing the removable wingtips. Particularly on the joints, wing retention and any extra strengthening. Also can you recommend any retracts that look scale for the OV-10 as well. Many thanks, Sarah"
Twinman: "Hi Sarah, Thanks for the kind words, but I married outside my class in life and Wife ( Santa) gave me a new VQ P-38 to start all over again. If you look at the OV-10 Bronco in the pictures here at rcwarbirds, I also built the wings removable. You can simply go to your local hobby store and they will have "Wing Tube Kits". These are basically fiber glass tubes that you epoxy into the fuse and wing with aluminum hollow tube that slides inside. I permantantly mounted the aluminum tubes in the wings. When I slid the wings into the fuse, I put a metal screw into the fuse tube mount to keep it from coming out. You can use one large tube on or near the center of the wing to carry the load and a simple dowel to prevent rotation of the wing near the end.
As for retracts, mine were fixed, but that was a lot of weight. Go to the section on retracts and talk to the expert there, or you can see his advertisement and go to his site at http://www.sierragiant.com/. He has a set for this plane. They look good, but like anything quality it is not bargan basement pricing. Remember reliability of the engines. This plane with such high wing loading does not fly well on one engine. Good Luck and send pictures, Twinman"
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Question 81: "Hi. Who out there makes a kit for a big C-46 and Skyraider with f/g parts? I saw them one time and can not remember where it was. Thanks, Mike Rounds."
Twinman: "Hi Mike, Try http://www.flyrcmodels.com/ This is American Eagle Models. They have both. Good Luck, Twinman"
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Question 82: "George, Have an interest in the DH Mosquito twin bomber. Do you know where a 60 size kit can be purchased? Good work. Robert, Nova Scotia"
Twinman: "Hi Robert, This was not the easy one. I did find one in the UK at http://www.atimanufacturing.co.uk/. You have to look, but they have it in the warbirds section. I built their P-38 and it goes together quickly, but has quit a bit of fiberglass, if that is ok,
Good Luck, Twinman. Update: Found another one, but an arf http://www.giantscaleplanes.com/Mosquito_73.htm Twinman"
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Question 83: "Hi George! I really enjoy and appreciate all your advise and time spent helping us with "Twins". Thank you very much! After a successful summer and fall building and flying my first twin (GP Profile-38) I have my next project on the way! The A-26 Invader from VQ Models. I noticed a earlier reply from you to a post regarding engine size for this twin. You mentioned Magnum 52 four strokes not being enough? I would like to use four stokes, what size would you recommend? Would Saito FA-56's do the job? I will be flying off grass (500') and will have retracts. I have downloaded the manual from VQ Models web site and noticed the front page indicates .40 - .52 class-4 cycles however the second page of the manual says 60 - 70 4cycles??
My second question is regarding retracts. I purchased my A-26 direct from VQ Models. They do not sell the retracts but Mike there at VQ recommended the spring air model 702 with firewall mount?? I've noticed Morris recommends model 102. Which would you suggest I use. I have no experience with retracts. I've looked at spring air's web site and was unable to figure it out? Please advise if possible. Thanks... Cal"
Twinman: "Hi Calvin, The planes I flew with the Magnum 52's also used three blade props and was VERY underpowered. Took full power to fly. Owner changed to Magnum 68's and was a completely different plane. I have also seen it fly with twin ST 45's and it is great. This plane can be surprisingly aerobatic if powered well, so do not under power. The firewall was modified from the earlier model. That is the difference in the nose retracts. You can contact spring air at http://www.retracts.com/ for further information. It is not a big deal either way, you just have to add blocks to mount the other retracts. Check how the nose gear mounts in your model. Good Luck, Twinman Remember to always do the vertical test before every take off. On board glow is a good idea."
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Question 84: "Hello George, could you tell me if 2/52surpasses will be enough for my 86" Henschel 129, weight is currently 13.5lbs, wing area 1044 sq ins, and wing loading approx 430oz per sq ft, I plan to test fly in primer first, and have an on-board glow system, it is a blown up plan from a smaller 55" hand-launched job....I usually have 12/6 master props on these engines, and they are both well run in on them,looking forward for your advice, here"s a pic of the model...... Clifford, Northern Ireland"
Twinman: "Hi Clifford, Will it fly?, Yes. Will it fly very scale?.....Yes. Will you like it?.....NO!!. Not at that wing span and wing loading. It will also not fly on one engine. My VQ P-38 has similar wing span and loading, I have seen it fly with other owners with .60's two strokes and three blade props. Flies well. I would seriously consider going to at least .60 size four strokes. Sorry, that is not what you wanted to hear, but I really worry that it will not be fun at all to fly at that size and wing loading. If you must go with those engines, check old RC Reports magazines for best size two blade props for most thrust..DO NOT ATTEMPT A LOOP!! It will snap roll and you have spent too much time and effort to risk that. I wish you the best of luck. It really looks great. Twinman"
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Question 85: "Bonjour Mr Twinman, I bought a VQ P38 and didn't find any instruction about the center of gravity. From your experience, where is the suitable point ? Regards Guy"
Twinman: "Hi Guy, If you go to the last page and box number 41 "Balance" is shows the balance point at 115-120 mm. Would suggest that you go to 125mm from experience with two of the planes balanced in both places. Too far forward and it lands very hot. Good Luck, Twinman PS Remember RELIABILITY. Check the engines for consistant run via the vertical test before every flight.
Best of luck and welcome to the crazy club of muli-engine pilots."
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Question 86: "Hello again. I just purchased a VQ A-26. I have a piezo gyro that I purchased with a helicopter that I may use in the A-26. Will this type of gyro work for this purpose? I'm assuming that I should connect the gyro to the rudder? Also, would it be beneficial to program a mix into my radio to couple the ailerons with the rudder? I was thinking this may be helpful during an engine out in that if I don't react quick enough with the rudder, the mixed rudder/aileron may help counteract the engine out. One more thing... what 3 blade props would you recommend for the A-26 with two .46's for power? I think you mentioned 11x5 or 12x4 before, but I was wondering if that would leave sufficient prop clearance on the A-26. I know of one person who uses 9x7 three blade props with ST .45's and he said it flies very well and fast. I'm not interested in all out speed, I would be looking more for power and single engine out performance rather than blazing speed. Many thanks again for your advice... Dan W."
Twinman: "Hi Dan, The V A-26 with the ST 45's I have flown has Master 9x6 three blade props. It looks small, but it flies very well. If you go to two blades, consider 11x5 for more thrust or even 12x4 which I use on my twin fuse twins, for fun fly style, but on this plane might be too slow. I do not recommend a helicopter heading hold gyro!!!! Yes, you can use it as long as you NEVER set the control for heading hold.The problem with the heading hold setting, is that the, in this case, rudder will not come back to center when you release the control. It stays there. Leave it in normal gyro setting and there is no problem. I do not recommend mixing the ailerons to the rudder. You MUST use the rudder coordinated with all twins and multi's at all times. Several reasons for this, including smooth control, heavy wing loading,ect.The important reason is that, if you lose an engine and you are not used to flying coordinated with the rudder, NOW IS NOT THE TIME TO LEARN!! You must also fly coordinated rudder if you install a gyro, or the gyro will fight you in the turns. Using the rudder cancels the gyro until something unexpected happens and makes the plane very stable. Don't worry about reacting quick enough with a gyro. It will react much faster than you can, and that is the reason for it. To dampen unexpected problems to the point that you can react.
Please learn to fly with the coordinated ailerons and rudder at all times, before advancing into multi's. You can also go to rcwarbirds sister forum, where I posted a test with this plane doing a single engine test at
Now remember, this was a test under controlled and predictable circumstances and without a gyro. Never do a take off without the vertical test first. Good Luck, Twinman"
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Question 87: "Hey Twinman, I'm building a 1/4 scale Grumman G44a Widgeon for competition, I hope. This engine configuration was an aftermarket upgrade done by SunVally Aviation using two 680R Lycommings. The plane has a reasonable vertical fin and rudder, but obviously not big enough for the Designer. He set the engine incidence at +4 degrees, and the engines are also canted out about 3.5 degrees, left engine left outboard, and right visa-versa. I'm using two Saito 4.5r's to carry this thing off the water pulling two 21" dia. three bladed square tipped props to replicate the Hartzell 84" steel blades. I am also thinking about slaving the throttles off the rudder using reverse exponential for better low speed control. This thing wont fly fast. I'm pretty sure this sounds nuts, but I've flown the real plane, and it seems a little soft on the rudder, and everything for that matter. What do you think? Control is important with a 50 lb. 10 foot WS plane. Thanks for your help. Jack McGeough"
Twinman: "Hi Jack, Sounds like a beautiful bird. Here is a post on how to mix the throttles into the rudders using a Futaba 9 C.
Now, as you read below, I am warning about setting this function to activate at too low of a throttle setting. I developed this mix for aerobatic manuvers. The warning is that you do not want the engines cycling individually at low speeds, or control at taxi can be a handful. It does aid in turns, but I would experiment on a less costly model before using it on such scale plane. I use this mix at all times, for better aerobatics. I f it is toned down, it will aid in turns, but I am not a full scale pilot, let alone a multi pilot. You can decide on this better from your experience. Most of the twin guys do not worry so much about engine offset. If the idea is to control the plane on engine out, 3-4 degrees will not make much difference. The positive placement of the engines, must have been to offset the drag of the floats, but could be "Interesting" if the model pitches down as the throttle is reduced. I would go 0 offset and vertical setting until you can see how it acts. Good Luck, Twinman
Now we are talking my language!!!
Set the total throw of the master throttle (3) to correct travel.
Put the second throttle servo on channel 8......or whatever, but that is what I did.
Go to mix number 6 or 7 as they have an expo function.
Using the expo function, map the response of the second engine to the response of the first. If you cannot get enough throw, you can change it using the ATV'S. This really helps with throttle up. Make sure the engines are adjusted as normal for flight.
Go to the basic (aero) and aux channel. Set channel 8 (My choice) to vr-8. This allows independent idle adjustment of the second engine. Remember which one you use!!! The second engine can be adjusted for idle, but as below, the link function ties the trim tab to both channels.
Turn on link function. This attaches the trim tab to both channels.
Rudder mix on top of this.
Use mix number 1 and set rudder as master and channel 3 as slave.
Set swtch to stk- throttle
Set position to 40% or more.
Use mix number 2 and set rudder as master and channel 8 ( Or whatever, but nine) as slave.
Set switch stk- thr
Set position 40% or more. Note, this setting must match the setting in mix number 1. I used 42% for both.
The importance of the above mix is that the rudder does not command the engines to cycle up and down during taxi. This can be very dangerous. The throttle must be 40% or more for the mix to activate.
I have not messed with the kill function yet, just use the trim tab.
Good luck, Twinman "
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Question 88: "I wanted to ask you about the oleo struts on the VQ P-38. At what length did you cut the 7/16" oleo struts, especially the nose for the static ground stance? I guess I could measure them when I install them, but thought I'd ask anyway. I'm also running into a problem with the rudder servo pushrods. I don't want to mount them as per the instructions using the "Z" bend, so I reversed the servo arm and moved the servo inboard so that the rudder and elevator arms are in the same direction. I now have the problem with the stock 2mm pushrods, as they are so thick that there is too much resistance in the pushrod guides with the fwd part of the servo mounted as low as it is, so I raised the fwd part of the servo to help alleviate the stress. However, the problem I now have, is that the rudder pushrods rub against the outboard wing mount bolt when the booms are installed. I'm thinking about trying 1.5mm pushrods and replacing the servo arms with longer ones. Any ideas would greatly be appreciated. Thanks for all of your great advice!!
Twinman: "Hi Robert, To others, Robert is serving our country in Germany. There are two ways to get around the wing bolt interferance.
1.Here is what I saw on one P-38 for the Elev/Rudd setup. The modeler did not bend a Z, but just bent the rod about 10 degrees. This provided non-binding movement and clearance for the wing bolt. It is important that you, glue the guide tubes to the former just after the wing-bolt plate, this will eliminate any play in the rod. This is the same setup used on another P-38, and have not seen any problems with it.
2. What I did on my P-38, is to install a servo reverser on one of the rudder servos and put the arm on the other side.
It also does not hurt to shorten the bolt a little bit.
Measurement as follows for your struts on the p-38:
Nose 6.5 from bottom of retract block to the center axle.
Main 5-7/8 from bottom of retract block to center axle.
Good Luck and be careful over there. We need more twin guys on this side of the pond safe and sound. Thank you for your sacrifice,
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Question 89: "Hello George, I just purchased the VQ P38 and bought Saito 65s based on VQs recommendation. Did I make a mistake?"
Twinman: "Hi Jim, Your engines will work ok. Do not go to three blade props until you have flown it with two blades and are comfortable with the performance. Several modelers are going to Saito 100's. I really like the sound of four strokes, but they have not got the power of two strokes. I would also consider 20% nitro on this bird and those engines. If you intend to try a loop, make sure you are very high the first time. A P-38 that is marginal on power will violently snap roll in a loop. Three blade are not as efficient as two blades. This is a 14 pound plane with high wing loading. I would hope that you plan to take off from a hard surface. I went with large engines as I wanted larger (13") three blade props for scale appearance. Larger engines are not recommended by the manufacturer due to liability reasons. A little common sense must come in if you over power the recommended engine sizes. I can say that the wings are very strong. Good Luck and send pictures. Twinman"
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Question 90: "Hey George, I copied your advise on the setup of the engines and it all sounds good. However, I have another question based on what you said. I've always used JR radios, and now mostly Hitec digital servos. Is the Futaba 9c the only radio throttle plotting can be done on, or is there a way to do it with say a JR 388s or 8103. Perhaps in glider mode using "spoiler" for throttle and mixing channel 8? I tried to find something in the manuals, but nothing jumped out at me. Also, I'll be running two Saito 450r's and I was wondering if there is any way to run a dummy engine in front of the Saito's without running hot. Karl said that isn't a good idea because the engines will need all the air they can get. However, this plane (in real life) has what is referred to as a turbo cooler. That is a large tail pipe sticking out the rear of the nacelle above the flap. This tail pipe is slightly larger than half the size of the intake opening on the cowl. I'm thinking I'll have a cooling problem with this setup, and I was wondering what you might think about using a dummy engine as a baffle to direct cool air directly over the cylinders and heads. Thanks for all the help George. You guys have been a treasure cove of help and information. Jack"
Twinman: "Hi Jack,I am sorry that I only own Futaba. Nothing against any other brand, but that is what I got started with and stayed with what I knew. The "Mapping" is really a helicopter function, but I would think that some type of exponential curve could do approximately the same thing. Suggest to to our sister forum at rcu and the radio section. You can ask this directly from the manufacturer's representatives. Cooling. I hope you must understand that without actually trying something myself, I am very hesitant to offer advice to others, particularly on engine's and a model as valuable as yours. Most of my advice is based upon mistakes I personally have made, and Lord knows there have been a bunch of those. Please send pictures of the finished installation.
On the P-38, there was a kind of movable flap below the nacelles, that was used for the oil cooler and temperature control, that I build into my models to create a low pressure zone to "Pull" the air through the coweling. There is also the idea of using baffels to force air to the specific cylinders and I think that is what you are getting at with the dummy engine, and perhaps opening only at the specific cylinders. There are several in flight recorders or you could insert a temperature probe and run the engine on the ground to check temperatures and constantly monitor the engine and head temperature. Note, this is a very severe test on the ground as the air flow in the air will be much greater. If it works on the ground, you will be safe in the air. "
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Question 91: "Have a chance to get a G&L p38 unbuilt at a good price. Do you know anything about this kit or flying characteristics. Please advise. thanks"
Twinman: "Hi Tony, No, I have not flown that plane, but do have a 108" P-38 that is built up. Would consider at least ST 3250's, Moki 1.8 or 2.1 or 38cc engines if gas. No P-38 is a trainer. I have heard that several people have built that plane and were happy over the years, and no I do not remember who they were now. Brain going with hair!!! Would I do it at that price and if I had the time to build it, you bet, but having owned five P-38's, I am nuts!!! Let us know how it comes out and send pictures. Twinman "
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Question 92: "Hi Mr. Lumpkin, I had also recently purchased the VQ P-38 ARF from VQ Models. I had seen your video and read your reviews, I do like the kit and wish to power it with a four stroke setup. I will be installing the 12 required servo's and retracts as well. My question is that I'm stuck on motor's. It's basically a toss up between two. First is the YS 63 FZ turbo engines, which I love and fit in the cowling just fine, but worry that it may be under powering for this aircraft with a guessed weight of around 15 1/2 pounds when done. The other being the Saito GK100, which is nice and light and powerful, but does require cutting to the cowling. I know the Saito is putting out 1.8 BHP but not sure about the YS 63, all I keep reading is that it is very close to the OS 91, but no real concrete numbers can be found. So I ask you, which one would you go with for this kit and why? Any help would be great and thanks again. Mike"
Twinman: "Hi Mike, Let me ask you a question. What is the surface you plan to fly off of? If grass, I am really worried about the YS 63's if you do not know the power!!! The P-38, any of them, have high wing loading and need a long take off run. Longer if it is on grass and you should really add some for best airspeed and control on take off.There are several modeler who have built this with the Saito 100's and are happy. Mine has ST 90's and is a blast to fly. Note, the manufacturer does not recommend such sizes, but the wings are very strong. One guy did report that he was really wringing it out and slightly bent the wing tubes. I never did that one, but I did put additional epoxy in the wing tube connection area, so I would sleep better.
P-38's also are tail heavy and you will have to add nose weight so why not use the enignes weight?
I must base this on my experience with the ST 90's that the plane flies great with lot's of authority. Running Master 13x7 three blade props.You really do not want an under powered P-38, or forget loops,it will tip stall and spin. Had the problem on a Wing Mfg P-38 with two ST 45's. Change to 60's and had a ball. Good Luck, Twinman"
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Question 93: "HI there I am considering building a twin engine aircraft, Have Warbird experience, scratch build YAK9, LAG7 and IL2 all were around the 72 - 74 inch wing span and used a SAITO 120 FS engine. I am considering building (Scratch building) a Pe-2 and was thinking building a "HAK" first to get some twin time before I ho to my scale project. So the question is for specs like:
W/S= 70 - 74 inch
Weight -11 - 13 lbs
What type of engine will give good performance? I know that this is hard to determine, fuselage, wing selection etch, etch However I I assume that a single engine develops 10 lbs of thrust with 2.1 horsepower, then in order to get the same performance from 2 engines would one devied the horsepower in 2? Any tips are appreciated. Kindly Regards James."
Twinman: "Hi James, No do not divide the engine size by two. Yes, you will hear a lot about larger disk size, being more efficient, but only to a point. I bashed an Ugly Stick 60 into a twin with two nacelles and use two 40's. Yes, it flew, but very under powered. Two 60's made it fun again. Now that was for a more aerobatic design than you are proposing, but consider this. If you are getting twin experience, do you really want a plane that will not fly on one engine? No, I did not think so. The problem that must be considered to bash a single into a twin is the increased wing loading from the other engine, and drag, if it stops. If you do not plane to increase the wing span from a single to a twin, the wing loading and so power requirement will rise quickly. If it does not look to crazy, I would consider to add approx 10% wing span to keep the wing loading down. Do you need two 120's for your project? No, but the 120 fs is somewhat equal in power to a 80-90 two stroke. If you want a fun plane to fly, I would really not consider to go below 60 two strokes at that size. Now, I really do not know what the wing shape is or drag, so this is my best guess based upon my mistakes, ( Experience).
Good Luck and send pictures. twinman"
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Question 94: "Twinman: I'm currently building a Ziroli P-38 and have been looking into the best engines for this aircraft for
quite some time. I admit that I am partial to rear induction engines due to fact that I do not want to cut holes in the side of the cowlings for side intake. The real P-38's did not have such a hole. Also, I want an engine that can swing a scale size 3 bladed prop in the range of 22" to 24". Accordingly, I've considered the DA 50, 3W-60i and 70i and was leaning toward either of the last two since those engines could probably swing a more scale size prop. I'm told that DA will soon introduce an engine in the 70 cc range and will consider that engine once on the market. Any suggestions? Larry Jones"
Twinman: "Hi Larry, I am very happy with your concern for using scale props and no extra holes. If you go to the P-38 section here in the fighters section, you will see that I installed zdz 80's for the same reason as you. Yes, I did reinforce the wings and yes, it was too much for the Yellow, but I know where the throttle control is. Make sure your wings are strong, though. It take a bit of power to run such large three blade props. If I remember correctly you need 24 inch three blade props for your plane. The smaller, and lighter Yellow, needed 23 inch. I got 6400 rpm with the Mejzlik 23x14n props. You might consider that you may have to have a back plate make of steel to allow lower rpm at idle. The carbon fiber props are very light, so flywheel action was almost nonexistant. This allowed a 400 rpm drop in idle speed. Make sure you build all the controls, including choke into the plane as you build with the rear induction engines. The Yellow, being a fiber glass plane, it was really a pain. Suggest the you use one servo for both chokes, to keep channel count down on radio. DO INSTALL BRAKES. The large three blade props produce an amazing amount of thrust even at idle. Good luck, Twinman"
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Question 95: "Elsewhere on rcwarbirds you will find the construction article on the P38 trainer I am doing. I have counter rotating Q50's and have installed them in their scale locations (so props turn out). It has been suggested that I change them around to help in an engine out situation. What is your opinion? The trainer is a break-in platform and eventually all of this equipment will be transferred to a Ziroli P38. The trainer is basically the same as the Ziroli with the major difference being the wing. The trainer is a constant cord semi symmetrical instead of being a double taper, so placement will be more critical on the Z "
Twinman: " have flown P-38's with counter rotating and standard props and see very little difference. The torque produced during engine out will be the least of you worries. You will not be running the engine at full throttle or you will go inverted instantly anyway. You will be at low throttle and trying to get down. If you plan on three blade props, prop selection is almost non existant for that size engine. Zinger component being the only one I am aware of.
I would really consider the twin gyro set up for control during engine out over the worry and hassle of counter rotating props.
Good Luck and keep up the good work. twinman"
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Question 96: "Hi T/M. A question came up today at the club about gyro positioning. I wanted to get a good clarification on the positioning of the gyros, mine being Futaba GYA 351's, before I go back and beat my chest with pride, as my instructions aren't very clear on this particular question. They only address the distance from motor drivers (electric, I assume) and servos. The question is, is there a concern about the distance the gyros should be from the battery pack and the receiver in respect to interference? My instructions only say 10cm from the driver motor and 2cm from the servos. Thanks again. Bob "
Twinman: "I have never seen interferance from the gyros, but if we are talking about electric motors, just like any receiver or servo, farther is better.Try to get near the CG of the the plane for better response. Good Luck, Twinman"
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