Question 25: "Twinman, How did you set up the linkages in your Bronco. The Uravitch Bronco uses a bellcrank system consisting of four bellcranks (two in each boom). Did you use something similar or design your own. Paul H"
Twinman: "Scale Fan, I must admit that I am not the ultimate in scale builders. Please see the builders section for the guys who really make the beautiful planes come alive. I enjoy flying more. The elevator has one low profile servo mounted inverted, centered, in and
under the horizontal stabilizer. Bell cranks have never been a favorite of mine. To me, you can't see the servo anyway from above with it sitting on the ground, and really cannot see in the air. Good Luck Twinman"
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Question 26: "My first trike warbird( Morris Hobbies A-26). I'm using Spring Air's retracts. How do I connect my servo to the front retract? (The retract connects to a vertical fire wall) The kit had no details on this. The control arm is a piece of black plastic, a brass rod connects to this with a piece of white plastic that slides on the brass rod. I see that Spring Air has a pull-pull control arm. Seems like this would work better but how do you keep the 3/16" strut wire and wheel from hitting this 'control mechanism'?"
Twinman: "Hi to Mr. Ohio The A-26 I did had the spring air's for the nose gear with the pull pull system for steering, and it was not fun. You ran two wires to the steering arm, on each side of the nose gear, and to the steering servo. The problem was two fold. You have to route the wires out to clear the wheel and the wires tended to fold up to the rear and get tangled as the nose wheel came up. All that had to be planned for and handled, and still was a bit of a mess. The gear you have is the newer gear from Spring Air that only uses a push pull rod, which should be easier to set up. Also your newer model has the gear firewall mounted as you noted, where the original kits were overhead beam mount. I have not actually used this new gear, but it should be easier than the two wire system.
I would suggest that you give the guys at spring air a call. I have always found them good and easy to talk to and very helpful. Their home page is http://www.retracts.com/index.htm Good Luck, Twinman"
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Question 27: "Much like yourself, my job that supports my hobby keeps me out of my workshop far too much. Because of this and limited financial "play money" I am very interested in the VQ A-26 Invader from Morris. The A-26 has long been a favorite of mine. I was wondering how well it would fly without gyros? Will mechanical retracts perform well in this plane? If so, do you recommend any particular brand? Would a pair of .32 2 strokes power it well or should I put in a pair of .46's? I have yet to fly a twin other than on a
simulator and I think I will take your advice and kitbash a plane or two before throwing my $ into the A-26. Many thanks for all of your postings and answers. Dan Willis McAlester, OK"
Twinman: "Hi Dan, I would do the kit bash route first. Cheap and easy. The two Long John's if you want to build,or two stick(or similar) for the arf route. I would go with the larger engines, defiantly. Now, kit bash using two forty size planes and you are set. Try to pick long tail moment planes and large rudders. Keep the fuse's close together. As for gyros, no, they are not necessary .....particularly if you already have twin experience. If we were talking about a P-38, I would say yes, The kit does not lend itself to mechanical retracts, so I would really suggest the spring air's for it. Could the mechanical be done? Yes, but extra trouble will make the spring air's easier. Good Luck, Twinman "
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Question 28: "Dearest Twinman: After careful review of twin engine operations, I placed my Twinstar very gently in the driveway and drove over it three times very gingerly with a 3/4 ton conversion van so as to flatten that sucker. I experienced much success. But now I have a hypothetical question.... If say that darn Twinstar wasn't dead,,,, and "repairable",, would the OS 40 LA's engines that I
purchased for it ,, done the trick?????? or would they have been too much power ??? Also, had that damn Twinstar survived, might I have gotten by with only a rudder gyro??????? PS , Any other recommendations for a Twinstar (if it survived) ??????"
Twinman: "Uh Ralph, Sir, Remind me to never make you mad!!!!! sir The twinstar is a fantastic flier with two LA 40's. Most around here have that combination. I have flown one with the LA 25's,,,,,,and it flew kind of scale (See "boring" in the dictionary) The only drawback to the LA forties in this plane is the small fuel tanks the do not allow much beyond and eight minutes safe flight, but do it anyway!!! Again, gyros are not absolutely necessary for this plane. None here have it. If you really want to use one, I would only suggest for the rudder. Reliability is the key for any twin. Learn to use the rudder, now, and always use it in flight. You cannot learn the rudder with only one engine running......way too late!! Always, ALWAYS use a helper, and hold the plane straight up at full power
before every flight and listen to the engines. Any change, means don't fly until those engines are absolutely reliable in this condition.
My personal secret is to always take a deep breath before each take off......keeps the shaking down!!! Off my soapbox. Good Luck
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Question 29: "Twinman I am finishing up a ZIROLLI B-25 and i have seen that very often you have 2500s on your twins . The zirolli is 102 inches , and I am thinking of using these engines . I have an acquaintance from LOUIVILLE KY. and he flew a p-38 with them and they just seemed to be rock solid. I never seen him have a engine failure . His name is JOHN MORRISON and he flew the 38 like most guys fly a sport plane . DO YOU HAVE ANY RECOMENDATIONS on doing anything to these engines or just leave them as they are? Thanks Tom Duncan "
Twinman: "Hi Tom, Per usual, the job keeping me away from the hobby. Sorry for delay to answer.
My two cents on the big ST's. Love them.
Here are my few tips.
1. Use only the Big ST blend fuel. It is lower on oil content than normal two stroke fuel and the engine will idle MUCH better with it. It also makes considerably less mess on the plane, than two stroke and will give actually better fuel economy due to more alcohol.
2. As you are going on a twin. Please consider on board glow drivers for reliable idle..more so if you intend to mount inverted.......a must!!! Remeber, Reliability is the most important thing for a twin.
3. I get the best idle and transition with the fox long idle bar plugs. Tried a bunch.
4. Now for reliability. I can assume that you are going to use some kind of open pitts style muffler. Good for power, lousy for reliability on a twin. Poor muffler back pressure and so possible lean out on take off........The absolutely worst time for reliability or engine loss. Consider a Perry regulator pump..the one that runs off of crankcase pressure.
5. Many people have transition problems with the original carb's. Note, the carb's on your engines are the same carb's from the ST 60 to 90's. There is a reducer bushing in the crankcase to reduce the carb to the large crankcase. Make sure the bushing that has a crack at the joint, is sealed and the low end properly set.
6. More power!!! Glad you asked. If you are worried about the transitional problems, and or cannot get the problem out, consider another carb. No, not the expensive OS 7.
Go with the ASP 108 carb's for approx $35.00 each. The transition is one thing, but the increase in power is the better part. If you look down the throat of the ASP carb's, you will note that they are much larger in diameter,,,more air!!! More fuel...On my engines on the P-38, I saw 400 rpm with 18x8 props. I have since switched to 18x6 for better thrust. Again, for reliable fuel flow, I am using the Perry pump.
7. Don't want to use other carb's, OK, check to see if you have the "Power Spray Bar"!!! Look down the throat of the ST carb's at the spray bar. Is it round or is the bar flat on each side of the spray opening. If flat, you have the good one's and more power. If round, let me know and I can tell you how to modify. The flat one's are not available from ST any more. Good Luck, Let us know how it comes out. Twinman"
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Question 30: "Ok, I'll bite. What is the mod to the round spraybar to flatten the ends? PH "
Twinman: "Hi, Scales Fan. The following is a reprint of one of the posts I did here at RCwarbirds. It does work!!
Spray Bar Modification
In the ever day quest for increased engine performance, I have discovered a few relatively simple ways to increase engine performance without breaking the bank (or incurring the wrath of the significant other). No, contrary to common held misconceptions, too much power is never enough!!!!!!!!!!!! You can always throttle back!!!!( If you believe that, I have a good deal on
a bridge over the ship channel for you) Supertiger ( my personal favorite)
1. The simplest method of increasing performance in the small (up to .51 size) is to change the spray bar in the carburetor to part number 22072813. This is the spray bar used in the .61 and larger ST carburetors. Warning, the part you get with that number may or may not be the preferable flat spray bar. Sometimes they substitute the round one. This bar was discontinued for a while at the last of the production in Italy. I have seen the new Chinese ST 90's and the flat spray bar is back!! In personal experience on the same day, same engine (ST.45), fuel, and a 12-4 propeller, I found a solid 600 RPM increase (Yes With A Tach) and no other modification. You may find that backing out the idle adjustment one turn may be necessary for reliable idle. I can find no loss of transition or reliability with this modification. Reliability is very important to me as I use two of these engines on an airplane. ( Note article on don't do twins!) This spray bar was discontinued even for the larger ( up to .91 size) and so you may have trouble trying to order or find one. Yes, I said it twice, so no one can say I did not warn you. Check your larger ST engines to be sure that you have the smaller spray bar. The milled spray bar from Super Tiger is now shipped with the new Chinese engines. Stores are having a hard time getting it.
To determine spray bar identification
1. The standard spray bar is completely round as you look down the
carburetor. The bar is a uniform .155" in diameter.
2. The preferred bar has flat sides milled on each side .098" across and
.336" long from the end.
3. It is possible to modify a standard spray bar to those dimensions
relatively easy. WARNING: If you grind too deep, you will break through to
the fuel passage and ruin a perfectly good $15.00 So be careful!!!!!! This
Hope this helps and have fun.
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Question 31: "I'm bitten by Mosquitos. After almost 50 years of building, I'm ready for a twin. I'm a very good builder and a reasonable pilot. I fly a 1/4 232 cap, a Pica Spitfire and a 90 size P51 among others. I'm thinking of a Brian Taylor 71'' or 81'' Mosquito. The engines are real close to center with a nice long tail moment and big rudder. I was thinking of building a foam wing and profile fuse/nacelles from the same plan, in the same size to get use to everything. Just paint it yellow and save the big investment of time and money for later while building the real one. Any suggestions re the BT plan? Any other plans or kits I should look at in this size range? Yes, I use a lot of rudder. Thanks. AG, Florida."
Twinman: "Hi Glenn, I understand the bitten part!!! I have never considered a profile warbird, but I like it. The only profile twins I have seen are from Morris Hobbies. I have seen the videos of these planes fly and they are amazing. As to you plan, it sounds like a really good idea. Simple and quick to build. Due to the long tail moment, large rudder, large flat surface of a profile, should be an excellent trainer. Please send pictures. As you get more accustomed to it, consider to increase the weight. This is good practice for the warbird. Unfortunately there are few twin engine kits or plans. The oldest is the pica dualist and if you check the posts on RCU in the twins forums, there is to be a larger dualist coming soon. Good luck and please send pictures and flying experience. Twinman"
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Question 32: "Hi Twinman, I just ordered the new VQ P-38 Lightning and was wondering if the Saito FA-100 would make a good pair of engines for this bird or if you have a better suggestion for a four stroke power plant. Also, is there any engine in particular you would put in this bird if money were no object (just curious). I plan on using three blade props and of course I will have glow drivers. One last thing
you've made mention of using gyros
any particular gyro (I'm a Futaba fan)??? Thanks!!!"
Twinman: "Hi Michael, The prototype is going to fly with MVVS engines and 14x7 props. Is now at 16 pounds. Really looks neat.
One good point about the four strokes is that they are not as concerned about back pressure as the two strokes........can you say scale exhaust outlet?? Futaba makes very good equipment. I also only use the radios. I would strongly suggest that you consider two gyros. Futaba has a single inlet and outlet that you would use for the rudders. The problem with the P-38 is that the rudders are too small to control the plane with engine out. Larger engines make the plane fly much better, but ( You knew there is always a but) it can be worse due to larger uneven thrust. I would look at the futaba gyro with two inputs and out puts for the ailerons. I have flown this combination on two other P-38's and a works horse that I tested this on and it really works to dampen the yaw and snap roll to a level that you can control. I know this sounds like a lot, but what have you got in this plane. I actually did a single engine take off with this twin gyro set up on one of my work/test planes. Good luck, Twinman"
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Question 33: "Before I build the profile job, I will need to settle on a final plan so that I can convert it. Thanks for your response to the back part of my question. But, I'd still like to know what you think of the Brian Taylor 81'' Mosquito. How does it fly? Is there an alternate to the BT plan that I should look at? Even a little smaller? This is where I would value your thinking. Thanks, Glenn"
Twinman: "Sorry for delay to answer, Off on business trip. I am not familiar with the kit from Bryan Taylor. You definately will have a show stopper at the field. Please keep us posted. Twinman"
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Question 34: I am building a Ziroli corsair powered by a G62. I have just about finished the fuselage and starting on the wings. This is my first giant scale and I am concerned . I thought maybe a gyro might help tame the beast so to speak. What is your opinion?"
Twinman: "Hi Frank, Any tail dragger will benefit from adding a gyro to the rudder. Take off and landing ground loops will be greatly reduced or eliminated. Yes, the purists do not like them, but it is your plane and work. Why not protect it for less
than $100.00? I use them on my warbirds, particularly the P-38's. I have never used the auto pilots so I cannot comment on them, but strongly feel that a gyro would be a good investment. I can give you another example. Ever try to fly a cub? Ever ground looped it? A gyro solved this on four of them at my field. Good Luck and send pictures. Twinman "
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Question 35: "George, I have a simple question. I have built the Stafford B24. I have been flying for 15yrs and this is my first multi engine. If you have flown this plane is there anything I should look out for? I have read your multi engine tips. Thanks,"
Twinman: "If you have read my advise.......Reliability!!!!!!! Every time,,,,EVERYTIME you fly it, hold the plane at full throttle( WIth Assistant) straight up and listen. Any sag, don't fly. Find and correct before the flight. Go as fast as possible on the ground to make sure that you have more than enough air speed for engine failure and climb gently. Good luck, and send pictures. Twinman"
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Question 36: "Based on your review of the A-26 Invader, I purchased the Hobbico Multi Purpose gyro and attached it to the rudder servo. I decided not to purchase a gyro for the ailerons due to weight concerns. I saw from the pictures in your review that you mounted the rudder gyro with gain/center adjustment screws face up just behind the retract air tank.
Here's my question: Based on the way that I see you mounted yours, what axis are you controlling? I assume pitch rather than yaw thinking that (for example) if engine 1 failed, the right wing would suddenly pitch up. Full right rudder would hold it in a "knife edge" (as best it can fly that way) until I used ailerons to level out. Is this correct? If so, the gyro will be of no use assisting in straight take off/landings."
Twinman: "Hi, Sorry for the confusion. I built that plane for another modeler and installed two gyros.Use the Hobbico for the rudder only. The Aero is for the ailerons. Yes, you can use the Multipurpose for the ailerons, but the rudder and controlling Yaw is what really gets one into trouble. My advice for this gyro. Set the center of the gyro centered and use 50% gain. Center the rudder without the gyro. Install the gyro and the rudder will deflect to one side. Do not recenter with the center adjustment. Move the control horn on the servo to recenter and fine tune the center with the center screw on the gyro. MAKE SURE THE RUDDER DEFLECTS TOWARD THE MOVEMENT DIRECTION!!! You must fly coordinated with the rudder for each turn or the gyro will fight you. Inputting rudder command over rides it until the sticks are recentered. This is not an auto pilot, so yes, the rudder will recenter after movement and that is correct. It will dampen unexpected movement to the degree that you can react. The permentantly fixed deflection is a helicopter Heading Hold gyro and you do not want to try that. Been there done that. Good luck and keep us posted. Twinman"
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Question 37: "Some where I read that there was an electronic circuit that helped synchronize twin engines and even cut both back when one lost power. Do they work and are they worth the trouble and extra work. Is there any manufacturers that I can contact.Dennis Pratt"
Twinman: "Hi Dennis, The only one I have heard of is Jomar Industries and I found the link for Jomar:www.emsjomar.com. The link does not always work. The problem with their system is that it is a Master/Slave system. My luck says the slave goes out and then no reaction to the master. The idea of this system is to sync the engines. You can do that by linkage or a mix using two engines and map the engines together. It works and it allows, using the rotary dial of the second channel to get them together on the ground.
Nothing takes the place of reliability with a twin. Good Luck, Twinman
PS This is the post I wrote for rcwarbirds a while ago. Hope it helps. Mapping the engines for linear response (post # 1)
OK, so a few of you are still complaining that you cannot get the engines to come up together. Yes, there are electronic sycronizers, but you may have the ability to do this already at your finger tips. I use the Futaba 8UAPS and 9CAPS eight and nine channel radios. OK, not don't start complaining that JR, Hitech, Airtronics, or whatever is better. I cannot comment on that argument. Started with this and am too old to change now. The Super Version of the 8 channel has seven mixes. The last two added with the Super Version, have an interesting feature that allows you to map the response on the control curve of one channel that is mixed into another
channel. The control curve of the mix can be set along five points on the stick movement. With this feature you can match two engines together on the acceleration curve. You did mix the rudder into the two engines and putting the engines on separate channels to allow individual adjustment, didn't you? Well, I sometimes still have problems with the two engines coming up together. For normal flight this is not necessary, but I am progressing into more aerobatic work with twins, so additional experimentation is required.
OK SO I NEED A LIFE!! TWINS DO THIS TO YOU!!!
As the engines are already mixed together, all that is required is to get one (The right engine) to be the slave of the other (The left engine) and get them to come up in RPM together. I have previously stated that you should use matched engines, (not new and old) but even matched engines have performance differences. Yes, you can go crazy and use a tach the whole way, but if you listen for the harmonic on the two engines running together, you will be very close. Now, the big safety message. DO NOT DO THIS WITHOUT SECURING THE PLANE!!!! You will be running the engines up and down, and adjusting the radio, for periods of time and you CANNOT DO THIS WITH ONE HAND!!!
First, get the engines properly adjusted as noted in previous posts. It is absolutely necessary to have the master engine (the left engine (the left engine should be on channel 3 for futaba and the right engine should be on channel 8)) reliable and ready to transition reliably. Always set the stronger engine down to the weaker engine, never the other way around. Both should be slightly rich- more so than you would do for a single engine plane. Remember, reliability is the key for survivability on multi-engine planes. Shut the engines down, as the next step is accomplished without the engines running.
Start at the idle position and get the engine's visual carburetor openings to match idle speeds based upon the first or last of the five position settings according to how you initially set up the mix of the two engines. ( For some instances, this maybe position five or position one on the mix). Once you have adjusted the values of the idle speed, set the values of the high speed position (the extreme opposite position (I.E. If idle was position 1 full throttle will be position 5). Each position of the five is completely independent of the others so misadjusting the idle position will not require a readjustment of the other four positions. However, because of this, you will have to have the throttle in the correct position to adjust each phase (I.E. If you are adjusting idle you must have the throttle set to
idle). After idle and full throttle is set, make position 3 of the opening of one carburetor, match the other carburetor opening at half throttle setting. It is critical to do this part next, because you will simply put positions 2 and 4 at a point that makes the engines sync (audibly or with a tach). The position of 2 and 4 may not be exactly between 1&3 or 3&5. It may vary according to the engine performance curves. Once you have set them up where they look similarly in the carburetor opening, from idle to full throttle
movement, it is time to start them and test them.
Tie the airplane down so you can operate the engines without fear of the plane getting away. Always stand behind a plane while the engine is running. Start with idle, make the engines match here first, using the mix. If you do not have enough throw in the mix use the ATV (This changes the servo travel) function and if you must, the subtrim also. Remember that Subtrim adjustments affect all the positions. Next, move to the full throttle adjustments, advance the throttle to full and make the slaved engine match the RPM of the master engine. If you do not have enough throw in the mix, use the ATV function for the right engine. Next, check that half throttle is
equal. Make the other two Joystick positions (2&4) match next. Finally confirm that the throttle response is linear, and if it is not, adjust position 2 or 4 (and maybe 3, but only if it is necessary) to make the engine response linear. You adjust only these two (points 2 and 4, and maybe three) because positions 1, 5 are set to make top and low end adjustments. The engines are now mapped for equal response. In the future, all engine mixture adjustments must be done at idle and full throttle as was done before you started to map the engine response."
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Question 38: "Good Evening "Twinman" There is a lot of buzz on the internet about the P-38 ARF's coming out. Based on the prices, I will have to go back to the old fashion way and scratch my own. I am currently "kitting" Col. Art Johnson's version of the P-38 and should be in the building stage (time permitting) within the next couple of months. Do you have or know anyone who has any experience with this particular plan or flight characteristics? I have been building and flying for 20+ years and usually hit the planed weight (in this case 13#). With a 94" wingspan and a pair of OS FX 0.61's I should be in good shape. Truly enjoy this forum. Cheers, Silas"
Twinman: "Hi Salis, I am not familiar with that kit for the P-38, but from my experience, If you can make 13# and 94" wing span, you are a genius and I am not worthy to talk to you. I am not in your league of builder. The flight characteristics at that size and weight will be much better than 90% of the P-38's. If you are interested, let me know and I can get you in touch with Mike Morgan, who has the model 322 shown in the P-38 pictures at rcwarbirds and his is also very light. Another idea, if you want to build a P-38 this size is try http://www.glhobbies.com/P38%20LIGHT/1_6P38.htm. Good Luck, Twinman"
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Question 39: "Sir, Do you have any experience with CBA F7F Tiger Cat .60 Size ? I purchased one second hand and it only included the plans. No instructions. I need to find out mainly where the CG is and it's control throws. Any help would be appreciated. Steve"
Twinman: "Mr. XP78 I do not have experience with this kit, but I do know a guy in South Carolina who knows the original owner of CBA and will forward this inquiry to him. Good Luck, Twinman"
Twinman Update: "This is the reply from my source:" " CUSTOM BUILT AIRCRAFT (CBA) BOB ANTONELL IS THE PROPRIETOR. UNFORTUNATELY HIS TIGERCAT F7F IS ANYTHING BUT .60 SIZE. ITS EXACT QUARTER SCALE JUST LIKE THE P-38. IT HAS A 120" W/S AND REQUIERS A MINIMUM SAX EQUIVALENT 4.2. JOE BRIDI PRODUCED A .60 SIZE F7F TIGERCAT MANY MANY MOONS AGO. I BELIEVE IT WAS ALL FIBERGLASS. I HOPE THIS HELPS. GREAT TO HEAR FROM YOU."
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Question 40: "Hi, Joe. Ive emailed you before about my Morris Hobby P-38. (from my office). Ive received it and it looks damn nice. I spoke with Bob there and he told me that they are putting together some packages for it, such as, Saito 100 engines for $495.00 a pair, a break system; weapons package for guns, rockets and drop tanks and the rear exhaust system through the turbo superchargers with the MVVS engines. I also mentioned to him about some discrepancies in the manual. Some he was aware of and some he wasnt. It states and shows the wing servos being mounted from the top of the wing, when in fact they are mounted from underneath where the servo access panels are and it also states that all 12 holes in the bottom of the wing are pre-drilled at the factory, where they are not. The screws that are supposed to be used for screwing into the wing tubes are not near long enough to screw into the wing and into the tubes. That one he was aware of and hes sending me the correct mount bolts along with my back ordered retracts and robo struts.
Anyway, I decided to build the 2/40 Duellist as a trainer for the P-38 and was wondering if you could help me out with bashing it, as I just want to make a trainer out of it. Id like to know some things like what wood I dont need or should replace, what engines would you recommend, where should they be mounted in relation to distance from the pod center line, what I dont need to pay attention to, if anything, etc. By the way, I passed on the plans you sent me of the C-47 to my English pal. Hes pretty much into the completion stage, now but had a look at them anyway. I dont know how hes going to transport it, as the fuse is about 9 long! Anyway, Ill quit rambling and let you go. Thanks for your help in advance. Robert Duncan Giebelstadt, Germany"
Twinman: "Hi Robert, I can answer some of this, and maybe Joe can finish. The duelist is a very good larger size twin trainer. I would not use the single servo, with linkage, for the engine throttles. Too much slop and harder to sync the engines. I would also congratulate you on a choice to delay the flight of the P-38 until you are more accustomed to the characteristics of a twin. You patience will result in less frustration with the P-38. Robert at MVVS is also getting the Sonic Tronics landing gear door hinges next week and sending them out to customers. Some of the spring air gear is also arriving. Unless you are really into aero design, I would not modify the duelist. It is a good flying plane. One possible suggestion, bearing in mind the plane you are training for, make the landing gear stronger than normal. Get used to twins, and add weight to increase the wing loading. The prototype Morris P-38 weighs 17 pounds with thin and tapered wings. The Duelist I flew had .45's in it, but if you plan to increase weight, I would consider 60's. Good luck, Twinman "
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Question 41: "Twinman, For the VQ P-38, I was planning on using OS .91 2 strokes with master airscrew 14X7 3-blade props. I was worried about too many 'horses' and was considering OS .61's but I saw in the 'twins' advisor, question 22 that you powered the VQ P-38 with MVVS 91's and 14X7 3-blade props. Stats on the MVVS .77 is 2.25 HP. I couldn't find the HP for the MVVS .91 but I'm guessing around 2.6- 2.8. The OS .91's are 2.8 HP.My rational was that I could run them at slower RPM's and get more thrust
with the 3 blades, yet have the extra power should I need it if one engine goes out. I just want to check with you and see if I'm 'overpowering' the VQ P-38. This is my first twin but I've purchase 2 more for 'starters'. I've got Airborne's P-82 that I'm putting OS .46's in. I'm using APC 10X6 4-blade props. I've seen on the Web that one flyer had his Fox engines go out all the time and this plane flies great on one engine. After I get experience on the P-82, I've got a VQ A-26 with OS .46's. I'm using master airscrews 10X7 or 11X7 3-blade props. In my single engine warbirds, all these props work well with my OS engines using wildcat 15%nitro/16% oil. All engines are inverted. Last to be flown will be the P-38(probably in August). Since my trainer days, I went straight to warbirds and have never flown anything but warbirds. You're right: 'twins make you crazy...and I haven't even flown any yet. They thought I was crazy jumping straight from a trainer to warbirds so I was crazy BEFORE deciding on twins! Thanks for all the useful info that you put on the web. Sam Parfitt"
Twinman: "Hi Sam, Thank you for the kind words. The MVVS 91's and Super Tigre 90's turn the Master at 9200 rpm, but reduced
to 9000 for safety. The P-38 will snap roll with low power and loops, so a little more is good, as long as you don't go crazy on maneuvers. Do not pick engine size based upon single engine operation. Yes, it can be a consideration, but not on a P-38. Do not even think of trying to fly it on one engine. Can it be done, yes. Is it a sane thing to try......NO!!!!! These planes will snap roll in an instant with engine loss. Don't try it. The bigger engines allow more scale size props, which I thing are better looking. Good Luck, And send pictures to rcwarbirds. Twinman "
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Question 42: "George, First I wanted to just say thanks for the obvious huge effort you and your team have put into the RCWarbirds forum and advice articles. I find them very useful! I am about 2 months into building my first twin a Ziroli P61. I plane to use the new YS140DZ motors. I have read your "So you want to do twins" and most of your Q&A area. No one has ever accused me of being smart so I am going forward into what I hope will not be the hopeless abyss. I do plan to get some twin experience prior to pulling back on the right stick of the P61 for the first time but had some questions I hoped you might help me with. While I do plan to use gyros in the P61 I thought it may be a good idea to get a cheap twin and have a friend fill one tank up all the way and the other half full (not knowing which was which) and practice unexpected single engine operations. Is this insane on something like the hobbico avistar twin? Are single engine characteristics so different from model to model that such practice is of only marginal value? You also mention the issue of the two engines not being linear in RPM increase while on the takeoff roll causing yaw during transition to full power. Being the electronics weenie that I am I was wondering if anyone has designed a master/slave twin engine system that would keep the two engines at the same RPM throughout the flight? One quite obvious downside is that while not always the case there certainly are times when one engine is better then no engines and if the master dies the slave would also die. Just wondering if this is such a good idea and not so difficult to design why don't I see these systems for sale? Just can't resist asking if you have any experience with the P61 or know about it's flight characteristics? Any experience with how the spoiler system and tiny ailerons might affect single engine recovery?
Thanks again George and the entire staff...We appreciate your efforts! Tom Rainwater"
Twinman: "Hi Tom, Welcome to the Twin Big Boys club. I cannot comment on the P61 other than to be jealous. Looks like larger rudders, for the plane verses P-38 and larger side section. All of this helps stability. I would not do the blind sided engine out test. If anything, mix the engines together with computer radio on two channels. The second engine is to be controllable, on a rotary dial, set to only bring the second engine to idle....NOT DEAD!!, upon command. You will also find that setting equal idle speeds is much easier with this set up. Use helper to "Kill" the engine while you fly. This, for your safety, and the plane's, makes the practice session easier to handle. I have done this in the early stages, and it works. ( If you notice the big letters on NOT DEAD, you can tell, my assistant killed one of the engines on this practice, and I got more experience than I was ready for.) When you are shaking enough for one flight, slowly have assistant bring up the other engine. You might find that a son has way too much fun watching the old man sweat!!!
A company called Jomar, makes a Master Slave system as you describe, but only one way and Murphy's Law says the Master will die and not effect the slave. As for that size plane, you are going to use gasoline engines, and sync'd is not too difficult. DO NOT ASSUME THAT GAS ENGINES WILL NOT FAIL!!!!!!! Remember the key word is reliability!!!
As for the practice plane, and reality, as you become more accustom to the "Challenges" of twin operation, increase the weight and wing loading to approximate what you are building. Make sure the landing gear can stand this. You will find out that, as wing loading increases, so does the engine out problems. By all means put your gyro or gyros in the practice plane. My test bed for the various articles on twins was a converted Ugly Stick, The wing cord and thickness is not exactly ideal for scale practice, but worked well and still exists. If you go that route, add 8" to the wing span, or you will get high wing loading practice early. Try to get similar power to scale with your target plane.
Spoilers are not usually a factor in single engine recovery. Ailerons are, as the plane will yaw and raise one wing. I would also concentrate upon as much rudder throw as possible.
You do fly coordinated with the rudder and ailerons, don't you??????!!!!!!!!! If not, 1. Learn now, 2. Defiantly install the gyro on your trainer on the rudder. If you then don't use the rudder, you will have a new experience trying to turn. They gyro will fight you.
Good Luck and let us know if we can help. Twinman"
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Question 43: "I have cut out and sanded smooth all the parts for a 72" A-10 made of "blue styrofoam" . The body is huge! Total weight of all parts is 3 - 1/2 lbs. with a solid body. I want to first fly it with a single in the nose. Wing area is 5 sq. ft. When I finish a full load of AGM tank missiles she is going to be one of the "draggiest" planes to fly. What engine will fly it at about 35 - 40 mph and a finished weight of 5# less engine andfuel and no Robart retracts. Thanks for any help. I do not fly any of my WWII planes, I enjoy building them. A aerobatic pilot files them. He loves the ST-90 powered Global ARF Spitfire 48" W.S. and 5# fly weight. It pulls straight up out of my hand -very fast. Would like the A-10 to be similar if possible.I will put in a full depth drilled and lightened keel when I know the engine needed. Thanks for any help, Rich."
Twinman: "Wow Rich, I really like that idea of flying it with a single......( Just don't spread it around!!!) While the weight is light, the wings, if scale thickness, have a lot of drag, and little lift due to short length, so what is that ST 90 doing....maybe with a 14x6 prop or 14x5? I am sure your friend won't mind!!!!!! I would think a good 90 would be the minimum. Good luck,,,,,,and send pictures, interesting idea!!!!! Twinman"
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Question 44: "Thanks for your response on my question about th S.T. 2500s. You mentioned that I shouldn't use pitts style mufflers with them so what do you use on yours? Thanks Tom "
Twinman: "Hi, I have pitts style mufflers!!!!!! Do as I say, not as I do. OK, the reason warn against pitts style mufflers is that the back pressure reduction is good for increased power. Bad point, the reduction in back pressure is not good for tank pressurization.
I also added ASP 108 carb's, which are a direct bolt in, on mine for approx 400 additional rpm. As I fly twins all the time, reliability is the most important thing on my mind. I put the Perry regulating pump on my engines to make sure they get fuel. If you always do the vertical test, and have no problems, then go for pitts mufflers. With twins, I always want the extra insurance. Good Luck Twinman"
Update: "I had to "Make some repairs" to my Bronco with two MDS 148's. Went out today to recheck all that was well, and guess what? The engines ran fine on the ground. Did the vertical test and one leaned out every time I brought it down from full throttle. The engines have pitts mufflers. Blocked one port, readjusted the engines, as they were now very rich, and all is good with the world.
FYI Watch out for pitts mufflers for lack of back pressure. These engines do not have pumps.......yet!!!!! Twinman "
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Question 45: "Hello Twinman! I've been flying for a long time now (25 years), and have finally procured a partially built Royal P-38. Unfortunately I have two copies of "sheet 2 of 2" plans, and don't have sheet 1. Do you know of a source for obtaining sheet 1, and any other documentation that originally came with the Royal P-38? Tom Dunn"
Twinman: "Hi Tom, In a way, you are in luck, The old Royal kit was built by Marutaka and is still in production. Last I heard, it is distributed out of Arizona by the Hobby Barn. You can reach them at http://www.hobbybarn.com/airplanes_marutaka_kits.htm.
Good Luck, Would suggest adding flaps or landing is really exciting!!!!!!! Use the preformed wire for separate elevator controls, and one servo for each pair of flaps. Do not use one servo for the elevator or it will flutter!!!!!!!! Do not use one servo for the engine throttles. Too hard to control. To gain space, consider mini servos with metal gears. Worked fine in mine......Uh, do not have my copy of the instructions.....Went with the plane to the hanger in the sky. This was my first twin......DON'T DO THAT!!!!!!!
Good Luck, Twinman"
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Question 46: "hi twin man, im building a century jet 100in wingspan corsair that will dress out at around 45 pounds complete, will a zenoah twin pull it? thanks cant afford the ultra high dollar ones"
Twinman: "Hi Donnie, At 5.5 HP it should fly it, but would not think much aerobatics are in order. I would agree on the cost of these monsters. This is not a cheap engine, have you considered a single, such as the ZDZ 80 at 8 horsepower? Mine turns a three blade 23x14n at 6200 rpm and costs less than the twin, and it would fit inside the cowl. Just a thought. Good Luck, Twinman"
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Question 47: "Twinman - If I could ask a few questions regarding VQ P-38:
1). The instructions say the wing is pre-drilled for the screws to attach the wing to the aluminum tubes. Mine has no pre-drilled holes. I received a picture from Bob showing where they were on the prototype. I want to hide as many of these screws as possible, so is it important where the screws are actually located?
2). Wing screws again. Screws have a way of enlarging the hole they're placed in, especially if they're removed/inserted several times. Do you think it possible to enlarge the screw holes and use larger nylon-type bolts threaded into the aluminum/wood insert?
3). This is my first ARF, so this may be a really dumb question. Since the servos are spread throughout this plane, and the multitudes of connectors, is it really sensible to even consider dismantling to transport this thing?
4). What are the engines YOU are going to use in your P-38? What about mufflers/exhaust systems?
5). What are the servos YOU are going to use? Y-connectors, etc.? Radio?
6). Landing gear door hinges: What is the best way to attach/mount these hinges? How do you determine the CORRECT location? What mechanism would you use to open/close the doors?
7). A hundred other questions: Dummy machine guns in the nose: How do you make them? Do you recommend the counter-rotating engines? What would you add/remove/replace to make this a better plane? On-board glow system: How/where would you locate? Fuel system: How/where would you locate the filler(s)? Air retracts: Where are you mounting the inflating port for the air container?
I'm sure there are a number of folks out there with the same - and more - questions. Inquiring minds want to know! And this is simply a magnificent airplane! As are the folks at Morris Hobbies, especially Debbie. She has been most helpful, but somewhat limited due to the amount of work she has been doing. Therefore, anything you can provide would be most appreciated. Looking forward to seeing your plane in the air and your review. Can't hardly wait........ Thanx..........Wood"
Twinman: "Hi Woody, Please do not fly this plane if this is your first arf or first twin. This is not a beginners plane. Please believe me that I am not talking down to you. Been there and made this mistake. I have build the wing, aerotech, and Yellow P-38 and working on this. My two cents is to only build it so that the wings plug into the center section. This is of course due to the size of your car or suv. The plane is shipped so torn down to allow reasonable shipping costs. Mine will be glued permanently together in the center area. The Yellow P-38 has the wing dowel, struts, whatever you wish to call them, permanently attached to the wing and slides into the center wing section. A hidden screw is attached from inside the wheel well. I am not sure this can be done yet on this plane. Then you only have to attach a ball joint to the fowler flap push rod, and connect the wiring to the aileron servos. The first prototype, that was not built by me, connected the wings using a screw, as you are worried about, from above. This meant that the plastic supercharger cover had to be removed each time the wing was installed. I do not like this set up and plan to change it, somehow. The engines on the prototype are MVVS 90's. Yes, this is too big, but allows the more scale looking 14" three blade props. The other thing about the MVVS is that the head will swivel 360 degrees in 90 degree segments. This allowed rear exhaust and down only exhaust outlet toward the firewall and very narrow engine arrangement. The landing gear door kit comes from Sonic tronics and mechanically opens
and closes the doors. Spring open and mechanical close. Have used this on others doors and works well. You can find at http://www.sonictronics.com/products/hinges/prod08.htm. I will install two gyros on my plane, as I do on all of my P-38's to control
engine out situations. One for the rudders and one for the ailerons. The fuel system has special made tanks and cut outs for them. I will also add on board glow for the engines. This plane more than any other, need reliablity.....remember that. If I can help, let me know. Good Luck, Twinman "
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Question 48: "could you tell me the center distance that I should use for the mains and nose gear from bottom of plane to wheel center on the Wing P-38. I'm not using retracts. I understand that it does need to be nose high. Thanks"
Twinman: "Hi Tony, I do not still have my Wing Mfg plans, but make sure of good prop clearance. I used fixed gear and spring type on the mains due to high loading and high landing speeds. DO NOT MAKE THE PLANE TOO NOSE HIGH!!!!!!! Yes, you see it in all the pictures. If you do this, as you see in the pictures, the plane could lift off, due to ground effect before it actually has enough speed to fly and tip stall. Maybe 1/4" nose high is OK, but not much more.
I also installed flaps in mine with fixed wings. Do not use on servo for both engines. Use separate for each engine. Do not use only one elevator servo for the elevator as the plans say. Will flutter. Use two, one on each end. You can save a lot of space and weight if you use mini servo with metal gears. Good Luck, Twinman"
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