jcole43

im building a wing P38 with OS 46 la`s for power it will have retracts with robart struts and gyro`s on rudder and ailerons.I have been considering flaps also but things are getting tight ! Will the two 46la`s be enough? i am not to the point where i can get a projected weight yet i emailed wing and they suggested staying within their recommendations for the engines.I`m new to twins i know this is not the recommeded first twin so ill build it and find a twin trainer to learn with.Any suggestions will be highly appreciated!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! !!!!!!!!!!!!!!!!!!

TLH101

My Feedback: (90)

I built one several years ago, flew with Magnum 40 XL's. Was a rocket ship at full throttle. I think the 46's will be perfect. One word of recommendation though. Mount the motors sideways. It wont look as scale, but they are much frendlier that way, and the tanks are eisier to set up. They are a little high for inverted engines. I had mine inverted, and never had any problems, but would do the next one sideways. In fact, I am nearly finished with a 100" P-38 with OS .91 4strokes, and I mounted sideways.

jcole43

the lightning in the pic is it the wing P38? if so did you glass it and does it have retracts . PS great looking job on it thanks for the feedback!!!!!!!!!!!!!!!!!!!!!

TLH101

My Feedback: (90)

No, that's not the Wing, it's the 100" one I am working on now. I did not glass the Wing kit, covered it with Ultracoat aluminium.

William Robison

My Feedback: (3)

jcole43:

For suggestions on the first twin go here:

http://www.rcuniverse.com/showthread...97&forumid=220

HTH.

Bill..

jcole43

i would like to hear and see the results of any one that has built or is building one . i would like any info on flap installation on this plane especially. im at the point of construction now that i need to make a decision as to whether i install flaps or not . any help and suggestions as to the best way to do flaps on this plane would be extremely appreciated.im using os 46 la`s for power and will have gyros on rudder and ailerons and robart retracts and struts so as you can imagine things are getting tight in the structure now. hopefully i have been good enough in my building skills to keep the weight within reason and not go to far past the 8 to 10 pound range.

twinman

My Feedback: (2)

OK, we will give my humble thoughts.
1. Do not use the single servo for engines. Use two micro.
2. Consider the metal gear mini servos to save space and six volts. Plenty of power.
3. Do not follow instructions to use only one servo for the elevator. Will flutter.
4. I did install flaps on mine. At this stage, it is fairly simple. Go to hobby store and find the split elevator linkage with the soldered arm. Install this in each boom and connect flaps to each end of the wire and only one servo for each set of flaps, inner and outer.
5. Put the two gyros and receiver under the canopy area. Receiver to the rear, and battery to the front. Very high probability that it will turn out tail heavy, so plan for it now.
6. Those engines are a bit marginal. If you approach 10-12 pounds....grass runway is not a good idea....skip the loops as it will tip stall, rolls OK.
7. For the flaps, you will need to hollow out the wing in four areas so that the wing is smooth with flaps retracted. Build a small box in these recesses and make strong. Warning, the sharp courners of this box can and will reduce the strength of the wing due to stress riser effect.
8. If you contact RC Report magazine, they did a build and fly story on this approx 8 years ago.
9. ALWAYS do the vertical engine test before every take off. The two gyros will make the plane controllable, but don't test this!!!!
10. If you plane to invert the engines, consider onboard glow driver......yes, more weight...sorry. If no glow driver, consider remote glow plug connection. Too dangerous to lift, while starting.
11. Set the rudders for maximum throw.......more than the instructions say. Rudders on the P-38 are too small and that is why you get into trouble with engine out...coupled with wide engine spacing and high wing loading.
12. Suggest sensitive setting for the rudder gyro , depending upon the gyro, 75% is starting point,and 50% on the ailerons.
13. The plane is not too big, so I would consider to build it with the wings fixed.
That should keep you busy for now,,,,,and worried........good,,,,,,never get too confident with twins.
Good Luck,
Twinman

jcole43

thanks for the input twinman!!!! i have already went the 2 mini servo route on the throttle control,ill have to rethink my elevator servo installation now! would a spar running from the root out in the area of the flaps help with the weakening of the wing in that area?i have 2 new KB 61s maybe ill reconsider using them for power! also i have been looking at onboard glow would you suggest 1 unit to control both engines or 2 individual units?or would a simple micro switch actuated by the throttle servos be better? would the glow driver wires on a single unit cause intrferrence running in such close proximity to the other servo wires?and lastly would increasing rudder area be of any benefit

twinman

My Feedback: (2)

Would definately consider the larger engines.....particularly if plan to take off on grass. Also, do not lift off early. In other words, keep it on the ground and build as much speed as possible before lift off,,,,,,,on this, but also any twin....is extra insurance.
As for wing reinforcement, there will be many suggestions including "leave it alone". I put small carbon fiber arrow shaft into my wings and they survived two engine out crashes intact, so use your own judgement, but,,,,do not underestimate that adding the flaps will make is land better, but will weaken the wing area in the modified box area. If you try to go with outboard servos for the flaps......now you have four more holes and sealing problems.....
Glow drivers....... Twinman's only ideas....do not use the microswitch idea....yes, many have and had no problems, but I have also had radio glitch when the switch makes or breaks contact. If you must go that route, install a small capacitor across the wires to "Kill the Spark".
I have tried several makes of glow drivers for twins wired in Parallel and never been happy. Murphys law says that one engine will always have less resistance and so the current goes there, and not the other....so only one lights. Now, it does work if the driver can handle 3v and you wire the glow plugs in series. While I have by no means tested all drivers, I will state that parallel connected single drivers will give problems.
As for the elevator, I repeat,,,,,,,do not use on servo!!! It will flutter at any higher speed. If you can find the old rcreport story, they had the same problem.
As for increasing the rudder area.....depends.......do you want it to look really scale, then no......but if you want increase control and stablility, them yes, increase it as much as you want. If you really increase the size, then reduce the sensitivity of the rudder gyro,,,perhaps proportionally.........Do not ever turn the gyros off!!!
Told you twins make you crazy!!!!!

Edwin

My Feedback: (2)

Need to throw my two cents in. After a 45 min. preflight by me and other old timers (with real experience) and following Twinmans hold it up for 10sec. rule, mine would not rotate on takeoff. Ran off the end of the runway and busted up the fuse pod. The problem as I see it, now in hind sight, was my gear setup. It sat level when on the table. But when runing down the runway I noticed a little too late that it was rolling slightly nose down, which must have been creating pressure on the top of the wing. Also a grass runway. I throttled down too late before runing off the end of the runway. I didnt think there would be any damage until I saw it, rolled over some rough ground. Only the fuse pod was damaged. There was no problem with speed, had plenty with TT .46's. In later discussions with Twinman at our swapmeet, it was considered a good idea to beef up the fuse pod lower sides with 1/16" ply laminated to 1/8" balsa instead of using 3/16" balsa. It builds tail heavy anyway so that is what I am doing in the repair job. Mine is glassed with .5 oz cloth and painted with luster kote and century 21 paint. I switched to century 21 OD because luster (AGAIN) gave me problems with spitting. Very inconsistant. Used spring-air retracts and basically followed all the other suggestions. Didnt do flaps. If I remember correctly, weight came out to about 12.5 lbs. The gear will be setup with a nose high attitude next time. Will fly it at the other field on a paved runway next time. Just goes to show, no matter how thorough, you sometimes miss the obvious.
Edwin

jcole43

thanks for the input guys. i think ill do a little head scratching but install a spar in the area of the flaps to help with the loss of strength also ill keep the front of the booms unsheeted until i can get an idea of where im at on weight so that i can go with the 61s if needed. i only have paved runway available to fly off of so grass is no subject.