windowman

Hello all
can anyone help with advice on my J3 cub it has an inverted 46os engine
first time out ,my mate flew it, all was going he said it was handling great
then it went well out of control 2upward loops then smashed into the ground
big time my mate has rebuilt it. it looks great again but i"m scared to fly it again i"m
still a novice. every thing checked out fuel pipes and feed ect dont know if any of you lads have any pointers for me
any advice will be gratefully recieved .
Regards to you all
Windowman[8D]


May the force be with you all

lomcevek1

There is no substitute for experienced hands on help. If you have to drive for a while to talk to a club instructor it is worth it.

sebo

I had a similar occurance last year.
Had several people look at it at the field and no one could find anything wrong.
I Sent my radio off to the repair shop and learned that it was my battery.
If it was flying well then went crazy, it may be a radio related issue (receiver, servo, battery, battery switch, connectors, etc).
Yup, take it to an instructor first.

Ron

Villa

Hi windowman
I have had three 71" wingspan J3-Cubs. It is always a challenge to fly. It loves to snap roll. It is best to always use rudder with the ailerons to make coordinated turns. You should be an experience flier to fly it. There are a lot of comments on this site if you want to read about other's experiences.

digital_trucker

If it's anything like the Great Planes .60 size Cub I have, the balance point specified on the plans and in the manual is too far aft (mine needed to be moved a good inch forward). Mine did the same exact thing on maiden.

AA5BY

Some Cubs can benefit from some simulated wash out at lower throttle settings. Those that have barn door ailerons and when flown with a radio that will do some mixing can be set so that the ailerons trim up about 1/8 th inch at lower throttle settings. This was recommended by an old gent who has a lot of hours in the full scale version. Also, a Cub definitely needs a good bit of differential aileron with 30% or more up aileron compared to down. The down aileron on the wing foil of the Cub produces a good bit of yaw inducing drag.

IMHO, a full wing Cub should be built with some washout as it generally isn't going to be asked to do much inverted flying. A clipped wing can be very aerobatic however and I'd not build washout into them or adjust the struts for any washout.

I've two Cubs a Goldberg Anniversary built with generous washout that is a great flier and never hints of a tip stall. A World Models Cub ARF however needed taming as it had some nasty habits. Mixing the differential, the simulated washout and some coordinated rudder has greatly altered its manners for the better.

skylark-flier

Hey guys, I appreciate this particular string too. I've got one of the GP Cub-40's (kit) that's about 5 years old and I've had problems right from the start with tip stall, especially on take-offs. I also found that the kits tend to be tail-heavy, had to add MANY bullet-sinkers to the nose to bring it forward to a point where she would glide decently when dead-stick (and that was after quite a few crashes) .

Will definitely look into the aileron differential thing. Might help those wild and crazy take-offs.

Dave

Dc3Mek

I've flown Cubs for many years. If I can brag about one thing, it's my flying skills with a Cub. Also, I'm an A&P mechanic. First off, I have to ask the question, did you do a range check, since you said it flew well and THEN started to behave badly? Also, did you do a load check on the batteries?
As for the "Wash out" AA5BY was talking about, I think he meant "dihedral" wash-out is the amount a wing deviates from forward to aft at the wing tips from standard. I can't see wash out doing anthing but causing bad handing characteristics in high wing loading manuevers. Something you probably don't want.
As for dihedral, you don't need that either with the Cubs high wing.
Flying the Cub is extremely challenging because of the ground handling characteristics. Not so much the flying.
On takeoff and landing it can be a bear. You have to remember that the center of mass is behind the main wheels. So at slow airspeeds, the rudder doesn't have a lot of "authority" in other words, the plane can be pushed around by crosswinds.
When that happens, the main wheels veer to one side, they dig in because the mass of that high wing, and that causes the center of mass that's trying to go forward to swing around the wheel. So the airplane makes a very sudden 90 degree turn!
I recommend LOTS AND LOTS AND LOTS OF TAXIING in a nice big parking lot!!!!! Using same direction ailerons as rudder. Don't be afraid to use a LOT of rudder. RUDDER RUDDER RUDDER!!!!!
Also, I'd get some wing tip protectors! A bunch of Duck tape would work also as a protector.
I love flying Cubs in a scale manor, and if you need any help I'll be happy help out. The Cub is a beautiful airplane.
Darrell

AA5BY

I did mean to say wash out. Most planes that have a nasty tip stall habit can get relief with washout. Most good things however have some trade offs and the one here is degraded inverted performance so it is not a good choice for planes that will fly inverted or be doing outside movements during aerobatics.

However, a bit of washout can be simulated on wings with barn door ailerons by mixing a slight bit of up aileron trim at low power settings thus not interfering with aerobatics that are performed at high power settings. I've a World Models Cub employing this tactic and it greatly reduces its nasty tip stall character. I've 1/8 inch up mixed in at less than 1/3 throttle. Also, that plane yaws bad without differential aileron movement. Ailerons should have considerably more up movement than down.

Both of these trim mixes require setting the transmitter to a wing configuration that will provide for the mixes and on JR that is Flapperon ON. This of course then requires the aileron servos to be on independent channels. One plugs into the aileron and the other aux 1 if I recall correctly. These are features on all but very basic radios.

windowman

thanks you all for you"r help and idea"s its great to know there are still
cracking mates out there ,all the best to you ,sorry for the cock -up Mboland
on your reply to me ...
Windowman.



A good pilot is one who has the same number of landings as take offs ..

cublover

My Feedback: (47)

The best advise i could give is, "dont try to re-invent the wheel"!! A cub CAN be a handful if your not understanding how it flys, you have to remember that a cub is what many pilots learned in, as most of the people ive taught in RC. I have had so many cubs and i love the plane. I just bought a new one!!! this is what helps me when i fly a new plane,,,,any plane, not just a cub. Close the garage door,turn off your cellphone, and go through the WHOLE plane, check all clev's and connections tie it up so you can run it hands free, and go to half throttle walk away with the radio in your hand" antenna down. "THE THROTTLE SHOULD NOT BOUNCE AROUND" at 70 steps. If it does, the vibration of the engine with the antenna down is killing the signal. and if it does it there, it WILL do it in the air. I have been doing this for years, with ALL my radios,"even shaking the transmitter a little, just to see if i have a short there as well,, and i have NEVER lost a plane due to transmitter or rec. failure. Cubs are fun, and level turns are AWESOME!!!. but fly her slow,,,thats what its made for. its the ultimate relaxing Sunday plane

Hisham

skylark-flier

What engine r u powering ur cub with???
Regards
Hisham

spitfire66

I had the same problem with my airplane (cub) flying and then suddenly go out of control. I had my radio sent in and it tested fine. Finally after a lot of time spent searching and many headaches I found that my throttle linkage that runs out the fire wall to the carb was touching the muffler and crankcase occasionally and causing interference. Make sure you have no metal on metal or your airplane will be flying perfect and out of no where come crashing to the ground. It took me 2 planes to find that out. Hope this helps!

morganflyboy

My Feedback: (14)

If a Radio problem is not found, then it sounds like you need someone to teach you how to fly the Cub. This is all I fly, from 40 size to 1/3 Scale BUSA. I am a club instructor and one of my students second plane choices was a Hanger 9 Cub. He was only off of the buddy box no more than a week, and he is doing great with the proper help. I have never had to add weight to a Cub after building it, and I have never added wash out too one either. And if it is doing strange things on take offs and its not a Radio problem my next question is did you build it per the plans if it was a kit. If your still having problem with the Cub then is it the person holding that box in there hand, 1. You can not jam the throttle wide open from a sitting position on the run way. They want to torque to the left instantly. 2. You can not force them off the ground during take off, without the proper run out on take off, they will tip stall or the good old #9 ground loop back to the mother earth. I have seen more than one person take a Cub home in a trash bag more than once, don't be afraid to ask for help. We have guys in the club that fly different planes from 40 size sport planes too 40% 3D planes. I just happen to be the CUB Head.

Good Luck
Morgan

morganflyboy

My Feedback: (14)

Hey Skylark - Flier
I built the same Cub about 5 years ago also, except I made the clipped verson. I never had any problems since its Maiden Flight and it still flys as Sweet as it's first flight. Are you running it out before trying to rotate it. 1. The only time I have seen a Cub tip stall on take off, was when it was forced off the ground to early before the flying speed was reached. 2. The other was, the plane was never Latt balanced side too side. 3. Or if the C.G. was to far AFT, I fly Cubs from the 40 size to the 1/3 Scale BUSA, A Cub is a different breed of Airplane. I hope you get your problems worked out with your Cub. There is no comparing this airplane to other planes, it's like the saying go's.

NOTHING FLYS LIKE A CUB !!!!!!!!!!!!!!!!!!!!!!!!!!!
Good Luck
Morgan

morganflyboy

My Feedback: (14)

FLY IT, LIKE YOU STOLE IT.

morganflyboy

My Feedback: (14)

Fly it like you stole it.