farr301

I recently built a Great Planes Pt-40 kit with the greater amount of wing dihedral, or the A mode. On it's maiden flight, it rolled over and dove into the grass about 10 seconds after takeoff. The cause of the crash was a faulty control horn on the ailerons not the dihedral. When my Dad and I talked to the local hobby shop owner about the aileron problem, he told us that I should have built the kit with the lower amount of wing dihedral or because it would have been more stable and easier to control in slow flight.

I was just wondering if anyone had built and flown the kit with either the low or high dihedral wing, and how stable the plane was in flight. If either of the wing options caused trouble with basic and slow flight, please let me know.

If you were wondering, the plane is being repaired right now and the only damage was to the landing gear and firewall, both of which are easily fixable.

Thanks a lot,
Farr301

aerowoof

more dihedral to a point is more stable.the more dihedral the more effective the rudder and less effective the airlerons .how much dihedral to you have at the raised tip with the other wing panel laying flat.usually 1" dihedral for every 10" of total span ie a 55" span should be about 5 1/2" total dihedral.on spoert type/arobatic planes it is about half that amount.the only thing I can think of in reference to slow flight is maybe the airlerons do not respond well and you will need to use rudder.

gboulton

My Feedback: (15)

Dihedral's a funny thing...just the right amount can stabilize a plane in the roll axis, while going above or below that amount can have "other" effects. I'd be, however, a bit leery of the idea that the lesser dihedral OF THE TWO SUGGESTED BY THE KIT would produce a MORE stable airplane. This isn't to say it WON'T, just that it's a bit counter-intuitive.

My immediate question, however, would be "How did you determine the cause of the crash was a faulty control horn?" The crash you describe sounds very much like an airplane that simply didn't have the airspeed it needed, and stalled. Now, please understand, I'm NOT saying "that's what happened", just that the description WOULD fit that scenario...so, essentially, i'm asking "how can we be certain?".

farr301

The cause of the crash was a faulty aileron conrol horn because I had slipping problems with it during setup(mistake one), but it seemed fine the day of the flight. After inspection after the crash, the servo horn would still slip when the ailerons deflected.
The control deflections were also off during final check the night before the flight. Both ailerons were slightly deflected down when in the neutural position(mistake two).

The flight was recorded so my Dad and I are pretty positive that the cause of the crash was aileron problems not something else.

I might be able to upload the video to the thread but it probably wouldnt help anything........


Thanks,
Farr301

farr301

Sorry for double posting......

The 60in. wing has 8in of dihedral according to the manual and the ailerons did not move enough up and too much down............It seems that rudder will have to be worked in the first few flights to help with the high wnid dihedral so that the turns look like turns and not spins.....

Thanks,
Farr301

carrellh

I agree that you'd be better off with lower dihedral but I disagree with the shop owner's comment.

I've seen two PT-40s with the high dihedral wing. One had functional ailerons and the other had them locked. Both were very stable and exhibited a LOT of self leveling characteristics. The instructors who flew them said they had to fight the plane more than they liked to keep it banked in a turn. Neither plane could take off or land well with any crosswind at all, even with an instructor in control. The slightest crosswind would blow the plane over.

I built a PT-60 with the low dihedral wing. It was very stable and handled crosswinds fairly well. It did not exhibit the same self leveling characteristics that the high dihedral PT-40s did. At the end of a turn it needed a little opposite aileron to level the wings.

Since you wrote in another post that you've already soloed with your dad's plane, I wouldn't attempt to modify the wing. I'd repair the damage and fly it as is while building that second plane.

AERORICH73

Hi Farr: From what you have written, the servo arm is slipping on the servo output shaft? Both ailerons are slightly down when the servo arm is horizontal with both aileron control arms at a 90 degree angle to the servo arm, is what I understand you are saying. What you have written is that the servo arm splines do not fit with the servo output shaft spines. Next, both ailerons are to be fared with the wing trailing edge when the servo arm is parallel with the wing spar. This adjustment is made by lengthening the servo linkage to each aileron control horn to raise the ailerons to match the wing trailing edge. My purchased used PT-40 had dihedral in the wing, and flew very well getting me through flight training and soloing. Had many hours of enjoyment with it until it stalled to far from the field, and was never found. It really stumps me that the field safety check done by the club safety officer did not spot this problem before attempting the first test flight. I am happy to read that the hard landing did not cause to much damage. Hopefully after the next inspection, your plane will soar like a bird under control, and give you many hours of flying enjoyment. Let us know how your next flight goes.

[email protected]

farr301

Thanks to all the comments so far....
The whole aileron linkage was redone and a new horn that fit correctly was put on, so the movement is correct....
I might try this new field that is frequently used by modelers but it not an AMA site rather then the dead end street i have been useing with its many obstacles, making landings much harder. The other field is short grass and is wider so landings with slight crosswinds wont be such a problem for my plane.
As soon as the firewall is repaired the plane should be up and flying if a calm weekend comes around. I'll be sure to inform yall on its first complete flight!!

Thanks a lot,
Farr301

aerowoof

you should be using more up airleron than down.post the amount of up and down airleron measured at the trailing edge in inches.

farr301

The original throws on the plane before the crash were 1/4 up and 1/2 down...the throws now are 7/17 up and 1/4 down which is the recommendation in the manual. Since im a beginner and a kid i made the mistake of leaving the control throws off for the first flight. Now i have learned to have a little more patience..

Farr301

farr301

Sorry for the double post but that should be 7/16 up not 7/17

Farr301

prgonzalez

Farr301,

I built this kit five years a go and still have it. GP manual recommends wing "A" for three channel setup (locked ailerons) and wing "B" (sport wing) for four channel setup. But, it is just a recommendation.

I built the sport wing "B" setup. Either way, the plane is very stable. One thing you need to pay attention to is the washout. If the twist of the wings are different, the plane will have the tendency to roll in one direction all the time.

farr301

ok...cool
The washout seems to be even but i will double check it

Farr301

tucker1865

My Feedback: (6)

The 'A' wing is too much dihedral...the 'B' or sport wing or even a little less is fine. A good flyer and it will self-level enough to be a good trainer. Wind affects it less than the 'A' wing. If it's not too much trouble I would recommend changing. I learned with the 'B' wing, no problem. To check the washout (allso un-necessary) mount the plane on a stand or table, put small piece of anything (a checker or piece of balsa) on each wing tip in the same place. Now lower your eye level, as you look at the plane from the front, about 6 feet from the nose, until the checker disappears. The small pieces should disappear at the same time, if not the low one needs to be twisted up while heat is applied to the covering, until they are the same.

farr301

Ok.. thats great
I'll definitely consider the the transition to the B wing, but it could be a pain to do if its not worth it

Farr301

prgonzalez

In my opinion and probably the majority here, it is worth the work to go with the "B" wing setup.

Pedro

farr301

Ahhh... i think i'll just keep it the way i have it....it should be ok...and i will fly on days with low winds the first few times....i think I will be ok....im sure many people have trained succesfully using the A wing mode since it is what Great Planes RECOMENDS as the best set up for a beginner.

Farr301

joeccrc

My Feedback: (3)

I began building a PT-40 some time back and got distracted with life. LOL Anyway I'm a builder, I use to built plastic models, then built a small trainer back in the 60's, Yes I'm am over 50. Haven't been in RC for over 35 years, so I guess I'm a beginner again. Anyway I love the raw building of buying blueprints and cutting the balsa with a band saw. I'm in the middle of converting my PT-40 into a tail dragger, I changed the wing tips and of course the location of the axels. I'm thinking of finishing up this poor bird. I can post some picture if anyone would be interested or start a new post