Calvinman

Hello,

I am building a Great Planes PT20 for a relaxed flyer for myself and to let guests take the buddy box to get the rc experience. To me the dihedral seems extreme, what do you think I should reduce it to? Does anyone have any other mods that I should do? I think I am also going to make it a tail dragger, me and nose gear just don't get along.

Calvi.

JohnBuckner

My Feedback: (1)

Are you flying this with or without ailerons? The PT20e did not use ailerons and this question is very important to be able to properly answer your question.

John

Calvinman

Hi John,

Yes I am going to be using ailerons on it.

Calvi

JohnBuckner

My Feedback: (1)

Then yes you can reduce the dihedral a bit and I would suggest about half of the stock dihedral, I would not go to a totally flat wing but you could actually go to anhedral, agine about half of what the suggested dihedral was. Anhedral gives you as close to that totally neutral roll response possible with a high wing cabin type airplane.

An airplane using just rudder for roll/yaw control is dependant on dihedral to properly function and unlike when ailerons are used to increase roll response with a rudder only airplane the dihedral must be increased , to decrease roll response the dihedral is reduced. A totally flat wing with a rudder only system will not work and it will be uncontrollable.

I still have a Pt 20e I built about twenty years ago and it still flys albeit with a better brushless system. Will post a a picture when I get a chance this afternoon.

John

Calvinman

I think I will go with half the stock dihedral. I would love to go electric with this one, but I have an OS32 looking for a home, I hope it does not end up nose heavy with this motor. Looking forward to seeing a pic of your PT20. I would have liked to be building a freedom 20, but the PT20 is the closest thing I could find to it.

Calvi

JohnBuckner

My Feedback: (1)

Calvinman

Nice John, my freedom had the transparent red on it also.

52larry52

My Feedback: (1)

John's suggestion to use "1/2 the stock dihedral " is spot on. I've built several classic 3 channel high wing kits, adding strip ailerons and using 1/2 the stock dihedral (Debolt Live Wire champ and Ace Air Scout). I made servo pockets in each wing and a servo for each aileron. Both are enjoyable relaxed flyers. I wouldn't go with John's anhedral idea though. Just on looks, it's not for me. The anhedral might be fun when all the ARFers at the field tell you that you've got the wing on "up side down"!

Top_Gunn

My Feedback: (6)

I agree with the half-dihedral recommendations. Too much dihedral on a high wing plane with ailerons can mess up aileron-only turns, which is probably the kind of turns the people you have on the buddy box will be making. In extreme cases, the adverse yaw combined with the excess dihedral can make a plane turn left when you give it right aileron, and vice versa. It won't happen with every plane. I know a guy who added strip ailerons to a stock Kadet Senior, and it flew fine. But why keep dihedral you don't need?

Rubbernecker

My Feedback: (22)

I have built a PT 20 as well, but mine had options for the 3 or 4 channel. The 4 channel had less dihedral as well as matching dihedral braces for each version????????

John

From Great Planes website:Wing Configuration
You have a choice in the type of wingto build – the
trainer (“A-wing”) or the sport(“B-wing”). The A-wing
has more dihedral than the B-wing andwill allow your PT
to fly just great as a 3-channel modelwithout functioning
ailerons.We show you how to build theailerons but “lock”
them down. You can always hook them uplater. Building
the A-wing without functioningailerons saves you a little
money (most four channel systems aresold with three
servos) and building time. If the PTis your first R/C
model we strongly (that's strongly)recommend that you
build the A-wing with more dihedral.If you build the sport
wing you will lose the full benefit ofthe self-recovery
features of the PT – features thatwill help you solo faster
and safer.
With the lower dihedral angle of theB-wing you may still
fly your PT without functioningailerons, but it performs
best with ailerons – thisconfiguration will suit
intermediate and sport flyers.

Calvinman

Hi Al and Rubbernecker, Yes I am sure my PT20 has the two options, I have just not read that far in the instructions. I usually read the construction manual over several times before starting a build, but I am expecting my brother for a visit in a few more days and have been building page by page, not sure how this is going to make the build go any faster, I am just finishing the fuse and will pre read the wing construction chapter to be sure I am going to come out with the wing I want. Calci

Calvinman

Well my brother has come and gone and Ionly got as far as gluing in the landing gear blocks Just as well the only day we got away to thefield the wind was 20kph gusting to over 40kph. I flew the heck out of myTiger 2(aka frankenstien) which was a lot of fun with stationary barrel rolls,backwards flight etc.




I would have let my bro do a take off but the turbulence at ground level wascrazy. We have a drainage ditch angling from north west to south east onthe west side of our field and all the bull rushes have recently been dug outof it, leaving mounds of mud and reeds to stir up the air. Landings werevery predictable until about six feet off the ground, then the right wing woulddrop, then the plane would just about settle in for a picture perfect landing,then jump up to 2 feet and hover, then I would push the nose over and land justa little on the hard side, but all in all a blast was had by all.

Calvi.

Calvinman

Ok, I have the wing joined, I went for 1" dihedral on each wing(it was the handiest blocks I had). My next question is should I build in the washout or just go flat? I understand the benefits of washout, but like anything there is usually a downside.

Calvi

JohnBuckner

My Feedback: (1)

Based upon my experience with the old PT- E, I did build in washout by using blocked up trailing edges near the tips which was suggested on the plans as I remember although do not recall how much., I do know it is obvious if you look down the trailing edges, I found the slow speed and stall behavior to delightful.

So I would suggest its a good idea on your glow version of the same airplane.

John

Calvinman

OK, thanks John, the wing has jigs to set the washout, I will just measure them to see how much to shim up the trailing edge.

Calvi