Pitts S2 scratch build

billyshaw22

Active member
The main thing that i found when getting any biplane to fly straight in all orientations is to have the bottom wing 0 deg, or parallel with thrust line, no dihedral and the top wing ether 0 deg or slight negative (leading edge slightly down) and no dihedral. If you are flying at higher speeds a slight negative incidence in the top wing is good, but make sure there isn't positive in the top wing, it can cause extra stress and try and pull it off. Another factor is if you put dihedral in the wing or wings. The dihedral will tend to make the plane climb to the canopy in knife edges. this could actually cause a snap roll when you apply rudder without giving the right amount of down elevator at the same time
 

TDL

Active member
that won't be the same, that could act like a spoiler to the top wing and can make it do some strange things if the top wing is stalling at a different speed then the bottom wing. this could cause some issues when doing slow speed flying or landing could get scary, i had to do some tinkering with my first design to get it right ( cut apart reagle and re-glue) my question to you : When you roll it to the right and put it in knife edge what does your plane do when you add rudder? side note: my esc is made by Alien Power Systems.
Got you, seems that I have lots of things to learn in multi-wings design.
I only have three flights on the foam Pitts yet, still trying to trim her to my liking. However, the 10x4.5 slow fly is not up to the test, I have replaced it with a 11x5.5 to see if that helps. As to your questions, as soon as I add left rudder, plane would roll to left then drop altitude, need to add throttle and more right aileron to maintain in knife edge, so far I can‘t establish knife edge long enough to see whether she would pull to gear or to canopy. I normally don’t have expo on rudder, I might try adding some expo too.
 

TDL

Active member
The main thing that i found when getting any biplane to fly straight in all orientations is to have the bottom wing 0 deg, or parallel with thrust line, no dihedral and the top wing ether 0 deg or slight negative (leading edge slightly down) and no dihedral. If you are flying at higher speeds a slight negative incidence in the top wing is good, but make sure there isn't positive in the top wing, it can cause extra stress and try and pull it off. Another factor is if you put dihedral in the wing or wings. The dihedral will tend to make the plane climb to the canopy in knife edges. this could actually cause a snap roll when you apply rudder without giving the right amount of down elevator at the same time

yes, that‘s exactly what I felt during a few attempts, she wanted to do snap roll and I had to add more right aileron. Next time I would add some down elevator. I have about 6 degree dihedral on the bottom wing ( as scale) and I just checked with my Topflite Ultimate EC which has much less dihedral on the bottom wing, I remember the ultimate was much easier to do KE.
As to the trust angle, I have about 2 degree down and right, so far she flies straight up to about 3/4 throttle, slightly climbing at wot. so, should I changed the incidence of the bottom wing to negative 2 degree? Will that sacrifice low speed performance? Anyway, I realize that I cannot compare folding foam board wings to balsa so I am not too worry about this Pitts, I just love to learn more on RC design, this is my third one, and picking your brain! Hahah...
Thanks a lot!
 

Tench745

Master member
The main thing that i found when getting any biplane to fly straight in all orientations is to have the bottom wing 0 deg, or parallel with thrust line, no dihedral and the top wing ether 0 deg or slight negative (leading edge slightly down) and no dihedral. If you are flying at higher speeds a slight negative incidence in the top wing is good, but make sure there isn't positive in the top wing, it can cause extra stress and try and pull it off. Another factor is if you put dihedral in the wing or wings. The dihedral will tend to make the plane climb to the canopy in knife edges. this could actually cause a snap roll when you apply rudder without giving the right amount of down elevator at the same time
I was very confused about this comment until I saw the "fly straight in all orientations" on a second reading. As I understand it most civilian biplanes with positive stagger will have a positive incidence to the upper wing. This causes the upper wing to stall before the lower, moving the center of lift aft, and giving them a quick stall recovery. Obviously, this would fight you in aerobatic maneuvers and inverted flight.
 

billyshaw22

Active member
yes, that‘s exactly what I felt during a few attempts, she wanted to do snap roll and I had to add more right aileron. Next time I would add some down elevator. I have about 6 degree dihedral on the bottom wing ( as scale) and I just checked with my Topflite Ultimate EC which has much less dihedral on the bottom wing, I remember the ultimate was much easier to do KE.
As to the trust angle, I have about 2 degree down and right, so far she flies straight up to about 3/4 throttle, slightly climbing at wot. so, should I changed the incidence of the bottom wing to negative 2 degree? Will that sacrifice low speed performance? Anyway, I realize that I cannot compare folding foam board wings to balsa so I am not too worry about this Pitts, I just love to learn more on RC design, this is my third one, and picking your brain! Hahah...
Thanks a lot!
when designing the foam board plane try and keep everything at 0, or close to it. in my opinion for the size a weight you can end up fixing one problem and make three more in other aspects of the flight. another thing, it is foam and the qualities that make it so great also make it difficult to use (light and flexible) i would get your power set up worked out first and get it all trimmed to your liking then start looking at the small things like the knife edge, the power can play a big toll on this
 

TDL

Active member
Billyshaw22- You are absolutely right about foam board plane, I have a few planes I built two months ago, now they all need to be re-trimmed on orderto fly straight. Flexibility is good for building, not good for things require precision. I think I got carry away by my previous experience in Pitts (EPO, balsa and EPP- have I said I love Pitts? ) so the KE question is more of a general perception. Anyway,it is so great to learn from expert.

My town just shutdown all the parks and school yards. I need to go to a remote place for flying;
hopefully tomorrow I can test the new props. Be healthy, everyone.
 

billyshaw22

Active member
You ever need anything just ask, i will do my best to help, and if i don't know the answer i will find someone that can! the best part of this hobby for me is even after almost 30 years of flying i still learn and meet new people. hopefully you can get out and get some flying in!
 
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TDL

Active member
Well, yesterday I found my son put his trainer on top of my Pitts, with motor stacked right on the horizonal stab/ elevator. The HS/elevator was bent to about 30 degree! I was beyond pissed but what can I do? I carefully bent them back as best as possible but could not go 100% straight. So I cover them with packaging tape and add carbon rods underneath the HS. Any idea of fixing this without major surger?
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TDL

Active member
Anyone has an idea for fixing this without major surgery?

Went to a remote site to test the EMP 11x5.5 prop this afternoon, all surfaces needed re-trim, could not believe a slightly bent elevator would cause that much of difference in flight. I took the EMP prop from an old FW190. oh man, that prop sxxks! No thrust until over half throttle and less thrust at WOT than a APC 10x4.7 slowfly....I think I need to buy some APC props, not sure if I should go with 11x4.7 slowfly, or 11x5.5 thin EP.

on the second flight, the Pitts was acting weird, need tons of down elevator to fly invert. After landing I found the neck of the elevator broke, the left halve broke free from the carbon strip reinforcement so only the right halve would go down. Anyway, never a dull moment while flying with kids.

No video today. My daughter FaceTime her friend using my phone for the whole time we were there; so I won’t show you my embarrassing moment at landing..
 

billyshaw22

Active member
i would say what you did is probably the best with out trying to replace foam, if it is too bad flying wise you might have to replace that stab and elevator, but i would try what you can before that point. just in my opinion....
 
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TDL

Active member
i would say what you did is probably the best with out trying to replace foam, if it is too bad flying wise you might have to replace that stab and elevator, but i would try what you can before that point. just in my opinion....
I agree.

Had two flights yesterday, the first one she performed fine despite the prop. Had done some basic pattern flights and she did okay except 4 points roll. On the second flight I tried to hang on KE a bit longer, but she pull heavily to the gear. I then did an invert 45 degree climb and found the CG is correct. So I was at lost. Later I found the the left halve of elevator broke free, so, I will have more test next time.

Luckily NJ governor has not banned outdoor activities in the latest mandate. There were two police patrol cars came to the field watching and then left without any interruption. Hopefully that will stay the same for the next few months.

Stay healthy everyone.