Building PT-40 MkI, should I add washout into the wings?
09-05-2014, 05:52 AM
#1
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Building PT-40 MkI, should I add washout into the wings?
I found a new old stock PT-40 MkI kit at the LHS that I picked up for $20, I just could not pass it up. I am building it for my 7yr old son, he is sitting with me as I build watching and learning. I am letting him do a few things along the way teaching him how to cut and trim parts in a safe manner so as not to cut himself up as I did many, many times as I taught myself when I was his age. It's also what he will learn to fly on. I know that I could buy a Nitro Models trainer or something like it for under $100, but then he would be learning how to assemble and not build, big difference. Besides, I have so many wheels, fuel tanks, covering and other unsupplied matierials sitting around that I will really be into for just a few more dollars than what I bought it for.
Anyway, the kit was complete exept for the plans and instruction book. Another gentleman on here was able to send me a pdf of the book and someone else sent me the plans and book for a MkII (which I appreciate) but the MkII construction is pretty different from the MkI so they really do not apply. As such I have just built it from the book with no plans, but it is a REALLY simple airplane so this is not an issue exept for one thing. The book does not mention washout or setting the wing up to build in washout, and I do not have the plans to look at to see if they mentioned if or how they wanted it to be incorporated. It would be simple enough to add in by putting a 1/8" scrap at the mid point TE and a 1/4" at the TE outboard tip. The TE and LE are both notched so the ribs will just fall into place at the correct spacing so there will not be any other issues and the location of the CG is spelled out in the manual so I have all of the pertanent information otherwise. If they flew well without the washout then I will not worry about it but I know from many years of experience that some airplanes (some cubs) can go from snappy to gentle by adding 2 degrees of washout.
Add it or just build the wing flat?
Anyway, the kit was complete exept for the plans and instruction book. Another gentleman on here was able to send me a pdf of the book and someone else sent me the plans and book for a MkII (which I appreciate) but the MkII construction is pretty different from the MkI so they really do not apply. As such I have just built it from the book with no plans, but it is a REALLY simple airplane so this is not an issue exept for one thing. The book does not mention washout or setting the wing up to build in washout, and I do not have the plans to look at to see if they mentioned if or how they wanted it to be incorporated. It would be simple enough to add in by putting a 1/8" scrap at the mid point TE and a 1/4" at the TE outboard tip. The TE and LE are both notched so the ribs will just fall into place at the correct spacing so there will not be any other issues and the location of the CG is spelled out in the manual so I have all of the pertanent information otherwise. If they flew well without the washout then I will not worry about it but I know from many years of experience that some airplanes (some cubs) can go from snappy to gentle by adding 2 degrees of washout.
Add it or just build the wing flat?
09-05-2014, 08:45 AM
#3
My Feedback: (1)
The MK 1 version is a great free flight airplane. One trimmed out, it flies best if the pilot does nothing with the radio. It's just too stable to be considered a good RC trainer, since the pilot is always fighting the aerodynamics for control. But with a 7 year old, dial the throws down and it might be the right airplane.
09-06-2014, 10:18 AM
#5
Banned
About wings washout
JoeyCoates,
I do not know what you understand about the effects and reasons for having wing washouts.
I suggest that you build 1 1/2 degree to 2 degrees of washout.
It makes less violent behavior of the model approaching the stalling angle of the wings.
Instead of using small scrap pieces as you mentioned just cut out of scrap two wedges to use at the wing tips and assure that the trailing and leading edges are using straight pieces. That will make the washout proportional to the distance from the wing roots.
I will not elaborate for the reasons to avoid any washout. I will just say that these reasons are not advantages for a behinner.
Zor
Added by editing _ _ _
I wrote the above before going to see the manual.
The manual in ' the table of contents page ' says "ADD WASHOUT AT THE WINGS TIPS".
End
I do not know what you understand about the effects and reasons for having wing washouts.
I suggest that you build 1 1/2 degree to 2 degrees of washout.
It makes less violent behavior of the model approaching the stalling angle of the wings.
Instead of using small scrap pieces as you mentioned just cut out of scrap two wedges to use at the wing tips and assure that the trailing and leading edges are using straight pieces. That will make the washout proportional to the distance from the wing roots.
I will not elaborate for the reasons to avoid any washout. I will just say that these reasons are not advantages for a behinner.
Zor
Added by editing _ _ _
I wrote the above before going to see the manual.
The manual in ' the table of contents page ' says "ADD WASHOUT AT THE WINGS TIPS".
End
Last edited by Zor; 09-06-2014 at 10:42 AM.
