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Question: High elevator trim Old Fogey and Flyer???

#1
Have scratch built an FT Flyer and Old Fogey, both are all up heavier than the original designs with paint, glue, reinforcements, landing gear, B pack motor, 3s850a and either 8 or 9x4.7 props, Zero thrust angle, have been swapping the same power pod between planes. They both required constant up elevator pressure unit I finally just mechanically trimmed them high so the plane would fly level hands off. The Flyer took a few dirt naps until figured this out, on the Old Fogey maiden I at least knew then, to pull back on the stick when it kept losing altitude. What flight characteristic is the cause: Are they too nose heavy? Too high of wing loading? Thrust angle? Errors in building? Photo below shows the elevator trimmed high to the point where the Old Fogey flys level, hands off the stick with light throttle.
IMG-3154.jpg
 

Hai-Lee

Old and Bold RC PILOT
#2
Your list of possible causes is accurate as almost any one of them could give you the problem.

When you state that you builds are too heavy may I inquire as to what percentage of overweight are we talking about?

Does the plane fly with the tail and wings level or do they fly in a slightly tail down attitude?

Does your balance point agree with the suggested balance point on the plans?

With answers to the above questions a clearer picture will be had by all thread respondents!

Have fun!
 

SlingShot

Maneuvering With Purpose
#4
When you state that you builds are too heavy may I inquire as to what percentage of overweight are we talking about?

Does your balance point agree with the suggested balance point on the plans?

With answers to the above questions a clearer picture will be had by all thread respondents!
Agree with all of this. Not intending to prematurely rule anything out, but these 2 things are the primary suspects.

Also, what pitch on your 8 inch prop? Do you have the same performance as the 9x4.7?
 

Merv

Well-known member
#5
What flight characteristic is the cause: Are they too nose heavy? Too high of wing loading? Thrust angle? Errors in building? Photo below shows the elevator trimmed high to the point where the Old Fogey flys level, hands off the stick with light throttle.
All the things you mentioned are possibilities. It all depends on what you mean by “light throttle”. If you are trying to fly very slowly, what you are showing looks about right. I trim my planes to fly at full throttle.

I’d try flying a bit faster & see if you start climbing. You may find you need to reduce your trim.
 

SlingShot

Maneuvering With Purpose
#6
All the things you mentioned are possibilities. It all depends on what you mean by “light throttle”. If you are trying to fly very slowly, what you are showing looks about right. I trim my planes to fly at full throttle.

I’d try flying a bit faster & see if you start climbing. You may find you need to reduce your trim.
Good catch! I missed the light throttle part.
 
#7
Your list of possible causes is accurate as almost any one of them could give you the problem.

When you state that you builds are too heavy may I inquire as to what percentage of overweight are we talking about?

Does the plane fly with the tail and wings level or do they fly in a slightly tail down attitude?

Does your balance point agree with the suggested balance point on the plans?

With answers to the above questions a clearer picture will be had by all thread respondents!

Have fun!
Thank you, I’ll have to weigh the planes and record the actual weighs. CG is at the checked at the marks from the plans with a test machine on a bench to keep the results consistent. With the trim, the planes look level from 30-70% throttle and when slowing moving the throttle. Before trimming, more throttle was typically ending in high powered crash.
F575775D-2933-46AA-9794-D8F0E5F1AA11.jpeg

Your list of possible causes is accurate as almost any one of them could give you the problem.

When you state that you builds are too heavy may I inquire as to what percentage of overweight are we talking about?

Does the plane fly with the tail and wings level or do they fly in a slightly tail down attitude?

Does your balance point agree with the suggested balance point on the plans?

With answers to the above questions a clearer picture will be had by all thread respondents!

Have fun!
 
#10
Agree with all of this. Not intending to prematurely rule anything out, but these 2 things are the primary suspects.

Also, what pitch on your 8 inch prop? Do you have the same performance as the 9x4.7?
Broke all the 8 inch props in crashes ;-) think they were 8x4.5, it seems like the 9 inch flys better overall anyway.
 

Merv

Well-known member
#11
CG is at the checked at the marks from the plans with a test machine on a bench to keep the results consistent.
It's a bit hard to tell from this picture, but this plane looks slightly nose heavy to me. A side picture, from a 90 degrees would be more helpful, the camera is too far forward and a bit high. Also spin the prop so it's vertical, so we can judge the thrust angle.
 
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Hai-Lee

Old and Bold RC PILOT
#12
With the CG in the recommended position I would ask you to do an EXPERIMENT for me. Fit and Icy pole/Popsicle stick under the wing LE and do a test flight. If the problem is too much weight the increasing of the wing incidence by a VERY SMALL amount may make it just a tad better.

If it actually does make it better then it would be up to you to determine exactly what incidence angle would best suit your current build.
It will also help if there is a tail incidence angle build error!

Just a thought!

Have fun!
 
#14
With the CG in the recommended position I would ask you to do an EXPERIMENT for me. Fit and Icy pole/Popsicle stick under the wing LE and do a test flight. If the problem is too much weight the increasing of the wing incidence by a VERY SMALL amount may make it just a tad better.

If it actually does make it better then it would be up to you to determine exactly what incidence angle would best suit your current build.
It will also help if there is a tail incidence angle build error!

Just a thought!

Have fun!
Thank you, I'll have to test the popsicle stick under the wing and see what happens. I did find the Fogey actually is closer to the all up weight at 520g is only 7% over the specified 489g. The Flyer however is about 25% over weight at 386g all up, specs says 320g.
 

Bricks

Well-known member
#15
I know that when I started building foam planes I had a tendency to add reinforcements and extra glue did the same when I first started building balsa back in the60`s. What I come to realize they fly much better building as light as possible and they still hold up well to crashes. If I can build lighter then the stated weight to me that is an accomplishment to better flying.