Go Back  RCU Forums > RC Airplanes > Questions and Answers
Reload this Page >

Biplane trimming problem

Notices
Questions and Answers If you have general RC questions or answers discuss it here.

Biplane trimming problem

Old 06-02-2008, 05:06 PM
  #1  
Dzlstunter
Thread Starter
 
Join Date: Dec 2001
Location: Jacksonville, IL
Posts: 485
Likes: 0
Received 0 Likes on 0 Posts
Default Biplane trimming problem

I have a Phaeton II which I built and cannot find the trim problem. Five experienced RC pilots have examined the plane and watched it perform in the air. All agree that the surfaces are straight and properly aligned. The balance (both fore and aft and lateral) is on the money. All throws are equal and set to specification. Here's the problem: When flown into a 5-10 mph wind and trimmed to fly straight with "hands off" it will drop the right wing every time it is turned down wind. No exception. Always the same wing the same way. Ideas?
The bipe in question:
Attached Thumbnails Click image for larger version

Name:	Qo39647.jpg
Views:	7
Size:	53.9 KB
ID:	962463  
Old 06-02-2008, 05:42 PM
  #2  
PMAXX
Member
My Feedback: (5)
 
Join Date: Apr 2005
Location: ISLAND PARK, NY
Posts: 60
Likes: 0
Received 0 Likes on 0 Posts
Default RE: Biplane trimming problem

Make sure your wing incedance is set equally throughout and not twisted. It really doesn't take much to throw you off.
Old 06-02-2008, 06:17 PM
  #3  
daveopam
My Feedback: (9)
 
daveopam's Avatar
 
Join Date: Oct 2002
Location: ELK CITY, OK
Posts: 7,519
Received 4 Likes on 4 Posts
Default RE: Biplane trimming problem

Have you checked all the aile linkage and servos? Could gravity be pulling one servo a little? The incidence will be different when it is inverted. Are the elev halfs even?

David
Old 06-02-2008, 07:10 PM
  #4  
Dzlstunter
Thread Starter
 
Join Date: Dec 2001
Location: Jacksonville, IL
Posts: 485
Likes: 0
Received 0 Likes on 0 Posts
Default RE: Biplane trimming problem

pmaxx: It sure doesn't LOOK like itand several of us looked; but I'll check it out. Thanx, Dzl

daveopam: No split elevator; and until I get it trimmed better, I'm not even considering flipping it over! It's that bad. Thanx, Dzl



Old 06-02-2008, 08:33 PM
  #5  
chashint
Senior Member
 
Join Date: Dec 2001
Location: Rowlett, TX
Posts: 1,309
Likes: 0
Received 0 Likes on 0 Posts
Default RE: Biplane trimming problem

When trimmed for straight and level into the wind does the wing drop when you change the throttle setting ?
What position are the ailerons in when trimmed for straight and level, do they look like they are at netrual or are they offset from netrual ?
Finally is the rudder at netrual ? When you use the rudder does it induce roll or does it just yaw the plane ?
Old 06-02-2008, 11:59 PM
  #6  
Ralph White
 
Ralph White's Avatar
 
Join Date: Feb 2007
Location: Neoga, IL
Posts: 610
Likes: 0
Received 0 Likes on 0 Posts
Default RE: Biplane trimming problem

Is the wing dropping or is it tip stalling? If you turn too sharply the change in air speed from up wind to down wind is 20 mph if the wind is 10 mph. This assumes it takes the aircraft a few seconds to increase its airspeed after turning down wind. If you are flying at a low airspeed that 20 mph drop in airspeed may be enough to stall the aircraft. Another thing that could be happening is torque roll if you are changing the engine rpm a bunch.
Just a couple ideas for you to consider.
Good luck,
Ralph White, Neoga, IL
Old 06-03-2008, 07:05 AM
  #7  
ronwc
My Feedback: (404)
 
ronwc's Avatar
 
Join Date: Jan 2002
Location: LARGO, FL
Posts: 496
Likes: 0
Received 0 Likes on 0 Posts
Default RE: Biplane trimming problem

Just put about 2 clicks of left rudder trim, then retrim ailerons slightly if needed for level flight -
Old 06-03-2008, 08:04 AM
  #8  
Edwin
My Feedback: (2)
 
Join Date: Feb 2002
Location: Leander, TX
Posts: 6,204
Likes: 0
Received 0 Likes on 0 Posts
Default RE: Biplane trimming problem

Whatwind has been trimming his new P90 lately and discovered last week he is getting some aileron flutter on the right side. His setup is one big ***** servo to drive 4 ailerons. My setup used two servos to drive 4 ailerons. Needless to say, he is changing over to the dual servo setup. His thread has a lot of trim discussion in there about setup and incedence. Might be of some help. Mine flew best with a -1 1/2deg incedence on the top wing.
Edwin

http://www.rcuniverse.com/forum/m_66...tm.htm#6617840
Old 06-03-2008, 09:46 AM
  #9  
jaka
 
Join Date: Dec 2001
Location: Upplands Vasby, SWEDEN
Posts: 7,811
Likes: 0
Received 1 Like on 1 Post
Default RE: Biplane trimming problem

Hi!
It's easy!
If one wing drops when you fly straight forward...you have a wing that is twisted! Check it with an Robart incident meter or use your eyes. Just look from the wing tip inwards to the wing root and eyeball the difference in wing incidence from tip to root.It's very easy when you can.
Old 06-03-2008, 09:52 AM
  #10  
Rodney
Senior Member
 
Join Date: Dec 2001
Location: FL
Posts: 7,769
Likes: 0
Received 1 Like on 1 Post
Default RE: Biplane trimming problem

Relative incidence has a big effect. On over seven large bipes I have had, they all flew best with the upper wing at minus 1.5 degrees relative to the lower wing. Also, they all had the lower wing and the stab at the same incidence setting with 1.5 degrees right thrust and 3 to 5 degrees downthrust. Now as to downwind versus upwind, it makes absolutely no difference. The plane is in a moving mass of air and doesn't know the difference between downwind and upwind. Now, you on the ground, may notice a difference in speed relative to you but, the plane doesn't know this and will fly the same whether going upwind or downwind or crosswind as long as you are higher than the turbulence caused by ground contours or buildings.
Old 06-03-2008, 11:25 AM
  #11  
alfredbmor
Senior Member
 
alfredbmor's Avatar
 
Join Date: May 2005
Location: El Paso, TX
Posts: 1,789
Likes: 0
Received 0 Likes on 0 Posts
Default RE: Biplane trimming problem

You can use this home made incidence meter.
Attached Thumbnails Click image for larger version

Name:	Zx69899.jpg
Views:	13
Size:	25.1 KB
ID:	962850  
Old 06-03-2008, 12:31 PM
  #12  
Dzlstunter
Thread Starter
 
Join Date: Dec 2001
Location: Jacksonville, IL
Posts: 485
Likes: 0
Received 0 Likes on 0 Posts
Default RE: Biplane trimming problem

Ralph: The dropped wing effect isn't just at or after the turn, it remains as one flies straight after leveling off from the turn; does this with NO handling of the throttle at all. Thanx for your imput, Dzl

ronwc: When we corrected with rudder, it just yawed. Good thing to try, tho. Thanx, Dzl

Edwin: Got one servo on each aileron now, and this is a smallish wing. Thanx for the imput, Dzl

jaka: The incidence meter comes out tonite in the shopif all goes well. Thanx for the suggestion, Dzl

Rodney: If all else fails, I will mess with the factory recommendations on incidence just as you suggest. Who knows, I may have inadvertently messed with them already!!! Thanx for the suggestion, Dzl
Old 06-03-2008, 01:46 PM
  #13  
TFF
 
Join Date: Oct 2006
Location: Memphis, TN
Posts: 4,183
Likes: 0
Received 0 Likes on 0 Posts
Default RE: Biplane trimming problem

Does it drop the opposite wing when turned the other direction down wind, and is one wing swept more in relation to the centerline of the fuse than the other side? Has the distance between the wings been modified? Plane looks good though.
Old 06-03-2008, 01:54 PM
  #14  
Dzlstunter
Thread Starter
 
Join Date: Dec 2001
Location: Jacksonville, IL
Posts: 485
Likes: 0
Received 0 Likes on 0 Posts
Default RE: Biplane trimming problem

TFF: Well, it could be that the other wing is going up, rather than dropping the right wing, but the situation remains the same; it can be trimmed to fly level one way, but then drops (or raises?) going the other. It DOES look ok, and all five people concur, but I will be putting the meter on it tonight if all goes well. Thanx for taking the time, Dzl
Old 06-03-2008, 04:39 PM
  #15  
Ralph White
 
Ralph White's Avatar
 
Join Date: Feb 2007
Location: Neoga, IL
Posts: 610
Likes: 0
Received 0 Likes on 0 Posts
Default RE: Biplane trimming problem

Dz, Another thought is the aileron servo may not be returning to exact center after the turn.
Ralph White, Neoga, IL
Old 06-03-2008, 05:44 PM
  #16  
Dzlstunter
Thread Starter
 
Join Date: Dec 2001
Location: Jacksonville, IL
Posts: 485
Likes: 0
Received 0 Likes on 0 Posts
Default RE: Biplane trimming problem

Good thinking, Ralph. Unfortunely, it's one of the things we ruled out in the early going. Thanx again, Dzl
Old 06-04-2008, 09:28 AM
  #17  
Dzlstunter
Thread Starter
 
Join Date: Dec 2001
Location: Jacksonville, IL
Posts: 485
Likes: 0
Received 0 Likes on 0 Posts
Default RE: Biplane trimming problem

Well, gents, it looks like jaka may get the gold ring. He wrote:
Hi!
It's easy!
If one wing drops when you fly straight forward...you have a wing that is twisted! Check it with an Robart incident meter or use your eyes. Just look from the wing tip inwards to the wing root and eyeball the difference in wing incidence from tip to root.It's very easy when you can.


When I got to the shop last night, I dusted off the old incidence meter, and the readings didn't make a whole lot of sense. So.....I'm calling on a local guru to come over next weekend and we'll try to sort it out together with a couple of meters he has plus mine at the same time. Anyway, let's put this thread on "HOLD" unless this doesn't solve the problem. Then, as Arnold says, "I will be back."

Thanks for all the great suggestions. They may yet hold the key to this thing. Dzl
Old 06-11-2008, 06:28 AM
  #18  
Dzlstunter
Thread Starter
 
Join Date: Dec 2001
Location: Jacksonville, IL
Posts: 485
Likes: 0
Received 0 Likes on 0 Posts
Default RE: Biplane trimming problem

I think we found the problem. I had the local guru over Monday nite and cleared out the garage so we could put the plane on a table in the middle and go round and round with incidence meters, straight edges, carbon rods banded to the wings, and levels. We found that both the wings apparently got the same small twist in them during covering, and this was made worse by one of the interplane struts which was a bit too short and when tightened exacerbated the problem. All has been corrected, and we are looking forward to test flying it Wednesday nite if the weather permits, though it looks as if the wind god is not going to cooperate.

Thank you all for your concern and suggestions. I'll let you know how it goes when it goes. Dzl

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off


Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service - Do Not Sell My Personal Information

Copyright 2018 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.