Go Back  RCU Forums > RC Airplanes > Aerodynamics
Reload this Page >

Trailing Edges on Large Scale Aerobatic Planes

Notices
Aerodynamics Discuss the physics of flight revolving around the aerodynamics and design of aircraft.

Trailing Edges on Large Scale Aerobatic Planes

Old 02-28-2002, 02:47 AM
  #1  
Don Szczur
Thread Starter
My Feedback: (1)
 
Don Szczur's Avatar
 
Join Date: Jan 2002
Location: Chantilly, VA
Posts: 2,112
Likes: 0
Received 8 Likes on 7 Posts
Default Trailing Edges on Large Scale Aerobatic Planes

What are the thoughts and exeriences of razor sharp vs thick trailing edges on large scale aerobatic planes, about 40%

Carden has pretty thick trailing edges.

Fiber Classics has very thin (like sailplane) trailing edges.

Both have been very competitive in IMAC, Masters, and TOC events.

Which works better and why or why not?

Don
Old 02-28-2002, 03:24 PM
  #2  
can773
My Feedback: (1)
 
can773's Avatar
 
Join Date: Jan 2002
Location: Calgary, AB, CANADA
Posts: 2,286
Likes: 0
Received 1 Like on 1 Post
Default Trailing Edges on Large Scale Aerobatic Planes

Don

Cant speak on GS, but when I was in Ireland this summer I was shocked to see the size of the TE on CPLR's, and actually a lot of the European guys (as well as Japanese) planes. The rudder TE must have been 1/4" thick, possibly more (I forgot my ruler, but I will have it in Poland!!!!). Dont know yet if it is better or not, but on my Evolis's I plan to run thick TE to see if it is better than the thinner ones I have used in the past.
Old 02-28-2002, 06:37 PM
  #3  
Ollie
Senior Member
 
Join Date: Dec 2001
Location: Punta Gorda, FL
Posts: 958
Likes: 0
Received 0 Likes on 0 Posts
Default Trailing Edges on Large Scale Aerobatic Planes

A 1/4 inch thick trailing edge 12 inches long has a frontal area of 3 square inches and about the same drag as a three square inch plate perpendicular to the air stream. Drag is an advantage for pattern competition in that it limits acceleration and makes it easier to fly a pattern that appears to have a constant speed. Other than looks and style, I can't imagine why pattern competition planes aren't equipped with more parasitic drag producing features. Why spinners and cowlings? Why not draggier landing gear, struts and open cockpits?

Rounded trailing edges produce vortex sheading that can power flutter. Blunt trailing edges may do the same but the energy may not be high enough to cause problems with a slow pattern and stiff linkages. The weight of a blunt trailing edge versus a sharp, gradually tapered trailing edge will reduce the flutter speed somewhat.
Old 02-28-2002, 09:14 PM
  #4  
can773
My Feedback: (1)
 
can773's Avatar
 
Join Date: Jan 2002
Location: Calgary, AB, CANADA
Posts: 2,286
Likes: 0
Received 1 Like on 1 Post
Default Trailing Edges on Large Scale Aerobatic Planes

Originally posted by Ollie
A 1/4 inch thick trailing edge 12 inches long has a frontal area of 3 square inches and about the same drag as a three square inch plate perpendicular to the air stream.

Please explain?? How can a TE have the same effect as a flat plate perpendicular to the flow?? I can understand there will be drag due to the airflow becoming turbulent after leaving the wing, but as much as a flat plate?? Be as technical as you want, I have a degree in mech eng and would like to understand the reasoning behind this My experience is in flow thorugh pipes and nozzles, not a lot in aerodynamics.
Old 02-28-2002, 11:35 PM
  #5  
Ollie
Senior Member
 
Join Date: Dec 2001
Location: Punta Gorda, FL
Posts: 958
Likes: 0
Received 0 Likes on 0 Posts
Default Trailing Edges on Large Scale Aerobatic Planes

Chad, you were right to question my statement about thick trailing edge drag. It is at least an order of magnitude less than a flat plate of the same area. I was wrong and I apologise for such a gross error.
Old 03-01-2002, 02:45 AM
  #6  
can773
My Feedback: (1)
 
can773's Avatar
 
Join Date: Jan 2002
Location: Calgary, AB, CANADA
Posts: 2,286
Likes: 0
Received 1 Like on 1 Post
Default Trailing Edges on Large Scale Aerobatic Planes

Originally posted by Ollie
Chad, you were right to question my statement about thick trailing edge drag. It is at least an order of magnitude less than a flat plate of the same area. I was wrong and I apologise for such a gross error.
Whew, I was starting to think that if it was true my plane would never come down from the sky Thanks!
Old 03-02-2002, 05:18 AM
  #7  
Don Szczur
Thread Starter
My Feedback: (1)
 
Don Szczur's Avatar
 
Join Date: Jan 2002
Location: Chantilly, VA
Posts: 2,112
Likes: 0
Received 8 Likes on 7 Posts
Default Trailing Edges on Large Scale Aerobatic Planes

These data points are extremely useful. Thank you very much. Chad, from the ones you saw, do you recall if the other control surfaces were also thick at the trailing edge?

Thanks much,
Don
Old 03-05-2002, 07:11 PM
  #8  
can773
My Feedback: (1)
 
can773's Avatar
 
Join Date: Jan 2002
Location: Calgary, AB, CANADA
Posts: 2,286
Likes: 0
Received 1 Like on 1 Post
Default Trailing Edges on Large Scale Aerobatic Planes

Originally posted by Don Szczur
These data points are extremely useful. Thank you very much. Chad, from the ones you saw, do you recall if the other control surfaces were also thick at the trailing edge?

Thanks much,
Don
Hi Don

Yes the elevators and ailerons were also thick, but not as thick as the rudder was. They were over the 1/8" "standard" maybe up around 3/16", but not quite 1/4". I will look through my pictures at home and see if I have one that shows a little.
Old 03-10-2002, 05:11 PM
  #9  
rcman-RCU
Senior Member
My Feedback: (31)
 
Join Date: Dec 2001
Location: Colorado Springs, CO
Posts: 173
Likes: 0
Received 0 Likes on 0 Posts
Default Trailing Edges

There was a post on this subject quite a while back relating to trailing edges on full scale aerobatic planes. As I recall, many of the full scales had control surfaces made out of welded tubing with rounded trailing edges maybe 1 to 2 inches thick. This would equate to .250 to .500 inches thick for a quater scale model. The thought was that if the full scale guys don't worry about trailing edges, maybe it is not too important for us modelers either.

It does seem to be well confirmed that rounded trailing eges are more prone to flutter than sqaured off edges. Also, heavy trailing edges are more prone to flutter than light ones. I think that stiff control surface designs and slop free control linkages are a lot more important than trailing edge shape.

On racing or high speed planes, a sharp trailing edge would result in a meaningful reduction in drag.
Old 03-13-2002, 01:41 AM
  #10  
Don Szczur
Thread Starter
My Feedback: (1)
 
Don Szczur's Avatar
 
Join Date: Jan 2002
Location: Chantilly, VA
Posts: 2,112
Likes: 0
Received 8 Likes on 7 Posts
Default Trailing Edges on Large Scale Aerobatic Planes

Not sure if I've seen many with 1 or 2 inch trailing edges- the Caps and Sukhois that I've seen were about quarter to half inch but the molecules are at a different scale there.

So far what I've heard is that its advisable to put angle stock on the TE to bring up the TE thickness. This makes the control surface more stable as well as less sensitive to minor inputs. Also having this kind of material on the rudder provides damping stability in the (yaw).

Thansks all for the input,

Chad, You are a lot closer to making it Poland than I am- I'm jealous!

Don
Old 03-13-2002, 03:29 AM
  #11  
gubbs3
Senior Member
My Feedback: (1)
 
Join Date: Dec 2001
Location: Coon Rapids, MN
Posts: 1,403
Likes: 0
Received 0 Likes on 0 Posts
Default Trailing Edges on Large Scale Aerobatic Planes

Originally posted by Ollie


Rounded trailing edges produce vortex sheading that can power flutter.
I feel the opposite. In my opinion, the bulky trailing edges may inhibit flutter at high speeds. My reason for this assumption is my knowledge of r/c boats. My unlce has a racing hydro that is capable of 70+ mph. This boats rudder is knife edged at the leading edge but 1/4" thick at the rear. As asked some guys about this, since it seems like it would produce more drag, but they said it keeps the rudder from fluttering since it creates an air pocket behind the rudder. It seems like a sound enough reason.
Old 03-14-2002, 12:21 AM
  #12  
can773
My Feedback: (1)
 
can773's Avatar
 
Join Date: Jan 2002
Location: Calgary, AB, CANADA
Posts: 2,286
Likes: 0
Received 1 Like on 1 Post
Default Trailing Edges on Large Scale Aerobatic Planes

Originally posted by Don Szczur


Chad, You are a lot closer to making it Poland than I am- I'm jealous!

Don
Hi Don

Benefit of being in Canada We dont much quite the number of competitors that you guys get down there. Sometimes I wish we had that level of competition up here, I am coming down to Muncie this year with some buds to get a little head start for Poland, probably catch up with you then!!!
Old 03-26-2002, 05:31 AM
  #13  
niccolai_m
Junior Member
 
Join Date: Mar 2002
Location:
Posts: 6
Likes: 0
Received 0 Likes on 0 Posts
Default Trailing Edges on Large Scale Aerobatic Planes

I would have thought at the reynolds numbers being operated at the trailing edge would have little effect on drag and that the flow at the trailing edge is problably pretty low energy, possibly close to detaching in some situation, if not detached.

So a thick trailing edge may have some other reason for being superior. Perhaps it leads to a stiffer component. This would improve roll effectiveness and may give an edge during tail slides.
Old 03-31-2002, 12:16 PM
  #14  
rmh
Senior Member
 
rmh's Avatar
 
Join Date: Dec 2001
Location: , UT
Posts: 12,630
Likes: 0
Received 2 Likes on 2 Posts
Default Trailing Edges on Large Scale Aerobatic Planes

Thick trailing edge allows for POSSIBLE increased structural rigidity.
BUT also increases potential for control surface having it's c/g further aft - bad news!
Full scale design has zero -or less relationship with our stuff simply because of size difference -
The trick setup on full scale -with the blunt TE gives better air attachment to control /flying surface -by creating low pressure at TE.
Best bet for model?
The stiffest -lightest control surface possible with it's CG being quite close to it's LE.
I use single ,individual, digital aileron servos on models with 1800 sq in wings - I lighten and balance all surfaces. No sealing tape hinge lines - just reasonably tight fitting.
Having tried a bunch of aileron types on larger models - barndoor - on Dalotels- full span 2-1 taper ratio on Staudachers- 10-1 aspect ratio on rectangular ailerons for CAPS- etc.,
The only common link I keep is to keep em stif and and lite and reasonably balanced (forward CG).
They all perform well with no flutter -
As far as any improvement in how the "thick vs thin TE" part of the whole equasion works--
I can't find any relationship.
On bigger stuff - It makes sense tho-
Old 04-03-2002, 02:52 AM
  #15  
Daniel Z
Senior Member
 
Daniel Z's Avatar
 
Join Date: Feb 2002
Location: SantiagoReg Metropolitana, Providencia, CHILE
Posts: 490
Likes: 0
Received 0 Likes on 0 Posts
Default Trailing Edges on Large Scale Aerobatic Planes

Im in pylon racing, and in this statment we all try to get sharp an stiff TE to reduce drag (turbulent flow behind the airfoils) and avoid flutter; in fact some people finish the TE with glass cloth to get optimal results (like a knife!) and almost all QM40 are composite made to help this. Maybe in aerobatics as the others said for the control throws and forces involved in freestyle flying the drag and the structural reinforcement may be usefull, but I think that there are other ways to increase drag more eficiently... just a couple of thoughts...

Greetings

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 2021 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.