logo
Thread Tools
Old 12-12-2014, 02:50 PM
rtfm is offline
Find More Posts by rtfm
Flyin' Around
Joined May 2014
6 Posts
Help!
Estimating torque required to deflect a control surface

Hi guys,
I am trying to estimate how much torque is required to deflect a given control surface. Is there a simple (ie not based on advanced math) way to calculate this?

What I am trying to do is to activate the control surfaces of my full size plane (single seat) with servos. I have split the control surfaces (ailerons, flaps and rudder) into a number of separate panels both so that I can tailor each panel's deflection to correspond to the lift distribution of the wing/rudder, but also to make servo activation more manageable.

The benefits of controlling the control surfaces with a RC transmitter are quite exciting. I'd like to leverage the huge benefits of all the mixing which is available on today's RC transmitters. I will build in a full cable-activated backup to a separate control stick in case of radio failure. But I'm not expecting to use it. Modern RC kit is pretty reliable.

For example, I am working with the following actual numbers for one of my aileron control surfaces:
Span: 8.7 inches
Chord: 5 inches
Deflection: 35 deg
Speed: 155 mph

The big question is, using the above parameters, what size servo would I need to do the job?

Another more demanding control surface is at the rudder:
Span: 10 inches
Chord: 8.2 inches
Deflection: 30 deg
Speed: 155mph

Anyone care to give me a hand with this?

Regards,
Duncan
rtfm is offline Find More Posts by rtfm
Reply With Quote Quick reply to this message
Sign up now
to remove ads between posts
Old 12-12-2014, 03:24 PM
db1331 is offline
Find More Posts by db1331
Registered User
db1331's Avatar
United States, SC, Sumter
Joined Jul 2007
470 Posts
http://www.wikihow.com/Calculate-Win..._Wind_Load_sub
Not sure if you answer is here or not but it will be a good start...
Have your next of kin keep us posted on how this works out
db1331 is offline Find More Posts by db1331
Reply With Quote Quick reply to this message
Old 12-12-2014, 03:38 PM
kce is offline
kce
Find More Posts by kce
kce
KCE
United States, MO, St. Louis
Joined Jun 2008
355 Posts
Thats Funny!
kce is offline Find More Posts by kce
Reply With Quote Quick reply to this message
Old 12-12-2014, 03:55 PM
rooman is offline
Find More Posts by rooman
They're get'n lower mate.....
rooman's Avatar
Argentina, Neuquen, Confluencia Department
Joined Nov 2006
3,075 Posts
Only 155 mph.......My Q500 does 185 +
rooman is offline Find More Posts by rooman
Reply With Quote Quick reply to this message
Old 12-12-2014, 04:09 PM
rooman is offline
Find More Posts by rooman
They're get'n lower mate.....
rooman's Avatar
Argentina, Neuquen, Confluencia Department
Joined Nov 2006
3,075 Posts

The Fly Seat was designed by Ed Henery and allowed a modeler to fly a radio controlled model airplane with the same type of controls used to fly a full-scale aircraft.
rooman is offline Find More Posts by rooman
Reply With Quote Quick reply to this message
Old 12-12-2014, 04:11 PM
Philkoury is offline
Find More Posts by Philkoury
Registered User
United States, MS, Picayune
Joined Feb 2007
419 Posts
Quote:
Originally Posted by rtfm View Post
Hi guys,
I am trying to estimate how much torque is required to deflect a given control surface. Is there a simple (ie not based on advanced math) way to calculate this?

For example, I am working with the following actual numbers for one of my aileron control surfaces:
Span: 8.7 inches
Chord: 5 inches
Deflection: 35 deg
Speed: 155 mph

The big question is, using the above parameters, what size servo would I need to do the job?

Another more demanding control surface is at the rudder:
Span: 10 inches
Chord: 8.2 inches
Deflection: 30 deg
Speed: 155mph

Anyone care to give me a hand with this?

Regards,
Duncan
43.5 square inch aileron and 82 square inch rudder. what kind of full scale are you building?
Philkoury is offline Find More Posts by Philkoury
Reply With Quote Quick reply to this message
Old 12-12-2014, 05:14 PM
.com is offline
Find More Posts by .com
Flyin' Around
Joined Aug 2014
43 Posts
.com is offline Find More Posts by .com
Reply With Quote Quick reply to this message
Old 12-12-2014, 05:25 PM
N233W is offline
Find More Posts by N233W
I Feel the Light and the Heat
N233W's Avatar
NorCal, East Bay
Joined Feb 2009
444 Posts
This is a cool idea. You could optimize control harmony!

I used to tell my kids fanciful tales when they were little and one revolved around a cat stealing my tx and getting in my giant scale plane and flying himself away to far-off lands, so this is even better.

Please show us photos of your plane/project.

I am thinking for a plane big enough to carry a person you would need a full-scale autopilot style servo system - you can't be thinking of using RC-style servos, are you? If yes, how would your backup system manage to overcome the resistance of the servos in the event of a radio issue?
N233W is offline Find More Posts by N233W
Last edited by N233W; 12-12-2014 at 05:36 PM. Reason: Barnacles filled my shoe
Reply With Quote Quick reply to this message
Old 12-12-2014, 05:49 PM
rtfm is offline
Find More Posts by rtfm
Flyin' Around
Joined May 2014
6 Posts
Hi Philkoury,
I have split my control surfaces into multiple separate panels. I quoted the size of single panels only. For ecxample, the ailerons are split into six panels, flaps into two, and rudder into 6 panels also.

I am considering all alternatives. RC servos would mean overcoming the residual resistance. But although this would tend to make the stick movements of the mechanical side sluggish, the plane wouldstill be flyable. And this is an emergency fail-safe only. Slow and gentle back to the airfield.

I am also considering autopilot servos which have a clutch and have zero resistance when switched off.

I'm also considering hooking up smaller RC servos (maybe in the 30 kg-cm range) between the control stick and hydraulics to the control surfaces.

Or I might simply drop the idea if it gets too weird...

But at the moment, I'm still thought-experimenting...

Cheers,
Duncan
PS Here's an X-Plane simulator screenshot of the plane.
rtfm is offline Find More Posts by rtfm
Reply With Quote Quick reply to this message
Old 12-12-2014, 05:54 PM
N233W is offline
Find More Posts by N233W
I Feel the Light and the Heat
N233W's Avatar
NorCal, East Bay
Joined Feb 2009
444 Posts
Quote:
Originally Posted by rtfm View Post
Hi Philkoury,
I have split my control surfaces into multiple separate panels. I quoted the size of single panels only. For ecxample, the ailerons are split into six panels, flaps into two, and rudder into 6 panels also.

I am considering all alternatives. RC servos would mean overcoming the residual resistance. But although this would tend to make the stick movements of the mechanical side sluggish, the plane wouldstill be flyable. And this is an emergency fail-safe only. Slow and gentle back to the airfield.

I am also considering autopilot servos which have a clutch and have zero resistance when switched off.

I'm also considering hooking up smaller RC servos (maybe in the 30 kg-cm range) between the control stick and hydraulics to the control surfaces.

Or I might simply drop the idea if it gets too weird...

But at the moment, I'm still thought-experimenting...

Cheers,
Duncan
PS Here's an X-Plane simulator screenshot of the plane.
Awesome, go for it - but I must say that you would need a lot of mechanical advantage to overpower the RC-style servos which would translate into very low control authority (no xwind landings, etc.), so I'd say get an old set of auto-pilot servos.
N233W is offline Find More Posts by N233W
Reply With Quote Quick reply to this message
Old 12-12-2014, 07:39 PM
Philkoury is offline
Find More Posts by Philkoury
Registered User
United States, MS, Picayune
Joined Feb 2007
419 Posts
Kraft RC servos were used to operate trim tabs on homebuilt airplanes. Servos have been used to deflect trim tabs on free floating control surfaces on large model aircraft as a means of flight control. Just watched an old Army Air Force training video on emergency procedures for landing damaged B-24s. One segment showed a B-24 with flak damage that severed the rudder and elevator cables. The plane made a safe landing by using the trim tabs to control the plane.
Philkoury is offline Find More Posts by Philkoury
Reply With Quote Quick reply to this message
Old 12-12-2014, 09:03 PM
N726AC is offline
Find More Posts by N726AC
Seven.Four Liters
N726AC's Avatar
United States, FL, North Fort Myers
Joined Sep 2006
7,517 Posts
And,,,,,, here we go !
N726AC is offline Find More Posts by N726AC
Reply With Quote Quick reply to this message
Old 12-12-2014, 10:43 PM
vmceachern is offline
Find More Posts by vmceachern
You can't fix STUPID
vmceachern's Avatar
Texas City, Tx
Joined Dec 2008
4,506 Posts
Call Grumann they do it all the time. Or NASA. They used to
vmceachern is offline Find More Posts by vmceachern
Reply With Quote Quick reply to this message
Old 12-14-2014, 08:19 AM
kce is offline
kce
Find More Posts by kce
kce
KCE
United States, MO, St. Louis
Joined Jun 2008
355 Posts
Now we can have a full scale brown out
kce is offline Find More Posts by kce
Reply With Quote Quick reply to this message
Old 12-27-2014, 05:33 PM
rtfm is offline
Find More Posts by rtfm
Flyin' Around
Joined May 2014
6 Posts
Hi,
First, (in case anyone missed this), I plan to break the ailerons into multiple panels (same for the rudder). This is both to facilitate any aerodynamic advantage from deflecting the individual surfaces by smaller or larger degrees. The outer panels will deflect less, the inner panels more). Secondly, it is to decrease the amount of force required to deflect any single panel.

The idea is to use hefty RC servos (some of them as used in giant scale are truly powerful) controlled by a standard RC radio transmitter, where all the mixing will take place.

Obviously, I would need a redundant physical control link in case of radio and/or servo failure. While I don't consider this eventuality very likely, I would need to have a physical backup. This would be a cable-operated direct link system acting on a single (outer) panel aileron, and the elevator and rudder. In the event of a radio/servo failure, I would pull the power to the RC control system and servos, and fly the plane with the second control stick. There would be the usual servo resistance to overcome, unless I used servos with a built in clutch - in which case there would be zero resistance if power to the servos is pulled. Flying the plane on the physical control links would be a no-brainer. And I strongly suspect, would seldom if ever be required. For precautionary purposes, one would practice with the physical controls on a regular basis.

There are only three significant questions I need to answer:
  1. How to hook up the control stick and rudder pedals to the transmitter controls
  2. How to estimate the size of the servos - taking shock forces, turbulence etc into consideration
  3. Where to get clutched servos - to get round the servo resistance should i need to switch them off and fly physical
Anyone case to jump in and offer any ideas?


One way to estimate #2 above is to build a full size mock-up of a wing/aileron section with a guessed-at servo size fitted, mount it to my car and hurtle down the motorway at 100kph and see what happens. Rutan did this sort of wind tunnel testing after all...

I have found two likely candidates:
http://www.pololu.com/product/1390 which offers 1600oz/in torque @ 12v and costs approx $259 ea
http://www.troybuiltmodels.com/items/PS050.html which gives 1271oz/in @ 8.4v and costs $228 ea



Regards,
Duncan
rtfm is offline Find More Posts by rtfm
Last edited by rtfm; 12-28-2014 at 03:48 AM.
Reply With Quote Quick reply to this message


Quick Reply
Message:


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Chinn yak profile kit yellowman2513 Nitro Power 43 03-08-2009 11:20 AM