Go Back  RCU Forums > Radios, Batteries, Clubhouse and more > The Clubhouse
reduction in torque at takeoff >

reduction in torque at takeoff

Notices
The Clubhouse If it doesn't fit in any other category and is about general RC stuff then post it here at the Clubhouse.

reduction in torque at takeoff

Old 10-25-2015, 02:17 PM
  #1  
Thread Starter
 
Join Date: Apr 2009
Location: Brooklyn Park, MN
Posts: 76
Likes: 0
Received 0 Likes on 0 Posts
Default reduction in torque at takeoff

How can I reduce torque for takeoff purposes, but still get enough speed to be able to takeoff? There are just some models which just seem to be so touchy about turning left when just off the ground and do a flop over to the left.

Wondering if reducing prop pitch or diameter are something to look at and experiment with?

Maybe I'm just on the wrong track here and need to just practice Right rudder at liftoff until I get it right. I'm just not ready to sacrifice a model on first or second flights more than I have to. Some of the CRASHES are really a REKIT process which means purchasing a replacement totally.

Thanks for any Ideas you may have or solutions which have worked for you.

Thanks - Darryl
Old 10-25-2015, 02:35 PM
  #2  
My Feedback: (158)
 
scale only 4 me's Avatar
 
Join Date: Jan 2002
Location: Avon Lake, OH
Posts: 10,396
Received 52 Likes on 50 Posts
Default

Long take off rolls at a lower RPMs, Most guys think they have to take off full throttle,, it just isn't so,, The plane flies much slower when you're landing right? On my warbirds I hold rudder taking off at around half throttle until I gain altitude and more speed,, it just takes practice. Scale planes like to fly scale, try it.

good luck
Old 10-26-2015, 12:34 AM
  #3  
 
TomCrump's Avatar
 
Join Date: Apr 2003
Location: Traverse City, MI
Posts: 7,614
Likes: 0
Received 5 Likes on 5 Posts
Default

Originally Posted by scale only 4 me
Long take off rolls at a lower RPMs, Most guys think they have to take off full throttle,, it just isn't so,, The plane flies much slower when you're landing right? On my warbirds I hold rudder taking off at around half throttle until I gain altitude and more speed,, it just takes practice. Scale planes like to fly scale, try it.

good luck
I agree.

Long take off runs, easing into the throttle, provide safe and predictable take offs.

The OP describes, perfectly, what happens with too much throttle, too soon.
Old 10-26-2015, 01:32 AM
  #4  
Senior Member
 
Join Date: Jul 2007
Location: Warner Robins, GA
Posts: 1,247
Likes: 0
Received 5 Likes on 5 Posts
Default

I don't know if there is a general answer! Obviously, at low speeds and high power, the roll left may not be fully compensable until there is enough air flow over the control surfaces.
Some of the full size WWII fighters had similar problems, the solution was to gradually increase to takeoff power and use seat of the pants feel to judge when power could be increased.

I have seen grossly over powered smaller RC models that had to be launched vertically, since the wing and control surface areas were too small vs the torque.
As the speed increased, controls became more effective. Landings could be a bit tricky, and a go around from touchdown speed quite difficult.

Watch and listen to some of the 3D larger RC planes as they take off. You will most likely see and hear that takeoff power is much less than that used in flight.
Old 10-26-2015, 05:38 AM
  #5  
 
Sport_Pilot's Avatar
 
Join Date: Jan 2002
Location: Acworth, GA
Posts: 16,916
Likes: 0
Received 1 Like on 1 Post
Default

Originally Posted by darrzemp
How can I reduce torque for takeoff purposes, but still get enough speed to be able to takeoff? There are just some models which just seem to be so touchy about turning left when just off the ground and do a flop over to the left.

Wondering if reducing prop pitch or diameter are something to look at and experiment with?

Maybe I'm just on the wrong track here and need to just practice Right rudder at liftoff until I get it right. I'm just not ready to sacrifice a model on first or second flights more than I have to. Some of the CRASHES are really a REKIT process which means purchasing a replacement totally.

Thanks for any Ideas you may have or solutions which have worked for you.

Thanks - Darryl

Although there is torque It is P factor not torque that will crash the plane. The descending propeller will have a higher angle of attack than the assenting propeller because the plane is pitched up to the forward motion during takeoff. Adding opposite aileron will not correct this and may make it worse. Reducing torque will not help either. The solution is adding right rudder during the rollout and the initial climb.
Old 10-27-2015, 07:51 PM
  #6  
My Feedback: (4)
 
DGrant's Avatar
 
Join Date: Dec 2001
Location: Clovis, CA
Posts: 2,194
Received 30 Likes on 27 Posts
Default

Some planes are tougher then others... and the rudder can be very sensitive on take-off roll... especially when there's too much torque. Throttle and rudder management and practice will be your friend.... just as everyone has said, easy does it. Most planes will take off easily at half-throttle.. very easily... but the biggest tools to battle torqure are #1 the rudder, and use of it, and #2 throttle, and again, use of it.

I've seen more planes crashed on take-off simply due to someone hammering the throttle. In my opinion, the only thing hammering the throttle does is give the pilot much less time to deal with the effects and torque, and get the plane flying...

I'm not saying anyone is hammering the throttle, but it sounds like there's a bit too much throttle going on, and not enough rudder input at the right time to overcome it... It does take some finesse to get some planes to transition smoothly into forward flight from take-off.

There's a balance of inputs that will work, no doubt, and its usually a matter of timing those inputs, and the tougher the plane it is, the more precise the inputs need to be, let alone the variables of winds and such, its all important though.

Just a guess here on what type plane we're talking about... First guess is it's a tail-dragger(that was easy)... next guess is the model.... could it be a Piper Cub, or something similar?... Piper Cubs are pretty tough sometimes... and some take the high-wing design as being easy stuff.... and a Cub is very easy to fly... Its usually the take-offs that are exciting.. to say the least..

If not that, then its some kind of short coupled aerobat... Sukhoi's are nutorious for being tough to take off....

I would say warbird, but they usually track decently compared to many other models... and its landing a warbird thats tough.. not usually torque.

I'm just kidding around here(sort of.. haha).... and I could be way off...

What kind of plane are we talking about though? There might be some specifics we could share if we know what plane.

I wish I had better help for you, hang in there. Good luck with it... I hope you get it worked out.
Old 10-28-2015, 02:16 AM
  #7  
My Feedback: (158)
 
scale only 4 me's Avatar
 
Join Date: Jan 2002
Location: Avon Lake, OH
Posts: 10,396
Received 52 Likes on 50 Posts
Default

Cubs have their unique tendencies, yes,, but you really want to test your skills, pick up a House of Balsa AT-6,, that by far is the toughest plane to get to track straight..

Two problems or issues, I see guys get into

1- they hold too much elevator, guys think if the tail wheel is on the ground they can steer better,, it just aint so,,tail wheels are for taxing,, that it,, let that tail come up asap without nosing over the plane, much easier to drive the plane when it's tail high, takes practice.

2-, impatience,, they see the plane starting to go left and hammer the rudder, then once the air gets on it it goes right hard and they get it to that right/left fight,, You have to wait and trust that little rudder input will kick in,, it will, then drive it down the runway like a rc car..

Again, just takes practice to gain confidence,, I can drive any plane I have, warbirds, cub, etc the full length of the runway at 1/4 throttle.

A good confidence builder also is Touch and Goes, I never see guys doing that anymore, it's good practice for you rudder thumb as well as throttle control.

good luck
Old 10-28-2015, 03:22 AM
  #8  
Banned
My Feedback: (8)
 
Join Date: Jul 2009
Location: Hartford, CT
Posts: 7,269
Likes: 0
Received 1 Like on 1 Post
Default

Picked up a Pilatus PC 9 recently and went to maiden it last week. 4S set up with a 4 bladed prop. Off I go down the center line and at 10 feet down I throttle up at 80/90 %. Boom...off to the left it goes towards the grass. I firewalled it and pulled back to get into the air, still some roll to the left. I probably should have read up on the plane in some threads, turns out everyone was having the same issue. Perhaps some higher speed taxi runs would have helped. Since then I just throw in some good hard right rudder on take-off and it's much easier. Trial and error.
Old 10-28-2015, 04:21 AM
  #9  
My Feedback: (1)
 
JohnBuckner's Avatar
 
Join Date: Dec 2001
Location: Kingman, AZ
Posts: 10,441
Likes: 0
Received 10 Likes on 10 Posts
Default

Darryl I am going to offer an alternative technique for takeoff of any airplane which displays difficult takeoff characteristics. It is often not considered politically correct since it is seemingly contrary to the normal slow throttle up advice during takeoff. It is also the dark secret of pylon racers everywhere and some call it a race start.

This requires two people, the pilot and someone to do the release. The pilot will run the engine up to at least half throttle or more, often full throttle while the launch man holds the airplane usually by the fuse just in front of the tail and lined up in takeoff position on the runway. Only after the engine is spooled up and stabilized does the pilot nod his head to the launcher and he lets the airplane slide from his hand.

This sounds kinda wild but it is not and this technique bypasses the directional problems and the takeoffs are virtually always dead straight.

It is a useful tool at times for certain airplanes.

John
Old 10-28-2015, 04:30 AM
  #10  
 
Sport_Pilot's Avatar
 
Join Date: Jan 2002
Location: Acworth, GA
Posts: 16,916
Likes: 0
Received 1 Like on 1 Post
Default

The pylon planes have small props which are nearly stalled at takeoff. Also they take off fairly quickly. This won't make much difference for a plane with big prop that has a long roll out.

Last edited by Sport_Pilot; 10-28-2015 at 04:32 AM.
Old 10-28-2015, 04:50 AM
  #11  
My Feedback: (1)
 
JohnBuckner's Avatar
 
Join Date: Dec 2001
Location: Kingman, AZ
Posts: 10,441
Likes: 0
Received 10 Likes on 10 Posts
Default

And warbird pylon airplanes use large props and these are the ones that need this the most. The technique is a very, very useful tool for any propeller driven airplane that presents difficult takeoff performance regardless of the length of the takeoff roll.

A tool is just that nothing more and if one chooses to ignore its use on the occasions it may be usefull
Then that is a personal choice.

John
Old 10-28-2015, 06:17 AM
  #12  
Thread Starter
 
Join Date: Apr 2009
Location: Brooklyn Park, MN
Posts: 76
Likes: 0
Received 0 Likes on 0 Posts
Default

The plane in question was hit right on the head by DGrant. It's a Pheonix Models "Decathlon". High wing, Tail dragger similar to a Cub. powered by OS .55 with an 11x7 APC prop. One of the problems is that I'm not usually a Tail dragger fan. Most of my planes have been Trike gear. Great looking model and put together very well from the factory.

Great thoghts by everyone. If there are more thoughts out there keep them coming. The results of the first flight are just broken windsheild and cracked cowling, all repairable.

Thanks again to all. Sincerely - Darryl
Old 10-28-2015, 06:56 AM
  #13  
 
rgburrill's Avatar
 
Join Date: Dec 2010
Location: Dallas, Tx CT
Posts: 2,879
Received 77 Likes on 68 Posts
Default

Go electric. As I recall electric motors have their highest torque when they are first turned on but as they spin up the torque reduces. Use gradual throttle to accelerate from stopped but continue on up to hgh throttle.
Old 10-28-2015, 07:21 AM
  #14  
 
Sport_Pilot's Avatar
 
Join Date: Jan 2002
Location: Acworth, GA
Posts: 16,916
Likes: 0
Received 1 Like on 1 Post
Default

Originally Posted by rgburrill
Go electric. As I recall electric motors have their highest torque when they are first turned on but as they spin up the torque reduces. Use gradual throttle to accelerate from stopped but continue on up to hgh throttle.
Torque is a minor effect, and if it was seems that having more torque before winding up would only make matters worse. P-Factor is the problem, if you convert a model to trike you don't have the issue because the plane is almost level. With a taildragger you use less right rudder when the tail goes up. The torque is not reduced, but P Factor is.
Old 10-28-2015, 01:05 PM
  #15  
 
rgburrill's Avatar
 
Join Date: Dec 2010
Location: Dallas, Tx CT
Posts: 2,879
Received 77 Likes on 68 Posts
Default

Originally Posted by Sport_Pilot
Torque is a minor effect, and if it was seems that having more torque before winding up would only make matters worse. P-Factor is the problem, if you convert a model to trike you don't have the issue because the plane is almost level. With a taildragger you use less right rudder when the tail goes up. The torque is not reduced, but P Factor is.
Hogwash. A taildragger uses less right rudder when the tail goes up BECAUSE THERE IS AIRFLOW ACROSS IT DUE TO AIRSPEED!.
Tell me oh wise one, why does a dragster veer to the left on leaving the gate? It doesn't have a tail to be push by a cir circulating airflow. The same thing is true of a drag boat - it's propellor is under water and at the back end of the boat!
Old 10-28-2015, 01:11 PM
  #16  
Banned
My Feedback: (8)
 
Join Date: Jul 2009
Location: Hartford, CT
Posts: 7,269
Likes: 0
Received 1 Like on 1 Post
Default Uh oh

Attached Thumbnails Click image for larger version

Name:	dc3y6jzmzdr1midypv78.png
Views:	452
Size:	117.1 KB
ID:	2128069  
Old 10-28-2015, 05:49 PM
  #17  
 
Join Date: Nov 2007
Location: West Palm Beach, FL
Posts: 54
Likes: 0
Received 0 Likes on 0 Posts
Default

Surprised that no one has mentioned slipstream effect, gyroscopic precession, or the possible appropriate toe in of the landing gear...
Old 10-29-2015, 01:37 AM
  #18  
My Feedback: (158)
 
scale only 4 me's Avatar
 
Join Date: Jan 2002
Location: Avon Lake, OH
Posts: 10,396
Received 52 Likes on 50 Posts
Default

To much to think about,, you pit bench engineers can argue over that stuff, who cares what you call it, just hold a little right rudder
Old 10-29-2015, 04:16 AM
  #19  
 
Sport_Pilot's Avatar
 
Join Date: Jan 2002
Location: Acworth, GA
Posts: 16,916
Likes: 0
Received 1 Like on 1 Post
Default

Originally Posted by rgburrill
Hogwash. A taildragger uses less right rudder when the tail goes up BECAUSE THERE IS AIRFLOW ACROSS IT DUE TO AIRSPEED!.
Tell me oh wise one, why does a dragster veer to the left on leaving the gate? It doesn't have a tail to be push by a cir circulating airflow. The same thing is true of a drag boat - it's propellor is under water and at the back end of the boat!
Well hope you had a good hogwash! I don't think your analogies are accurate especially the dragster because if you have a locked differential the torque would tend to cause the left wheel to dig into the ground and thus veer's right not left. Without a locked differential or limited slip differential the right wheel will lose traction and spin and it would veer to the left as all power shifts to the spinning wheel. But most veering in dragster's, especially nitro dragsters, is from a cylinder that is out and can veer left or right because of the lack of propulsion from the header on the missing cylinder. Boats have torque effect but no or little p-factor and as remember mentioned has no slipstream effect. I notice very little veering in fast motor boats. Admittedly not a speed boat. P-factor is actually worse when the plane is moving and there is more air flowing, and then there is more right rudder needed. But when the tail goes up the plane will tend to veer right because the P-factor is reduced and the rudder is more effective. P-Factor for both taildraggers and trikes is probably highest when the plane lifts off and climbout is initiated. But because the pilot is no longer worried about veering off the runway or a ground loop, it would seem less. But if you watch full scale propeller planes take off you will often see the wing tilt to the left right as it leaves the ground.
Old 10-29-2015, 05:59 AM
  #20  
 
TomCrump's Avatar
 
Join Date: Apr 2003
Location: Traverse City, MI
Posts: 7,614
Likes: 0
Received 5 Likes on 5 Posts
Default

Originally Posted by scale only 4 me
To much to think about,, you pit bench engineers can argue over that stuff, who cares what you call it, just hold a little right rudder
LOL

It's funny how some like to make things overly complicated.
Old 10-29-2015, 06:18 AM
  #21  
 
Join Date: Oct 2005
Location: Carolina, PUERTO RICO (USA)
Posts: 37
Likes: 0
Received 0 Likes on 0 Posts
Default

Originally Posted by scale only 4 me
To much to think about,, you pit bench engineers can argue over that stuff, who cares what you call it, just hold a little right rudder

LOL work's for me!!
Old 11-02-2015, 08:26 PM
  #22  
My Feedback: (4)
 
DGrant's Avatar
 
Join Date: Dec 2001
Location: Clovis, CA
Posts: 2,194
Received 30 Likes on 27 Posts
Default

Originally Posted by darrzemp
The plane in question was hit right on the head by DGrant. It's a Pheonix Models "Decathlon". High wing, Tail dragger similar to a Cub. powered by OS .55 with an 11x7 APC prop. One of the problems is that I'm not usually a Tail dragger fan. Most of my planes have been Trike gear. Great looking model and put together very well from the factory.

Great thoghts by everyone. If there are more thoughts out there keep them coming. The results of the first flight are just broken windsheild and cracked cowling, all repairable.

Thanks again to all. Sincerely - Darryl
Ah ha... I know exactly what kind of plane you're dealing with. I have a GreatPlanes Decathlon I built many years ago, with the same inherent traits. It took me a bit also to get the hang of it... It was a plane that really taught me alot about planes in general, and that each type really can have personalities all their own.

For my Decathlon, as I described above, it was a matter of learning the timing of the commands, and the order needed to reach airspeed for take-off. I might suggest a large area, with no obstructions if you can find it.. no curbs... preferably a few hundred yards square that you can get a real feel for what the plane will do, and have plenty of time and area to adjust your commands accordingly.

I see you're in Minnesota... Do you have any lakes there?... haha.. I'm thinking just maybe.. We have a local lake here, fairly large, with several very large parking areas.. yes, a few hundred yards each way of pavement (albeit some kind of rough).. There the parking areas for the truck/boat-trailers... and theres usually a few open depending on the level of the lake.. and wide open space every way you look.. This is just a suggestion really.. but might give you a few ideas...

Its an area I learned on many years ago how to handle a few different challenging planes... plenty of room. It allowed me to hone some skills so I could take off from much narrower/shorter runways.. That kind of area might give you the flexibility and time to get a handle on the technique that best works for you...

With that said... With my Decathlon, It takes some rudder input immediately when advancing the throttle, as that seems to be where the major torque will pull the plane left... As I'm advancing the throttle, and plane is gaining speed, I ease off the rudder a bit, as needed to keep it tracking straight as I can. There is a point(it doesn't take long either).. that the vertical stab/rudder will take over.. thats the point you need to release the rudder(straighten it out).. and let the airplane accelerate to take-off speed... Don't overhold that rudder!!... Don't underhold it either.. It will take more right rudder upon initial throttle up.. then the stab/rudder will quickly take over ... If these things aren't timed correctly... you're plane will probably "ground loop" as they call it, or it will be like a "chicken with its head cut off".. all over the place until its at flying/lift off speed... Again a big key is having enough space to learn the particular technique your Decathlon requires..

I feel ya...I know where you're at... I honestly don't think its too much about the plane.. These things are tricky.. I'm saying from first hand experience here.. Hang in there... Read what everyone is saying too, as there's alot of experience everyone is sharing... and get back to us and let us know how things are going with it.
Good luck.

Last edited by DGrant; 11-02-2015 at 08:30 PM.
Old 11-03-2015, 01:15 PM
  #23  
My Feedback: (5)
 
Join Date: Jan 2002
Location: San Tan Valley, AZ
Posts: 5,768
Likes: 0
Received 0 Likes on 0 Posts
Default

Many years ago I learned to fly full scale in a Taylorcraft, a very similar aircraft. I had trouble steering it down the runway. The instructor said I should give it full throttle and get the tail off the ground. That gets wind over the control surfaces and gives you control..
Now that works great with a model if you have plenty of power. If you dont then get yourself a gyro. That will fix it.
Old 12-01-2015, 08:30 AM
  #24  
Thread Starter
 
Join Date: Apr 2009
Location: Brooklyn Park, MN
Posts: 76
Likes: 0
Received 0 Likes on 0 Posts
Default

Seems there was a lose tail wheel bracket screw in addition to a little too much nose heavy. I rebalanced and did some work on the tail wheel bracket(still seems a bit flimsy) but it worked for now. Being in Minnesota and now we have some white stuff on the ground and not too great a temperature There may be a while before I can try to fly. It definitely is very touchy on the ground for takeoff. I now see that the Decathlon is in the short coupled category. I going to really concentrate on rudder and speed during the takeoff. Maybe the sun will melt our poly runway and open the field up for some winter flying.

Thanks for the advice from all of you. This is a great site for info.

Darryl

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
Trackbacks are Off
Pingbacks are Off
Refbacks are On


Thread Tools
Search this Thread

Contact Us - Manage Preferences Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service

Copyright © 2024 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.