Go Back  RCU Forums > RC Airplanes > RC Jets
 Exponential on Elevator?? Is it required on a Bandit. >

Exponential on Elevator?? Is it required on a Bandit.

Community
Search
Notices
RC Jets Discuss RC jets in this forum plus rc turbines and ducted fan power systems

Exponential on Elevator?? Is it required on a Bandit.

Thread Tools
 
Search this Thread
 
Old 02-19-2012 | 07:33 PM
  #1  
roger.alli's Avatar
Thread Starter
 
Joined: Aug 2008
Posts: 1,016
Received 1 Like on 1 Post
From: Sydney NSW , AUSTRALIA
Default Exponential on Elevator?? Is it required on a Bandit.

How much, if any elevator exponential do you use??

I have been having a little trouble landing my new Super Bandit.. I am not really in control of it pitch wise, in the final hold off, right before touch down. Instead of getting a nice flair and nose high touch down, I am tending to do a little balloon climb to 5’ or so, which results in a nasty flop onto the run way.. (Fortunately the SB is built tough.)

My theory is I am over controlling, possibly due to elevator exponential.

Typically Bandits need a lot of elevator throw to hold off in the final stages of landing. (If you touch down early/fast, the dreaded Bandit bounce happens). To compensate for this high travel rate, I have been running 35% exponential, in an attempt to de-sensitise it at normal flight speeds.

However, I fellow modeller suggests this might be getting me into to trouble. Right before touch down, while holding in a lot of back stick, the exponential is actually making it more sensitive to pitch, which when I think about it would seem to be the case..

Any ones thoughts would be appreciated..

Thanks

Roger
Old 02-19-2012 | 07:53 PM
  #2  
My Feedback: (14)
 
Joined: Dec 2008
Posts: 321
Likes: 0
Received 0 Likes on 0 Posts
From: Bakersfield, CA
Default RE: Exponential on Elevator?? Is it required on a Bandit.

You use as much as you need. I use very little, if no exponential. But that cannot be true, since the output wheel on the servo it self has reverse exponential induced.
And I like it that way. Better to have response then measure it with more than waiting for something to happen. If you have a little tremor, its nice to have some cushion there.
It sounds like you need a more positive response, so i would suggest using less expo. I know that when i fly my freinds jet it feels very sluggish. And when others fly mine they seem alarmed at my settings. So it really comes down to what you get used to become imprinted with, or adjust to your liking. Have fun.
John
Old 02-19-2012 | 10:19 PM
  #3  
InboundLZ's Avatar
My Feedback: (10)
 
Joined: Oct 2004
Posts: 1,945
Likes: 0
Received 0 Likes on 0 Posts
From: Las Vegas, NV
Default RE: Exponential on Elevator?? Is it required on a Bandit.

Jake has ZERO expo in his bandit ( I should know as I set it up) and he greases his landings every time. Maybe you have a balance problem?
Old 02-20-2012 | 01:37 AM
  #4  
 
Joined: Jun 2002
Posts: 13,258
Received 788 Likes on 571 Posts
From: Watford, UNITED KINGDOM
Default RE: Exponential on Elevator?? Is it required on a Bandit.

Where is your balance point? But Bandit generally needs small amount only as they are rigged soft in pitch, I would say 10% on my Comp Super Bandit.

Dw
Old 02-20-2012 | 02:39 AM
  #5  
Countryboy's Avatar
My Feedback: (25)
 
Joined: Dec 2001
Posts: 2,657
Likes: 0
Received 2 Likes on 2 Posts
From: Lawrenceburg, KY
Default RE: Exponential on Elevator?? Is it required on a Bandit.


ORIGINAL: roger.alli

How much, if any elevator exponential do you use??

I have been having a little trouble landing my new Super Bandit.. I am not really in control of it pitch wise, in the final hold off, right before touch down. Instead of getting a nice flair and nose high touch down, I am tending to do a little balloon climb to 5’ or so, which results in a nasty flop onto the run way.. (Fortunately the SB is built tough.)

My theory is I am over controlling, possibly due to elevator exponential.
Typically Bandits need a lot of elevator throw to hold off in the final stages of landing. (If you touch down early/fast, the dreaded Bandit bounce happens). To compensate for this high travel rate, I have been running 35% exponential, in an attempt to de-sensitise it at normal flight speeds.

However, I fellow modeller suggests this might be getting me into to trouble. Right before touch down, while holding in a lot of back stick, the exponential is actually making it more sensitive to pitch, which when I think about it would seem to be the case..

Any ones thoughts would be appreciated..


I would say your theory is probably correct. When I set up my F-4 elevators, I put in 30% expo and found that the expo was causing an overly senstive elevator on the flair. Dropping the expo to 10% helped and I am thinking of even taking that out and using the servo slow function to slow the servos a bit. If you watch the video here with Lewis Patton at the sticks, you can see on the landing that the elevator is a bit senstive due to the expo.

http://www.youtube.com/watch?v=EInnRANOm7s





Thanks

Roger
Old 02-20-2012 | 05:11 AM
  #6  
My Feedback: (8)
 
Joined: Dec 2001
Posts: 2,317
Likes: 0
Received 2 Likes on 2 Posts
From: Lancaster, CA IL
Default RE: Exponential on Elevator?? Is it required on a Bandit.

Hey Roger,

I would look hard at the CG and stab incidence. I am pretty confident you have the stab incidence per the plans. The elevator should have a small amount of up elevator trim for flight when in the flaps up flight mode. About 1/16" at the tip. If you have more than that, adjust the stab incidence.

Pull the CG back a bit, we used to run in the 9 - 9 1/4" back on the old Bandits and Super Bandit's. At this point landings became a breeze. You should be able to settle the Bandit on the runway with a slight nose high position with about 1/3 - 1/2 the elevator travel. Travel on the elevator was around 22 degrees up and 24 degrees down. The factory CG on the old Super Bandit was a bit forward in most of our eyes back in the days.

I believe BVM has updated the web page to reflect this but the old plans showed an 8-1/2" CG or somewhere around there.

Also a number of us pattern guys alwyas flew with around 15 - 25% expo on the elevators, dependant on where we found the CG to end up.
Old 02-20-2012 | 07:37 AM
  #7  
My Feedback: (1)
 
Joined: Nov 2003
Posts: 551
Likes: 0
Received 0 Likes on 0 Posts
From: Caracas, VENEZUELA
Default RE: Exponential on Elevator?? Is it required on a Bandit.

Hi Roger:
A couple of general thoughts:

- Good and consistent landings are the result of a properly balanced model and a correct landing technique. The use of exponential doesn't fix a any of this. If any, it will make things worse.
- Tail heavy models do not want to land. They want to stay in the air until they drop.


It is hard to advise on your situation without seen the approach, so I may be just wasting your time. But in general, I will say that you may be approaching low, without a good and constant rate of descent, and not maintaining the nose above level all the time. If you are trying, but the model doesn't want to get on a good rate of descent (nose high), then you are tail heavy.


I would suggest: use as little expo as possible (say 10%), and move the CG fwd.
Again: general comments. Don't know your particular set up.

Jack

Old 02-20-2012 | 07:50 AM
  #8  
eddieC's Avatar
Senior Member
My Feedback: (2)
 
Joined: Nov 2002
Posts: 2,102
Likes: 0
Received 0 Likes on 0 Posts
From: Jackson, MI
Default RE: Exponential on Elevator?? Is it required on a Bandit.



I use very little, if no exponential. But that cannot be true, since the output wheel on the servo it self has reverse exponential induced.
I believe the wheel and control horn, when properly set up, cancel each other out. Geometry.</p>
Old 02-20-2012 | 01:59 PM
  #9  
roger.alli's Avatar
Thread Starter
 
Joined: Aug 2008
Posts: 1,016
Received 1 Like on 1 Post
From: Sydney NSW , AUSTRALIA
Default RE: Exponential on Elevator?? Is it required on a Bandit.

Thanks for the replies everyone. Nice to log in this morning and have some input from people who truly know their stuff.

To the Daves (both American and English) and country boy, thanks for confirming that only small amount of expo are commonly used..

It took me a bit of thinking through, but it finally dawned on me that using expo on elevator can actually have the opposite effect than intended, during the final flair for landing. At this point (holding nearly full up elevator) the expo curve is working to make the elevator MORE sensitive.

Old 02-20-2012 | 02:11 PM
  #10  
 
Joined: Jun 2002
Posts: 13,258
Received 788 Likes on 571 Posts
From: Watford, UNITED KINGDOM
Default RE: Exponential on Elevator?? Is it required on a Bandit.

The amount of flap you have will affect the final flare, there are so many things that affect this. I have never seen a tail heavy Bandit and personally the kit balance is too far forward-I understand Bob V's reason for setting it there, but for the vast majority of people its too far forward...

How much flap are you landing with? How much does your Bandit weigh?

Dave
Old 02-20-2012 | 02:22 PM
  #11  
eddieC's Avatar
Senior Member
My Feedback: (2)
 
Joined: Nov 2002
Posts: 2,102
Likes: 0
Received 0 Likes on 0 Posts
From: Jackson, MI
Default RE: Exponential on Elevator?? Is it required on a Bandit.

Expo doesn't add sensitivity unless it's set up backwards. At the end of the throw/limit, you're nearing normal throw and rate. You still have thumb/finger expo and rates, remember. [8D]
Old 02-20-2012 | 02:29 PM
  #12  
roger.alli's Avatar
Thread Starter
 
Joined: Aug 2008
Posts: 1,016
Received 1 Like on 1 Post
From: Sydney NSW , AUSTRALIA
Default RE: Exponential on Elevator?? Is it required on a Bandit.

Dave W,

I ALWAYS land with the full flap setting. BVM use a jig to set up. I think it is 45 deg.

This is the Comp Super Bandit which is STRONG, but heavy. It weighs 24 lbs bone dry, and carries 3.5 litres of fuel..

I also own a classic Balsa Bandit which I do recall needed the CG way further aft then the plans indicated. That model is only 19lbs dry)..

It is all pointing to moving CG back, and reducing expo..

Roger
Old 02-20-2012 | 02:40 PM
  #13  
roger.alli's Avatar
Thread Starter
 
Joined: Aug 2008
Posts: 1,016
Received 1 Like on 1 Post
From: Sydney NSW , AUSTRALIA
Default RE: Exponential on Elevator?? Is it required on a Bandit.


ORIGINAL: John Redman

Hey Roger,

I would look hard at the CG and stab incidence. I am pretty confident you have the stab incidence per the plans. The elevator should have a small amount of up elevator trim for flight when in the flaps up flight mode. About 1/16'' at the tip. If you have more than that, adjust the stab incidence.
That is interesting information and new to me. I set up the model using a laser incidence meter and went to great lengths to get the wings/stabs incidence correct. The main wing carries ½ deg pos incidence (leading edge up) compared to the stabs. This is as per plan and matches the Fuse wing/stab saddles exactly.

On the test flight the CG was at 8 ½†and I had to put in 3-4 clicks of up trim, this is about 2mm at the tip, a touch more than 1/16â€. It also needed a lot of down to maintain inverted, all indicating a forward CG. Plus, I am landing with a good amount of fuel on board.

Pull the CG back a bit, we used to run in the 9 - 9 1/4" back on the old Bandits and Super Bandit's. At this point landings became a breeze. You should be able to settle the Bandit on the runway with a slight nose high position with about 1/3 - 1/2 the elevator travel. Travel on the elevator was around 22 degrees up and 24 degrees down. The factory CG on the old Super Bandit was a bit forward in most of our eyes back in the days.
Yep, CG seems to be a consensus. I will move it back to 9" and endeavour to land with a bit less fuel. That and remove most of the elevator expo.

Roger
Old 02-20-2012 | 03:07 PM
  #14  
roger.alli's Avatar
Thread Starter
 
Joined: Aug 2008
Posts: 1,016
Received 1 Like on 1 Post
From: Sydney NSW , AUSTRALIA
Default RE: Exponential on Elevator?? Is it required on a Bandit.

ORIGINAL: Jack Diaz

Hi Roger:
A couple of general thoughts:

- Good and consistent landings are the result of a properly balanced model and a correct landing technique. The use of exponential doesn't fix a any of this. If any, it will make things worse.
- Tail heavy models do not want to land. They want to stay in the air until they drop.


It is hard to advise on your situation without seen the approach, so I may be just wasting your time. But in general, I will say that you may be approaching low, without a good and constant rate of descent, and not maintaining the nose above level all the time. If you are trying, but the model doesn't want to get on a good rate of descent (nose high), then you are tail heavy.


I would suggest: use as little expo as possible (say 10%), and move the CG fwd.
Again: general comments. Don't know your particular set up.

Jack

Thanks for this Jack. Your advice is always worth heeding.. My full size instructor (Cesna 152) told me that a good landing is always the result of a good approach.

I attempt to set up my final approach to landing with the model configured correctly. i.e. full flap, a slightly nose down attitude, a little power on, a constant rate of decent and speed. Ideally, crossing the thresh hold at 3-4 ‘ altitude. Then reduce power to idle and begin to flair by applying elevator, holding the model off a foot or so above the runway until it settles onto the main wheels..

Of course this is not what always happens in my approaches, but is what I am attempting.

It is in the flair that I am becoming unstuck. I think I am over controlling elevator in the flair and the model balloons up to 6’ of so.. Nasty.. The photo below actually captures the moment exactly, right before the balloon.

I am definitely going to reduce the elevator expo,

Roger.
Attached Thumbnails Click image for larger version

Name:	Lj21666.jpg
Views:	58
Size:	74.8 KB
ID:	1729657  
Old 02-20-2012 | 05:39 PM
  #15  
DAN AVILLA's Avatar
My Feedback: (12)
 
Joined: Dec 2001
Posts: 834
Likes: 0
Received 27 Likes on 21 Posts
From: Prescott, AZ
Default RE: Exponential on Elevator?? Is it required on a Bandit.

<div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: rgb(255, 255, 255); font-family: Arial; font-size: 12px; ">I use 25 % expo on my bandit. I also use about 3/8 inch of crow to make it not float. One thing that I have seeing many times is people fly their planes with to much over all travel. If you keep reducing the elevator travel to the point were when it touches down and stalls the stick is almost to the bottom it will make the landings have less a pitch problem. BMV,s settings are usually to high for thumb flyers. He grabs the sticks with two fingers and does not move them as much as a thumb flyer. Good Luck Dan Avilla BVM rep</div>
Old 02-20-2012 | 06:37 PM
  #16  
roger.alli's Avatar
Thread Starter
 
Joined: Aug 2008
Posts: 1,016
Received 1 Like on 1 Post
From: Sydney NSW , AUSTRALIA
Default RE: Exponential on Elevator?? Is it required on a Bandit.

Thanks Dan,

That makes sense. I fly thumbs and have the recommended elevator throws.. I might try reducing overall throw just a little bit to desensitise it further. I do know that Bandits need to land with a lot of back stick, if you touch down too fast they will bounce, so I do not want to run out of up elevator.

Crow is a thought. Some swear by it of course. I haven't needed it on my Balsa Bandit so have not tried it yet.. I will put that in the list of thing to try..

Roger
Old 02-20-2012 | 07:04 PM
  #17  
My Feedback: (1)
 
Joined: Nov 2003
Posts: 551
Likes: 0
Received 0 Likes on 0 Posts
From: Caracas, VENEZUELA
Default RE: Exponential on Elevator?? Is it required on a Bandit.

Roger, go by the consensus.... move the CG back. If it doesn't work, go by my suggestion: Move it forward !!!. LOL.
Remember, tail heavy airplanes don't want to land !!!!
In fact, the way I figure out the correct CG location on my planes, is by the landing behavior.

Also, your "slightly nose down attitude " on the approach is not helping either. As a hint: you have to always be able to "see the bottom of the wings" during the final approach. If you are able to see the top of the wings, you are in trouble !!!!

One thing is to land, and another one is to fly low and touch the ground.
Jack
Old 02-20-2012 | 07:13 PM
  #18  
My Feedback: (28)
 
Joined: Jul 2005
Posts: 2,902
Received 66 Likes on 57 Posts
From: Sun Valley, NV
Default RE: Exponential on Elevator?? Is it required on a Bandit.

Slow down, ballooning means you're still at flying speed, for however short a time.

Use expo you are comfortable with.

Fly with a little down elevator trimmed in, so you are constantly using the stick.

I learned down elevator and now I can do low level high speed passes easy as pie, and land beautifully every time.
Old 02-20-2012 | 07:14 PM
  #19  
My Feedback: (28)
 
Joined: Jul 2005
Posts: 2,902
Received 66 Likes on 57 Posts
From: Sun Valley, NV
Default RE: Exponential on Elevator?? Is it required on a Bandit.

duplicate since RCU still hasn't addressed any of the issues they are having.
Old 02-20-2012 | 08:18 PM
  #20  
Erik R's Avatar
My Feedback: (32)
 
Joined: Jan 2002
Posts: 1,067
Received 18 Likes on 11 Posts
From: Fogelsville, PA
Default RE: Exponential on Elevator?? Is it required on a Bandit.

ORIGINAL: DAN AVILLA

<div style=''margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: rgb(255, 255, 255); font-family: Arial; font-size: 12px; ''>I use 25 % expo on my bandit. I also use about 3/8 inch of crow to make it not float. One thing that I have seeing many times is people fly their planes with to much over all travel. If you keep reducing the elevator travel to the point were when it touches down and stalls the stick is almost to the bottom it will make the landings have less a pitch problem. BMV,s settings are usually to high for thumb flyers. He grabs the sticks with two fingers and does not move them as much as a thumb flyer. Good Luck Dan Avilla BVM rep </div>

Dan,

I don't want to hijack this thread,but I feel this is pertinent,and will ask you here.I recently bought a classic bandit that doesn't have a speedbrake,and was considering crow.I've had 3 classics,and 1 super,but they all had speedbrakes,which I feel helped the float/speed control on final.My question is,with 3/8 inch up aileron deflection,do you have to mix any elevator with that for neutral trim?If so,how much,and which direction?Also,do you notice any significant degradation of aileron authority at low speeds in that configuration.Thanks in advance,

Erik
Old 02-20-2012 | 11:27 PM
  #21  
roger.alli's Avatar
Thread Starter
 
Joined: Aug 2008
Posts: 1,016
Received 1 Like on 1 Post
From: Sydney NSW , AUSTRALIA
Default RE: Exponential on Elevator?? Is it required on a Bandit.

ORIGINAL: Jack Diaz

Roger, go by the consensus.... move the CG back. If it doesn't work, go by my suggestion: Move it forward !!!. LOL.
Remember, tail heavy airplanes don't want to land !!!!
In fact, the way I figure out the correct CG location on my planes, is by the landing behavior.

Also, your ''slightly nose down attitude '' on the approach is not helping either. As a hint: you have to always be able to ''see the bottom of the wings'' during the final approach. If you are able to see the top of the wings, you are in trouble !!!!

One thing is to land, and another one is to fly low and touch the ground.
Jack
Thanks Jack,

The Bandit does have very big flaps which when extended, to me at least, it does give it a slight "nose down" attitude when on finals. Weather that is real or imagined I am not sure. I'll try to take more notice next time, and use your tip at looking at the under surface of the wing..

Edit

I just found a pic of my Classic on finals. (It is much easier to land and I don't have have the same ballooning issues with this model. It is of course much lighter).. This photo is on finals at about 15' altitude and it seems to be sitting pretty much level.


Roger
Attached Thumbnails Click image for larger version

Name:	Tq48783.jpg
Views:	55
Size:	41.5 KB
ID:	1729878  
Old 02-21-2012 | 01:45 AM
  #22  
 
Joined: Jun 2002
Posts: 13,258
Received 788 Likes on 571 Posts
From: Watford, UNITED KINGDOM
Default RE: Exponential on Elevator?? Is it required on a Bandit.

This could end up with a whole thing on landings, but I disagree with Jack on this type of model. I teach new to jet people to look for shade on top of the wing (ie nose down on the approach) Nose high is fine if you are flying in on power and can judge the speed and "feel" the stall coming, we have fatter air and lower temps, but nose up here and a draggy well flapped model will quickly get the back side of the drag curve and stop flying. Many pilots use the throttle like a three position switch and cannot adust it on the approach (why RC heli pilots are better fixed wing pilots ) Guys who fly F-15/F-16 models learn the power on and nose high method, but I have seen some otherwise tidy pilots really struggle to land this type of model.
There are so many different models, that behave completely different at full flap. BVM at least try and get consistancy by offering a gauge for flap angle, even putting figures in a manual means nothing as people go their own way (not always knowing what they are doing) or just don't check carefully. Many moulded aeroplanes with live hinged flaps have a slightly different flap cord, one wing to another and measuring to the TE root might give the same flap amount, but the angles are completely different!
I always straddle any aeroplane and look down the flap upper surface to compare angles.
End of the day there is no right or wrong way, if it works for you then great, but if its not working out try something different.

Dw
Old 02-21-2012 | 03:16 AM
  #23  
Senior Member
 
Joined: Apr 2008
Posts: 599
Likes: 0
Received 0 Likes on 0 Posts
From: Sydney, AUSTRALIA
Default RE: Exponential on Elevator?? Is it required on a Bandit.

Try crow. This will definitely help stop ballooning. Higher wing loading simply means higher landing speed. So you can tug harder on the elevator on your balsa as it lands slower. Maybe you are so used to this that you naturally do it with the heavier super and walla flair results in an undesirable climb just before the stall (when you need to be 1 inch off the ground!)???

Mav
Old 02-21-2012 | 07:57 AM
  #24  
My Feedback: (1)
 
Joined: Nov 2003
Posts: 551
Likes: 0
Received 0 Likes on 0 Posts
From: Caracas, VENEZUELA
Default RE: Exponential on Elevator?? Is it required on a Bandit.

Come on Dave..... you are underestimating your students abilities to manage power !!!!!!! Or.... you are making a fortune selling flexplates
Just pulling your leg, btw. Don't get mad at me !

Will I see you at Florida Jets?

Regards
Jack
Old 02-21-2012 | 09:04 AM
  #25  
eddieC's Avatar
Senior Member
My Feedback: (2)
 
Joined: Nov 2002
Posts: 2,102
Likes: 0
Received 0 Likes on 0 Posts
From: Jackson, MI
Default RE: Exponential on Elevator?? Is it required on a Bandit.

Slow down, ballooning means you're still at flying speed, for however short a time.  
Absolutely true.

If ballooning remains a problem, you might want to take your plane up 3 mistakes high and practice real slow flight. It may surprise you just how slow it will fly.


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

Copyright © 2026 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.