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  #1  
Old 06-23-2017, 11:15 PM
lr172 lr172 is offline
 
Join Date: Oct 2013
Location: Schaumburg, IL
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Default X-wind take-off technique in A models

I fly from an airport with an E-W strip. Most strong wind is usually from the south and we have buildings and tall trees just south of the field. It makes for challenging landings due to the rotors, turbulence and variable gusting. It's not uncommon to see all three wind socks pointing in different directions. However, we never see really strong sustained cross wind at the runway level, only 30' above it.

I have mastered landing and taking off in these conditions, but don't get to do many x-wind landings or take-offs with more traditional cross wind conditions. Today I did some T&G's at a nearby airport with a 90* x-wind 15G20 (pretty sure most wind was 20). The landings were no issue, but I had an issue with the take-offs.

I have been carefull to do all of my take-offs with the nose wheel a few inches off the ground. I was taught to let the cross wind aileron out as the take off progresses, however, I rarely need much aileron in the situations that I fly and therefore don't get much practice. Today, I kept skipping sideways during the take-off roll and was subconsciously keeping the aileron full in too long to keep from skipping. On my final take-off, the gusts were strong and I must have had most of the aileron in to track down the center line. As I lifted off, the wing went down quickly and scraped. The damage is only the size of a quarter on the wingtip and an easy repair.

In thinking through what I did wrong, I realized the error of full aileron at lift-off, but it raised the issue of how else do I keep from skipping sideways. I had remembered reading that you need to keep some down elevator to keep the wheels planted and use tire friction to avoid sideways movement. I had become so afraid of going easy on my nose wheel that it seemed unnatural.

I was wondering how others manage this type of situation in their A model RVs.

Larry
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RV-6A / IO-320, Flying as of 8/2015
RV-10 in progress

Last edited by lr172 : 06-23-2017 at 11:38 PM.
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  #2  
Old 06-24-2017, 06:47 AM
Robert Anglin Robert Anglin is offline
 
Join Date: Mar 2008
Location: houston, texas
Posts: 890
Default Rudder as well.

An RV has a lot of good rudder force available and you may want to start practicing using it along with you stick inputs. You may want to practice full slip landings and change from side to side during your practice. I would start you off at 3,000 AGL to be safe. Just a suggestion, Yours, R.E.A. III #80888
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  #3  
Old 06-24-2017, 07:59 AM
lr172 lr172 is offline
 
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Quote:
Originally Posted by Robert Anglin View Post
An RV has a lot of good rudder force available and you may want to start practicing using it along with you stick inputs. You may want to practice full slip landings and change from side to side during your practice. I would start you off at 3,000 AGL to be safe. Just a suggestion, Yours, R.E.A. III #80888
My question was about the take off roll. I am struggling to understand how a full slip would help. I know how to slip and routinely use slips to lose altitude on final and also kick out a crab to a slip over the numbers when necessary

I actively use my rudder on landing and take off (all phase of flight actually) and have no problems tracking down the centerline with the nose parallel in landing or take off. My question was about rotation/lift off. Are you suggesting to put in heavy rudder opposite the aileron at lift off? I had been holding just enough rudder to keep my fuse parallel with the centerline as I roll. If I had used anymore prior to lift off, I would also have been skidding as well or heading off the runway. A slip at lift off seems counter-intuitive due to it's increase in drag as well as a crab is fine once off the runway.

Larry
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RV-10 in progress

Last edited by lr172 : 06-24-2017 at 08:12 AM.
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  #4  
Old 06-24-2017, 08:45 AM
Schooner69 Schooner69 is offline
 
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Larry:

What would be your control inputs just as you touch down in a crosswind?

Logically, they should be the about the same in a take off in similar conditions.

True, in the former situation, you're decelerating while in the latter, you're accelerating; however, the theory should hold true.

John

PS No refunds...
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  #5  
Old 06-24-2017, 09:01 AM
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Steve Melton Steve Melton is offline
 
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for takeoff, when the wind is from the left it is more difficult than when it is from the right. when it's strong from the left I have needed to ride the right brake slightly until speed increases. I keep all three wheels on the ground until lift off.
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  #6  
Old 06-24-2017, 09:03 AM
lr172 lr172 is offline
 
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Location: Schaumburg, IL
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Quote:
Originally Posted by Schooner69 View Post
Larry:

What would be your control inputs just as you touch down in a crosswind?

Logically, they should be the about the same in a take off in similar conditions.

True, in the former situation, you're decelerating while in the latter, you're accelerating; however, the theory should hold true.

John

PS No refunds...
I typically take out my crab over the numbers and then apply aileron into the wind and rudder in the opposite direction. I apply enough aileron to hold the centerline and apply whatever rudder is required to keep my longitudinal axis aligned with the the centerline. On takeoff, I am doing the same thing, the difference is that the plane is being forced level due to the wheels on the ground. It doesn't need the opposite rudder, as it is forced level by the wheels. The ailerons can't create a banking motion as they do on landing/flare.

In yesterday's case, the ailerons were opposing the x wind during the roll and the wheels on the ground were opposing any banking. As soon as the tires broke free, it banked. It seems to me as I think more about this that I just needed to hold it on the ground until ready and then simultaneously pitch up and take out the aileron. This would have prevented the skipping and avoided the wing drop at rotation. I suppose I subcounciously do this most times, but was overreacting to the excess wind. I also feel that I should have had the nose wheel planted in that situation and should not have followed my SOP of keeping it off the ground.

Maybe there is a technique where you bank it hard enough to get on one wheel and then use opposite rudder like a slip. I have heard of this, but was never taught it and never tried it.

Larry
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Last edited by lr172 : 06-24-2017 at 09:13 AM.
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  #7  
Old 06-24-2017, 09:16 AM
lr172 lr172 is offline
 
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Quote:
Originally Posted by Steve Melton View Post
for takeoff, when the wind is from the left it is more difficult than when it is from the right. when it's strong from the left I have needed to ride the right brake slightly until speed increases. I keep all three wheels on the ground until lift off.
Thanks Steve. I am thinking that my issue here was not keeping all three wheels on the ground and using that friction/stabilizing force. Keeping the nose wheel up was likely keeping me light on the mains, as well, due to the extra AOA. The extra force would have likely prevented the side skipping and I wouldn't have had the urge to put in all of that aileron to oppose it.

Larry
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  #8  
Old 06-24-2017, 10:21 AM
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flyeyes flyeyes is offline
 
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On a crosswind takeoff, until the airplane leaves the ground the only thing that is capable of keeping you from being blown to the downswing side of the runway is friction from the tires.

If you can remain in place while not moving on the taxiway, then there's enough friction available to keep you straight on the runway, as long as you keep weight on the tires.. Use the wing to keep weight on the tires by using neutral or a small touch of forward stick until rotation. Use ailerons into the wind-fully deflected at the start, relaxing as you accelerate and the downwind wing starts to feel light.

Accelerate to a little faster than your normal liftoff speed and rotate positively so that the airplane leaves the ground cleanly. Typically the downwind wing will liftoff first, you need to be ready to relax the crosswind correction, which means to level the wings and relax the rudder correction to allow the airplane to weathervane into the wind.

Climb out with the airplane coordinated, in whatever crab angle relative to the ground that it takes to track the centerline. Strong crosswinds ar often gusty, so you might want to climb at a slightly higher airspeed than normal for better control authority.

If you use the "hold the nose wheel off and it will fly when it's ready" technique on a blustery day, there will be a brief period where you don't have the control authority to be much more than a passenger. Fortunately even the lowliest RV is well powered enough that this is a pretty narrow window and you'll usually get away with even sloppy technique.
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  #9  
Old 06-24-2017, 11:23 AM
rvbuilder2002 rvbuilder2002 is offline
 
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Location: Hubbard Oregon
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The purpose of aileron input during a cross wind take-off is to counter any rolling tendency the wind is inducing. At low airspeed, the ailerons are not very effective so a lot of input is need, but as you gain speed the effectiveness is increasing so you keep reducing the input as needed.
If you are doing it properly so that you are correctly countering the rolling influence of the cross wind, the airplane should lift off exactly wings level.
If you are rolling suddenly as you lift off it is an indicator that you are inducing way more roll force (way to much aileron input) than the cross wind is influencing in the opposite direction.
RV's have very powerful ailerons. If you are using anything more than a small amount of aileron input at the moment of lift off, you are likely using to much, regardless how strong the cross-wind is.
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  #10  
Old 06-24-2017, 11:34 AM
lr172 lr172 is offline
 
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Quote:
Originally Posted by flyeyes View Post
On a crosswind takeoff, until the airplane leaves the ground the only thing that is capable of keeping you from being blown to the downswing side of the runway is friction from the tires.

If you can remain in place while not moving on the taxiway, then there's enough friction available to keep you straight on the runway, as long as you keep weight on the tires.. Use the wing to keep weight on the tires by using neutral or a small touch of forward stick until rotation. Use ailerons into the wind-fully deflected at the start, relaxing as you accelerate and the downwind wing starts to feel light.

Accelerate to a little faster than your normal liftoff speed and rotate positively so that the airplane leaves the ground cleanly. Typically the downwind wing will liftoff first, you need to be ready to relax the crosswind correction, which means to level the wings and relax the rudder correction to allow the airplane to weathervane into the wind.

Climb out with the airplane coordinated, in whatever crab angle relative to the ground that it takes to track the centerline. Strong crosswinds ar often gusty, so you might want to climb at a slightly higher airspeed than normal for better control authority.

If you use the "hold the nose wheel off and it will fly when it's ready" technique on a blustery day, there will be a brief period where you don't have the control authority to be much more than a passenger. Fortunately even the lowliest RV is well powered enough that this is a pretty narrow window and you'll usually get away with even sloppy technique.
Thanks for the detailed response. After thinking through this more it seems apparent that my efforts to protect the nosewheel were causing problems and your explanation supports that. It seems clear now that a positive force on the wheels will keep me planted and eliminate the need for aileron to keep me from going sideways. Just enough aileron to keep from allowing a rolling motion on the longitudinal axis.

Thanks for the replies.

Larry
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