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Takeoff configuration effect on takeoff distance

nigelspeedy

Well Known Member
The other half of my learning how to land my 8 was learning how the takeoff configuration and technique affected the takeoff distance. I did an experiment to find out by doing a series of takeoffs using flap 0, 10, 20 & 40 degrees. For the ground roll I also used a tail up attitude (approximately 0 deg pitch attitude), tail low (approximately 5 deg nose up pitch attitude) and tail down (tailwheel lightly held on the ground to hold the 3 point attitude of 11 deg nose up). So a matrix of 12 takeoffs overall, which I measured with a DGPS on runway 24 at California City, L71, in nil wind at 1540 - 1600 lbs. For each takeoff I adjusted pitch attitude after liftoff to achieve 1.2 Vs for the particular flap configuration at 50' AGL. This resulted in 72 KIAS for 0 deg flap to as low as 60 KIAS for 40 deg flap. Each takeoff started with mixture rich, prop full fine with the aircraft held stationary on the brakes until throttle was fully forward. There was only one attempt at each configuration so there is no statistical relevance. I've made no attempt to correct for runway slope, aircraft weight, wind, air density or power so these results are only representative of my aircraft on the test day, which is a polite way of saying they are incorrect everywhere else so don't use them for operational planning. I was really only after the relative changes not absolute distances.

The results are shown in the graphs below.

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Tail%20Low_zpsvfi7elvl.png
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So in general tail low or tail down results in a shorter takeoff distance than tail up. The advantage for tail down over tail low is minimal.
On the farm dad alway said "if a little is good, more is better and too much should be just about right", but it doesn't seem to be that way with flaps. No flap is always the longest takeoff distance but 10 deg does just as well as 20 or 40 for the most part.
Taking off with the tail up gives the best field of view. Tail low allows you to see the runway centerline so directional control is still easy. Tail down might be a bit harsh on other than smooth surfaces and the field of view is a not as good as tail low or tail up and there is no real performance gain.
When using 40 deg of flap you get off the ground slower but the extra drag means it takes the same ground distance as 10 or 20 deg flap to get to the lower speed. Using 40 deg flap and maintaining 1.2 Vs to 50 feet is great as long as the engine keeps on running but 20 deg nose up, 40 deg flap, 60 KIAS and an engine failure would be pretty sporting combination.

So based on this I've settled on the following:

Normal Takeoff from a sealed runway with no obstacles. Rolling takeoff, Flap 0 deg and tail up.

Short field takeoff: Hold on brakes until power applied, Flap 10 deg and tail low during the ground roll, 1.2 Vs till clear of obstacles then accelerate to normal climb speed.

Soft field takeoff: Rolling start, Flap 10 deg, tail low, level off to accelerate to normal climb speed after ground break.

Cheers
Nige
 
Same results

Though the takeoff roll was shortest with 40 flap, I came up with essentially the same results in my 180HP RV-8. My AOA is calibrated for flaps up and flaps 20, no flaps 10 setting. I found the difference between 10 and 20 flap was minimal so I changed my short and soft field procedures to use flap 20 so I can take advantage of the AOA for more accuracy and therefore maximized performance.

Scott A. Jordan
N733JJ
 
The other half of my learning how to land my 8 was learning how the takeoff configuration and technique affected the takeoff distance. I did an experiment to find out by doing a series of takeoffs using flap 0, 10, 20 & 40 degrees.
Thanks for the data. Nice work.

I experimented with a single GPS precise positioning setup a few years ago, but never got acceptable results. I'd be interested to learn more about your DGPS setup.

Short field takeoff: Hold on brakes until power applied, Flap 10 deg and tail low during the ground roll, 1.2 Vs till clear of obstacles then accelerate to normal climb speed.
Be aware that applying too much power while stationary can result in sucking debris into the prop. I have a friend who destroyed the prop on a TB-21 Trinidad when taxiing on grass when the field was too wet. The aircraft started to bog down, so he applied high power to keep it moving. The prop sucked some tiny stones out of the ground and completely chewed up the back side of the prop. It looked like someone had attacked it with 20 grit sandpaper, and had to be scrapped.
 
DGPS Used

Scott,

I like your logic for using the 20 deg flap setting in your aircraft, like you say there isn't a significant performance difference between flaps 10 & 20.

Kevin,

Thanks for the timely reminder about stones and prop damage. I'll give mine a closer look over next time I am at the hanger and use full power on the brakes only when it is operational necessary.

The DGPS I used belongs to work and I just loaned it for a couple of days. It is a 'Novatel ProPak6'. We use 'Program: GrafNav/GrafNet Version: 8.50' to do the file merging between the base and rover to achieve the differential correction post flight. We don't broadcast the corrections real time.

We have 4 of these units, each is about the size of a house brick. They are pretty easy to use, on/off, record start/stop, power & antenna connection.

One unit is permanently fixed in the building as our base station. We determined the location of the base (BASE: 35 03 22.70460 N -118 09 01.53756 W 814.128m) by running it for 24 hours to record position and then applied the differential corrections from a local station. In essence running the base as a rover. Even with the differential corrections there was some dither over 24 hours so we took an average of these positions over that time and called it the surveyed point. Close enough for our main use which is education rather than certification.

The rovers are identical units to the base station just run off a battery rather than mains power. In my 8 I mounted the rover antenna using a RAM mount to the bar behind the pilot seat where it had a good view of the sky. The rover and battery were in a small bag on the rear seat secured by the harness and numerous zip ties to keep any cables from fouling the rear stick. The antennas we have only allow reception of the GPS L1 & L2 bands but with an appropriate (expensive) antenna you can also receive all the other constellations.

In the post processing you can adjust sample rate from 20Hz to once per 20 seconds, depending on your application and tolerance for file size. I just used 1 Hz in my test, 5 Hz would probably be better if you wanted more fidelity on the transition between ground and air. What I think is neat is that it is accurate enough in the vertical plane to detect the 6-8" change in height when the tail comes up during the takeoff roll. We teach that for the corrections to be valid the base and rover need to see the same constellation, which is a pretty solid assumption up to 50 nm, and pretty safe out to 100nm. The other thing that is pretty noticeable is the reduction in signal quality when maneuvering, so before any important test point it is best to be straight and level for 30 sec or so. During the base turn reception would drop from 12 to 9 or 10 SV used in the solution but would return as soon as you roll out on final.

Here is a portion of the processing summary from the flight.

Position Standard Deviation Percentages:
" 0.00 - 0.10 m: 99.2 %"
" 0.10 - 0.30 m: 0.6 %"
" 0.30 - 1.00 m: 0.2 %"
" 1.00 - 5.00 m: 0.0 %"
" 5.00 m + over: 0.0 %"

So for the most part 10 cm or less. Not sure what accuracy you experienced in the past.

Cheers
Nige
 
Take off

Good data Nigel and much appreciated. OT, but I was surprised you could open the throttle fully while holding brakes. In my -8 I cannot hold the tail down at full throttle with full up elevator. If I don't back off on power it's goodbye prop! Elevator motion has been checked a number of times and is within specs, even toward the upper limit for up elevator travel. Could be CG location. Where is your empty CG? Thanks
 
High/Hot/Heavy takeoff configuration

Very good summary and I like your conclusions. Especially the conclusion that when runway length is not really a factor, that zero flaps and tail high is the right configuration. As an old flight instructor, I have seen many students and rated pilots choose 10 degrees of flaps and a Vx (or slower!) climb when they are concerned about a high/hot/heavy takeoff. But when you really want best climb performance, getting to Vy as quickly as possible at zero flaps is the way to go. There are many mishap reports where the pilot is taking off (or rejecting a landing) with flaps deployed and attempting to climb at Vx (or slower!) and they wonder why they are not climbing. In the investigation, the pilot often indicates that they felt the engine was not developing rated power. Flaps up and Vy is your best friends when worried about climb performance.
 
Gross Weight Test

...

So based on this I've settled on the following:

Normal Takeoff from a sealed runway with no obstacles. Rolling takeoff, Flap 0 deg and tail up.

Short field takeoff: Hold on brakes until power applied, Flap 10 deg and tail low during the ground roll, 1.2 Vs till clear of obstacles then accelerate to normal climb speed.

Soft field takeoff: Rolling start, Flap 10 deg, tail low, level off to accelerate to normal climb speed after ground break.

Cheers
Nige

It would be nice to see at least a couple of test points re-run at gross weight and/or at a high density altitude to compare the effects of no flaps vs flaps on takeoff/initial climb performance. I suspect at higher weight, the extra drag of the flaps may be detrimental...
 
Bill TO Throttle

Bill,
Good questions. In truth I can't get the throttle full open on the brakes. What I did was to hold the stick full aft with the brakes on firmly. Then advance the throttle smoothly as far as possible, until the aircraft started to roll forward, then simultaneously release the brakes and add the remaining 1" or so of throttle. Mine starts to move by the time I get to about 2500 RPM. Good pick up I'll be more specific next time.
Cheers
Nige
 
If I may ask ... as a future builder ... these numbers are roughly double or more what Van's advertises for an RV-8 (depending on HP) ... is that ... normal?

I thought I'd read Van's numbers were usually pretty spot on ...
 
not quite vans numbers?

Kamikaze,
Variations will come down to several factors
The first being how you choose to define 'takeoff distance'. Do you just mean the ground roll or do you mean the total distance to 50'. Often in the kit planes industry you just see the ground roll quoted, or the distance not precisely defined.
The second reason for the difference is going to come down different test conditions (weight altitude, temperature, runway slope, engine & prop).
The third reason is going to be pilot technique. Rotation speed, pitch rate and speed at 50' are all going to make a very big change to the distances measured.
I doubt runway length is ever going to be a limiting factor on how I operate mine. Perhaps if you are planning to operate of short or sloped grass strips at altitude it could be more of an issue.
I think the takeoff performance is great regardless of how my measurements compare to the Vans published numbers.
Cheers
Nige
 
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If I may ask ... as a future builder ... these numbers are roughly double or more what Van's advertises for an RV-8 (depending on HP) ... is that ... normal?

I thought I'd read Van's numbers were usually pretty spot on ...

Quibbling over 300' vrs 600', it's a matter of pilot technique. Compare that to the Piper you are flying.:)

Go for any RV and you won't be disappointed.

I've flown a lot out of a 2200' strip and will testify the 8 with FP Catto will get off in less than 1000' hands down. CS is better but FP is not shabby.
 
I fly regularly off a private strip that is 2600' with powerlines at each threshold, so realistically 2300' usable each direction, and in a loaded Cessna 172 it's manageable on all but a 100F afternoon at max gross. I don't expect to have any trouble at all with my 9A on that runway.

My quick 30-second takeaway from seeing the data above was that all the variations managed to produce a takeoff ground run of 550' plus or minus 50'. I was surprised there was that little variation in the ground run with the flaps and attitude variables. It all comes down F=MA, acceleration on the ground run.
 
Performance

Awesome Article. Your 0/10* flap, tail up/down performance numbers seem to be spot on with my very "unscientific" experiences. Thank you for sharing.

Tim

Toga1, "Phantoms Phorever", RV-8, "Betty Jane"
 
Point taken, thank you! Notably if your measures are not roll, but to 50' ... that makes a big difference.

And yes, I am comparing to my Piper, which is why I want an RV :p
 
Nigel,

Thanks again for sharing the results of this test. I will respect your disclaimer and do some tests of my own to see what kind of performance my plane is capable of producing under my control.

In examining the graphs, it appears to me in most cases you were airborne at around 300 ground roll and achieved 50 feet agl in around 500 feet. That's very impressive.

Thanks,
 
Nigel TO throttle

Thanks Nigel. Our experience is similar, I think. After experimenting with various configurations I also use zero flaps for all normal takeoffs on hard surfaces. 10-20 degrees flap for soft, grass etc. Like you, I don't think the takeoff distance will be significant as a limiting factor anywhere I'm likely to fly.
 
Nigel,
Nice work here. Just a general observation and flying my -7 just over 200 hours. I've never actually documented and graphed my testing like you have done but I have come to realize that my -7 likes to jump off the ground at it's "normal tail dragger angle of attack". I was taught that when the elevator becomes "alive" (when you have stick control), you should pretty much hold that attitude and the plane will leave the ground nicely. Now there is obviously some exceptions to that rule. Long, wet grass for example...where the tail wheel is digging in to the ground and you need to get it off the ground as soon as possible. But runway conditions aside, I wanted to let you know that my experience has been pretty much exactly as your charts state. When I hold a tail low attitude I get off the ground noticeably faster. With that said, weight plays a pretty big part on how well it gets off the ground obviously. When I have full fuel and a passenger, my -7 wants to come off the ground at it's normal attitude but then start to immediately sink causing it to bounce and starts porpoising . I have to hold it on the ground (tail up) until the speed is appropriate for take off. I wanted to bring this up to you to see if you planned on doing any testing with a passenger.

Also, same disclaimer from me.... I'm just sharing what happens with my particular plane. O-360 - Wood prop - VSO 51 Kts
I'm sure it may be way different with a CS prop.

Just some food for thought.
 
Dust off this excellent and useful thread

I have to belatedly say thanks to Nigel for this data. I am finally getting some more accurate data for my RV7 POH and want to see what was available.

I have 180 hp with the Hartzell composite - the wide blade one. I tried the lift the tail on a cool day , 34F, and got about 450 ft for lift off. The G3X data was used to calculate the position and speeds. VS defined the lift off point.

450' seems high compared to Vans (275) and my estimated weight was 1480 lbs, so it was not heavy. I could probably make a little more RPM on brakes and certainly use the tail low lift off technique for slightly reduced roll. Maybe higher tire pressure will help too. Cold tires rolling drag coefficient can not be good.

I really appreciate the detail Nigel has provided, it will shorten the test work.

One snag is the accuracy of the WAAS gps data, but way better than the next best and it is really easy.

One last thing, if anyone has governing equations to make a definitive correction of TO roll and climb to different temp, altitude conditions, please post or send an email.
 
I never operate out of marginal strips so the t/off run or distance isn't of concern for my RV8/180/CS but it's always interesting to read others figures they come up with.
As just mentioned, DA makes a big diff as does surface type, tire condition/pressure and obviously prop type and condition, add pilot technique the numbers can be somewhat different. As long as pilots realise that TORA and TODA are different calculations :)
Im still amazed at some pilots who I run into occasionally think their 180 HP produces just that at all elevations inc FP props, the latter is very worrying!
Stay safe, Vans made us a very capable machine BUT it does have its limitations.
 
I did an experiment to find out by doing a series of takeoffs using flap 0, 10, 20 & 40 degrees.

....

Cheers
Nige

Thanks Nigel enjoyed reading through your data. It all makes sense and supports relatively established claims. Having some quantitative data on the other hand is the right kind of knowledge. It gives us all a more complete picture, increases accuracy in decision making, improves knowledge.. thank you!
 
Hi Nigel,

I realize this is an old thread but am wondering if you might be interested in measuring another set of tests?? Particularly since you appear to have some interesting equipment.

The test: Distance to take-off and clear a 50' obstacle.

The technique: Lift off at minimum flying speed and immediately begin the climb.

I cannot speak to the RV-8 but with an RV-4, this is lifting off at approximately 45 kts IAS, pulling the nose up quite dramatically as the airspeed passes thru 48 kts IAS, and climbing at 50 kts IAS until the obstacle is cleared.

The logic behind this is that at high density altitude, the time required to accelerate to Vx eats up a great deal of distance. Obviously, you have to sneak up on the speeds to ensure safety.

I would be very interested in hearing any suggestions you have for ways for the common man to measure/record this test. The problem we have faced is the 50' altitude. The altimeter and visual from the ground is imprecise, GPS too slow.

Thanks Nigel!
 
More Takeoff testing

Hi JD,
I was thinking that it might make a good subject for a KitPlanes article. The original testing I did was to help me decide on the optimum profiles for my aircraft. But as one poster pointed out I did not make any corrections to a standard weight or altitude so they are not meant to be compared to the Vans numbers. However, knowing the actual test conditions the corrections are not that difficult to make.
In my RV the actual Vx is as close to the stall as I can fly. But this slow just after takeoff is not a great idea, some margin is needed for safety even if this is at the expense of a slightly longer distance. In practice I use 1.2 * Vs as my best angle of climb speed.
If your field is so short that lifting off tail low and being at 1.2 Vs at 50' wont work then I think we need to wait for the STOL RV.
Cheers
Nige
 
The original testing I did was to help me decide on the optimum profiles for my aircraft.

I completely agree. Knowing exactly how my airplane would perform under a specific set of circumstances was also the reason for my testing.

In my RV the actual Vx is as close to the stall as I can fly. But this slow just after takeoff is not a great idea, some margin is needed for safety even if this is at the expense of a slightly longer distance. In practice I use 1.2 * Vs as my best angle of climb speed.

Agreed and that is excellent to hear.
My research leading up to my testing showed that there is a wide range of numbers being used by folks. At this point, I can't recall exactly what I found but it appeared to me that many were using a Vx that was very high - I believe 70 kts IAS was a common. In my airplane, 70 kts is 1.6 Vs. This struck me as odd which caused me to begin testing since waiting for the airplane to accelerate from 1.2 (52 kts) to 70 kts at 10,000' density altitude requires a good bit of time and distance.

If your field is so short that lifting off tail low and being at 1.2 Vs at 50' wont work then I think we need to wait for the STOL RV.

That's not the case - it does. The issue was KNOWING how the airplane would perform before attempting to operate off this airstrip. This led to a bunch of testing using a variety of configurations which led to a technique and numbers that are far different than one will typically read about here and elsewhere (in regards to RV's).

I suspect the instrumentation you were using was beyond was is commonly available but have to ask - what were you using? Is anything like that available to the rest of us? Meaning: recording the point at which 50' is reached - more specifically, the distance from the start of the takeoff roll to that point? I'm asking as we found this to be rather difficult and had to enlist the aid of a drone stationed at the 50' point (which took a good bit of trial and error).
 
Equipment

I'm pretty sure he said he was using 4 Novatel ProPaks......We use the same unit at work, they're great, but not really hobbyist equipment, a bit user belligerent and they are not cheap...I think(IIRC) ~$5k each.....however, this is a great thread !!!
 
Please elaborate

I would be very interested in hearing any suggestions you have for ways for the common man to measure/record this test. The problem we have faced is the 50' altitude. The altimeter and visual from the ground is imprecise, GPS too slow.

I used the GPS information recorded in the G3X, are you saying it is too slow to be reasonably accurate, at least compared to the next available source/method?

Could you please elaborate on why it is/might be inaccurate.

Thanks.

JD & Kevin, thanks for references on take off & climb (35/50')corrections. I sent a note to Kevin H and he referred me to a 1951 Air Force publication (Herrington) on flight testing. It has some empirical equations with corrections for 1.weight 2.Density altitude 3.Surfaces 4.Wind, and 5.Incline. The general references typical for weight are proportional to ^2 but Herrington said it was ^2.3. The flight manual is available in print for 1953 update or PDF (free) for the original text. Herrington states (paraphrased) the TO phase is so complicated based on first principles and so much variation due to pilot technique and skill, that empirical methods are best used.
 
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I used the GPS information recorded in the G3X, are you saying it is too slow to be reasonably accurate, at least compared to the next available source/method?

Could you please elaborate on why it is/might be inaccurate.

Apologies Bill, I was terribly vague. I was attempting to say that attempts to manually note height and position (using instrumentation and outside visual clues) was too slow/inaccurate. All required far too much attention from this pilot when workload is high and things are happening quickly (wheels up to 50' is 3-4 seconds).

I was really looking for pointers on how a 'common guy' can gather this data with reasonable accuracy (and, hopefully, without investing thousands of dollars). You have clued me into using the GPS track/recording functionality. I can see how this would work quite well. While no longer a pressing issue for me, I will still explore this as I'm a bit of a data junkie. Thank you!!
 
Apologies Bill, I was terribly vague. I was attempting to say that attempts to manually note height and position (using instrumentation and outside visual clues) was too slow/inaccurate. All required far too much attention from this pilot when workload is high and things are happening quickly (wheels up to 50' is 3-4 seconds).

I was really looking for pointers on how a 'common guy' can gather this data with reasonable accuracy (and, hopefully, without investing thousands of dollars). You have clued me into using the GPS track/recording functionality. I can see how this would work quite well. While no longer a pressing issue for me, I will still explore this as I'm a bit of a data junkie. Thank you!!


While not quite as accurate as instrumentation a good flight test engineer could probably get you something reasonably accurate. They did it before orange wire and high speed data. I?ve seen some rather accurate data gathered this way.
 
New to RV-8 here and I live on a grass runway airport. On take off I like to bring in power slowly as I roll forward (between 3-5 seconds to full power) to protect the prop and then I raise the tail as soon as possible to protect it from anything flying up and the runway bumps.

To those of you with more experience in the RV-8, does flap setting help to raise the tail any sooner?
 
New to RV-8 here and I live on a grass runway airport. On take off I like to bring in power slowly as I roll forward (between 3-5 seconds to full power) to protect the prop and then I raise the tail as soon as possible to protect it from anything flying up and the runway bumps.

To those of you with more experience in the RV-8, does flap setting help to raise the tail any sooner?

Lifting the tail is all about airflow ofer the tail and being deflected off the downward deflection of the elevator, flap won't have any effect. Another effect is the CG. Tail heavy means the elevator deflection won't be as effective at slower speeds. Generally the RV8 with 180+ gee gee's up front and CS prop gets its tail up very quickly anyway:)
 
New to RV-8 here and I live on a grass runway airport. On take off I like to bring in power slowly as I roll forward (between 3-5 seconds to full power) to protect the prop and then I raise the tail as soon as possible to protect it from anything flying up and the runway bumps.

To those of you with more experience in the RV-8, does flap setting help to raise the tail any sooner?

Yes. (extra characters)
 
...To those of you with more experience in the RV-8, does flap setting help to raise the tail any sooner?

Awesome, two completely different opinions about the same thing in less than 2 hours :):).


Lifting the tail is all about airflow over the tail and being deflected off the downward deflection of the elevator, flap won't have any effect....

Sounds reasonable.

Yes. (extra characters)

Could you give more detail as to why?
 
Prop blast onto lowered flaps will definitely contribute to raising the tail.
I have investigated more than 1 incidents where props got into the ground because of running up to full power with flaps down and brakes locked; even though the elevator was held full up.
 
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Could you give more detail as to why?
Not going to get into the depths of the fluid dynamics, but lowering the flaps will make it easier to raise the tail of the -8. Both with power and without (e.g., rolling out after landing).

But back to your point of protecting the airplane, I operate off these types of strips often. At home and traveling. I too am concerned about impact damage to the prop, the bottom of the elevator and the bottom of the flaps. To minimize this, I use moderate flaps and a tail low attitude to takeoff. I use moderate stick pressure to allow the tail to float off the ground a little for the tail low attitude. Go back to the original discussion in this thread. Nigel talks about this as the fastest way to get the (-8) off the ground. And getting it off the ground stops the main wheels from throwing up debris.
 
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Prop blast onto lowered flaps will definitely contribute to raising the tail.
I have investigated more than 1 incidents where props got into the ground because of running up with flaps down; even though the elevator was held full up.

Thanks Mel. So in my case since I live on a 2500' grass runway, the only reason I lift the tail quickly on take off is to protect it from anything flying up and hitting it. If I were to add 10 flaps on ALL of my takeoffs on my Before Take Off checklist, would it help get that tail in the air quicker, or would 10 flaps just be negligible and as I get used to that adding to the possibility of something worse by forgetting to raise flaps before passing 100mph or something now hitting the lowered flaps? I try to keep things as simple as possible but if it'll help I'll add it.
 
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Thanks Mel. So in my case since I live on a 2500' grass runway, the only reason I lift the tail quickly on take off is to protect it from anything flying up and hitting it. If I were to add 10 flaps on ALL of my takeoffs on my Before Take Off checklist, would it help get that tail in the air quicker, or would 10 flaps just be negligible and as I get used to that adding to the possibility of something worse by forgetting to raise flaps before passing 100mph or something now hitting the lowered flaps? I try to keep things as simple as possible but if it'll help I'll add it.

Optimum take-off flaps is in the neighborhood of 15?. This is why differential ailerons usually have 15? of down travel. Optimum compromise between lift and drag. If you have electric flaps, try pushing the stick to one side and align flaps with the "down" aileron. Try it. I think you will like it.
 
Optimum take-off flaps is in the neighborhood of 15?. This is why differential ailerons usually have 15? of down travel. Optimum compromise between lift and drag. If you have electric flaps, try pushing the stick to one side and align flaps with the "down" aileron. Try it. I think you will like it.

I'll do that, thank you !
 
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