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Take off technique

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PTAirco

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The current vogue in bush flying and popular STOL culture is to shove the stick forward at the beginning of the take off roll and the yank it back down with a more or less violent rotation. Often you see the tailwheel slapping the ground again. The argument is that lifting the tail reduced the AoA of the wing and therefore cause less drag. I would question this.

At the beginning of the take off roll, when they do this, drag is minimal anyway because speed is minimal. producing a couple of hundred pounds of lift to get the tail up dwith very little forward speed must in itself cause a lot of drag. Is the trade off worth it? Could somebody with a more mathematical mind crunch the numbers? Do I need Calculus of will Mr Newton suffice for this?

There are some people out there who have done comparisons and found no real benefit. If this method was so superior, would they not have used it for carrier take offs in WW2 (before they used catapults)? The Cessna 170 POH states for best short field take off the aircraft should be flown off in a three point attitude. You'd think Cessna had this figured out but every "bush" flying video out there does it the other way. I understand the concern about tailwheel damage but lifting it a couple of inches does the job, it doesn't need to be three feet up in the air.

Opinions? Facts?
 

TFF

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On a carrier non catapult, you just have to fly off the end. They have pitching decks to help. The roll starts at the bottom of the wave; deck going up throwing you up at the end of the deck. WW2 planes were also taking off at 6000 lbs or more. They just needed consistency with what they had.

Opinion.
Winning a competition is about winning. Winning accepts busting stuff up to win. 1 ft better is the difference of winning or not, they are going to do it, or more. People will crash for a $10 trophy. They will.
Out in the field, the difference of one foot is not important, it’s emulating the cool kids. If it’s not your style, don’t do it.
The only way to know is go out and fly ten of each with measurements. You are not getting a foot of confirmation from the cockpit. Side note, almost all the YouTube show offs have nosed over, flipped, blown up engines, or just plain crashed. With cameras rolling.
 

Dan Thomas

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We did it both ways with a Champ. Found no difference in the takeoff roll. When teaching taildragger in the Citabria on a student's first flight, I had them open the throttle with the stick wherever it wanted to be, and as the tail lifted off a few inches I had them start adding back pressure to keep the tail from rising further. It would lift off whe it was ready and that attitude was the right one to get the climbout speed. That won't work in all airplanes, of course, depending on power available, but it gave them a better sense of where to expect the nose to be when landing. And it showed them how the elevator back pressure needed at low speed disappeared as the speed built, with no trim changes.
 

Toobuilder

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I think AOPA did an article on this a few years ago using a C-180. They found a noticable difference in distance, but I cant remember what was better.
 

PTAirco

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I think AOPA did an article on this a few years ago using a C-180. They found a noticable difference in distance, but I cant remember what was better.
I think I saw that one and the tail down attitude won. But I'm not sure how well the test was conducted, they only did a few runs each way.
 

Daleandee

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I think AOPA did an article on this a few years ago using a C-180. They found a noticable difference in distance, but I cant remember what was better.
Is this what you are thinking of?

FWIW I generally use three point with either zero or 10º flaps. In grass I will use a tail low to protect the tail wheel. I need to try 20º flaps and see if it takes off any shorter.
 

BJC

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Ther differences are small, and technique is important.

The tail up, at the start of the roll, has more to do with aligning the thrust parallel with the ground than reducing drag. As the speed increases, drag comes into play, but for an airplane that flies at 35 knots, it isn’t much.

A rapid rotation can get an airplane flying in ground effect; with enough power (not a 7AC) it can accelerate and continue to fly. Banging the tailwheel into the ground is poor technique.

My airplane (tricycle gear) has the shortest T/O roll, about 400 feet, with full power, let the elevator float, at 40 knots, aggressive rotation (but don’t hit the tail roller) and simultaneously pull full flaps. Fly in ground effect, accelerate, ease the flaps up, and fly away. Haven’t measured it, but that probably is 200 to 300 feet shorter than setting an angle of attack, half flaps, and letting it fly off.


BJC
 

MadProfessor8138

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Given enough static thrust and enough elevator area to do so........the tail high technique can be used to 'muscle' the plane off the ground....if done properly.
You are basically transfering lift from the tail to the wings by bringing the tail down to spring the aircraft into the air......banging the tailwheel on the ground renders the technique mute.
It's hard to explain in words but basically think of the aircraft as a lever....push down hard enough on one end (tail) and the other end (nose) wants to rise.

Find an aircraft that is specifically designed for STOL capabilities and a pilot that knows how to truly fly it ....and go for a ride.
You will feel the transfer of energy from the tail to the wings when the tail gets yanked down hard.
It really feels like being on final and pulling back to round out for the landing.....during the majority of the glide the wings feel like they aren't even there for the most part...but when you pull the tail down to round out just before you touch down....you get a sudden sensation of all the lift and energy in the wings.

Kevin
 
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Victor Bravo

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Well I may get my butt thrown off this forum, but I have to offer a biased but educated opinion on one part of this discussion. This is for tailwheel aircraft only, the argument is less complex for a nosewheel airplane.

First of all, that AOPA video is nonsense, they did not test all possible combinations of flaps, tail up, tail down, etc. I tried to contact that guy and ask him why they did not test one or two particular methods, and the arrogant chimpanzee couldn't be bothered to reply. He's every bit as un-biased as the news reporters from the major TV networks.

As some of you know, I am in the business of mfg. a control device for aircraft with manual flaps. It's irrelevant here because it's for certified airplanes. And I promised Jake I would not be selling this product here. With that promise foremost in my mind, consider this:

It takes energy to raise the tail on a taildragger. That energy, regardless of airspeed, has to come from somewhere. It may come from the airspeed at which the tail lifts itself off the ground. It may come from the pilot using the elevator and prop blast to raise sooner than that. Whether that tail-raising comes from plain old airspeed or prop blast hitting the deflected elevator, then the energy to do that has to be somehow subtracted from the prop blast being available to move the airplane forward.

Another thing that helps raise the tail is the pitching moment from deflected wing flaps. Whether it is due to prop blast or airspeed, the energy created from that "fringe benefit" that raised the tail still has to come from somewhere. No free lunch.

Now of course all this is balanced against the additional drag from the airplane plowing forward at a deck angle other than level. So at some point, the drag from a high deck angle plowing through the air becomes larger than the energy loss from raising the tail.

But we know drag is related to the square of airspeed, so drag at very low airspeeds is also very low. I cannot quantify it (maybe one of you genius types here can... Mr. Wainfan???) but I believe that the energy lost from trying to force the tail up at low speed (using elevator or flaps) is higher than the energy lost from dragging the fuselage and wings along at a 12 degree angle... for well over half of the takeoff roll. As we get to 30, 40, 50 miles an hour, then the drag of the nose-up airplane plowing forward will start to be worth getting rid of by using the elevator.

Something important that was being discussed is the use of flaps on the takeoff roll. Most people were taught as students to set the flaps before takeoff. This is because only a few people really need the shortest takeoff roll where 20 or 40 feet counts, and also because our instructors didn't want students taking their mind off other things while chasing the shortest takeoff.

The flaps create significant drag. But... but... you said it wasn't significant at speeds below 30 or 40 miles an hour ?!! Yes, but remember the flaps are sitting in a six foot diameter propeller blast that is traveling a heck of a lot faster than the airplane's groundspeed at the start of the takeoff roll. Half or 2/3 of the flaps may be seeing 40-60 MPH of wind from the prop. The prop blast is trying to push the flaps backward with a significant force. If you don't believe me, take a flap from an aircraft repair shop, and hold it at a 20 degree angle when the wind is blowing at 40 knots!

So the prop blast is trying to push the flap backward off the wing, at the same time as the prop thrust is trying to pull the engine mount forward. Guess what: since the airplane can't stretch in both directions, you need to subtract the number of pounds of the rearward flap push from the number of pounds of the forward pull, to get the resulting NET achieved forward force.

So if you spend as much of your takeoff roll as possible without the flaps being pushed rearward by the prop blast, all of that thrust is used to move the airplane forward. The airplane will accelerate forward measurably faster with the flaps retracted.

But we also know flaps create lift, and allow the airplane to lift off the ground sooner. Ain't gonna win no STOL competition leaving the ground with the flaps in cruise position are we?

So the compromise is to start the takeoff roll with the flaps retracted, making the least amount of drag, and the flaps not being pushed rearward by a 40 knot prop blast. When we reach the minimum speed at which the airplane will fly with the flaps deployed, THEN we deploy the flaps and the airplane can fly. We will have reached this point in some measurably less time and less distance.
 
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BJC

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First of all, that AOPA video is nonsense, they did not test all possible combinations of flaps, tail up, tail down, etc. I tried to contact that guy and ask him why they did not test one or two particular methods, and the arrogant chimpanzee couldn't be bothered to reply. He's every bit as un-biased as the news reporters from the major TV networks.
That is typical of the arrogance of many AOPA employees / writers.
the energy created from that "fringe benefit" that raised the tail still has to come from somewhere. No free lunch.
The thrust vector with the tail raised verses tail lowered is significant (around 3%) for most tailwheel airplanes. A tricycle gear doesn’t need to use some of the engine power to raise the tail. Note that, with proper technique, my Cessna A152 had a shorter T/O distance than a C152 with a STOL kit and a tailwheel conversion. Part of my advantage was that I could rotate enough for max Cl, and the tailwheel could not.
So the compsomise is to start the takeoff roll with the flaps retracted, making the least amount of drag, and not trying to get pushed rearward by a 40 knot prop blast. When we reach the minimum speed at which the airplane will fly with the flaps deployed, THEN we deploy the flaps and the airplane can fly. We will have reached this point in some measurably less time and less distance.
Yup.


BJC
 
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flitzerpilot

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I think that on tailwheel/tailskid non-flapped types, ground attitude and wheel position relative to CG has a lot to do with the technique employed.

Pete Bowers' 1960s book, Guide to Homebuilts, recommended that the mainwheels be located between 12 and 20 degrees ahead of the vertical CG. This is a wide scope for reference and on my Flitzer biplanes I have tended towards the former.*

The Z-21 has a ground angle of about 15 degrees and uses a USA 35B wing section which, according to some tests at Langley in the 1920s, will hang on to lift at a much greater angle than that. The geared Rotec- powered Z-1R, by comparison swings a comparatively huge propeller, and has a steeper ground angle of some 17 degrees, added to which the incidence employed adds another 1.0 -1.5 degrees pitch to the wings. Thus, with this section, full-stall three-pointers are easily achieved.

On take off (Z-1 prototype with an 1834cc VW motor, weighing 480 lbs tare) after only a few seconds with the stick held slightly forwards, the tail rises easily and with no effort. After which acceleration continues smartly with the stick centered. With the change of attitude the mobile CP migrates forwards and there is almost no load on the stick during the remainder of the take-off roll which lasts maybe 6 seconds (quicker on tests performed some years ago at light weight - see images). Keeping the tail down or low rather than 'streaming' the elevator in a level attitude would increasingly add to drag and extend the take-off. Equally, there is no forward view with the tail down so on narrow strips it's important to raise the tail to avoid excursions, although the powerful rudder quickly sorts things out.

If left to its own devices, the aeroplane is perfectly trimmed and thinks it is flying, so would continue until ramming the scenery, so positive back pressure is required to levitate. At an earlier time I used to fly a Piper L-4H from a steep hillside strip. The technique there, depending on wind direction, was to point it down hill and stand on the brakes while raising the tail, increasing throttle into a level attitude, then slowly releasing the brakes. The aeroplane would become airborne in a very short distance. Failing to raise the tail going downslope would result in a very high AoA, increasing drag and extending the take off.

It's largely dependent on type experience, topographical and other conditions, so I am not recommending this as a general rule.

*On my Flitzer-Laird (which appears as my 'avatar'), the main undercarriage features a vertical front leg in side-elevation, so the mainwheel is somewhat further forward than on most Flitzer variations, similar to the position on the Wolf Boredom Fighter. The decision for this was partly a styling exercise, to replicate various Laird racing types, the LC-1W being a scaled hybrid, somewhere between the early Solution and the Warner-powered LC-DE. Of course the Flitzer range are smaller aeroplanes generally, but because of using Verner and Rotec radials which swing big propellers, the ground angles mimic those of the original racing machines. Those Lairds were chosen for 'near-replication' as they featured 'A'-frame cabanes, lower wing ailerons and simple 'I' interplane struts, all of which were also Flitzer design features, see second image.

The more forward-located main wheels will reduce any tendency to nose-over (injudicious use of brakes while momentum remains can cause a rapid somersault) but is more likely to induce a ground loop without proper attention and anticipation. The latter comes with experience and a feel for the tendency of the machine to wander on the roll-out. Airmanship is the key.
 

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TFF

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STOL flying is high performance flying just like aerobatics. There is nothing student pilot related.

The STOL planes have been evolved well beyond stock Maule or Cessna 180. To watch a Highlander pull off a takeoff and landing in 60 ft is pretty crazy. It’s also very precise. It’s all pilot taking advantage of the plane.

The Highlander is tail wheel is not normal. It has at least a foot of compression available. Probably two. There is an AOA advantage if you can compress that tail. Remember they only need to leave the ground and stay in ground effect to get full flying speed. Just an inch of altitude and hold it up until they are away. You slam a 180 tail down like that and the whole airplane is shuttering. Along with dumping the flaps right when they rotate, the game is to get off the ground under stall speed and accelerate in ground effect.

That’s all perfect skill with the perfect plane. Everything else notches back. You don’t have the tail wheel, you shouldn’t be banging it. Don’t have quick deploy/retract flaps, it’s not going to be optimal. Prop, mains, VGs, slats... until you end up with a stock plane flying bush. There are lots of those doing a good job.

Watching these planes, people think they are all the same size. They are not. C180 is an airliner in this group. Most planes are in a crash, at the rate a Highlander touches down or or really slams. Pegazar is not dainty like a Kitfox or 701. A working bush plane in Alaska pulling a moose carcass out is not the same as playing on a sandbar for kicks.
 

Dan Thomas

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You are basically transfering lift from the tail to the wings by bringing the tail down to spring the aircraft into the air......banging the tailwheel on the ground renders the technique mute.
It's hard to explain in words but basically think of the aircraft as a lever....push down hard enough on one end (tail) and the other end (nose) wants to rise.

You will feel the transfer of energy from the tail to the wings when the tail gets yanked down hard.
It really feels like being on final and pulling back to round out for the landing.....during the majority of the glide the wings feel like they aren't even there for the most part...but when you pull the tail down to round out just before you touch down....you get a sudden sensation of all the lift and energy in the wings.
You're not transferring lift from the tail to the wings. You're increasing the angle of attack of the wing and creating more lift.

In the landing flare you're increasing the angle of attack again and flattening the glidepath. You feel the G loading, that's all.
 

Dan Thomas

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When I flew the larger taildraggers I raised the nose a lot sooner than 40 or 50 MPH. The tail will come up on its own before that anyway, because the wing is behind the main wheels and it's lifting. There's a common misconception that lift isn't being generated until it lifts the airplane off the ground, and that misconception has caused an awful lot of accidents. People think the flight's over as soon as the wheels touch down, and they relax and the airplane gets away on them. Crosswinds are a particularly bad place for that. That wing is lifting anytime there's airflow over it front-to-back, and stall speed has nothing to do with it.
 

wsimpso1

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The modeling to run all of this is doable, but kind of big. And anyone with an opinion can call it invalid or lacking fidelity to reality, etc, including the author. I am not going to run it until I run out other of stuff that is more important to me. Now someone really interested in finding out could start doing this...

I will say a few things.
  • The drag at low speeds on the wings and tail are pretty small and an order of magnitude less than the lift they are making, but still something;
  • The drag on flaps and elevator from prop wash is measurable, but still an order of magnitude less than the lift they are making;
  • All drag is subtracted from prop thrust;
  • The cosine of 15 degrees is about 0.97, which means that the prop at static deck angle delivers about 97% of its total thrust to accelerate the airplane;
  • The sine of 15 degrees is about 0.26 so the prop at that angle is lifting the airplane with about 26% of its thrust, but it is well forward so it must be balanced with elevator inputs that do cost you something;
  • Suddenly dropping the tail works for getting the tires off the surface by increasing the wing AOA. Other effects follow;
  • Big elevator at rotation speed causes the airplane to try to rotate about its CG - the main wheels of a taildragger are forward of the CG and will be lifted some by this rotation. If the lifting is more than the gear deflection prior to rotation, the tires could come free during the rotation, before the CG actually starts going up;
  • A tricycle gear airplane will rotating the main tires further down during rotation, which will shove up on the CG, which may actually give enough upward shove to make some difference.
Have fun guys!

Billski
 

poormansairforce

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You're not transferring lift from the tail to the wings. You're increasing the angle of attack of the wing and creating more lift.

In the landing flare you're increasing the angle of attack again and flattening the glidepath. You feel the G loading, that's all.
Actually you're transferring down force from the tail to the wing. So VBs probably right with the idea of which way produces less drag/more thrust to get to flying speed.
 

WBNH

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Don't know if it was already mentioned (didn't read every line)...but I think the off-field guys are generally trying to get the nose down quickly on takeoff to see obstacles ahead, not necessarily trying to get the tail up.
 
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