Shortfield Takeoff Technique

[flat country pilot]

I believe that keeping the plane clean during the initial take off roll will result in the shortest take off distance. Nuetral elevator and let the tail fly itself naturally but keep the tail wheel as close to the ground as possible. This does give the greatest AOA and I believe the shortest takeoff roll.

In previous discussions on this website is the dilemma of larger tires increasing the AOA and therefore shortening the takeoff roll. Not everyone here agrees that increasing AOA with larger tires shortens the takeoff roll.

If keeping the tailwheel on or near the ground to increase AOA shortens the takeoff roll, then why not use larger tires to increase AOA and shorten the take off roll? Granted the larger tires increase weight, they should roll easier on grass, soft or rough strips which is where we want the shorter takeoff.

Bill

[lowNslow]

Good discussion and all good comments. But many times it is more than the length of field that must be considered.
1. long vs. short runway. What determines a "short" runway?
2. rough/soft field vs. hard surface. Is it really going to matter if you roll the tailwheel on a smooth surface? How rough before it starts to seriously affect acceleration.
3. headwind vs. crosswind. Do you really want to pop that tailwheel up as soon as you can with a stiff crosswind?
4. density altitude. Do you really want to use 20 degrees of flaps?
5. obstacle vs. clear path. What combination is going allow us to clear that tree?

You all could probably come up with more, and I'm not sure that there are right or wrong answers to some of these questions. I would just point out that although we like to boil things down to a simple technique we may sometimes have combine several techniques depending on the situation.

[AR Dave]

AR Dave,What do you mean "use the wing" to determine takeoff timing?

Add full aileron on take-off. When accelerating, the wing will start to rise, indicating airspeed. The plane will be in the air by the time the aileron can be balanced. There's a lil more detail to it, but that's enough to warrant a tongue lashing!

When the plane rolls up onto one wheel the wing can now reach a greater angle of attack without dragging the tail. If your airplane is like all other 170’s you will notice that when doing a full stall landing that the tail touches first. This means that the airplane will fly at a greater angle of attack than it sits on the ground.

[GAHorn]

Taking off with full aileron deflection will indeed give an indication that a wing is producing lift. Unfortunately, it is not possible for both wings to have the same lift since the high-wing has more camber due to the applied aileron (which is down and, therefore contributing induced drag which counters idea of it being a helpful technique for shortening takeoffs.)

The shortest takeoffs will also be made with the least induced drag, which is the point of my earlier comments. By the time the average pilot sees one wing leaving the ground because of applied ailerons, then he's already wasted valuable runway that he could have already left behind with a more efficiently configured airplane. (Bluntly, this is a sloppy, un-co-ordinated, cross-controlled takeoff technique. It's a takeoff in a forward-slipped configuration which wastes available lift. The airplane will fly as soon as BOTH wings develop sufficient lift, and that can be more accurately discovered by a tail-low, co-ordinated technique.) The only reason to apply ailerons on takeoff is for crosswind technique, in my opinion.

[voorheesh]

When your taking off on glassy water, it is common to lift a float off with aileron. The other float then comes off easier. You get off the pond quicker. Of course you are overcoming water drag and I guess that is not the same as the surface on a runway or a strip. On rough water, flaps (sometimes 30 degrees in a Cessna) are helpful in getting off because they give better lift at slower speeds. This might help on a rough field too.

[ak2711c]

Again george we are talking soft field ops here. I have been in the situation many times when I had my stock motor where the strip was soft enough that it would just phisically not accellerate to lift off speed no matter how long the strip was. In this situation the only way to get the plane off the ground is one wing at a time then it comes right out. I am not advocating this technique for standard practice but it is a valid technique to keep in your back pocket in case you need it.
Shawn

[GAHorn]

Yeah, .... we're also measuring takeoff rolls with a micrometer too. I was just conversing theoretically.
The smooth-water takeoff can also be shortened by first roughing up the water (backtaxying) to get a little air under the float. But I ain't no expurt on floats.... (or anything else really, either!)

[KMac]

I learned taildragger in a decathalon and when I started flying my 170 I was trying to force her into the air before she was ready. This resulted in a very sloppy take off. I agree with what George wrote about the least induced drag allowing the shortest take off. I have an A model and when I used the first notch of flaps it SEEMED to take longer to get air-borne . With unscientific measurement (the feeling in my posterior) I think my old girl defies gravity quicker when I can get the tail up to a point where I can balance the drag caused by the AOA and the Lift caused by the AOA and then be patient enough to let her start flying. I have tried a couple of times to get the airspeed up (tail up) and put in the first notch of flaps to shorten the take off. It seemed to help a little. Have any of you tried this with any success?

[dacker]

KMAC, I use two notches quiet a bit on my A model. On one of our 100 degree high DA Texas days I don't see any benefit, the extra drag by far outweighs the benefit of what little extra lift our flaps provide (they do provide extra lift though). During the winter I believe that I can see benefit in getting off the ground faster... climb to 50' seems to be slightly improved. I guess it falls down to what the DA is. The Pilot Manual seems to think there is some benefit to use of from two notches to full deflection of the flaps for getting off of the ground faster, but doesn't go into much detail.
Bottom line for me when I am playing... if is somewhat cool I pop two notches, if it is hot it doesn't matter much. I think that we truly are measuring with maybe not a micrometer but with a ruler.
David

[flat country pilot]

I like the tail as low as possible for take off, but not touching the ground. This provides the greatest AOA with the tail wheel off the ground. If I would go measure with a yard stick, the plane leaves the ground in about 500'. I have not measured this with anything more accurate than stepping it off.

If I switch from 7.00s to 8.00s or 8.50s to increase the AOA and provide less rolling resistance, will the plane leave the ground in 450'?, 400'?

This discussion sure gives a list of reasons to go burn some gas and do a bunch of stop and gos. I can't wait. Might have to make a list of ideas and find some one to spot and measure for me. Maybe take videos. -15F here this am so the spotter won't be my wife.

Bill

[AR Dave]

Taking off with full aileron deflection will indeed give an indication that a wing is producing lift. Unfortunately, it is not possible for both wings to have the same lift since the high-wing has more camber due to the applied aileron (which is down and, therefore contributing induced drag which counters idea of it being a helpful technique for shortening takeoffs.)

As you apply full power add full aileron one way or the other depending on wind or direction of turn after take-off. Your aileron will be the airspeed indicator and as you learn the technique it will be very accurate. As you are accelerating you will notice the wing starting to rise, this is your first sign of Airspeed. In the amount of time that it takes to roll out half the aileron slowly and add a little more back pressure you will be in the air.


George do you remember Kelly Mahon from Priest, Idaho? He worked his 170B, Part 135, backcountry? He is the STOL Pilot that uses this wing rising technique when he abolutely has to have maximum performance. He says that the wing rising is the only speed indicator that he can afford to trust in these situations. Off the ground too early or too late is not optional. He said that it is an ugly technique and only used for absolute maximum short field take off performance. Any other time he uses 20 deg flaps, wheel 2" off runway, etc..

The only question I have is how did you measure the landing distance? It doesn't matter what the roll is. It matters where you stop in relation to the end of the runway. So was that 200 ft from the end of the runway? You have to have good spot landing ability to make truly short landings. My test that I use for good performance at my home field is this: The first taxi way at my home airport is 800' from the end of the runway. So the goal is to touchdown, stop, and take back off before reaching the taxi way. That is relatively hard. Our elevation is 2200' and my stock 170 can do this with two souls on board and better than 3/4 tanks. A 250' landing is a good consistant number. My short record was 165' from the end of th runway with 8 mph winds at 40 degrees and 2200' elevation. Take offs solo are consistent at 400' the short one with a little wind was just under 300' light on gas and solo. I have flown my 170 into the Mile-Hi strip in Idaho that is 5600' elevation' and 500' long - solo, gas and camping gear. I'll post a few pix on the new 170 photo page.

Kelly

[futr_alaskaflyer]

-15F here this am so the spotter won't be my wife.

Bill

Maybe, but you can bet your takeoff distance will be shorter at that temp

[flat country pilot]

flat country pilot wrote:

-15F here this am so the spotter won't be my wife.

Bill
Maybe, but you can bet your takeoff distance will be shorter at that temp

Yes, you gotta love winter flying

And no damn bugs either

Bill

[GAHorn]

An excellent example of how unnecessary drag/too-much AOA can lengthen a takeoff roll is: In the first days of jet aircraft, there are several examples of a too-early rotation in which the aircraft picked it's nose off the ground but rolled the entire length of the runway and departed off the end without ever flying. Too much drag to accelerate to flying speed.

(Famous examples are: 1) The early Messerschmidt 262 with a conventional gear would not fly until the pilot hit the brakes to get the tail up into the air. Too much drag to accelerate to flying speed in the 3-point attitude. 2) Lockheed Jet Star in the early '60's, which ran off the end of the runway at Chicago Midway when the pilots rotated too early. Too much angle-of-attack... the wing was stalled before flying speed was achieved...and remained stalled throughout the attempt.)


There are NINE ways to make a takeoff. EIGHT of them are wrong.

Try this illustration that you can do yourself:

Draw a "Tic-Tac-Toe" square, as if you are going to play the game.
The first COLUMN will represent rotation that is too LOW. The second Column will represent JUST RIGHT AOA. ("Just Right" AOA is specific to each airplane/model.) The third column will represent TOO HIGH AOA.

The top ROW will represent TOO EARLY in rotation (before flying speed is achieved.)
The middle ROW will represent ON TIME, and the bottom row will represent TOO LATE.

As you view the graph, you will see that in every case except ONE... (the one in the middle of the graph).... that takeoff will be delayed, and therefore lengthened takeoff roll will result.

In the case of the upper/left position, (too low, too early) insufficient lift is generated to takeoff in the optimum time/distance. In the case of the lower/right position (too high/too late) too much runway has already been expended before flight occurs.

In every other case except ON TIME/JUST RIGHT, runway distance is wasted.

(In tri-cycle aircraft there is another variable which equates to the too-early/too-late rows... it is rotation rate. If an aircraft is rotated at too slow a rate it will result in delayed lift-off, as will an aircraft rotated at too great a rate. Industry standard is 2-degrees per second, so an aircraft which is to be rotated to 12-degrees nose up for takeoff will be rotated at a rate that results in complete rotation occuring over a 6-second period,... after reaching Vr .)

[hilltop170]

There have been many good points brought up on this thread about making the shortest take-offs. I have found one technique works best for me every time.

My airplane knows when it wants to take off, the less input it gets from me, the shorter it takes off. With the elevators in trail and trim set to just pick the tailwheel off the ground (1/16" would be perfect), will give the shortest roll. That is true whether I choose to use flaps or not. Load and DA determines if flaps will help reduce ground roll.

If I force the tail up, the roll is longer. If I try to pull it off, the tailwheel hits the ground and the roll is longer. The best tecnique is to be patient and let the plane fly itself off, it looks best also. I cringe every time I see other pilots flail their planes around trying to force them to fly.

Of course, crosswinds and gusty winds factor in to how you're going manage the takeoff but you best not be trying to get off in absolutely the shortest roll in those conditions anyway.