STOL take off technique

Discussion in 'Rules and Regulations / Flight Safety / Better Pil' started by PTAirco, Aug 14, 2019.

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  1. Aug 15, 2019 #41

    PTAirco

    PTAirco

    PTAirco

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    Back to the topic, class! What is the best technique to minimize ground roll in a tailwheel airplane? Smooth runway, not long grass or gravel bars. Substantiate your answers, with physics and aerodynamics please.
     
  2. Aug 15, 2019 #42

    BJC

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    All good questions, narfi, and you are much closer to the industry than I am.

    Here is what I know, and I can't get more info because he died from long-term complications from an injury (shot in the abdomen by the VC) suffered while serving in SE Asia.

    He operated charter and scheduled flights.
    He owned and operated a top tier fishing and hunting lodge.
    He owned and operated an aircraft maintenance operation.
    He owned and operated a variety of aircraft from Super Cubs to Twin Otters, so none of the big stuff.
    After he moved back home to Florida, he bought, rebuilt and sold Beavers in addition to operating an aircraft maintenance and inspection shop.
    I asked him what his favorite bush airplane was. He said that it totally depended on the specific mission, but "the C206 is the best money maker."


    BJC
     
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  3. Aug 15, 2019 #43

    Aesquire

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    Given that long grass and mud require different technique, and we are talking a tail wheel on hard, smooth ground.
    And there's no clock ticking. It's distance.
    And it can be very different for different planes. How much flap, if there IS flap, and the exact speed you rotate.

    I'll go over how I was taught in a Citabria 150 horse C model with the longer wing, by a foot. :)

    Stand on the brakes and run the throttle up until you are on the edge of skidding. That gives max thrust as soon as possible, as you waste no distance on the throttle-up to that point. On the Citabria, at that point you are pulling back stick to keep the nose from going down and hitting the prop.

    Release brakes as you throttle up to max, smoothly but swiftly, and relax back pressure, letting the tail rise. Don't hit the prop. when you hit the magic number ( varies by weight, call it 47 mph ) or feel it lift, ( because your head should be out of the cockpit ) pull back to unstick and apply half flaps, doing both with speed and authority. Immediately put the nose back down and gain flying speed in ground effect, 55 mph and smoothly begin climb.

    The rationale for letting the tail rise without pushing the stick forward was that you want minimum drag, and the less control deflection while accelerating the better. But, the more level the wings, the better, too. ( for all the reasons given by better pilots above )

    The flap manipulation is also to minimize drag, but for other than short field take offs, just set them and take off.

    It was emphasized that smooth, but fast, rotation and lifting off was the most important part, that minimized distance and ground drag AND uneven inputs from the gear if you, or the ground, wasn't quite straight. #2 was getting the nose back down, smooth but fast, to get up to full happy flying speed.

    Generally I was flying off a smooth grass strip, so early mistakes pulling off too early just had the plane settle, and gently bounce back into the air. Bad for the Ego, and enough of an adrenal squirt to teach you not to lift off too soon. YMMV

    I found that in hang gliding, the need to keep the wing at minimum drag on takeoff run was even more important. Really low power available. Rotation varied depending on the take off site, but again, smooth swift and with meaning was generally best. ( there are exceptions )
     
  4. Aug 16, 2019 #44

    PTAirco

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    Hm. An aircraft should leave the ground when its lift equals its weight. Ergo, the object is to create that lift as quickly as possible. The argument is that by raising the tail you reduce drag, helping you to accelerate. Fair point. However, with the tail low and letting it accelerate, you're creating lift from the start. Less wheel drag on the ground since the airplane is getting lighter on the wheels from the moment you start to move. Especially with big soft tundra tires. (Ever tried pushing one of those?) I suppose you'd have to plot lift and drag plus ground friction for the entire airplane versus distance covered, with whatever technique one favors and the see what comes up. I'm a firm believer in real numbers, rather than "we tried this and it's better" . Too tedious to work out for this hot afternoon though...
     
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  5. Aug 17, 2019 #45

    TFF

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    It’s creating lift when the tail is up too. Most planes fly level. Tail down is trying to use lift right from the start but with great drag penalty. Tail up has to use a little lift to normal flying attitude and that is drag but a lot less drag than tail down.

    If you want to talk comfort zone, and whole different game. I’m not comfortable holding the tail up, modulating the brakes perfect, and leaving the ground right at ground effect and accelerating into out of ground effect lift in 6 seconds from zero. People say I want a STOL plane because they stall so slow I’m safe. STOL is precision flying. Much the same as the perfect aerobatic maneuver. A short takeoff plane operated normally is short for me. Anything more is pushing my skill.
     
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  6. Aug 17, 2019 #46

    Aesquire

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    I agree, my tailwheel time was long enough ago that it wasn't a rating. And not enough time in type to be playing expert games balancing the plane on the wheels, brakes vs. thrust. That's why I was taught the "hold the tail down until you release the brakes" technique. If I'd put another 100 hours in my instructor might have taught me more advanced skills.

    This was in my days of going to the gliderport, retrieving tow lines, walking tow lines, holding wingtips, and, yeah, sweeping the hanger. Then at the end of the day, or sometimes lunch, wind & light permitting, I'd drive up the mountain and fly off in my hang glider. Yes, I got a LOT of ribbing for that, until I got good enough to occasionally outclimb a guy in a thermal. Come to think of it, the ribbing never went away, but it never bothered me anyway.

    The technique above is also more or less how you take off with a glider on the line behind you. Gliders will lift off before you, and every take off is a STOL type and slow climb to keep to the glider's preferred tow speed.
     
  7. Aug 17, 2019 #47

    Victor Bravo

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    You should have seen the look on most of the tow pilot faces when I had the line boy run up there and tell him I needed a minimum of 70 knots for the first 800 feet ! They thought I was crazy. I was of course, but I wasn't wrong about that.

    ( I'm guessing you didn't have 11 and 12 pound wing loadings, 100+ degree temps, and 6500+ density altitudes where you flew gliders :) ) Not sure I'd want to fly like that myself any more... ain't it strange what age does to pilots!
     
  8. Aug 17, 2019 #48

    henryk

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    I propose return to the aerodynamic=Lift Coefficiant (Cl) is not constant...

    the moore acceleration, the moore Cl (called Cl dynamic ),concerned with vortex flow.

    a=F thrust/ m = moore Thrust, moore Cl dynamic.

    f.e. the electric booster to the IC motor...
     
  9. Aug 17, 2019 #49

    12notes

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    The object is not to create that lift gradually as soon as possible, it is to have that lift available and use it as soon as possible.

    Lift isn't free, it creates drag. By having the wing at takeoff angle of attack, you're maximizing induced drag for the entire takeoff roll.


    Or, you could just test it on an actual airplane. Which people here have said they've done, which the people up in Valdez have definitely done, and have come to the same conclusion, lift the tail for shortest takeoff. You're not suggesting a brand new technique that's never been tried before. That video posted doesn't ever use the recommended technique, he starts with the flaps at 10 degrees, and increases them to 30 degrees at about the midpoint of the roll, and uses almost no rotation, the tail is nowhere near the ground when lifting off. Look how high the tail is compared to every other takeoff from that video. He waited way too long to rotate, and put the flaps on way too early.

    In the battle of calculated numbers vs. reality, reality is still undefeated.
     

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