What exactly makes a plane be STOL?

Discussion in 'Aircraft Design / Aerodynamics / New Technology' started by Timstertimster, Apr 19, 2014.

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  1. Apr 19, 2014 #1

    Timstertimster

    Timstertimster

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    I'm impressed. Watching YouTube videos of people in a Zenith or Highlander taking off in what looks like 45 feet. Awesome.

    I realize some of it is head wind. But what else has impact on fast climb rate?

    Reading posts like this one makes me realize how utterly uninformed I still am. Sigh...

    Then there is engine stuff, right? Need power high RPM to create enough wind for the plane to climb, right?


    If you're so inclined, please feel free to educate a newbie on some basics. I hope to one day be as knowledgeable as many of you appear to be.
     
  2. Apr 19, 2014 #2

    akwrencher

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    I'm not nearly educated enough to give you the long answer, but one of the big things that makes short take-offs possible is the wing design. STOL planes have wings that are optimized for slow flight, so they develop lift at a slower airspeed and hence become airborne much quicker than, say, a Lancair, which has a wing optimized for speed at higher altitudes. The trade off is usually higher drag and slower top speeds. STOL planes tend to have larger wings (more surface area, less pounds of airplane per square foot of wing). Usually a longer slower turning prop is used, smaller higher speed props give less static thrust and do not accelerate the plane very quickly at first. Lot's of other details, but that will give you the idea. Hopefully one of our more educated members can add to this. Welcome to the forum.
     
  3. Apr 19, 2014 #3

    Dana

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    Low wing loading and an appropriate airfoil give low stall speed, and plenty of power are the basics. Extra power accelerates the plane to stall speed quickly so you can get off the ground fast, and that extra power translates directly into rate of climb. A good climb rate at low speed means a good climb angle, which important to get over those tall trees. Most STOL planes also have largish flaps to optimize the airfoil for low speed without too much of a hit on higher speed drag.

    Dana

    No trees were harmed in the transmission of this message. However, a rather large number of electrons were temporarily inconvenienced.
     
  4. Apr 19, 2014 #4

    GESchwarz

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    At low airspeeds the flight controls need a little boost of energy to maintain authority. There are a couple of ways to do this. One is to install vortex generators, or VGs. VGs generate a high velocity vortex across the surface which prevent the surface from stalling. The second way, particularly for ailerons and flaps is to drop them down into the high energy air below the wing; this configuration is called the Junkers aileron.
     
  5. Apr 19, 2014 #5

    4trade

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    [h=2]What exactly makes a plane be STOL?[/h]
    Most of all, RAW power and low wing load.
     
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  6. Apr 19, 2014 #6

    autoreply

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    Except for the above... optionally high drag In landing config. Landing short is useless when you can't land steep for real world operations.
     
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  7. Apr 19, 2014 #7

    BBerson

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    Low weight, good thrust at climb ( climb prop), tall landing gear for good static angle, big flaps and big wheels and long stroke gear legs for high descent angles and landing impacts. And some powered lift and good brakes.
     
  8. Aug 27, 2014 #8

    han

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    Flight at high angles of attack allows the propulsor to rais the CL , I think the storch had a CL of about 4 with the propeller turning .
     
  9. Aug 30, 2014 #9

    Two lane aviator

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    low wing loading, high power loading, high CL airfoil, high AoA before stall, low stall speed, reaches CL max easily, high drag, steep TO and landing, and beefed-up structures and landing gear.
     
  10. Aug 30, 2014 #10

    D Hillberg

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    STOL It's when you can take off across a run way NOT ALONG IS LEGENTH
     
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  11. Aug 30, 2014 #11

    DangerZone

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    An educated guess might come to something like this:

    Available thrust / wing load x the possibility of airfoil change, and for landing the addition of + stopping power (reverse thrust or baking action).

    Plain and simple: The more power/thrust there is and the less the wing loading multiplied by the airfoil change with slats/flaps results in better performance. The braking action and reverse thrust add to shorter landing, because landing is usually longer than take off.


    However, the trick is not to fly as slow as possible all the time but to fly slow while landing or taking off and flying fast while in cruise. If XSTOL aircraft are considered, then the Slepchev Storch with a good pilot might outperform many SuperCubs, Zeniths, Highlanders. Yet in cruise all of them would pass the Storch easily, cause the airfoil of the Storch is limited to slow flight.

    [video=youtube;x8eg-A8GT7U]http://www.youtube.com/watch?v=x8eg-A8GT7U[/video]

    The Pilatus Porter can take off and land in 50 feet, and has an impressive cruise speed for such a heavy and slow flying aircraft. The Slepchev Storch is a great example how a good aircraft design like the Fiesler Storch can be rescaled for homebuilt use. The same way a Porter could be rescaled, it might be a great aircraft for both bush/mountain flying and a long cruise across the country.

    [video=youtube;92ErTsiMwLw]http://www.youtube.com/watch?v=92ErTsiMwLw[/video]

    What determines success of an aircraft is not it's performance or XSTOL capabilities but most usually the price/cost of manufacture/building. I was once asked if the Porter could be rescaled for homebuilt use as a 2+2 seat aircraft and the answer is yes, even with better performance and tricycle gear and the use of a turbocharged motorcycle engine. But when we put it all on paper there was no way to beat the price of a Zenith or other similar metal aircraft.


    The 'best' aircraft would be one that could land high in mountains on short strips with 2 big adults and heavy baggage with a stall speed of 20kts, would have great carrying capability (thus a high coefficient of lift at takeoff/landing or heavy loaded) and the possibility to retract slats&flaps to have a nice laminar profile during cruise at 150kts an hour. Is it possible? Yes. Is it feasible and economically rational? Probably not, cause building such an aircraft would require +2000 hours so the price would be too high. Thus most people would rather opt for a solution to have the cheapest airplane they can get that has performance best suited for the way they intend to fly. And there is plenty of STOL aircraft that match this criteria, from SuperCubs to SuperStols/Highlanders and Storches.
     
    Last edited by a moderator: Mar 20, 2019
  12. Aug 31, 2014 #12

    clanon

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