Anon asked in Cars & TransportationAircraft · 7 years ago

How does a STOL aircraft wing differ from a wing currently used on modern civil airliners?

Based on aircraft forecast models, and the potential for growth in developing countries is high, I have decided to do my final year aerospace engineering research project on designing a new STOL 150 seat airliner. I understand that STOL wings have low takeoff/landing speeds, but disappointing cruise performance, but I dont understand why that is the case when compared to modern airliners.

6 Answers

  • 7 years ago
    Favorite Answer

    Lift is related to airspeed (squared), lift coefficient, and wing area.

    Interestingly, drag is also proportional to the square of equivalent airspeed , area and a coefficient, but this time drag.

    The airfoil is selected in such a way as to maximize the lift to drag ratio. The problem is that the lift to drag ration will be optimal for a very specific lift coefficient; usually this is the lift coefficient that is required for cruise, since aircraft would spend most of their time during that phase of flight.

    If the lift from that airfoil is inadequate to takeoff in a reasonable distance, then the airfoil basic shape is altered through the deflection or deployment of auxiliary surfaces, like slats and flaps. There is a price to pay for this, since the lift to drag ratio would not be as good as for the cruise, but if there is enough reserve power, more engine thrust is called upon to make up for it; as takeoff is a short duration operational phase, the extra fuel needed is a limited expenditure.

    In the case of a STOL, the balance between the cruise and takeoff lift to drag may be altered to accept a slight reduction in the cruise in exchange for an improvement in the takeoff characteristics.

    It could be seen that, with a much larger wing, the takeoff speed could be reduced (and with a lower speed comes a shorter runway run to reach that speed), while in cruise, the wing could have to operate at a lower lift coefficient than optimum as a consequence, i.e. the aircraft is hauling around a wing that is larger, and therefore more draggy and heavier, than needed in cruise.

    Source(s): Aerospace engineer
  • Texas
    Lv 7
    7 years ago

    A STOL aircraft wing may be bigger and thicker to generate higher lift or better low speed handling.

    The increased surface area and frontal area also increase drag which reduces top speed and increases fuel consumption at higher speed.

    STOL aircraft also requires very high power to weight ratio to take off in short distance, and the large engines and fuel for them offsets your payload capacity, and at cruise speed the engine is operating at lower % of maximum output so you get lower volumetric efficiency and thus poorer fuel economy. It is definitely not the cheapest way to fly. Long term the developing country in question will do better to field a conventional airport where commercial aircraft may safely land.

  • 7 years ago

    Study AIRFOILS. Those that are good at producing high lift at low speed cannot provide high-speed cruise performance due to high drag. Even with slats, flaps, slots and other devices, you can only do so much with an airfoil. The problem has been studied intensely for over 70 years and there is no way around the compromises one must make. You will also discover that prop-driven aircraft are much better in STOL operations than jets, and propellers themselves have size and speed limitations. .

  • John R
    Lv 7
    7 years ago

    To obtain the required lift for flight at lower speeds you ether have to increase the coefficient of lift, or increase the wing area.

    There is a limit to what can be achieved in improving the CL, so along with high lift devices like large flaps, slats, and VG's, a true "STOL" plane has to have a lower wing loading.

    You can stow flaps and slats in cruise, but that extra wing area is not needed for, and is detrimental to, high speed cruise.

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  • 7 years ago

    An aerospace researcher that doesn't understand the effects of thickness and camber. Exactly where is this research project being done?

  • JetDoc
    Lv 7
    7 years ago

    There are DOZENS of books written on the subject. I'm not going to waste my time trying to reinvent the wheel. Go read one.

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