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STOL Performance Observations

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  • STOL Performance Observations

    I was looking for a thread summarizing STOL performance and slow flight, without success, so this could be such a thread.

    We had a run of clear and calm mornings lately, so while out flying, I took the opportunity to do some slow landings to re-confirm the STOL performance of our Bearhawk 4-place. With the aircraft modestly loaded, around ¼ fuel and one person, the Bearhawk was running out of lift at ~37 kts GS (almost stalled) and touching the ground at ~33 kts GS allowing a half-second for measurement. Approaches can easily be flown below 40 kts indicated and GS. I'll explain the method below.

    As a preface, this was an opportunistic performance check for interests sake, not a pre-planned exercise. So hold any questions on experiment design - this is only a practical check. My method was rounding out and holding off during the flare using a small amount of additional power, and using the GPS speed to confirm slow flight speed at steady-state pre-touchdown. I did landings on several different different vectors (the vectors are arranged in a triangle) to help identify the effect of any imperceptible breeze. All landings considered, it seems the practical results are +/-1 knot. Ambient conditions were about 200 ft AMSL, with temperature and pressures approximately at ISA for that altitude - which was convenient!

    It’s hard to fly an aggressive STOL landing safely, with eyes inside the cabin monitoring speeds, while holding the aircraft at steady state pre-touchdown. Holding it a couple of feet off the ground, in other words. For that reason I didn't do an aggressive STOL landing, just an "average" STOL landing with a small margin for safety. So these results are not the best possible result, like you would expect in a STOL contest scenario. The plane can certainly land slower if pushed to the limit.

    Note that our aircraft has extended hoerner wingtips fitted, not the common rounded wingtip.

    So to summarise:
    Approaches 38 kts
    Rounding out / flaring at 37 kts
    Touchdown somewhere just above 33 kts, without pushing it too hard.

    Of course the safety caveat - each homebuilt aircraft is different, has different performance characteristics, and air conditions do vary. Please fly to the ambient conditions and your own aircraft's limits!

    I think this is awesome performance for an honest 4-place aircraft.
    Over the years, the 4-place has certainly allowed us to keep up with Super Cubs, in terms of landing on the shortest gravel bars etc. Given the high cruise speed and low-end STOL performance, it's hard to beat.

    The best fun is had when very lightly loaded, with a cold high pressure morning, and a steady headwind. The plane can do some truly amazing things on those special days. For instance, a 30% climb angle with decent headwind is practically achievable from a standing start - measured over the ground, not through the air. Again, this is about practical or "useful" STOL performance, rather than a highly accurate measured result. Being able to land two full grown men and a decent load gear in a 60 metre (200 ft) space is a lot of fun, and challenging. Lately this has proven useful, on a couple of occasions.

  • #2
    Great stuff, I would be more than happy with an approach at 45mph and touching down at 38mph.

    Can you give us some ballpark numbers on takeoffs?
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    • #3
      I would like to caution everyone that Jonathan is an exceptionally capable pilot. With 800+ hours in his plane. His BH also has VG's as well as the Hoerner style wingtips which both help lower stall speed some. My point - don't assume you can safely use the numbers Jonathan reports. Pilot skill is the most important factor in this STOL flying.

      Another situation where pilot skill made a big difference: Bob Barrows & I were coming back from a trip to the kit factory in N303AP. When we got back to my home airport, the winds were 60-90 degrees crosswind from the right 25 kts gusting to 30 kts. Bob was flying fortunately. He planted that right wheel on the runway and made it look pretty easy. If I had been flying it would not have turned out as well. The plane is plenty capable. In a lot of cases, pilot skill is the limiting factor.

      Just a cautionary note for you guys to practice before exploring the edges of what is possible. Mark


      • #4
        Originally posted by Utah-Jay View Post
        Can you give us some ballpark numbers on takeoffs?
        Well - that's a tougher one to investigate for a casual observer like me Having full power applied is a large part of the take-off equation, so holding the aircraft at steady state to make observations isn't an option. It happens very fast in a IO-540 powered ship.

        Horsepower is a huge factor here, but ultimately thrust (ergo horsepower plus prop selection) and weight have most influence for given set of ambient conditions. Unless there's long wet grass or similar reducing acceleration...

        ​In the conditions mentioned in the original post, I would expect to see the aircraft breaking ground somewhere between 30 and 40 metres (100 to 130 ft) ground roll, and developing a strong positive rate of climb almost immediately. During takeoff, airspeed is changing so quickly that its hard to make any coherent observations about airspeed. We are using the Hartzell Trailblazer prop with two blades. According to the Lycoming performance charts, at our measured manifold pressure and RPM limit, we are seeing between 270 and 275 horsepower under standard atmospheric conditions. We do get noticeable ram air effect, which helps.

        Clearly takeoffs become a lot of fun as conditions become more favourable. A headwind kinda breaks the conversation, as in theory you can take-off on the spot with a steady 35 kt headwind.
        With a steady headwind in that comfortable range between 10 and 20 knots and favourable ambient conditions, takeoffs can be shorter than 25 metres (80 ft), or about three plane lengths - as lightly loaded as can be.

        A three-blade carbon prop with wide paddles should further improve both take-off and landing distances, offering both more thrust and more drag.
        Last edited by Battson; 11-05-2023, 07:29 PM. Reason: Fix typos


        • #5
          Battson thanks for the response

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