V-173 / XF5U - Flying Flapjack


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Light Plane Philosopher
HBA Supporter
Dec 16, 2007
Port Townsend WA
That'll do it to any light aircraft..
Right. I don't think the high aspect ratio of Draco was the direct factor in his loss of control. But the extreme low aspect ratio of the V-173 is more roll stable in the high angle transition to vertical hover. The V-173 stalls at around 40° and Draco may have stalled at around 25° with the slats. I don't have the data on slat wing stall angles.
Mike might have got away with that takeoff in a Helio Courier. The Helio has big spoiler knives in front of the ailerons and with full spoiler on the left wing it might have kept his left wing down.


Well-Known Member
Oct 31, 2005
Evans Head Australia
I’m sure there are dozens of “conventional” aircraft that you can buy/build that will have all of the specs. for Stol/speed/range, the formula has been done to death - overpowered Cub or similar, with slats an very large flaps.
To really push the envelope requires some unconventional thought and a step beyond. The ultimate STOL is not short takeoff and landing but standing takeoff and near zero roll landing - to accomplish this requires a very unconventional approach - helicopters can do it, jump gyros can do it and I believe a low aspect Zimmerman like fixed wing could do it. The challenge is the simplify the design for amateur construction.


Well-Known Member
Nov 17, 2014
Call 1-800-BAR-NABY
There really shouldn't be any question about the fact that low aspect ratio wings are less efficient than high aspect ratio wings, at the speeds we fly. But everything's a compromise, and making high aspect ratio strong enough takes a lot of structural weight. Those of us who haven't read all of Barnaby Wainfan's writings about how to make the low aspect ratio compromise work, should. ;-)



Well-Known Member
Apr 30, 2014
rocky mountains, rocky, usa
Low aspect ratio wings have distinct advantages and disadvantages, Cl(max) being a large one that is more complex and/or heavy to achieve in a higher AR design.

It's a pretty clever approach to a number of ideas for a range of reasons not yet mentioned.

The aircraft essentially exploits a blown surface approach and the AOA is no longer merely a function of the angle of incidence but the power as well. This is well documented in the reports from the flights.

My models use a rectangular Clark Y wing section with similar effect and takeoff vertically at a wing incidence of 45 degrees with a thrust line incidence of 20 degrees. In this configuration, pitch control is maintained with the tail surfaces still, albeit very marginal at the moment. Directional control is difficult until established in forward flight, but is mitigated by using a single ESC for both motors. Directional and pitch control are impossible s the thrust line incidence goes beyond 20 degrees (slipstreams too far inclined away from control surfaces).

My dreamy napkin calculations indicate that, scaling from my model, a twin engined, 200HP total design weighing 1400-1450 lbs would be able to take off vertically at a 6000' DA (with 200HP available) with approximately a 5% lift margin, or take off at 20mph in under 100' with a 9% margin at Cl(max) at that speed.

My only plans for this spring for the model is to add a pair of RC truck differentials to explore single engine operation after an engine failure. A differential is a torque mixer, essentially, and the link between the two does not rotate when the torques are equal. If the ESC's are set the same, then torque at the command RPM will be equalized, and perhaps the cross shaft could be monitored to make engine power adjustments.