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Home>STOL Flying
This is a series of articles that I intend to present on the specific challenges of
STOL Operations. 
Tune in for more as they become available.
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STOL Ops Tips
 
Full Flaps Take-Off Caution......
 
There are rumours abounding right now about an incident in northern NSW where a Savannah sustained minor damage from an aborted take-off from a short and very rough paddock.  The pilot’s incident report, already submitted, will clarify the facts of this particular situation, but I still feel the need to use this incident as a learning experience for all of us enjoying the challenge of STOL Ops.
 
I’ve talked with the pilot, who is considerably experienced and competent, and I think I understand pretty much what he was attempting.  Due to the very rough ground, he elected to use full flaps momentarily to  ‘jump’ the aircraft off the ground really short, then go to first stage flap while holding the aircraft down in ground effect to build up speed for the climb-out.  This is a recognised technique for EXTREME STOL Ops, and it sounds like he did it right, but the margin is so fine that many factors can make it go wrong very quickly.
 
Just imagine the situation – 100 hp at full bore, so heaps of torque trying to roll the aircraft about it’s longitudinal axis, high angle of attack so P-factor at max, rapidly changing angle of attack so gyroscopic forces at max, slipstream swirling about the fuselage – all these forces at max while airspeed is very low, so minimum aerodynamic forces from the control surfaces to counter it all.  It just didn’t balance out this time – very close but not quite........  
 
At these very fine margins, all it would take is a 2 kt wind shear on the most challenged wing to upset the balance.  And it was a hot mid-day in early summer, right next to a hill, so a bit of a random swirl in the air would be very likely.......
 
Yes, he had removed his slats and hadn’t yet installed the VGs.  But I really don’t think the VGs would have saved the situation, just as I don’t think the original slats would necessarily have done it either.  Just remember how a Savannah with the original slats could just about ‘hover’ by hanging on the prop at a very low airspeed, but if you applied full power it instantly flipped inverted!  That’s the same balance of forces at work, just the height above the ground is different.......
 
The lesson I see in all this is that we should never use full flap for take-off in a Savannah, because it will jump off the ground at such a low air speed that control is very marginal.  The Savannah Flight Manual recommends, for short take-off - “flaps 40º ” and “control stick pulled on until  taking off”.  I reckon that I.C.P. should delete those recommendations.  I note that Zenair discontinued 30º flaps several years ago, as I understand it because too many 701’s were getting bent while trying take-offs with full flap..... (a lesson there?)

I now know of at least three Savannahs that have been wrecked on take-off due to this method....
 
And there’s no need for full flap in a Savannah either.  With my Savannah, first stage flap is excellent – good increase in lift and improved low speed handling.  At full flap, the control changes completely - it becomes heavy and slow, with heaps of adverse yaw.  The only time I apply full flap now is in the final landing flair, just as it’s about to touch down I can ease the flap to full and hold off for a couple of knots slower touchdown.  But I’ll only do that if the air is really steady – the marginal difference in landing roll is of no use in real life STOL Ops – it’s only useful for showing off!
 
As for using full flap to steepen the approach, I find a forward slip to be much more effective and much better control.  More on that another time.....
 
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Lots more to come when I get the time,
stay tuned....