Are there any FIKI planes with vortex generators? Cessna Caravan?
P46T. Never saw ice on or near them.
About two weeks ago a DA42 at our airport did get VG’s applied. Not only on the wings but also in front of the rudder. See pictures. One of the owners, which happens to be also the maintenance man for this aircraft, said there is no difference in cruise speed. But the stall speed is lowered with about 9 knots. No change to the POH however so the VG’s will give you only a bigger margin in the stall speed region. Which is great, I think. The rudder has now more authority.
Edit: Resized the pictures.
Interesting to see how far aft on the wing they are on the more laminar flow wing of the Diamond. They will surely have a significant drag penalty on a laminar wing though?
I think the real reason they aren’t used much is the cost/benefit is limited for general flying, and only apparent when regular flight close to the low speed/high AOA end of the envelope is required.
They seem to promise much, but don’t deliver quite so well on the downside of things:
Upside: lower stall speed, better stall behaviour i.e. increased margin for safety if you maintain the same approach speeds. If you subsequently start lowering your approach speeds you lose this margin. Which you get back in return by increased margin against landing overruns.
Downsides:
- get knocked off in certain circumstances, i.e. when refuelling, when washing. How many can be knocked off before your airplane becomes unairworthy? Can you replace them yourself or is it certified maintenance?
- you don’t gain any economic benefit, unless you generate your own take-off and landing charts. So they cost money but don’t deliver greater payload.
- lower lift-off speed means diminished cross-wind performance due to less directional control at the lower lift-off speeds
Archie wrote:
get knocked off in certain circumstances, i.e. when refuelling, when washing. How many can be knocked off before your airplane becomes unairworthy? Can you replace them yourself or is it certified maintenance?
Carry a few spares, stick them on if one is missing. Hope nobody notices.
lower lift-off speed means diminished cross-wind performance due to less directional control at the lower lift-off speeds
How about not lifting off at the lower speed, but sticking to the “old” ones?
The Gulfstream wing prides itself being VG free. The high speed aerodynamics may have more of a balanced cost benefit, than the free lunch of slower speed airfoils.
The Gulfstream wing prides itself being VG free.
And that’s quite an achievement that few jets can claim. Look out of the windows of any airliner and you can see hundreds of these things. The higher the speed, the more drag they create. On a Mach .85 (or more) aircraft like a Gulfstream no vortex generators means a lot of fuel saved.
One other caveat with aftermarket vortex generators whose purpose is reduction of stall speed (and/or enhance control surface effectivity at low speed) is that they lower the stall speed into a regime which is way “behind the drag curve”. If a late go-around is required from such a low speed – together with the unusually high pitch attitude – it may take quite long to achieve a positive rate of climb. On twins, the safety margin between stall speed and Vmca can be significantly reduced by vortex generators. I once flew a C421 with VGs that had it’s stall speed 20KT below Vmca. Very nice for a short field landing, but if one lifts off early or needs to do a go-around and an engine coughs (rich cuts are not unusual with these engines) that means instant and total loss of control at very low altitude.
Personally, I would not stick vortex generators on my plane.
I thought that some of the VG kits for twins actually claimed to reduce Vmca to below the stall speed (VGs on the vertical stab for better authority), not the other way around. Effectively eliminating Vmca altogether?
The other way around as you describe it, rotating at 20kts below Vmca, sounds very risky.
VGs certainly make a very nice change to low speed control on a Luscombe. They really do make the plane feel more solid on a short field approach. A friend stuck them on his plane illegally (to match the rest of his mods!) and they worked great. We all enjoyed trying it out, and on that low speed plane you couldn’t detect any difference in cruise speed. Then somebody STC’d VGs for the plane and the owner bought the STC to make his installation quasi legal. The only problem now is that on a classic plane they destroy the looks… and for some of us on some planes that’s too much to bear.
what_next wrote:
And that’s quite an achievement that few jets can claim
Do jets really wear VG from initial conception ?
I had never noticed that on airliners.
