Slots And Slats Aerodynamics Game
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How Zenair 701 & Savannah aircraft fly better with VGs than with Slats!!!

Slats and flaps are high lift devices, intended to produce maximum lift coefficients on aerodynamically designed wings of aircraft. The use of aerodynamic extensions are done in order to increase the effective plan form area of wing thereby generating extra lift force required for an aircraft wing. A typical passenger aircraft has three. Thanks for the question Slats are aerodynamic surfaces on the leading edge of the wings of fixed-wing aircraft which, when deployed, allow the wing to operate at a higher angle of attack. Slats and flaps are high lift devices, intended to produce maximum lift coefficients on aerodynamically designed wings of aircraft. The use of aerodynamic extensions are done in order to increase the effective plan form area of wing thereby generating extra lift force required for an aircraft wing. Watch and share Aerodynamics: Airfoil Camber, Flaps, Slots-Slats & Drag: 'Smoke Lifts' Circa 1938 NACA Langley GIFs on Gfycat.

See also, the more recent detailed test results:

http://www.stolspeed.com/flight-testing-slats-vs-vgs

It was way back in 1990, at the Sun’nFun fly-in at Lakeland, Florida that I first heard about the possibility of flying a Zenair CH701 without the leading edge slats. I was very interested in the CH701, so was hanging around the Zenair display, and there met a couple of CH701 fliers from Colombia. (Usual reaction at this point is that, “.. it must have been for the drug trade…”, but that’s nonsense – this was the days of 532’s and early 582’s, and the drug syndicates didn’t need to fly over the jungle in two-stroke ultralights, they had the best of Bell helicopters!) The real reason there were so many CH701’s flying there, is that Columbian men are real macho and always ready for adventure, and a local manufacturer was building them ready to fly, so this aircraft suited them very well!

Anyhow, these fellas told me that they had removed their slats and their aircraft flew better! This was a real surprise, since those leading edge slats are one of the main distinguishing features of the Zenair CH701! They spoke a bit of English, and I spoke a bit of Spanish, so I questioned them over and over again just to be sure, and they assured me that it flew faster without slats, and landing speed was only a little higher.

Ever since that encounter I’ve been telling the story to Zenair CH701 and Storch fliers, suggesting that they might try flying without their slats, but no one would, so it had to wait until I had a similar aircraft myself to give it a go. Now I’ve thoroughly tested it out on my Savannah (a brother of the CH701), and the results are astounding! I’ll never put the slats back on. Two Zenair CH701 fliers at our airfield have also removed the slats from their CH701s, and the results are equally impressive. So we now have a surplus of used slats hung up in our hangars…….

Leading Edge Slats on a Savannah aircraft

Much cleaner - an excellent STOL wing!

The vast reduction in drag allows all these aircraft to fly considerably faster for the same power, climb better, glide better, and with the benefit of Vortex Generators, lift-off and touch-down just as short as with slats, but with more control.

In summary for my Savannah:

Fast cruise @ 5200 rpm has gone from 79 kt to 85 kt. = + 6 kts
Top speed has gone from 94 kts to 103 kts! = + 9 kts.
Fuel burn @ 75 kts has gone from 17 L/hr to 13 L/hr. = 23.5% less!
Best climb rate @ 55 kts is 140 fpm higher.
Best glide @ 40-45 kts is 100 fpm better.

Stalls (idle power, no flap):
With slats – no real stall, just a stable high-descent mush @ less than 30 kts.
Without slats, no VGs* – a distinct stall and roll to the left @ 34 kts.
Without slats and with VGs – no stall, just a stable mush @ less than 30 kts.

*VGs = Vortex Generators, more about them elsewhere.
L/hr x 0.26 = US Gal/hr.
Kts x 1.15 = mph.

Note that the best rate of climb is 140 fpm better without slats.

Below 40 kts the rates are very much the same, so angle of climb is unchanged.

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This testing was done in a ‘Savannah’ aircraft, a kitplane from I.C.P. in Italy . It’s a copy of the MXP 740, designed by Max Tedesco. It has the same wing profile as a CH701 but a longer, and a different tail section. Powered by a 100hp 912ULS, 4-blade Brolga prop pitched for climb (16° blocks), carrying pilot (73kg) and 30 litres fuel.

All tests were done in as similar conditions as possible. It only takes minutes to remove the slats, so comparison tests with and without were conducted within one hour of each other, at the same altitude, in calm conditions, at first light before any thermal activity. Climb and descent figures were timed with a stopwatch between 2000 and 3000 ft QNH. Stalls and straight and level trials were conducted at 2000 ft QNH. The with/without tests were done three times to re-confirm the figures. The ASI was compared with the GPS by flying a 4-way course and averaging the legs, and found to be 1 kt low at 70 and 80, 1 kt high at 40 and 50, and spot on at 60; these corrections have been worked into the results. Indicated airspeeds at 30 kts and less are truly only ‘indicated’ – inherent limitations in the ASI and the pitot at these low speeds won’t necessarily give a true airspeed, but is still adequate for ‘before and after’ comparison purposes.

For more detailed comparison testing of Slats vs VGs go to

http://www.stolspeed.com/flight-testing-slats-vs-vgs

There was no change at all in the trim setting required for the same cruise speed, with or without the slats. Which just confirms aerodynamic theory that the slats aren’t providing any lift at cruise angles of attack – they just allow the wing to operate at an angle of attack above the normal stalling angle of about 16°.

This has solved a mystery that bothered me while building the Savannah, in that the C of G range quoted in the manual was forward limit = 30% and rear limit = 38.5%!! Most wings need a rear limit about 30% and a forward limit about 23% so this seemed to be way too far back?? Mine weighed right in the specified range, at 31% and 37% so I flew it, and it flew really well as all Savannahs do, but it certainly didn’t feel like a C of G in the 30’s - puzzling???? This was measuring from the leading edge of the slats, with a chord of 1435mm. However, without the slats and now measuring from the leading edge of the actual wing itself, instead of f

Slots And Slats Aerodynamics