The True Story about Leading Edge Slats
How Zenair 701 & Savannah aircraft fly better with VGs than with Slats!!!
See also, the more recent detailed test results:
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……. Source https://stolspeed.com
A guy I knew, now passed away, removed the wing slots from his Globe Swift, among many other modifications that IIRC included changing the outboard wing section to replace the slots. The slots on the Swift had been inherited from the Culver Cadet, of which the Swift was a kind of scaled up, all-metal copy. The plane flew well and was definitely faster than a similar slotted-wing Swift with the same power – he had one of those too, his previous project, both powered by 180 HP Lycomings. He was able to get the wing changes on the second plane FAA field approved. Both are still flying with new owners.
Meanwhile another guy (also passed away) had built up a Culver Cadet with an original wood wing but with a steel tube fuselage that he designed and built. He deleted the slots too and his son, who still flies it, says it has unpleasant stall characteristics. It does climb and fly nicely otherwise, I flew in it a couple of times. It’s licensed as a homebuilt and he sold plans but I don’t think any others were completed. Link
who still flies it, says it has unpleasant stall characteristics
Does it have VGs?
No, the wing is clean and otherwise unmodified.
The son (now owner) is a big fan of VGs on other planes so maybe he should try them on the Culver.
Also interesting bits on the origin of the CH701 here
Very interesting to read about the CH701/Savannah
I can’t tell about the CH701, but on the rallye, slats effect is very noticeable. I tried once to land with flaps retracted, and the slats extended 1s before touchdown, and pull the plane out of ground effect (immediately some feets) and kepts it for some time wobbling over the runway. On the rally, it really extends the wing area and energizes the air flow.
Just incase anyone else didn’t know, to save them having to look it up, VG is short for Vortex Generators.
I can absolutely confirm the benefits of the VG’s which I fitted to my 601. The slow speed safety is greatly improved and if you wish to do so you can land and depart in a very short space. Quite a contrast to the Longeze.
A detailed report on effectiveness of VG on an RV8. My guess is that similar conclusions would be applicable to other aircraft with NACA 23 series wing airfoil