Zenith Aircraft Builders and Flyers
Retractable Slats?
I have made it a point to examine just about every model of GA aircraft with slats on them, and read up as much as I can digest on the design and placement of slats. Conclusion for the CH 801: Unless doing STOL competition, take them off and install VGS. The fixed slats on the CH801 only reduced stall by 1.5 knots compared to without (but with VGs installed)and I picked up a whopping big 12 KTAS in cruise at same power setting and added about 200 fpm ROC. I have done this on both of my 801s with the same results. And you get a gentler stall.
Fixed slats are by their nature a compromise. The 801 slat bottom edge is about flush with the bottom edged of the wing instead of about 1 to 1.5 inches below the bottom edge of the wing as they are on all the retractable ones I have looked at and as all the design literature indicates. Thus you really don't get the radical STOL improvement that you could be getting from properly deployed slats. And you get a lot of parasitic drag in cruise. Also the retracted slat designs I have seen present a sharper, lower drag leading edge profile. They cruise faster with retracted slats than the same wing with no slats.
On my second 801, the slats were rigged just a fraction low. STOL performance noticeably better than in factory spec location. BUT, the drag in cruise was noticeably higher, and as you approached cruising speed it got unstable in pitch, wanting to "tuck" the nose and was very vague on the stick (like a plane flying too far aft of CG limit). Decidedly not the way to fly it.
This summer I plan to re-mount my slats in several locations from full back and tight against the leading edge and sealed, to forward and down to 1" or more below the bottom surface of the wing. I will share the flight test data. If it works as expected the challenge is going to be to come up with the simplest way possible to modify the stock slats to retract and deploy. Not going to rest until the 801 approaches the performance of the SuperSTOL. It has the potential to be really great not just good.
Comments and suggestions?
Fixed slats are by their nature a compromise. The 801 slat bottom edge is about flush with the bottom edged of the wing instead of about 1 to 1.5 inches below the bottom edge of the wing as they are on all the retractable ones I have looked at and as all the design literature indicates. Thus you really don't get the radical STOL improvement that you could be getting from properly deployed slats. And you get a lot of parasitic drag in cruise. Also the retracted slat designs I have seen present a sharper, lower drag leading edge profile. They cruise faster with retracted slats than the same wing with no slats.
On my second 801, the slats were rigged just a fraction low. STOL performance noticeably better than in factory spec location. BUT, the drag in cruise was noticeably higher, and as you approached cruising speed it got unstable in pitch, wanting to "tuck" the nose and was very vague on the stick (like a plane flying too far aft of CG limit). Decidedly not the way to fly it.
This summer I plan to re-mount my slats in several locations from full back and tight against the leading edge and sealed, to forward and down to 1" or more below the bottom surface of the wing. I will share the flight test data. If it works as expected the challenge is going to be to come up with the simplest way possible to modify the stock slats to retract and deploy. Not going to rest until the 801 approaches the performance of the SuperSTOL. It has the potential to be really great not just good.
Comments and suggestions?
Shay King
looking forward to hearing the results too.
May 7, 2017
Daniel Niendorff
May 7, 2017
Timothy Aanerud
Since the title is retractable slats, what other aircraft have had retractable slats?
May 10, 2017