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Slats, pros and cons

Slats increase Clmax and critical angle of attack, and are popular with some STOL designs, and as lift augmentation on swept wing jets.

http://www.theairlinepilots.com/forumarchive/principlesofflight/flapcurve.jpg

Would need to check the Valdez, AK rankings but expect to see slats on some of the winning aircraft.

However, the Helio Courier has a modest 10 knot demonstrated crosswind component at landing, I understand, because of the risk of asymmetric slat retraction. They could be operated with crosswind main gear and a free castoring tailwheel to allow landing and roll out in a crab. They also used spoiler ‘interceptors’ as roll control with slats deployed, again I presume to avoid asymmetric slat retraction. The interceptors acting as spoilers just behind the outer wing slats.

In effect the combined crosswind method is not recommended for a Courier, again second hand understanding, because as you kick out the crab, and roll in some side slip the advancing upwind wing may retract the slat and result in a wing drop. See above how pronounced the reduction in critical alpha is with slats retracted. For the tailwheel pilot used to keeping her straight in the flare with rudder, this is all quite counterintuitive, effectively you drive them on with spoiler control landing typically across the runway.

I believe limiting the flaps to 20 degrees allow them to be operated in normal mode, rather than C/STOL.

Presumably slat deployment has a big effect on the manoeuvring – gust envelope, as a gust with slat deployment would produce higher Clmax requiring a lower, possibly much lower Va.

The 1979 TWA 841 incident is an interesting case study on the risk of slat deployment at higher speeds.

https://en.m.wikipedia.org/wiki/TWA_Flight_841_(1979)

Not sure if any EuroGA forumites operate wings with slats, outside commercial transport, but the unique Helio Courier handling characteristics, and wing design, seemed an interesting topic to discuss.

Oxford (EGTK), United Kingdom

I used to have a PZL Koliber, which was a Polish licence built Rallye, and the slats were very effective and could not deploy asymmetrically. It was good in crosswinds as I recall.

Darley Moor, Gamston (UK)

Robert,

At Valdez it’s becoming even more pointless to ask who won than in recent F1 races. Bobby Breedon Jr. is undisputed world champion of precision slow flight and landing:



I gather that Mr B practises quite a bit, but his latest “cub” does have leading edge slats.

I owned a Zenith 701 which had fixed leading edge slats and would mush controlably at ridiculous AoA – as long as the prop was blowing air over the tail. I used it to nip down to our nearest beach for an early morning swim, or to the village shop for newspaper and milk, but it was a nose-dragger, with all the disadvantages that entails, and cruising speed was pitiful. My current machine has VGs but no slats, cruises twice as fast for eight hours, hauls sheep and motorbikes, and lands shorter on beaches and gravel bars by using the water. It’s three times the price, infinitely more useful, but hardly more fun than that ugly duck with slats.

For the reasons you’ve given, I don’t like the idea of automagic retracting slats like the Rallye, and even handraulic ones would be something else to add weight and fail. Still there’s no disputing that they work as well or better than VGs for STOL ops.

ATB, Peter.

Glenswinton, SW Scotland, United Kingdom

A very entertaining novel by Michael Crichton called Airframe deals with slats on a passenger aircraft, inspired by the TWA accident. A good read, not only for aviators.

Last Edited by achimha at 30 Oct 06:34

Yep. Remember reading it a bit over 10 years or so ago. Enjoyed it.

Mainz (EDFZ) & Egelsbach (EDFE), Germany

Most of the disadvantages referred to seem to be to do with asymmetric slat deployment, but that cannot happen when they are mechanically linked together. I found the Koliber great fun.

Darley Moor, Gamston (UK)

I’ve got the real deal, a 1973 180HP Rallye with slats. Like ’em.

Tököl LHTL

Have a look at the DO27 and the DO28, just great aircraft.
www.do27.com

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