From: mkfeil@bcrki9.bnr.ca
Newsgroups: rec.models.rc
Subject: Re: Slats v.s Flaps
Date: 15 Apr 92 16:51:37 GMT
Organization: Bell-Northern Research

In article <1992Apr14.210454.16695@bmerh2.bnr.ca> petera@bcrka398.bnr.ca (Peter Ashwood-Smith 1600361) writes:
>   Has anybody given any thought to slats? I read a while
>back in rec.aviation that slats can contribute more than flaps
>to increasing a wing's lift. I've seen dozens of models
>with flaps/spoilers but never one with working slats, what gives?
>
>   Peter Ashwood-Smith

There are 3 main types of high lift devices one can consider for use
at the leading edge of a model's wing:

1) A fixed slot. The advantage of this is a fairly small increase in drag
   and low complexity. No moveable surface or servo control is required,
   however the slot cannot be retracted for optimum efficiency at cruise
   speeds.
                             fixed slot
                            /
                           /
                        *   *********
                      *   *          ****************
                     *   *                           **********
                      *  ******************************************


2) Retractable slats. On full size airplanes, slats are usually designed
   to deploy automatically under decreased flight loads as the wing
   approaches stall. This method is not often desirable on a model due to its
   complexity and weight. You would probably end up having to use a servo to
   deploy and retract the slat anyways. A reliable automatic mechanism would
   be an amazing feat for a model since due to scale effects the mechanism
   would have to be more sensitive and more accurate.

                             slot
                            /
             slat          /
          (extended)        *********
                   \   *  *          ****************
                    \*   *                           **********
                    *    ******************************************
                     *

3) Retractable leading edge flaps. These are similar to trailing edge split
   flaps but with the pivot point near the leading edge. The flaps would
   swing forward over 90 degrees until they became effective. Again there
   is a fair bit of complexity involved. (You could also do this by having
   a variable camber leading edge, but the hinge mechanism can get
   complicated.)

                        **********
       flap           *           ****************
    (extended)       *                            **********
              \      /*******************************************
               \   /
                 /
               /


In summary, I would say that slats and leading edge flaps are just too
complex to be worth it on models. At the leading edge it is important for
airflow to be smooth, so attention has to be paid to the hinge mechanism.

The best high lift combination would probably be a fixed leading edge slot 
combined with a slotted TRAILING edge flap. This could easily allow for
an extra 10 degrees before stall angle of attack is reached.

See ya!
Max

(Reference: R/C Model Airplane Design by A.G. 'Andy' Lennon)
--
Max Feil                 
Bell-Northern Research    Internet: mkfeil@bnr.ca
P.O Box 3511 Station C,
Ottawa, Ontario, Canada.  - What do I know? I'm just a Nerd on the Big Ranch. -