Leading edge slots

I do not know - but to others - here is leading edge slots described:

/Glenn

As far as I know they'll be just as effective with a model as with full size. The details of just where to put them for best performance will vary, but if you don't mind extra drag at speed you're free to experiment.

You may want to get Martin Hepperle's airfoil computation software and figure out how to use it for slotted airfoils -- it should help out a lot.

Designer Andy Lennon is THE expert on lift enhancement and STOL for model aircraft. He has several books.

Here is one of his planes in kit form.

Hope that leads to some help Earle

Ted shuffled out of his cave and grunted these great (and sometimes not so great) words of knowledge:

FWIW - I recently completed an 82" span Lysander (British STOL for covert missions during WWII ). I have not maidened the plane yet. The Lysander has leading edge slats. I discussed these with a gentleman in the UK who has built and flown this Lysander model.

He stated that he could see no noticeable difference with the leading edge slats. He found that by using flaps he had substantially better STOL than by relying on the slats.

Based on his statement and several other people on RC Scale Builder I built my plane without the leading edge slats, however, I did allow for

45 degrees of flap movement. The general consensus (at least the impression I received ) was that while the leading edge slats work on full size aircraft, due to the size of model aircraft a model would need to be a minimum of 1/4 scale before there was any noticable difference in take off/landing.

You may want to check the forums on RC Scale Builder to see if there is more detailed information.

Hope this is of some help.

Slots are normally used on full-scale airplanes to control the stall pattern so that control surfaces are still flying when the rest of the wing is stalled. A good example is the Stinson 108, which has them in the leading edge ahead of the ailerons. Slots are sometimes used on stabilators to keep them from stalling in the landing flare; Cessna found that they had to put them on the Cardinal (177) to prevent stabilator stall with the resultant nose-drop and gear damage in some landing configurations. STOL airplanes use leading-edge slats (not slots) for low-speed lift improvement. The Helio Courier is an example, with newer slatted aircraft like the Zenair 701 and 801 benefitting from them.

Dan

I bought the 20 size Druine Turbulent plans by Gordon Whitehead from RCM years ago. According to his construction article, the leading edge slots have a noticeable effect on performance. I haven't gotten around to building this particular plane, unfortunately. I've had the plans for only 15 years, I guess I'm just not ready yet....

All info helps. I had heard something similar, which is why I'm a bit hesitant to go for slots before asking here. I suspect they me need to be different on models to be much use. Maybe they need to extend further back, ie the leading edge of the main wing may need a gentler slope at the intake and the gap may need to be bigger.

Funnily enough, my 2nd after-school job in the 70's was helping assemble wing ribs for Druine Turbulents for the owner of Rollasons (temperamental old git, and founder of the Tiger Club) who had bought all the jigs. I saw him land one on one undercarriage leg once. The plane was virtually stationary by the time the legless wing dropped. The ones I helped build didn't have slots as far as I can remember (could be wrong). Also turns out one of the team leaders of the Turbulent display team is my old geography teacher who has promised me a flight in his Pilatus P2.

That's what I remember hearing. I don't need high speed performance, so maybe a very blunt leading edge is as useful at smaller scale.

I'll check.

For max effectiveness they must be properly designed (profound :)). If properly designed they will significantly reduce stall speed. Back in the

60s I install them on a Senior Falcon. I just guessed at the shape - I figured if it looked right it would be close :-) I experimented with the gap ( I used bolts so that I could easily adjust the gap). My Falcon had a Marco 61 installed and when I got the gap right the STOOL characteristics were great for hot-dogging :-)) The IF-100C had slats (slots that move) and they worked well. That is until you got asymmetrical deployment in an accelerated stall at 500 kts! WHAP! Instant snap roll

LOL - I should have edited more closely. Marco = Merco, STOOL = STOL :-))

If I do incorporate them then adjustable bolt-on ones are an excellent idea. Not jonly for adjustment but also for easy replacement, they are in quite a vulnerable position.

Yes, I have seen a model with home made slats (not slots) fly and I was not impressed. There seemed to be significant controllability problems at high alpha, which is the purpose of slats wings in the first place. The purpose of slots is different and that is to retain control surface effectiveness into deep stall. The problems with that in the modeling environment is that my mark I eyeballs are not calibrated well enough to tell when that actually happens.

I disagree Six but I'm not going to start an aerodynamic discussion here. I

*will* say the slats on a model would be difficult because of the small friction deltas coupled with other factors would make asymmetrical deployment the rule rather than the exception. I wonder if Bob Violett has slats on his F-100s?

"Six_O'Clock_High" >> > It needs to be as STOL as possible as TO/L space at locations may be

snipped-for-privacy@digiverse.net wrote in news:1177917711.798504.189210 @n76g2000hsh.googlegroups.com:

That would make sense. Without any firsthand knowledge of LE slots (I try not to let that stop me), I'd think that Reynolds Number effects would just ruin them for small models. Re effects are pretty severe over a 6" wing chord; what must they be like over a 2" LE slot?

I'm not sure what specific geometry changes would be needed, but I sure wouldn't expect a full-scale design to work very well.

What? You think MY Mark I eyeball is calibrated better than I do? Or that the particular application of slats I saw worked better than I thought it did? LOL I do have to admit that it very well may have been radio problems I saw. You know the nut on the sticks of the radio...

The purpose of deployment is to be able to reconfigure the wing from a low drag high speed airfoil to a high drag high lift slower speed airfoil. If the wing is straight leading edge, asymmetric deployments can be minimized by moving the entire leading edge. However, that probably is not what anyone really wants to do since straight leading edge wings are not normally found on high speed ships anyway.

In the words of another, Cheers

Sounds like a nice thesis for an aerodynamics student, to come up with the ultimate *model* STOL wing. In fact I know one, I'll send him an email.

Hi Mark

By a mistake I found this page. I was searching for some other wing information:

Anatomy of a STOL Aircraft: Designing a Modern Short Take-Off and Landing Aircraft.

"... Figure 2 ? Lift Coefficient vs. Airfoil Angle of Attack ... Figure 4 ? Fixed Leading Edge Slat Lift vs. Drag ... Also, because a high lift wing is designed to fly at an unusually high angle of attack (30 degrees compared to 15 to 17 degrees for a conventional wing) we need to achieve this high angle by pushing the tail down much more than with a conventional wing. ..."

/Glenn

Hi Mark

Look at:

Aircraft Airfoils

"...The chord is measured from leading edge to trailing edge and the the slot is not added but the slot is cut in the airfoil... We have also seen that the proposed airfoil has a favorable lift to drag ratio at high lift..."

The Robin by Andy Lennon:

"... For short takeoffs and gentle landings, I incorporated large, slotted flaps into the Robin's wing. To obtain effective aileron control at high angles of attack (AoA), I used the NASA "safe wing droop" at the leading edge (LE). ... It has true short takeoff and landing (STOL) capability and with flaps fully extended, the stall speed is 15mph. I estimate that its maximum airspeed is 80mph...."

/Glenn