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Old Feb 07, 2007, 11:55 AM
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Tim H.'s Avatar
USA, TX, Fort Worth
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Saw Tooth Leading Edge - STLE

Well, finaly got off my duff and worked on my F3X Evo a bit. I did decide on the Leading edge configuration I have been working on, so I decided instead of keeping it under my hat, I would share my ideas.

I've been doing some testing with chuck gliders with some ideas I had regarding the doubled up LE that has gained notice. The doubled up LE has many similarities with the Kline-Fogelman airfoil that has been around for years and has gained popularity and a huge following elswhere here on Ezone. There was also an article in Quiet Flyer Magazine a while back about serrated leading edge configurations and it got my mind going. I wanted to try the serrated idea, but didn't want a fully serrated leading edge. For one thing, it would be extremely fragile for our purposes and any "hangar rash" or dings would be catasrophic. I also didn't like the look so much...

Anyway, I came up with and idea that I'm hoping will have the benifits of the serrations, without the drawabacks, as well as the benifits of the doubled leading edge. I came up with a leading edge device that I'm calling the STLE (Saw Tooth Leading Edge). While I certainly can't claim I thought of either configuration, I do know (as far as I can tell) I'm the first to put the 2 together in this confguration. Only time will tell if this works as well as I'm hoping.

The tests I did showed that my saw tooth configuration worked extremely well. I need to do some more testing on the width of the step (chordwise) but I'm starting with the width shown. The tooth pitch is also canted to match the sweep of the leading edge so that the airflow is not separated differently on either side of the teeth in level flight. This would not be a problem on lesser swept leading edges, but would increase as sweep increases.

I posted some pics below in hopes we can start some disscussion on the effects the STLE will have, and if it will be benificial for our purposes. I'm hoping to have my F3X Evo flying by early next week so the "proof will be in the pudding" as they say.

Oh... Just a side note... The paint job on the proto did NOT turn out as planned, so it's going to be strictly a test bed airframe...

Tim H.
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Old Feb 07, 2007, 12:15 PM
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Tim H.'s Avatar
USA, TX, Fort Worth
Joined Nov 2001
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A few more pics of the build.
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Old Feb 07, 2007, 12:21 PM
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Very interesting Tim! I know what my expectations of the STLE are, but what were yours.......?

BTW, I've flown your Evo. Interesting plane.
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Old Feb 07, 2007, 12:52 PM
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Hi Tim,

Very nice idea and thanks for sharing! Is the plan to get more lift across the whole span due to these devices (vortexes?)? You might even be able to play with the lift-distrubution across the span. Nice for a next project!

I was also thinking about making saw teeth on the leading edge of a wing, but more like some F1 cars have/ had them on their barge boards. or just like a flat delta shaped plate at a high angle of attack. They should create vortexes over the wing...but experimenting will tell more. Just like with your design, playing with shapes and sizes across the wing should give some very interesting results.

What exactly are the devices on the ailerons for? Just for directing more flow to the tail, or also like I read somewhere else, to have a higher centre of pressure during knife edge? This because the "plate" on the upper wing generates more lift due to the angle of attack.

Keep up the good work!

Luuk
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Old Feb 07, 2007, 01:01 PM
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Quote:
Originally Posted by matchlessaero
Very interesting Tim! I know what my expectations of the STLE are, but what were yours.......?

BTW, I've flown your Evo. Interesting plane.
In a nutshell, more lift, more drag, decreased pitch sensitivity, delayed airflow separation via the vortex generation of the step and the teeth. More later, I have to be at the airport in 15 min.

Interesting good, or interesting bad????? Did you fly AC's proto? I do know that he didn't round the doubled LE, so I don't know if that increased the pitch sensitivity or not. Let me know what you thought. I'm always interested in hearing.

Tim
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Old Feb 07, 2007, 03:52 PM
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Nice job Tim.

I think the approach of setting angular cavities into leading edges has been tried before on full scale planes. It's definitely worth a try. I'm not really sure what the influence of low Reynolds numbers will be. I'm guessing it will not be as effective as a full saw tooth LE but it does look a lot better! As an alternative you could try making the sawtooth LE lamination a bit smaller and set it on edge a little aft of the LE. However you'd lose the strengthened/stiffened LE and you might still get detachment right at the LE.
I've a few things I'd like to try if I get around to it but they won't be as tidy as your approach!

Aidan
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Old Feb 07, 2007, 03:53 PM
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Tim,

That is much like the turbulators that I used back when I was flying F1A gliders. They should work very well. I am not sure that I would have tapered the thickness at the leading edge. I have been playing a bit with laminated leading edges on my bipes and have tried both rounded and square. I was supprised that the square seems to work better. Either helps decrease pitch sensitivity but the square LE also seems to help slow the downlines more than the rounded LE. The square LE model also seems to have a faster roll rate so I think that there is less airflow seperation.

Jerry
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Old Feb 08, 2007, 03:27 AM
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Do you remember which issue of Quiet Flyer that article was in?

I seem to remember them saying that larger teeth - very large teeth - had a much more profound effect on performance, but I could be misremembering.

I suspect that Jerry is correct on tapering the leading edges, but testing will tell.

Very interesting concept!

Larry
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Old Feb 08, 2007, 11:16 AM
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Great observations all around! This is completely experimental at this point. I'll definately try squared off on the next one. I may retrofit one of my other planes I have sitting around.

Aidan - I was hoping you'd pipe in...

Larry, I think it was the April 2006 issue. Pic below of the cover. You can download the pdf article here: http://www.kionapublishing.com/catal..._89_108&page=2 It's the "Theory, Testing, & In-Flight" article. I do think you are remembering correctly. I just want to try for some of the benifits, without the fragility. I think in 3mm, the teeth would be very easily broken off in the slightest mishap.

Jerry - we used to use some kind of Zig-Zag sewing tape on our gliders. It was a cloth tape in a zig zag pattern that you could get at sewing stores. I remember that it worked very well as a turbulator strip. I remember using it on an SOS 60 sloper and it enhanced the light wind lift tremendously. I could keep my SOS up when others were coming down. I loved that plane! One of my top 3 all time favorites in 20+ years of RC flying! I must have built and destroyed 10 or more of those. It was kitted by a local guy named Mark Rebeck. It was sloper Nirvana back in the late 80's in So Cal. I wish the SOS was still around.

Tim
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Last edited by Tim H.; Feb 08, 2007 at 11:30 AM.
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Old Feb 08, 2007, 01:55 PM
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Tim,

For F1A gliders we used chart tape triangles generally about 3% to 5% back from the LE, kept adding layers until performance peaked and removed one layer. Usually worked pretty good. This was back in the early 60's just before the freeflight crowd got into auto surfaces.

I didn't know you were an ex slope pilot, where did you fly? I did most of my flying at a hill in Riverside but also flew Costa Mesa and a little down at Salt Creek. This was during the late 70's early 80's. I mostly flew the Freedom design. Sure miss that glider!

Sorry for the off topic

Jerry
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Old Feb 08, 2007, 11:36 PM
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Wow, we were neighbors then too... I flew Kite Hill, Salt Creek (before the Ritz), Torry Pines, Huntington Beach, Laguna Niguel, top of Saddleback Mtn... Pretty much all over. I started in about 86-87ish with sloping. I taught myself to fly at Kite Hill. Then, after a few years, I went off to flight school in Oklahoma and have lived in the flat lands ever since. I'd give my left .... for a good slope site close to home. I miss sloping more than I could ever describe. I flew quite a few, learned on a Gentle Lady (electric), then moved on to hotter stuff. My all time Fav. was the SOS 60".

Tim
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Old Feb 18, 2007, 11:59 PM
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This is a great idea. I'm going to try this on my Pitts Python foamy (original design). I'll let you know how it works out. So far it looks really cool. It flies great and I was the first one to make one of these from scratch. Awesome stuff!
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Old Feb 19, 2007, 12:54 PM
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Old Feb 19, 2007, 06:33 PM
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Guys I tried this today on my own design monoplane and to make a long story short ----- SUCKS. Bad idea to do. I may mess around with different configs but I think it might not be a good idea.
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Old Feb 19, 2007, 07:03 PM
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What happened?

You can expect a good bit of extra drag when flying at hi alpha, but it shouldnt have been very noticable at straight and level flight.

Got any pics of your install?

Larry
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