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Leading edge slats?

Old 09-25-2002, 08:59 PM
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Default Leading edge slats?

Are they worth the effort? Building a F4D Skyray which had spring operated slats. Found an article in a MAN mag which describes how to make them. Question is, do they work on a model other than for looks. Anyone have any experience with them?
Old 09-26-2002, 03:12 PM
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Default Leading edge slats?

wsmalley,

I don't have any experience with slats on models, but my answer would be that you could expect them to be effective, if they are configured correctly. Generally, the effect of slats is to 'delay' leading edge separation until a higher angle of attack is reached. This means you can get to a higher AoA before stall, and achieve higher lift. Whether you would get any benefit from this depends on whether you would want to, for instance, land more slowly by going to high AoA. You would probably want to couple slats with flaps, although it sounds like the slats are a one-time thing, if they are spring operated. Maybe they could be set up to deploy when flaps are at maximum.

Sounds like a cool project; I've always wanted to try slats & flaps on the right kind of plane.

Good luck,

banktoturn
Old 09-26-2002, 05:49 PM
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Default Slats

Thanks for the comment! The 'Ray apparently had triangular shaped thingys, called'trimmers', on each side of the fuse which were set upward for T/O and leveled for flight. Supposedly, they had a very high angle of attack for landing and looked like a duck landing. There was one fuzzy photo of one making a carrier landing and it was nose HIGH! It had no flaps, but, in theory, the slats should help in a slow, high angle landing approach. From reading, it appears several of the 'Golden Age' jets had spring loaded slats/l.e. flaps(F 86,e.g.) but were bolted up since they were problematic in combat. I would make servo operated, since I wouldn't know how you could figure out air pressure on a model at say 25mph-but that would be interesting- so as to determine what size springs to use.
Old 09-26-2002, 06:00 PM
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Default Leading edge slats?

I bought a plan built plane called the "Pharoh" which had fixed leading edge slats, plus flaps and huge ailerons. The slats were made from venetian blinds and were fixed near the leading edge, spaced about 1/4 inch away.

It looked cool, but the ailerons were totally ineffective and the poor thing made slow left turns regardless of aileron deflection.

At the time (a few years ago) I was not comfortable with rudder control and it ended up in a pine tree. By the time it was recovered (a few days later) chipmunks had nested in it and chewed up some of the fuse. I stripped it down and still fly the little Enya 0.35 heli-head engine that came with it!

I wish I still had it, as I'd like to have another go at it now!
Old 09-26-2002, 06:08 PM
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Default Leading edge slats?

wsmalley,

I am going to look around a bit for some pictures. What you describe doesn't sound like what I am referring to as slats. Of course, any high-lift device will be cool to put on a plane. What I mean by a slat is a section of the leading edge, sort of like a very blunt flap, which extends forward and down, leaving a gap for air to flow through. You will see these on most any large airliner you fly on. Your description sounds like a deployable strake. I think it's purpose is to initiate a vortex to give some vortex lift at high AoA, but I will do some reading, and let you know what I find out.

banktoturn
Old 09-26-2002, 07:56 PM
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Default Leading edge slats?

wsmalley,

Unfortunately, I couldn't find a picture anywhere on the web that showed the trimmers, but I did find a little write-up that describes the Skyray. It did indeed have conventional slats on the leading edge and trimmers on the trailing edge. The best way I can describe these, if you haven't seen them, is that they look a lot like pieces of leading edge stock that extend forward and down, leaving a fairly clean leading edge behind them, and a nice channel between the slat and the wing when extended. The air that blows out of this channel onto the top surface of the wing is important to delay stall. The trimmers are small supplemental elevators used, as you mentioned, for takeoff. It seems that the reason for them is to keep the nose up without having to deflect the elevons. This was desirable because the elevons were most effective when they were near neutral, so they didn't want to use them to keep the nose up at takeoff and lose roll authority. If you wanted to implement both trimmers and slats, I am not sure whether you would want to control them separately or mix them. The article only mentioned using the trimmers during takeoff, while you might want to use your slats for takeoff and landing. If you have a computer radio, you could put them on separate servos and decide later. It would be great to see pictures when you get that far.

banktoturn
Old 09-26-2002, 08:35 PM
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Default Slats, L.E. flaps, etc

Again, thanks for your research. I, too, have tried to research the Skyray but there is not much on the web that I can find. The slats are- judging from a 3 view I found in an MAN construction article on this plane- on the outboard portion of the LE. The trimmers I figured I would put on a dial channel on my computer radio. I don't know if they had a 'down' position but I will have that capability. I've got a Fiesler Storch about 80% done that has fixed LE slats and elevator 'slats' also. I suppose I could slave the slats to trimmer in some fashion and try it way up high. If I decide to build working slats though, I would try the trimmers first-both operating at once could be a problem.
Old 09-26-2002, 10:35 PM
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Default Leading edge slats?

wsmalley,

In principle, you would want the slats deployed when you used the trimmers, since they will help you stay attached at high AoA. Looking at the Skyray, though, with its small aspect ratio and swept leading edge, it probably doesn't stall until pretty high AoA anyway.

Good luck,

banktoturn
Old 09-27-2002, 01:18 AM
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Default slats

One thing about slats or leading edge flaps(no gap) on highly swept or delta wings is that they also decrease drag significantly at high angles of attack. So using them at takeoff would be a good thing.

They actually aren't known for increasing max lift dramatically, but for allowing a higher angle of attack.

- Still thinking about putting them on a Y/A A-4.
Old 09-27-2002, 01:42 AM
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Default Slats

To the best of my knowledge, the Storch was among the first, if not the first to use LE slats and it was pretty legendary in it's climbing ability. Supposedly, the Skyray was developed using German studies, I presume during the war years-it was a 50's era plane. As a Navy carrier plane, I guess they wanted all the T/O Lift and slow, high angle approach-so slats. That plane had a small retractable tail because it landed with such a high A/A. Do the present day jets (fighters) use slats? Seems like pix,etc. I recall show flaps. RWH: I think I recall an article way back about the Pharoh with regard to high lift devices. High T.E.K. Models, in CT had balsa slat material according to the '94 MAN article about slat const., don't know if they're still around.
Old 09-27-2002, 02:43 AM
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Default Leading edge slats?

wsmalley,

I don't know about all modern fighters, but there are some that have used slats. Slats and flaps are frequently ( usually ) used together. Flaps give higher lift at a given angle of attack ( and actually, since the effective trailing edge of the wing moves downward as the flap is deployed, flap deployment increases the angle of attack ), and slats allow higher AoA to be used. Certainly, it is not either/or. The Skyray could not have flaps, since it had no tail. If I get a chance, I will cruise the web tomorrow to see which contemporary fighters use slats.

banktoturn
Old 09-27-2002, 09:57 PM
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Default Leading edge slats?

I have an old delta called the Hustler.It has sharp leading edge at the root and a blunt LE at the tip. It takes off and lands like a concord at about a 30 degree angle. No sign of tipstall. Might be another option just by changing the shape of the LE.
Old 09-28-2002, 03:45 AM
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Default Leading edge slats?

The F-100, the F-4 (starting with the E and most later models) used leading edge slats. BVM employs leading edge slats on their F-100. They are very slick in operation although they are somewhat of a pain to do. (Just finished them on a D model) On his model they slide on some carbon fiber rails that slide up into a phenolic socket machined out of G-10. You can see some pictures of them on BVM's website. www.bvmjets.com look under the F-100 kit details.

If I am not mistaken they actually make the wing aerodynamically thicker.

DR

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