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LE slats and flaps-worth the effort?

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LE slats and flaps-worth the effort?

Old 03-06-2005, 08:20 PM
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wsmalley
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Default LE slats and flaps-worth the effort?

Got two planes on the bench I'm trying to decide whether or not to add slats and LE flaps. I'm at the point in construction to decide on each. One is an F4D Skyray-it had spring loaded slats, which closed with airspeed. I think I would go with a servo operated system. I wouldn't have a clue how to determine the necessary spring requirement-though I guess you try hit or miss. This plane also had triangular shaped 'trimmers' aft, adjacent to the fuse and inboard of the elevons, I'm also going to try to incorporate. The other plane, an SU 27, had LE flaps which operate automatically on the full size-in conjuntion with the air brake. I guess it boils down to whether these things just look cool, or whether they would povide any noticeable flight characteristics. I might add neither plan incorporates these, I just like the scale effects. Any thoughts? Bill S.
Old 03-06-2005, 10:08 PM
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Tall Paul
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Default RE: LE slats and flaps-worth the effort?

I've played with the leading edge slats on a full-scale Bf-109E.. these move with finger pressure, in and out.. Expecting a model with free moving slats like this would be practically impossible to construct.
A servo is required. but as for the utility.. probably not much. The models tend to have high wingloadings, which require keeping the speed up anyway. Any attempt to fly one slowly ends up in the garbage can.
On the Ford, it might be more practical to have them working.. but the mechanism MUST be reliable on both sides. If one side sticks, the plane goes into the garbage can also.
These kind of sliding mechanisms can be difficult to accomplish in model sizes, friction is a big problem. Simulating the slats by hinging instead of sliding would be more reliable, but less scale-like.
The trimmers would be something else to distract you in flight. You have only so many thumbs...
The Flanker slats/brakes could be a handful also, requiring some mixing of the elevator to control ballooning-diving when they extend-retract.
One -or- the other is practical, but both might be a handling problem.
Old 03-06-2005, 10:56 PM
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Default RE: LE slats and flaps-worth the effort?

The may I understand automatic slats to work operation is dependent on the leading edge stagnation point moving down from the leading edge to the lower surface as the angle of attack increases. When it hits the right spot the airpressure actually forces the slat open rather than the spring pressure. Hence Paul's experience with slats that move by light finger pressure. As I recall my reading the pilots could hear the slats bang back and forth in tight combat as the turns tightened and the angles of attack reached the trip point regardless of airspeed. Making automatic slats that work with RC sized models would be a sensitive watchmaker like project. Servo operated leading edge slats would be far better. At least that way they will both operate at the same time.

My own feeling is that this is an area where there just is not enough wing tunnel work at the sizes and Reynolds numbers we work at. So for my own efforts I'd use flaps in an instant but forget the slats.
Old 03-06-2005, 10:58 PM
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Mike James
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Default RE: LE slats and flaps-worth the effort?

As to whether they're worth the effort, you have to decide that. Although better performance is generally predicted, you'll never know until you actually experience the same plane with, and without the devices.

In recent simulator tests of my sport jet, ( http://homepage.mac.com/mikejames/ne...t_x-plane.html ) the results were remarkable. Flaps and speed brakes produced the desired results, but not "surprising" results. However, the biggest difference was with the leading edge flaps. They made the stall/snap behavior a thing of the past. At some point in our flight testing, I'll be building these on the actual model, and then we'll know. Simulator results have been reasonable, but not perfect, for other designs of mine in the past.

In the meantime, you may find this set of pages helpful. It has drawings and animations of both actual and RC-scale mechanisms, which you might choose to experiment with. http://homepage.mac.com/mikejames/ne...ift_index.html

If you incorporate them, please come back here and let us know your results.
Have fun!
Old 03-06-2005, 11:49 PM
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Rotaryphile
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Default RE: LE slats and flaps-worth the effort?

I think that retractable leading edge flaps would be a tremendous amount of work to make, but carefully shaped fixed slats would not be too much bother, and would increase lift coefficient by at least 40%; less than most retractable slats, but a fixed slotted wing normally produces much less drag than a wing with extended slats. It is best to bear in mind that anything that increases lift coefficient of a wing usually also results in a more abrupt stall, and that high lift coefficients mean high induced drag. Increasing lift coefficient by 40%, for example, will nearly double induced drag at near-stall airspeed, and at the decreased airspeed made possible by the higher lift coefficient, the tail feathers will be much less effective, particularly the vertical tail in resisting yaw that may lead to a snap roll into the ground.
Old 03-07-2005, 12:25 AM
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Default RE: LE slats and flaps-worth the effort?

Bill-- I have no technical suggestions to offer, but can tell you that it's possible to do it. I got in a lengthy discussion with a pilot at our local yearly airshow (Warbirds Over Hickory) who flew in in a Helio Courier, and later demo'd the STOL and slow flight characteristics of the plane. As you may know, it utilizes a set of leading edge slats, that deploy on the principle that BMatthews was talking about, but they are not spring loaded on the Courier, they have a curved track and open from their own weight. Anyway, when he learned I flew R/C (I was asking about availability of plans for the Courier), he told me of one of his fellow pilots (they fly mission flights for JAARS) who builds not only giant scale R/C planes, but ALL ALUMINUM giant scale R/C planes, and had built a 1/4 scale Courier with functional leading edge slats. This guy is from South America, he has a website called
www.allmetalplane.com You may be able to contact him for the technical info you need. His planes are awesome, check them out.
Old 03-07-2005, 10:05 AM
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Default RE: LE slats and flaps-worth the effort?

I have been working on a model Helio also. The whole thing seems to depend upon the size of wing. I tried working slats on a 42" span model and they only made noise, and gave no noticible effect. The alteration of the flaps made more noticible effect. The L.E. slats opened up about 3/16" and it took a whole week to make each one move. Then the weather changed, the holes swelled up, and that became another wasted effort. Next model was without slats, and it perfomed same as the one without (until the fiddling of the flaps began).

The effort may work on a model, but you need to apply it to a LARGE model, and for S.T.O.L. appearances, it is simplier to overpower the model and acheive the same look.

Wm.
Old 03-07-2005, 11:30 AM
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HalH
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Default RE: LE slats and flaps-worth the effort?

I think the leading edge slats would be helpful. They would have to be servo operated. I believe Bob Violett has designed a system he uses for his F-100. He has gone to graet lengths to make sure they work. I am not sure he would share his design with you since he, I believe inserts the tracks when constructing the wings while in a jig to insure proper alignment. The trimmers for the Ford are most likely an unecessary added complication.
Old 03-07-2005, 11:47 AM
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Default RE: LE slats and flaps-worth the effort?

Size does matter, then! So many planes, so little time. I have a Fiesler Storch about 80% built, lack one aileron and one LE slat, about a 7' ws. Anxious to see how it flies. Stagnation point again (my post on 'stall warning device')! I did not , unfortunatly, take any pics of the bottom portion of the slats on the Ford when I was at Pensacola NAS. Therefore, I can't mentally grasp the engineering design ( I'll have to do alittle more research on this). I recall reading they welded some of those slats shut-problematic in combat. I think this was concerning Korean War vintage jets though. Reynolds numbers: can someone explain simply how they equate to 'models' in a practical sense- never did understand this. The SU flaps appear to be straight hinged along the bottom (Modern Military Aircraft Anatomy) and look to move down about 40 degrees-based on pics. There was video of the SU 35 here a week or so ago-in'Jets', I think, what an amazing aircraft! Mike: I will visit your sight again, I forgot about it. All this poses an interesting dilemma though: How scale is scale? Looks like a whole range of things to do some serious research on. Our planes are getting bigger, faster and more sophisticated, up to and including UAV stuff-check out some of the projects over at RC-Cam forum sometime. Then there are the nano-tech craft. I have pretty well set up the SU wing to cut the flaps out, so I think the flaps are a definate go. The Ford slats, I'll pray over a bit longer-that damn stagnation point again! Damn interesting stuff!
Old 03-07-2005, 12:10 PM
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Default RE: LE slats and flaps-worth the effort?

Hal, you slipped a response in while I was typing mine. You may be right about the trimmers, but at least half the fun of this hobby is the building. I still have and fly my first plane, an Eagle 2. When I was learning, I drove that thing straight in one day, I about cried when I saw the number of pieces that thing was in. My flyin' bud -and instructor, said we can rebuild this. I thought he was crazy. Well, that was years ago and I have rebuilt it several times. Since moving, my new partner looked at it one day and said "the tail is cockeyed on that thing". Yep, there's no dihedral left in the wing and the 'a-- end is little crooked but she still flies. He can't fly it though! I usually fly 'my Ford' a few times before moving on to my better planes. Guess the worst thing that I come up with is to glue 'em in 'neutral'. BTW William, pretty sure the man who owns are field has a full size Helio in the hanger. Said some Japanese were looking at it to purchase for a rebuild-Don't make 'em anymore?
Old 03-07-2005, 01:09 PM
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Mike James
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Default RE: LE slats and flaps-worth the effort?

Here's the arrangement I'll be using on my sport jet for the leading edge flaps.

To make this work, I've made a male mold, from which I mold the round interior piece... the "leading edge within a leading edge. (second photo)


Bob Violett has 'em on his F-100. Bob Fiorenze put them on an F-18, and Larry Wolfe has put them on several aircraft. The camber change does make a difference, at larger-than-park flyer size.
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Old 03-07-2005, 02:36 PM
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wsmalley
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Default RE: LE slats and flaps-worth the effort?

Okay, Mike, when the LE flap is deployed, will there be an extension that slips over the top of the wing. Therefore, the flap when 'retracted' (is that the phrase?) would, in effect slip over the top of the wing? Hope my question is clear! I thought about using miniature piano hinge along the bottom to keep things even and lesson the chance of getting uneven airflow. Also, is 25 degrees something you've worked out the math on? I'm guessing as to the flap degrees on the SU-where are all the Flanker drivers when you need them?
Old 03-07-2005, 06:32 PM
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Default RE: LE slats and flaps-worth the effort?

No extension is required, if the underlying circular section fits well. That's what prevents a gap.

25 degrees seems to be coincidental with full flap deflection on many fighters, and is what Bob Fiorenze used on his F-18. I've attached an image of the published F-16 deflections in various modes, for comparison.
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Old 03-10-2005, 06:46 AM
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Default RE: LE slats and flaps-worth the effort?

HI.. I BUILT MANY YELLOW F-18.. SOME FOR BOB,,GOOD FREIND.. I PUT SLATS ON AN 18 FIRST, FOR BOB.. I THINK THEY MADE TAKE OFF RUNS LONGER..NOT NEEDED.. RD
ORIGINAL: Mike James

No extension is required, if the underlying circular section fits well. That's what prevents a gap.

25 degrees seems to be coincidental with full flap deflection on many fighters, and is what Bob Fiorenze used on his F-18. I've attached an image of the published F-16 deflections in various modes, for comparison.
Old 03-10-2005, 11:08 AM
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Default RE: LE slats and flaps-worth the effort?

I can't say I'm surprised. If you look at the image in my post above, you'll see that this type of "manuevering flap" isn't really for takeoff. They exist to extend the angle of attack range without stalling, which is how all the fighters use them... Sharp "yanks" that normally would make the airplane stall.
Old 03-10-2005, 11:28 AM
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Default RE: LE slats and flaps-worth the effort?

With respect to LE flaps, I have two books with photos ( MIG Dynasty and Mil-Tech SU-27)of the Mig 29, and the Su 27, in take-off mode. Both aircraft-assuming the photos are labeled correctly- show LE flaps in the 'down' position. The Mig caption refers to a full flap, short take-off with what appears to be minimal elevator deflection on rotation. Another Mig photo at rotation, also with LE flap down, shows full taileron deflection, realizing that deflection can change in an instant. How does one correlate a long t/o with a model and a short t/o with full sized? Is there some other part of the equation, or configuration of the AC, that doesn't match?
Old 03-10-2005, 12:49 PM
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Default RE: LE slats and flaps-worth the effort?

I'd be interested to know that too.... Could just be the extra weight made takeoffs longer.

I remember the article (I think it was RCM) on Bob Fiorenze's F-18. In the article, he mentioned that for each wing, he had one servo deploying both flaps and leading edge flaps at the same time. So, in Bob's case, it couild simply be that for a relatively-heavy DF model with full or nearly full flaps deployed, the interaction wasn't right.

Interesting to note that once the leading edge flaps are deployed (alone or with flaps) these fighters' elevator goes to neutral, or in some cases, even to the "down" position. The leading edge flaps seem to move the lift vectors forward, and pitch the plane up. (the desired effect)

Here's a photo of an F-18 doing a sharp pullup. The tailerons are actually deflecting in the "down" position.
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Old 03-10-2005, 03:21 PM
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Default RE: LE slats and flaps-worth the effort?

Time of day, season, weather, flap setting, any one of which might have a noticeable effect. Was the model 'over' powered, 'under' powered. How do relative speeds affect flight characteristics between a model and full size? E.g., a full sized F-18 rotates, and lifts off, at what speed and lands, compared to a model. Perhaps, asked another way is there a mathematical ratio? I guess we need a full size pilots input, and radar readings at model speeds for accurate info. The obvious problem with a photo, the split second in time-the pilot could have pulled/shoved the stick full aft or forward a moment later. Another question, the incidence of the wing to ground in the roll, how near to full size is the 'average' model, thus its effect.
Old 03-10-2005, 06:51 PM
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Default RE: LE slats and flaps-worth the effort?

I agree... It's deep.

In regard to the photo though, that really is typical. I have many photos of F-16's, F-18's, F-22's, and F-35's, especially in the landing configuration, where the taileron is actually in the "down" position. I've attached a photo of an F-22 and an F-35, as further examples.

One other thing. i was reading another post, which was, paraphrased, "The leading edge flaps won't make much difference on a model". Well... Think about it from another point of view. (See the 3rd image.) If I came here and said, "Do you think there would be any difference between these two airfoils?", I think you can imagine the response. There certainly would be a large difference! As to how useful they are, only those that have used them can say. I'll be putting them on my sport jet in the next couple of months and will let you know how they work there.

I've only used them on two other aircraft. The first was my very first sport jet, in about 1992, which crashed due to a weak taileron linkage, before I had a chance to use them, so I can't say. The second was on an Andy Lennon-ish high wing design I did in the same time period. (with the leading edge flaps built ala Larry Wolfe's instructions, which were published in MAN) and they made a huge difference, especially when combined with slotted Fowler flaps. That plank-wing airplane was a real speed demon with the devices stowed, but would slow to a crawl with everything deployed. Can't wait to see the effect on my jet.
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Old 11-20-2022, 03:38 AM
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Default Slats

I know this thread is dated but the question is still relevant in 2022. The research ive done hasnít been definitive, aerodynamic studies and the science of the concept in full size is proven but on models it seems to come down to the model type, performance envelope, weights etc.

To properly test what I believe will be a beneficial modification to my F-16 I am going to do a series of test flights with slats fixed in various positions (fixed in place no servo) to determine benefits in various phases, the only configuration I canít test this way is reflexed slats which I do plan to incorporate but Iíll have to wait until the system is operational (pending test results) to test that.

I fully expect a marked effect on stall speed, approach speeds and angles, manoeuvrability and take off and landing distance, the reflex I expect will give me better speed and being able to go from reflexed to fully extended should give me greater control over manoeuvrability. All of this subject to tests and Iím also waiting on some very specific wing servos which are the only type I trust on a single servo jet slat system (1 per wing) the slats, like that ofthe full size run nearly 90% of the span and will deflect 40, 20 & -10 degrees



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