Some pics of the 'first cut' of the LE flaps. In spite of much discussion regarding the pros and cons, I decided to go ahead and try them. All the film of the 27 I've seen shows the LE flaps in the lowered position, including the 'Cobra'. I guess flat out, they are retracted, but every other maneuver shows them down. I haven't figured out the linkage system yet, but thats next. Interestly enough they make an arc moving downward which is why the full sized flaps are curved on the ends. I did not forsee that!

Very cool.

I had thought about using these from time to time and have even come up with off-the-shelf solutions which would allow the LE flaps to be mixed into elevator and would still droop when the trailing edge flaperons to be used.

It's basically a series of "Y" cables and on-board elevon/flaperon mixer used in conjunction with the transmitter flaperon that will allow this type of action.

If you're interested, I can draw up a schematic that better describes how it's wired. The linkage is fairly straight-forward as it just requires a servo per control surface.

Keep up the good work! You should be flying in no time.

Dan

Yea, Dan, I'd love to see your idea. As you may have noticed, the plane is made in sections. In the 'fore' section, I'm balancing the wings in the wind to check balance. As many times as I've watched 'Ram-K', including freeze framing the DVD, the flaps- during landing are imperceptable as far as movement as flaperons. The elevons are working like crazy. I can only conclude the flaperons function only at hi speed maneuvers, and then seemingly very slight. I figured I would use piano hinge on the bottom edge and lithoplate skin to slide over the gap. That too is very hard to figure out in the FS.

I would like to see your plans for the LE flaps (slats) as I'm looking to do that for a A-6E model, which is linked to semi-fowler flaps and the horizontal stab; e.g., flaps / slats extend and the horizontal stab LE depresses; i.e., up elevator.

No plans for the flaps. With a built up wing, I simply measured where the back edge would be and started the wing skins on the edge (top and bottom) of where the rear of the flaps would be. The width was determined by scaling off a plastic model and cutting inside of the inner and outer ribs. This meant making a false rib for each end of the flap. A Zona saw was used, letting the saw rest against the upper and lower wing skin. Actually is it was pretty easy. Slats would be a little more difficult, but if you do a search here there is some good info available. I'm sure we would enjoy some pics of your progress. Bill S.

The leading edge slats on modern aircraft are all coupled into the other controls. For example during a high speed flyby the slats, flaps and elevator are all set level (or near to) but during a pitch up maneuver the flaps and slats lower as the elevator angles for the pitch control. A negative pitch maneuver would reverse this with the slats and flaps going up above the "flat" position to alter the camber for higher inverted lift. Similarly I believe you'll find that the ailerons are also coupled into the slats so that when the aileron goes down the slat does as well (very slightly) and conversly the up traveling aileron is linked to that slat going up slightly as well.

On the angled fins of the F18 the rudders actuallly turn in slightly during pitch up and out slightly during pitch down to minimize drag relating to how the air flows past them.

Ain't computers wonderful?

Yep, they are. That's why they don't let the F-18 pilots touch the controls on a catapult launch; computers do a better job.

I wouldn't go so far as to say the computers do a better job. F-18 pilots keep their hands off the stick during catapult launch to avoid a pilot induced pitch oscillation during the abrupt transition to flight. If the flight control system were a little better, they would be able to fly the airplane during the transition without worrying about an undesirable response. In one case quite a few years back, the fight control system pitched the aircraft down in response to a stuck angle of attack sensor. I bet the pilot who was killed would argue that he could have done a better job than the computer did.

I guess that's why there are shoes. There once was a CO of mine who detested computers even though he was one of the earlier testers of ACLS, but it's been proven that there are more mishaps due to crew induced errors than due to computer error or actions taken when the crew thought there was a computer error. And, it's as if he didn't realize, or want to realize, that computers were the best part of his capability to fly let alone land. After a few thousand hours in carrier aviation and over 700 arrested landings, I can arttest to that fact as well. And looking at the mishap report of the incident, it wasn't all computer induced.

Part of the difficulty in trying to replicate control surfaces is in knowing exactly how a particular aircraft was designed in the full sized. And, not all 'designs' necessarily stayed with that AC. For example, I believe The F4D Skyray had LE slats-not flaps- were welded shut after it was discovered they popped out at inopportune moments during combat maneuvers, or so I've read. Looking closely at pics of the Su-27, there is something like an inverted 'V' on the interior root of the wing and a ball-shaped protrusion on the flap which would lock its uppermost travel. I could certainly be wrong-never saw one up close- but I think this would preclude the flap from moving upward. Indeed, the flaperons may go into a reflex position I just don't know. Darn, where is Victor Pugachev when I need him! I guess we don' have any Flanker drivers dropping in here. The Su is supposedly a fly-by-wire plane, so the question is what effect LE flaps, by themselves, will have. I just had to have them to add to the scale.

Thanks. I know from personal experience in the Scooter (A-4 Skyhawk) and the Whale (EKA-3B Skywarrior) that leading edge slats without positive control; i.e., hydraulically actuated, are problematic. I believe I've solved how to have symetrical leading edge slats that extend properly along the full length of the wing, but it'll take a bit of time to fabricate and bench test them.

Here's the image with the schematic that shows the control system I was describing.

It can use a simple 6-channel radio or computer radio. Since my computer radios won't cross-mix the flaps with elevator and flaps, I'd need two elevon mixers and a servo reverser. If your computer radio can't do this, then you'll need these, too.

EM1 mixes elevator and flaps so that the LE flaps droop with up elevator. With my Futaba 7-channel computer radio, I can set it up so that flap travel is limited to one direction only. You'd need to utilize the same sort of functionality here so that the LE flaps don't go up with down elevator.

EM2 mixes aileron and flaps in a standard flaperon configuration.

The servo reverser is necessary only if you want the pushrod to come off opposite sides of the servo. Our Su-27 requires this because of the tight quarters for the elevator pusrod.

I have to use external mixers because my computer radio won't allow me to cross-mix flaps with both elevator and ailerons. I can do one or the other, but not both. This is because it requires that one control (flaperon or elevon) gets plugged into the flap channel and the other control (flaperon or elevon) be plugged in the the other respective channel (aileron or elevator).



So, here's how I envision a system working.

The flap channel is programmed on the computer radio to only go in one direction. This prevents the flaps from reflexing upwards.

EM1 works in conjunction with the elevators. Up elevator causes the LE flap to droop. Because the flap channel is programmed to only go in one direction, the LE flaps remain at 0 degrees with down elevator.

EM2 works primarily off the ailerons. Application of flaps causes the ailerons to droop, but still provide roll control.

Application of flaps would cause both the LE flaps and the TE flaps to droop. The LE flaps would continue to mix off the elevators and the TE flaps would mix off the ailerons. At full flaps, the LE flaps would become more or less fixed at a full-down position as would the TE flaps. When ailerons are used, the respective TE flap would actuate to effect roll control.

My computer radio has two types of flap/elevator mixing. The first mixes flaps with elevator like a control-line stunter and the second mix trims the elevator with the application of flaps. I personally would select the second so that I could trim the airplane so there would be no pitching with the application of flaps.

If you wanted roll control on the elevons, you'd just add a "Y" to the aileron and another "Y" to the elevator channels and add a third elevon mixer to control the tail feathers. Naturally, these would be active all the time regardless of the flap settings.

That's about it.

Dan

Thanks a bunch for the schematic. I was going to use the same control for the LE slats as for the flaps as well as controllling the LE of the horizontal stab. The electrical is relatively easy; it's the bloody mechanics of smooth operation of the airfoils. I have to solve the flaperon issue for the A-6 since it extends the length of the flaps and also (as flaperons do) operates in only one direction.

BeanerECMO:
You're welcome. Yes, the mechanical linkages can work, but tend to get pretty complicated when you want to do stuff like this. It sounds like you need to have have a "Y" cable on the flap channel with one leg going to the flaps and the other going to an external flaperon/elevon mixer on your ailerons rather than relying on transmitter mixing. For some of this weird mixing the simple transmitter mixing isn't up the the task. That's why I started thinking of using external mixers in conjunction with limited use of the transmitter mixing.

By themselves, the LE flaps should help the airplane handle higher angles of attack such as in turns and aerobatics without bleeding off as much energy as the wing without LE flaps. Or, at least that's what they're supposed to do.

I designed and flew an F-106 with fixed LE flaps without any problems. This model was based upon an earlier design called the Apex. That model's designer described in the article his early attempts at a pure delta that did not have the LE flaps. He said that the model lost a lot of momentum through the turns and the LE flaps cured this problem.

As long as the controls are torsionally rigid and don't deflect under air loads, you shouldn't have any problems with them. I seem to remember an article by either BoB Fiorenze or Dennis Crooks that was about adding LE flaps to a large Y/A F-18 twin DF. It was only used in conjunction with the flaps and featured a pin, operated off an air cylinder that went into a pocket built into the LE flap root to 'lock' the LE flap into place for high speed flight (a relative term given the power systems available at the time). Obviously they worked because he wrote and published an article.

But, his were only used at relatively low speeds when the flaps were being deployed and not active all the time. On a model the size of yours, I think one 1/4-scale servo per LE flap should be enough to actuate it, but also not be deflected by airloads. You could always build a Q&D test fixture and run it down the road in your car at 90mph to get an idea of how it would work. I did this to test free-floating foreplanes for jets and it allowed me to test my idea without wasting a lot of time building it into a model only to find out it won't work or that it needs more development in order to work.

But officer, I was only testing my jet leading edge flaps mechanical thingy! I am going to have to study your solution carefully. I think I have the concept but I'm not clear on a few things. For one, am I understanding flaperons operating in only one direction to mean they flex from 'neutral' downward, but not upwards? I am also building an F4D Skyray-further along with it than the Su. My wife has some heartburn with the number of servos, etc. I've been buying lately. I have thought about building the LE slats for that too. Therefore your solution would work for that also. I have an 8UAF and the Futaba Techy here said I could have flaperons and elevons/tailerons but I haven't figured it out yet. I have the elevons mixed on Ch's 1 and 6 I believe which is normally the flaperon method, but, I think there are other ways of doing it. In the Su 27 DVD, the plane takes off, climbs vertical, does an inside 90 deg 'loop', rolls over to level flight, all as near as I can see with LE flaps down( max 40 degrees according to the specs I've read).

WHOES KIT?? PLANS?? NICE JOB!!

On the planes (jets) with which I am familiar, the flaperons go from neutral and deflect up.

With flaperons, the neutral point moves downward. When the flaps are added both ailerons droop, but still function as ailerons. It's the same mixing functionality as elevons but on different channels.

On my Futaba 7UAF, the flap channel works like a standard radio channel. When the knob is centered, the flaps would be at the neutral position. Turn the knob to the left and the flaps go up. Turn to the right and the flaps go down. By messing with the settings, I can change this so that with the knob is turned fully to the left, the flaps are in the neutral position and turning the knob all the way to the right moves the flaps to the full down position (or vica-versa). IOW, by monkeying with the settings, I can make the flap channel behave as it's supposed to behave.

What the Futaba tech is talking about is probably channel-to-channel mixing. My 7UAF does the same thing, but the problem with using that solution is that only one channel (the primary) is moved with the trim slider. So, using this on ailerons or elevator is useless because only one side is trimmable.

Elevon mixing is built into my 7UAF and is done on channels 1 and 2 (Aileron & elevator). Channels 1 & 6 are usually used for flaperon mixing as you wrote.

The full-size probably has the ability to select manuevering flaps (or whatever they call) where the LE flaps droop to a more or less fixed position. I also thought about ways to do this where you could drop one notch of flaps and the LE flaps would droop. Next notch would cause the LE flaps to drop to their full-down position and the TE flaps would go to half position and the last notch would cause the TE flaps to go to full. But, this setup would be even more difficult to mix, so I decided to pursue the method I described earlier.

Dan

To Rapptor: The plane is built from Bertelli plans (from Italy), modified a good bit. Wish it were kitted! Dan: I like your approach and will probably go ahead and buy some mixers to experiment with. I need to work out the air brake mechanics too. I think I'd like to slave the brake to the flaps(flaperons) but not sure of that 'mix' either. An interesting side note-I think-was found in the Mil-Tech series book, chapter 'How to fly the Su-27', stating that it can be flown with control at under 100 kts! One of my favorite full size exercises is mushing about at slow flight. If you screw up, it says you push the little button on the upper right of the stick and you're straight and level-regardless! The 'Cobra' is commenced at 220 kts, 85% power, pull back with 35lbs pressure-to overide the AoA limiter, etc. It touches down at 125. You gotta love the Flanker!

Yes, you're going to love flying it. It's a very honest airplane with no surprises or nasty habits. It's very well behaved at low speeds.

Speaking of Cobra's... I'm not sure if you've already seen this video, but here's a [link=http://www.allaboutguppys.com/flanker/su-27_2_cobras.mpg]short clip[/link] of Daren executing a couple of Cobra's with his Flanker. The second one turned out pretty well. He hasn't quite reached 100 degrees, but it's close. As you say, we've discovered it works best if initiated at low speeds and high power.

Dan

You are right, the second one looked great! Hard to tell it from the real one, I think just the sheer mass of the FS makes it appear slower. The "Ram-K" DVD has a couple with Pugachev doing the maneuver, it's really an awsome looking maneuver. I like watching it do the tailslide too. I've ordered my first mixer and will experiment with your design.

Not only does it appear to fly slower, but it also makes it easier to pitch the airplane up without altering the flight path. Our little Flanker is pretty lightly loaded (28 oz./sq. ft.) so you have to enter the manuever at a pretty slow speed. If you enter too fast, the model pitches up just fine, but it looks more like an entry to a square loop than a cobra.

Since your's will be much bigger and heavier, it'll be easier to pitch it up without causing a change in the flight path. I really got a taste for this with our 1/4-scale PT-19. It has to be flown using full-size techniques. If we allow it to build up too high a sink rate on final approach then yank in a bunch of elevator to flare, it'll change attitude but still continue on it's flight path right down to the ground.

Cool! Which mixer did you order?

I got something called an 'Art-tech'-maybe I should have asked first, does it matter? I've never used one so I figured one is as good as another. Didn't want to spend $55 for a top of the line. I ordered 2 since think that it what I need to start with. I use a Futaba and a Hitec servo so I don't need a reverser. I'll probably set up a dummy rig to test it out. Figure I need pretty heavy duty linkage on the LE flaps to minimize any flexing.

No, I don't think it matters as long as it works as advertised. I agree that short, stout linkages are a good idea. I like these kinds of little side projects. They make model-building interesting.

Dan

[quote]ORIGINAL: DanSavage

Hello Dan,

Thank you for the diagram.
I can follow the diagram and your explanation
on 2 mixers and one servo reverser closely.
But the above part of adding the third servo
with two Ys on the elevator and ailerons for tail feathers, I am
not quite sure I fully understand it. Please give more
details, explantion for this part. Or better yet, a diagram
of it would be nice. I would appreciate your
help very much. I guess I am "step by step" kind of guy.

Thank you.