RE: Su-27 L.E. flaps
 

You're welcome.

No problem. This diagram should help. You just set up actual elevons using an elevon mixer. But instead of plugging the mixer directly into the receiver, you plug it into another set of "Y" cables on the aileron and elevator channels. They'd be active all the time, but I don't think having roll control on both the elevators and ailerons at the same time would adversely effect the handling characteristics of the Flanker. We've flown then with both elevons only and ailerons and there's no difference in how it handles with either one.

http://savagelight.com/images/SU-27Controls2.gif

RE: Su-27 L.E. flaps
 

Interesting discussion. You've probably already seen this video, but it does show some of the control functions of the various control surfaces during pre-flight (except the leading edge flaps, of course). From what I can see, there may be some upward reflex in the flaps used during certain maneuvers. There is in the pre-flight check.

In the roll pass, I think he's using ailerons and elevons. I can detect some deflection in the elevators. Good cobra footage too.

Su27.mpg (7.5 Mb - no sound)

And some others I'm fond of for obvious reasons.

rtp-cobra.wmv
rtp-double_pass.wmv
rtp-roll_loop.wmv
rtp-tailslide.wmv
rtp-takeoff.wmv
rtp-taxi.wmv

They look like mine! ;)

Right click and Save Target (or Link) As. I will keep these online for a week.

Daren

RE: Su-27 L.E. flaps
 

No difference with or without ailerons-very interesting. I wonder to what extent the speed differential between FS and model may make some controls unnecessary. Maybe the wing loading has more effect than the speed factor. Have you ever clocked your plane? BTW, what size servos do you use for the elevons?

RE: Su-27 L.E. flaps
 

What I meant was that the model flew the same with the elevons controlling the roll as it does with the ailerons controlling the roll. Yes, arount 90 mph. Hitec HS-81MG. They're pretty small and light and have a reasonable amount of torque.

RE: Su-27 L.E. flaps
 

Hi dan,

Could you please give a guide on how much
the LE and TE flaps should be drop? More TE less LE???
Look to me that the TE flaps should drop much more, twice???,
than the TE flaps.
I need a safe guide to start on mine and I would appreciate very much
for your help

RE: Su-27 L.E. flaps
 

While I couldn't say for sure what they both should use, if I were to set up my own, I would start with the throws shown below:

I would ignore the high-speed cruise setting, however. ;)

Dan

http://SavageLight.com/images/WingControls.jpg

RE: Su-27 L.E. flaps
 

I attempted to set up the mixer configuration using 2 mixers to test the operation, only to discover one of them was DOA. It will take a while to get a replacement. I see one thing that may or may not be an issue and wondered what your thoughts were. The mixer(s) are going to respond respond to the amount of stick you feed in, right? E.g., if you give full up elevator, you would get 'full down' LE flaps. On take-off, you would 'level' the elevator which in turn would 'level' the LE flaps. It seems you would want down LE flaps until you got to speed? I noticed there is something called an 'Omni' by Vee-Tail which is a programable mixer- they're apparently not shipping now though. I guess my point is I don't think you'd want the flap configuration constantly changing. I could, of course, be missing something!

RE: Su-27 L.E. flaps
 

Correct. Technically, they're the RC version of CL stunt flaps where the flaps operate in conjunction with the elevators. I had been thinking about something you wrote in an earlier post where the video of a full-size flanker showed the LE flaps deployed instead of operating like stunt flaps. So, I came up with yet another control setup seen in the pic below.

Instead of tying the LE flaps into the flap channel, you'd tie them into the aux channel of a 7-channel radio. This way you could deploy them seperately from the TE flaps, but still get the effect of stunt flaps when the LE flaps are retracted, ie down flaps with up elevator. As far as the flap position constantly changing, I don't really see that being a problem as long as the amount of flap and elevator are more or less aerodynamically balanced. CL stunters have been doing this for years to increase manueverability. I'm thinking of building a system like this for my Platypus.

Dan

http://SavageLight.com/images/SU-27Controls3.gif

RE: Su-27 L.E. flaps
 

I must have been wrong about the VeeTail Omni mixer, I tried again and it took my order. It's a programmable system that appears to have a lot of options (www.veetail.com). With a replacement and the Omni, that will give me the 3 mixers to experiment with. With my 8UAF, I should be able to come up with something! I've watched that DVD dozens of times and go through segments frame by frame to try and understand how the surfaces work. I'm PDS(pretty da.. sure) the LE flaps do not reflex upward, though interesting in the above pic. If you guys could could chip in $10,000 + travel to Russia, I'd go ride in one and clear this up once and for all! If only my wife would win the Powerball.............

RE: Su-27 L.E. flaps
 

This mixer sounds pretty cool. I read their manual and they talk about using their mixer for both elevons and flaperons and how to set up for both. They explain how flaperons differ from elevon mixing in that the flaperons start at a neutral position and only go down, just like we're talking about doing instead of up and down like elevons. So, while it'd be pretty expensive, three of these mixers would give you pretty much complete authority over all the controls and have them pretty much behave like you want.

I've been thinking about it and can't really see a reason why it would hurt to have the LE flaps (and/or TE flaps, too) reflex upwards with down elevator. If I were flying inverted, I'd want the same sort of manueverability available as when I were upright. I wouldn't want it to be super-manueverable when upright and relatively un-manueverable when inverted. But, if the mixer is able to inhibit the reflex, then it sounds like it might be the ticket to be able to make the controls behave either way.

Combining these mixers with the on-board transmitter mixing opens up a ton of possibilities. For example, by slaving the aux channel to the flaps channel using the transmitter's programmable mix, you'd be able to couple and decouple the LE and TE flaps in flight with a flick of a switch. So, if you wanted max manueverability mode, such as you've seen in the video, you would decouple the flaps, then twist the aux channel knob to dial in some LE flaps. Then, when you're ready to land, you'd flick the switch back to couple the flaps again, then twist the flaps knob to lower both the LE and TE flaps simultaneously. You get the idea.

Dan

RE: Su-27 L.E. flaps
 

Some pics of the LE flaps mounted with full length piano hinge on the bottom. I use a laser level mounted on my camera tripod to check the surfaces. The light gives a very interesting flow over the surfaces and seems to 'flow' as one would expect air to move. I took these late in the evening to allow the light to be seen. Have my 3 mixers now to experiment with. The next step is working out the mechanical linkage.

RE: Su-27 L.E. flaps
 

Very cool. I was looking at where I wanted to hinge my LE flaps and I think I've decided to hinge them at the top rather than the bottom as you've done. I'll post a drawing to show the rib profiles.

I was thinking about the mixing and I've pretty much decided to hook my LE flaps to the aux channel and not have them mixed with elevator. Instead, I'm going to program the pre-mix to slave the aux channel to the flaps.

Thinking a little bit more about how they'd be used in flight, I've decided that the best way to do this would be to have the aux channel knob already twisted to full deflection, then control them using the pre-mix swtich.

When the pre-mix is disengaged, the LE flaps will droop to max manueverabilty. To retract the LE flaps, I would simply flip the pre-mix and the LE flaps would retract to the TE flap position (zero degrees). When I need flaps for landing or slow flight, I would then only have to twist the flaps knob and both LE and TE flaps will deploy.

This is much simpler than what I'd written before --too many knobs to twist, way too much pilot work-load.

This way, you only have to flip one switch to deploy and retract the LE flaps and one knob to twist to deploy and retract flaps. Everything else is handled by the mixers (Trx & on-board).

RE: Su-27 L.E. flaps
 

Since my flaps were not designed into the wing, I opted for the bottom hinge location with some lithoplate strips on top to cover the gap with flaps down. I use a dressmaker's tracing wheel to make rivots from the reverse side. It actually adds quite a bit of rigidity. In the 'up' position, the strips slide over the covering and barely raise the surface. Note the gap created on the root side with the flap down. This is why the full size has a circular taper built in. I can cure this with some work but note it's presence. I'll study your new sytem, agreed lessoning the workload is important. The full size has a computer to do this.

RE: Su-27 L.E. flaps
 

I had thought about hinging mine at the bottom, too. I couldn't think of a suitable wiper system that would be easy to build into a small model, yet light enough and strong enough to work well in the air. So, I used full-size airliners as an examples that keep the top surface relatively clean and the bottom surface dirty (aerodynamically, speaking). So, I opted to have the gap on the bottom.

I'm also attaching the latest wiring diagram that removes the mixing between the elevator channel and the aux channel.

RE: Su-27 L.E. flaps
 

Hi Bill,

I thought you'd be interested to see the latest news on my LE flap installation.

I created a test rig to configure and test the mixing and to use for aerodynamic testing to confirm the torsional rigidity of the LE flap and whether the servo would handle the loads.

So far, so good. The control is torsionally stiff and the servo was able to actuate the control at 75% of the maximum speed that the model is expected to achieve.

I've made a few changes to the wiring. Instead of using an external mixer (EM2) for the flaperons, I'm using the internal mixing. I'm also tying the flaperons to the elevons through the transmitter's internal mixing rather than the "Y" cable shown in the schematic above. This allows me to couple and decouple the elevons/flaperons with a flip of a switch.

I've also created a short video showing the mixing operations. If you'd like to see it, I'll post a link once I've put it on my web site.

So, the next step is build the wings that will be used on the model. There will be minor revisions to the LE flap linkage to make it easier to use and more precise. I'm also going to make changes to the servo hatches to make those lighter and easier to adjust the linkage.

The last two pics illustrate the camber changes to the wing when LE and TE flaps are deployed.

FWIW, in reviewing some video I have of some Flankers, I discovered that the Flankers use both elevons and flaperons which appear to be coupled all the time in the roll axis. So, I will be duplicating this on my model. (See: [link=http://savagelight.com/video/Su-27Elevons.mpg]Su-27Elevons.mpg[/link])

Dan

RE: Su-27 L.E. flaps
 

Hi Dan! Definitely would like to see the video. If that's an active link at the bottom, I couldn't get it to come up. I agree the flaperons/elevons do appear, on the 1:1, to be coupled, albeit, doesn't appear to be much movement on the flaperons. Honestly, I like your hinging solution better. The wiper is problematic, but I will probably try some 1/64th ply before abandoning the bottom hinges-the lithoplate is too stiff. In terms of the pressure exerted, I don't know which method is stronger. I haven't made much progress on mine lately, frankly, trying to finish up some other planes on the bench. As cold weather moves in here, I need every inch of space to work on the Su. Since my wings are built up, my servos will have to be placed in the fuselage area. In watching the Ram-K DVD of the full size, it appears the LE flaps are down throughout all the acrobatic maneuvers shown. I'm assuming, therefore, the LEF's come up only at flat out, level flight. I'm not sure what size servos are needed, however, when they're 'extended'-or deflected- they should be at the servo's max position and not really 'holding' anything. Bill

RE: Su-27 L.E. flaps
 

Hmmm....... I got the video to work. That is a lot of movement in the flaperons! Guess it doesn't show up that much in flight ,and it may take much less to actually roll the plane.

RE: Su-27 L.E. flaps
 

Here's a link to the video. (See: [link=http://SavageLight.com/video/WingControls.mpg]WingControls.mpg[/link])

Before I explain what you're seeing in the video, I'll respond to a couple of ponts you made.

Yes, that's my take on the LE flaps, too. As near as I can tell from the videos I have, the LE flaps are all or nothing, which I have duplicated in my mixing set up. I can actually mix the LE & TE flaps to the elevator, ala CL stunter, but will probably end up with scale controls.

Yes, I'm setting up my servos so that the linkage will be in line with the servo shaft when retracted so that any loads will be transferred to the shaft/case and not to the arm itself.

================================================== ==========================

TE Flaps
Background: My TX (Futaba 7UAFS) incorporates flaperon and elevon mixing. Flaps are usually assigned to channel 6, which is controlled by a knob. The TE flaps are controlled using the internal flaperon mixing. Someone who has a non-computer radio may incorporate flaperon mixing by using an external mixer, such as the VeeTail Omni.

Video: TE flaps are lowered, aileron stick is wiggled to show flaperon mixing.

LE Flaps
Background: As the schematic shows, I hooked the LE flaps to channel 7. On the 7UAFS, channel seven is controlled by a knob. Early on, I decided that I did not want to be messing with knobs for the LE flaps. Since I knew that I wanted to couple LE flaps to the TE flaps, I set up a pre-mix (PM1) to couple the LE flaps to the TE flaps so that when I lowered the TE flaps, then the LE flaps would be lowered at the same time. A side benefit is that my Tx has a switch to enable to disable the pre-mix, so by turning the channel 7 knob to full (down LE flaps), and leaving the TE flaps up, I can flip the mix switch and lower and raise the LE flaps instantaneously.

Video: LE flaps are lowered by the knob, then the switch is flipped several times to raise and lower LE flaps.

LE & TE Flaps
Background: Using the internal mixing, I coupled the LE flaps to the TE flaps so that when I twist the knob, both LE flaps and TE flaps are lowered together when I twist the TE flap knob. Mixing of the two channels is controlled by the pre-mix switch. When the switch is flipped and the LE and TE flaps are decoupled, the result is that the LE flaps 'flip' between full-down and whatever position the TE flaps happen to be at the time. If I have the LE flaps already at full down (pre-mix off), then twisting the knob simply lowers the TE flaps.

Video: LE and TE flaps are raised and lowered together using one flap knob. Ailerons are always available.

LE Flaps & Elevator
Background: The full-scale Flanker appears to have a 'maximum manueverability' mode in which the LE flaps are lowered to about 15 degrees. In practice, this transforms the LE flaps into vortex flaps, which helps recover lost energy (momemtum) in high angles of attack situations. But, when the LE flap is lowered, it does impart a little bit of drag. I set this mode up to allow me to test a variable flap system that is coupled to the elevator ala CL stunters. When the elevator is pulled up, the LE flap is lowered, increasing efficiency in the turn. When the elevator is released, the excess drag si removed and the airplane speed is preserved. The programming is set so that only up elevator actuates the LE flaps. Down elevator stick has no effect, although it could be programmed to reflex the LE flaps for inverted manueverability. Unfortunately, this mixing is controlled internally and by itself, may not be disengaged in flight.

Video: LE flaps are coupled to elevator channel and are actuated by pulling on the elevator stick.

LE & TE Flaps & Elevator
Background: Most TE flaps serve two functions; lift and drag. When flaps are deployed to less than 10-15 degrees, they provide additional lift. Beyond that, the drag increases. TE flaps can also induce a nose-down pitching moment. I set up this mode to give the maximum lift and efficiency without causing excessive negative pitching. In my installation, this mixing is controlled by the internal Flap -> Elevator mixer, which can be engaged and disengaged in flight. In addition, manipulation of the pre-mix switch (described in LE Flap section above) allows the LE flaps and TE flaps to be coupled and decoupled. There are several mixing modes possible here.

Video: LE flaps and TE flaps are coupled together, then slaved to the elevator and both are acuated by the elevator stick.

RE: Su-27 L.E. flaps
 

Impressive operation, Dan! I have an 8UAF, so I can attempt to copy your configuration. How soon do you think it will be before your ready for a flight test? My only comment would be whether or not you could, or should consider, adding a delayed response(slowing) time to the LEF deployment/retraction. Of course, with a proven airplane like yours, it should be easier to test the effects in the air. I don't know of much testing out there on the effects of the LEF's to know what one can expect. This summer, I placed some pieces of thread at various places along the chord and used a floor fan to see what they (the threads) would do. With the slow airflow of a fan passing over and under the wing, there was quite a noticeable change in the pattern of the flow. How that would translate to actual flying I don't know, but I think the created lift would be quite noticeable. As I recall, the airflow shifted back which I suspect would create some pitching. I thought about cranking up the leafblower to test the flow but never did. BTW, what model servo are using on the LEF's.

RE: Su-27 L.E. flaps
 

Thanks!

Upon reflection, I realized I still need to use EM2 because once I dedicate channel 1 (aileron) to flaperons, I lose the channel for use with elevons. So, I'll be using all three VeeTail Omni's after all.

I'm shooting to have it flying by the end of the year.

Yes, thankfully, the Omni's allow a delay. I've thought about whether I should slow them down or not. I probably eventually will, but initial tests will have them slam up and down, if for no other reason than if I don't like how they're trimmed, I want them up and out of the way --pronto! All joking aside, once I have them trimmed, I probably will add a delay to them.

Because I'm going to have several sources for potential roll control, I've worked out a testing/trimming schedule.

First flights will be made without LEFs or flaperons, just ailerons. The elevators will be programmed to act as simple elevators. This way, any roll trim will be concentrated on just the ailerons. Once they're trimmed, I'll reprogram the elevators to act as elevons, then trim roll again. Next, I'll add LEFs and re-trim roll as needed. Finally, I'll lower flaperons and do a final trim.

I had thought about putting tufts on the test rig, but when it came right down to it, I dropped the idea. I already had a pretty good idea of what the airflow was going to do, so I ended up just testing for proper operation and to see if I could get a feel for pitching moments.

My LEFs are pretty small ( 1" x 14.5" ), so I'm using Hitec HS-81MG servos (one each).

RE: Su-27 L.E. flaps
 

Just joining the thread. I'm about to start building my SU-27 propjet and would like to try this. Any new news?

RE: Su-27 L.E. flaps
 

Hi Bill,

Here's the latest news on my Su-27IB.

I've finished the model and I test-flew it yesterday. I was a little worried about how the LE flaps would affect the handling, but my concerns were unfounded. The model behaved normally, which is all I was hoping for.

I didn't use the LE flaps during the maiden voyage. Because of the complexity of the flight control system and the multiple sources of trim issues, I'm going to isolate the introduction of each new control system to limit the trouble-shooting to that one new control.

I've started a new thread on EZone. See: [link=http://www.rcgroups.com/forums/showthread.php?t=618948#post6645791]Sukhoi Su-27IB Platypus[/link].

Dan