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Jan 09, 2013, 12:25 AM
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Speaking of Su35 Retracts...

Here is what I did to my front retract after the trailing arm linkage flew off on a rough landing

Freewing Su-35 Front Retract Trailing Arm Mod UNBLOCKED (5 min 22 sec)
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Jan 09, 2013, 12:47 AM
You are a "go" for reentry
Maxthrottle's Avatar
Originally Posted by IntheTubeDeep View Post
Hey MaxThrottle do you have a YouTube channel? Was hoping to see a few of your Su35 vids (sorry got mixed up)
Sorry I don't have a camera crew. I would if I could hook up a channel tracker and a camera together.
Jan 09, 2013, 06:49 AM
Flying Hazard
SU-4ever's Avatar
Originally Posted by Maxthrottle View Post
Sorry I don't have a camera crew. I would if I could hook up a channel tracker and a camera together.
If you pay me a flight wherever you are, I can film... hahahahahaha!

Originally Posted by Maxthrottle View Post
I flew CG165. Odysis I think you set a new record for aft CG. That's actually past stable neutral. Mind you the stickers vary as they are... stuck on. But curious on the details of your flights. Did you post Video?
I don't agree.

If you follow this easy procedure to find approximate mean aerodynamic chord, CG should actually be at 25% from leading edge of that MAC (That is just a common design parameter for a fairly nose heavy setup). I'm well aware that on the pic the plane isn't 100% perfectly flat, and that I'm not counting the lift generated by the LERX and thus I'm making some mistakes but that gives a good approximation anyway as to where CG should be. And that is pretty much AFT of what you are calling neutral, guess where the true neutral really is, even farther back. Stock Su-35 from freewing with factory setup needs A LOT of stab trim to center. Consider that you are trimming with HUGE stabs, that is, very little change in angle is a lot comparing to other aircraft. I'm not telling anyone to make that CG centering, don't want to hear anyone blaming me for a crash but since that approximation is for Noseheavy CG, I'm pretty sure "neutral" is very much aft of that drawn line. At least a 10 to 25% more of MAC.

Hell yeah, I love fat-ass planes!

PS: The 2 parallel black lines are MAC.
The black line that intersects both is expected position for CG.
That is right just ahead of retracts, and thus a great place for easy rotation.

Last edited by SU-4ever; Jan 09, 2013 at 07:17 AM.
Jan 09, 2013, 07:00 AM
Life begins at transition
Where'd you get that diagram from? I was taught to always project the LE and TE to the fuse c/l - it works as a very rough approximation for the wing/body.

As is it would produce a tail-heavy AC compared to extending to c/l...
Jan 09, 2013, 07:02 AM
Registered User
I interpretted the CG pictures wrong when I looked back at the one of the attached drawings...
Jan 09, 2013, 07:25 AM
Registered User
Delays.... I only had/allocated about 45mins to the Su tonight.....

I made up the 5mm 10ply 'hinge arms' and the 'airbrake backing plate' (160mm x 20mm x 2.5mm ply plate).
Then cut out the 'fuselage' (hatch) hinging arm slots and tested things (distances, angles, rotational clearances etc), and everything operated as planned so then I glued in all those bits.

Rather than build a whole 'jigsaw puzzle' of pieces to assemble together, it is all done 'piece made at a time", so that each next part is made to perfectly fit its position and task. Which allows some flexibility to alter, or correct, not so perfect prior pieces, or alignments.

To assemble.... the backing plate is just glued onto the airbrake foam by itself first. The 'hinging arm' slots are cut into the hatch foam ahead first, then the arms, which are spaced further out of that airbrake backing plate, are fit into the foam to each be vertical and in those cut out 'arm slots' - thus assuring alignments are dead right.
Later on I will add a 2.5mm ply flat plate cross piece that bridges the backing plate to the arms, for 'more than adequate' total strength to that whole 'under airbrake' structure.

The arms get a pivot pin across them at their front end, which pivot off a structure that will look very similar to the airbrake underside assembly, and which goes into the front hatch end. A 3mm pivot shaft, which runs through 3mm sleeves inserted into the under-hatch assembly for bearings. A nylon steering arm is used for the airbrake control horn (a flat filed onto the airbrake pivot shaft of course).
A 2.5mm x 30mm approx 'backing plate', which runs right to the hatch's front bulkhead. Which then also gives the servo mount support - so that it is all directly 'linked' and can't have any loss of zero tolerance due to the servo 'moving' (like a freely mounted servo assembly could allow).

The airbrake hinging arms pivot off their pivot rod which is situated only 3mm approx off the inner top of the hatch. You need this sort of pivot point to have the airbrake come up and out of the 'slots' correctly, and it also reduces any 'angular motion fouling' of edges etc.

I will probably run 1mm or 2mm thick balsa 'edges' down the airbrake edges. Maybe even on the hatch facing sides also. Seeing 'raw foam' is pretty weak and rough looking. (and what's another 20mins of effort! hehe). Balsa 'capping' gives a clean strong finish to edges.

I will build up the 'under airbrake' internals (the upper side of what is in the cutout hatch area, right above the battery) from balsa, so I can shape it as required and also do a bit of 'battery dodging' in the rear hatch area.

I have an idea for the ram - which will just be a slave anyway, two CF tubes sliding freely one inside the other. Dress them up a bit with 'ring sections' etc, and paint silver (or whatever color they are meant to be).
The main issue with the ram will be how it attaches at the rear end of the hatch area, seeing that is now in the main fuselage and thus not 'removable' like the hatch is - but the current plan is that its end will just be a 'click in' T-bar, so it will easily come off with the hatch still. The exact design yet to be finalised.

I like seeing things being done operate, to give an injection of enthusiasm(!), so I will be doing the pivot and servo stuff next and have that all operating off the RC... then on to the finishing of edges, ram etc.
Hopefully that 'operating' part all done for tomorrow night.

Hmmm, I just noted in my quick "on the fuselage" check and pic..... there are EIGHT other aircraft in that pic! Making it a bit like a 'spot the difference' pic, LOL. (plus a few parts of two other aircraft that are not caught in the pic - and the tail of a heli (500) seen too.). Turn the camera about 60deg left and there would be a different 7 aircraft in the pic! That room is FULL to the brim with aircraft (about 16 complete, and 5 boxed still) and 1000 other bits and pieces!

Last edited by PeterVRC; Jan 09, 2013 at 07:38 AM.
Jan 09, 2013, 07:26 AM
Flying Hazard
SU-4ever's Avatar
@Peter, nice pilot there, better than original!

Originally Posted by Odysis View Post
Where'd you get that diagram from? I was taught to always project the LE and TE to the fuse c/l - it works as a very rough approximation for the wing/body.

As is it would produce a tail-heavy AC compared to extending to c/l...

Yes, your method should also work.
Like considering the plane as a huge flying wing!

Ok that's right, doing that you get a CG ahead of factory recommended. In any case, "stable neutral" is farther back, like drawing a line uniting both MAC centers.
Jan 09, 2013, 07:42 AM
Registered User
acesimmer's Avatar
Peter.... Nice implementation. With you guys doing this mod it inspires me to now do mine. I'm thinking to just pull a mold off the top section then lay it up in epoxy glass. This way I can laminate the mechanism into the layup and it will be thin yet strong and light weight. Just have to figure if I want to have a nice smooth skin finish or have the foam detail built into the mold so it all matches. I use a special PVA release that should allow me to pull the mold straight off the foam fuse without using film etc. I'll wait until you finish yours and see how it works.

Those of you who have done the air brake mod.... Any change in pitch etc when deploying? Peter, when will you have your slats finished. I'm thinking of maybe making up a glassed wing version slat installation that is mixed into the air speed. So that maybe around half throttle and below they begin deployment proportional to speed and can be turned off with a switch. Does this make sense? Now if we could hook them up to a G device and include a high pressure smoke device to create the visual pressure wave coming off the surfaces would be way cool.
Jan 09, 2013, 07:45 AM
Life begins at transition
The line joining both MAC's is the wing's AC.
Combine that with the tail's AC, and you can get the neutral point.

Either way, all that I only ever use for a first flight of something that hasn't flown yet (scratch or new model, like the HK viper). After that, flight testing is where it's at.
Jan 09, 2013, 07:50 AM
Registered User
Why do you use "50% of the chord"?
Wouldn't it use a line along the "thickest part of the chord"? Thus then a line along the main wing panel's CoL. eg likely to be some amount ahead of, but still parallel mainly, to that used line in the pics(?).

Then draw all the 'cross angles', as per done, and then try to fudge in what the fuselage lifting body adds in. More ahead... more aft....???

In all those many possible ways of doing it, I can see a LARGE variation in what various people's ideas would come up with!

Seeing it doesn't rotate very well - yet most people have a stable enough, but also pitchable enough, aircraft - that would suggest it is somewhere ahead of the main gear.... a reasonable amount ahead (seeing it won't rotate). Probably going to turn up about that 155mm area... hehe. (let's say from 150mm to 170mm..... somewhere in there).
Jan 09, 2013, 07:51 AM
Suspended Account
HEY does anyone here live in the Tucson Arizona area?
Jan 09, 2013, 08:15 AM
Registered User
Yeah, doing these things with glass and moulds etc, would be a far nicer/lighter AND stronger (hmmm, well at least easily strong enough) manner of adding things.
Too hard for me though!! (Well it sounds like it is hard enough to do!)

LEF's on a mix..... I haven't decided what to do with those yet!!
First is to just see WHAT they even do! By just manual Pot control.... at a safe height! lol
It will need quite a number of tests, of surface interactions, speeds, AoA's, too. eg flaperons on/off and varied angles etc. THEN onto predicting optimal interactions for their combined total uses/results, and mixing and testing those then. (most likely only flaperon/LEF, and likely NOT a good idea to have a throttle mix in there at all.)

But my VERY FIRST mission is STOL !! So it even gets airborne in my 22m !!
"Take-off flaps" helped my F-16 to just make it, so Flaperons might be the go for the Su - but the F-16 doesn't really seem to have any rotation issue like the Su (and F-22), so its task was an easier one anyway.
I will assess a total grass take-off process on the actual day, seeing they mow the ovals every week.

As for airbrake pitch effects..... that was one consideration I was assessing as weight for the side of fitting it more rearwards. I figured they would very likely place it to have either no pitch effect, or rather at least a pitch up than down effect. Thus my 'operational effects' weighting over-rode the 'easier to do' weighting.

Being X amount high when deployed, at the angle it is, I would guess its 'static' force vector is maybe halfway down its 'fuselage opening length'.. PLUS a bit more due to air deflection angles off it. So maybe 3/5 to 4/5 down its length rather than 1/2 way.
Thus getting close to CofG area.....
As it deploys more, it physically 'moves forwards' effectively... but I think the airflow resultant would keep the actual vector in a similar position for any airbrake angle anyway. (bound to be at least some movement of it, but not as large as you might think if you only went by the physical position change of it)
And.... another thing to test at a safe height first! hehe

Plus I might be forced into using different batteries, or a battery position mod, to get things all balanced out. Or at worst..... ADD LEAD!!! (at the rear end) I would hate to have to do that.....
I would just throw in a set of Lander 10 bladers instead then!!! Heavier.. down the rear.... and more power too.
Jan 09, 2013, 08:57 AM
You are a "go" for reentry
Maxthrottle's Avatar
Well I agree with your assessment on the model makers intend for Static Stable by setting the 145-155mm CG range.
You picked up on how the original posted picture was off. You measure to the center line of the aircraft like I posted in I think post #9 (how come you didn't say anything before?). In that diagram I used 35%, as an estimated optimal lift for the foil on this model and came to the 167mm from which the model should tend to stay in its most recently commanded attitude or condition, without oscillations, and it will neither tend to return to its previous state or diverge from its new attitude.

The full scale has the main gear swept forward slightly and 10-15* forward of the tire from the ground you get a sense of the datum. But the full scale foil for one is different and I couldn't be bothered to calculate the lifting body, but its somewhere around the 200mm+ mark.
When Analucas I think it was tried 170mm he found it needed correction, difficult to handle. I interpret that such for this model as moving from Neutral Static Stable depended on velocity.
180mm as Odysis thought he was at or even to 190mm and you're in my guestimate, unstable neutral conditions where you start needing counter input to seek equilibrium. Past that you're in need of a good FCS.

You're the one in school . Do the full calculation on the model as an assignment and come back with the Tailerons dynamics and velocity range along with the lifting body in the equation.
But putting the CG way forward even 155 and its still nose heavy enough that its self correcting. I found that when I was diving and vertical trimming it, to get a true neutral, I needed an even less sensitive movement in the stab with servo/linkage setup. So for now I sit at 165.

Originally Posted by SU-4ever View Post
@Peter, nice pilot there, better than original!
Yes, your method should also work.
Like considering the plane as a huge flying wing!
Ok that's right, doing that you get a CG ahead of factory recommended. In any case, "stable neutral" is farther back, like drawing a line uniting both MAC centers.
Jan 09, 2013, 09:25 AM
Lori, hey, you're home early
CarreraGTSCS's Avatar
...and 165mm is about the center of the aileron wire entry hole in the fuselage which Odysis had mentioned as well. Lots of very interesting theoretical conversation but really the proof is in how if flies. It's very tempting to fly nose heavy as the plane will be more stable but once one actually flies a well balanced model and experiences flight at the "sweet spot" there's no going back.

I've, for a long time now, been doing this with my prop warbirds as a matter of course but for some reason not with my EDF's. Perhaps because early on they didn't feel adequately powerful I unknowingly flew them noseheavy which in the case of an underpowered model is somewhat self defeating. In any event one day while flying my Sapac Eurofighter after not having flown it for some time I noticed that it was flying so much better. It wasn't dropping the nose in the turns. It was maintaining high alpha better and I could slow it way down wiyhout it falling off. I realizex that I'd pushed the battery back much further than ever before. Transformed the plane.
Jan 09, 2013, 09:55 AM
Suspended Account
I just wanted to take a moment and thank all who contribute to this forum!. The information provided here takes me awhile to digest, but I know I will benefit. 1 Year ago I suffered a MAJOR brain stem stroke and chose RC flying as a kind of rehabilitation method. At 54 years old this stroke was devastating to say the least!. I lost my vision as well as my whole left side. I have since recovered my vision and have full use of my left side . Although I can use my left arm and leg and have good dexterity and full strength my left side is still 100% pins and needles numb. I guess I am lucky I am not dead from the stroke as the stem controls heart, breathing, and other important things. I have this jet and am assembling it as well as adding all the upgraded electronics you all have talked about here. I will set this jet up for flying 100%. I wont however fly it until my skills get lots better (I am practicing on another much easier airframe). I just had to own this as its a work of art!. I guess the reason I am telling you all of this is so you can better understand any DUMB questions I post here. I truly appreciate any and all help I receive here.

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