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Old Jan 07, 2013, 10:54 PM
You are a "go" for reentry
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Originally Posted by Whiskey Whiskey View Post
...batteries come down quite warm. ...
.....
I like the idea of energy dissapation and the spacers to angle the mains forward. As far as energy dissapation though, you have less than 1mm to work with where the trunion meets the backplate. That doesn't present for many options. Anythin that would add resistance when the gear nears extension will draw more amps from the BEC, and I REALLY don't want to do that after my past fiasco with burning up BECs.

Aluminum plates it is for now. I suspect the next weak failing point will be the plastic trunions.
Thanks WW. I'll add the vid to the list. You are pushing it but you're off the throttle it sounds when you can. Turnigy and Nanos seem to be hit and miss. Sometimes better than everyone is telling you and others are thoroughly disappointed. They put out 125amps it just the last 2000mAh that are dicy where over time if you keep pushing into that zone you might see a drop. Get your heat gun and check the wires and the open ends of the battery.

As for shimming an angle of the main retracts you can do plenty. I did it only about 3-4* forward like the full scale. But you're right the L brace is specifically position not to hold the retract from engaging the cut off switch. It just doesn't allowing the retract to push against the plastic any farther. The L brace also allows small degrees of flex if the impact is that hard. All that nose slight high seems to absorb a lot of the landing force without trying to rip the mains off.

I keep forgetting you added that to the nose. I did actually shim the nose strut with washers on the back screws to also cant the strut forward.
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Old Jan 07, 2013, 11:58 PM
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Is this for the drag on grass, or the impact on landing?
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Old Jan 08, 2013, 01:25 AM
You are a "go" for reentry
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Which part?
The plat and stop protects over extending and flexing the trunnion (and therefore the worm gear and block) against the retract housing walls which occurs both with drag from grass and the impact from the tuffs of grass that sometimes snap the struts back. I'd definitly change out to metal trunnions just for the ware between the trunnion and the worm gear block.

The Nose strut shock is for landing rotational impact.

The trailing shock arm is for forward impact to the nose retract.

Shimming the backs of the retracts is for forward landing impact. And it lowers the mains slightly for the ground stance.
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Old Jan 08, 2013, 04:12 AM
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I got a heap of scale drawings of many of the Su-35/37/27 series with air brakes.
They all seem to be the same 'item'... size etc.
It is surprisingly narrow, and looks much like InTheTubeDeep's size anyway.
When you see a top view drawing it is just under 1/4 of the fuselage width at that area - pretty well equal to the cockpit glass width.

...
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Old Jan 08, 2013, 04:53 AM
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Pic 01 is a maintained scale overlay. (Original drawing to correct ratio).
Pic 02 has our Su stretched to suit the drawings proportions. It needs a reasonable amount of stretching. The reference points I used were the engine 'bulge' starts, the wings approx, and the cockpit/fillets line.

The overlay shows how far REARWARDS the airbrake really is, compared to our hatch. To make it like that you would have to cut out further rearwards of the hatch and splice that to the current hatch. I am pretty sure the ESC bay/area is under there so the amount to carve out would be limited. I would just cut it away, then make the replacement part from balsa and join that to the current hatch.
This also messes up the magnet/release system in its original form, so that would need a bit of thought to fix that up again. If you pulled on the current 'antenna cover' it would probably damage the airbrake before releasing the strong magnets!

The drive servo would still be done under the front end of the hatch, and use a pushrod down to the air brake. It would stay almost right along the hatch underside still.
Hinging would be done as per the correct design and position of the drawing.

Note how narrow it is!!
It doesn't seem to be an overly large area, relative to the massive plane and its weight! A bit of a "baby airbrake". Which is probably why it has to get to such a large angle at full deployment - for it to be of any great use!

...
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Old Jan 08, 2013, 05:24 AM
You are a "go" for reentry
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Up all night doing overlays Narrow but still outside the 35BM lines by about 5-6mm on either side. About as wide as the canopy. Doesn't need to be much wider. Considering the frontal area profile of the entire aircraft and then stick a panel this size up 56*, That's like opening all your doors driving down the highway. It'll slow down if your foots off the gas.

If you're serious about adding it, you may as well do a glass overlay. Get some plastic wrap, put a panel of glass epoxy, place another layer of plastic and add weight.... I use bags of sand to conform to the shape. Let it set and ... Air brake. Then just carve off just enough foam so that the glass overlay sits snug and .... well you can figure out the rest. And aft of the hatch you're still just taking off the surface layer so little anything to the structure and the brake would just sit on top.

I fabricated similar with the FW Euro from Kevlar. Just haven't finished it.
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Old Jan 08, 2013, 06:15 AM
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Oh, Whiskey, man!

That was a hot landing!
No wonder you experience so much trouble, you can try lowering a bit of speed, you are landing with a lot of innecessary energy... A trailing link mod would also help though!
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Old Jan 08, 2013, 07:17 AM
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Originally Posted by PeterVRC View Post
hmmm, the 25C seemed to perform very well !!! Amazingly well.
And how do they like their job??? Hot?
I wonder why he chose a 25C instead of say a 65C-100C? I wonderd as I will be ordering 2- 6 cell 65C-100C lipos today. If they are not a good choice I would like to know!
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Old Jan 08, 2013, 07:42 AM
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25 should be lighter, and deal with being abused (stored at full or empty) a bit better.

My 65C cells tend to be fairly fickle, I've had some rather nice batteries puff after leaving them fully charged for a week

If you can look after them, they'll reward you with better flights, and a longer life overall though.
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Old Jan 08, 2013, 08:33 AM
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I chose a 25C because theoretically it's supposed to work, and largely because it came out to $75 shipped from *bleep*. My power test showed the system pulling 101ish amps at WOT, which equates to 20C for a 5,000mAh battery.

The video may sound muffled because I'm learning my new GoPro. The skeleton case it came with and the skeleton backdoor must still be blocking some of the sound.

My intentions with the plates are to handle the aft directional forces from the trunions hitting the retract cases, which mostly occur during rollouts and landing impact.

I know my landings are ugly, but I have a hardtime slowing it down. The one time I got in a steeper & slower approach ended badly. I stalled after an overflare and collapsed the nose and a main gear. I didn't use my landing mix for the shown landing, but it doesn't see to make a difference anyways.

My landing/takeoff mix is 50% travel for flaps to maintain aileron effectiveness with some elevator deflection. 100% flap travel is bad, as you lose most of that aileron authority.
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Old Jan 08, 2013, 08:34 AM
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After a bit more investigation I opted for the 'scale' airbrake....
There was nothing of importance after the hatch, so that was a non-event to cut out. I used a printed out thin card template, made by that overlay of our model Su to drawings of the real one and cut/shaped to sit over the hatch outline for a reference.

My battery runs right at the rear of the tray area, so I have plenty of room for the hinge mechanism being further rearwards.
I have planned out all the parts and hinging system.... this will be ROCK solid!
Basically a plywood 'rail' is the basis of the whole assembly and strength, then the cut out foam outer just sits (glues) onto that. No stress/strength goes via foam. I have the same 'pivot arm extensions' they have to allow the airbrake to elevate above the fuselage when deployed, and it uses a 3mm pivot shaft across the ends of those which pivots off out-board 'bearing blocks' - and the pivot shaft has a control arm affixed mid way on that, so the drive system is powering the pivot rod, not an arm on the airbrake.

I made up half the parts, and should be able to get most of the rest done tomorrow night.

I just need to plan more on the 'under airbrake deck', because the negative part of my battery being more rearwards is that it comes very close to the inner top at the battery's highest point there, which is the point right at the rear end of the tray. This means that the inside 'deck' cannot be very thick at all - mainly there at least.
But I have a few ideas for that.

Servo... probably a 18g MG like on my elevators.

Oh... and I removed that 'fake' antenna stalk (hatch grip)... they don't even have one anywhere near as big as that anyway. I have an idea how to use the new 'much smaller' antenna stick I will put there to be used as a slide-catch release, and thus get rid of the magnet system. (or maybe keep it too - not totally sure yet).

I think I spent one hour deciding on where to have the airbrake!..... another hour pondering the 'scale' way and any problems it might cause - sussing out what things were exactly where and what interferences etc.... almost another hour deciding how to cut it (angles etc), and then to cut it all out and trim things up.... and another hour of planning structures and hinging etc, testing stuff.
I have to find, or get, a few bits for specific areas of it. I might have enough of the right things around here already anyway... hopefully.

I only took the first two pics after cutting and joining the airbrake "panel", can do others tomorrow.

...
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Old Jan 08, 2013, 11:04 AM
Lori, hey, you're home early
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Quote:
Originally Posted by Whiskey Whiskey View Post
...I know my landings are ugly, but I have a hardtime slowing it down. The one time I got in a steeper & slower approach ended badly. I stalled after an overflare and collapsed the nose and a main gear. I didn't use my landing mix for the shown landing, but it doesn't see to make a difference anyways.

My landing/takeoff mix is 50% travel for flaps to maintain aileron effectiveness with some elevator deflection. 100% flap travel is bad, as you lose most of that aileron authority.

WW-- I still haven't picked up my Su (bought it last fall and it's still at a friends house!!) so take this with a grain of salt. I fly most of my planes with the rearmost CG point possible without making them very unstable. You'd be very surprised just how slow you can get a well designed model if you take as much "nose-heavy" out of it. I'd rather add weight to the tail than fly a plane that's even a little nose down at CG. My 2 . (If it works let me know before I fly mine ).

Mike
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Old Jan 08, 2013, 11:55 AM
Flying Hazard
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Quote:
Originally Posted by Whiskey Whiskey View Post
My landing/takeoff mix is 50% travel for flaps to maintain aileron effectiveness with some elevator deflection. 100% flap travel is bad, as you lose most of that aileron authority.
Another reason to use fully functional tailerons
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Old Jan 08, 2013, 11:57 AM
Should've, Would've, Could've
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Nice job Pete, when's your Russian tank gonna fly again,
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Old Jan 08, 2013, 12:09 PM
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Originally Posted by SU-4ever View Post
Another reason to use fully functional tailerons
I agree, but my 9ch Tx is maxed out with the flaperon mix. If I can't get it down eventually, I'm going to scrap it and put in the taileron set up.

I agree with the aft CG shift recommendation, I just haven't been flying it enough to work on it much. That's mainly due to me grounding it after finding landing gear cracks. I still have 3/4 of an ounce in lead in the forward nose gear compartment. Now that you've reminded me, I'm going to remove 1/4 of it like I did previously.
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