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Dec 09, 2012, 05:58 AM
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I am "aiming" for 4.0Kg... LOL
Well 3.5Kg area, or so. Probably somewhere 3.3Kg to 3.4Kg now.

The nose gear has the 'Ram shock absorber' so that is enough for all normal situations, even on grass. But I guess over time the airframe will have 'metal fatigue', err 'foam fatigue' in other areas. Though if it was used only on a hard runway it would be totally fine long term.

The MAINS are a bigger issue... zero longitudal shock absorption. And the better retracts have no freeplay either. It can only come from wheels... and that is not much! Once the nose is down, the rears begin their punishment segment - landing on grass. Again, totally fine if on a hard runway.

More mass/inertia makes higher AoA landing even easier - everything is more stable and 'slower' acting, plus the higher weight can 'push through' higher AoA for the same speed as a lighter plane does for lower AoA (they can't even use higher AoA usefully - or they become a 'floater').... so you should be able to land the same speed as any lighter version anyway. Plus then add Flaperons etc.

I have not seen weight be an issue on any of (all) my 'overweight' planes. It is basically a 'composite' level of aircraft then. Heavier.... but I make them stronger too.... so it equals out roughly, hehe.
If I get around to eventually REPAIRING it all fully - to look pretty and new again., I will glass it all! (Very thin and with coloured [grey] WBPU 'resin').
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Dec 09, 2012, 02:45 PM
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Maxthrottle's Avatar
I'm guessing you'll be closer to 4kg with the repairs, LEF, plank ply, CF rods and plate steel and gear strut for nose gear trailing shock dampener, that all being just fuse weight. Then your radio setup dual BECs, heavier EDF setup etc, that's heavy even for a composite.

As for the AoA, that has a fixed limit for any weight; no more than a tail strike. More weight thus mean you will need more thrust and speed to maintain the same approach. Take off it just makes it that much harder and longer.

But like I said you're looking to cut down small trees with her I guess; though the foam shell will still frag on impact.
Look forward to your next attempt.
Dec 09, 2012, 03:38 PM
Should've, Would've, Could've
v8truckin's Avatar
Pete you can get rid of some of that weight by ditching your ram shock absorber and simple use a 1-2g spring vs the 50g that oleo weights, which in itself was a bit over kill but looks nice. Or do what Max did and incorporate the absorption into the trailing arm link, thus still a few grams heavier than the stock plastic trailing link. Also the armor plate for the retracts looks heavy just looking at it. If you can keep it 3.6kg max then I think the mains and nose retract foam won't take a beating on landings and crunch. I'm at 3200g with all my mods and sometimes she feels sluggish while doing TV manuevers. Hope you can get her off the ground.
Last edited by v8truckin; Dec 09, 2012 at 03:45 PM.
Dec 09, 2012, 03:58 PM
Registered User
No, I don't care about the weight... I am generally LOOKING for weight, in useful forms (never add lead etc). I had not weighed it before the prior flights, and the flights were 'distracting' with the notably nose heavy issue.... but I could still see it flew totally fine, fast... even with that nose heavy, large up trim, total. And even from many other aircraft I can predict the weight will be no issue at all.... out to even 4.0Kg.
So I will just weigh it as I finish it, but whatever it is it is... it won't matter at all.

When you watch any level of real plane (even a weeny Cessna etc) you can SEE mass and inertia.... and models don't have that. But mine do. The most visible time would be on landings.... how a plane moves at those slower, but still flying, speeds. eg light planes porpoise, unless avery ca;m day and a pilot makes large efforts to be super smooth. A heavy plane does not do that, nor need a pilot to 'fill in' the missing inertias - which can't even be filled in fully ever anyway. You must have the real weight to have real inertias.

But I have an ongoing issue that to do this stuff you NEED a proper runway! Not anything long... even 50m is enough.... but trying to get them off in 22m, into a shallow climbout (which is assisted by weight anyway, so that is ok), can be marginal... and then landing on grass is quite detrimental to the landing gear structures then.
You really do need a hard runway, or you are going to have damage costs ongoing!
Dec 09, 2012, 04:19 PM
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Maxthrottle's Avatar
Originally Posted by PeterVRC View Post a plane moves at those slower, but still flying, speeds. eg light planes porpoise, unless avery ca;m day and a pilot makes large efforts to be super smooth. A heavy plane does not do that, nor need a pilot to 'fill in' the missing inertias - which can't even be filled in fully ever anyway. You must have the real weight to have real inertias.

... even 50m is enough.... but trying to get them off in 22m, into a shallow climbout .....landing on grass is quite detrimental to the landing gear structures then......!
For the volume within the same air density, yes a FS will have a greater inertial effect but most of what you are talking about is how much force is required from the surfaces to move a light mass vs heavy. If you want a slow moment on a light mass then have the surface rate reduces. That will give you the less controlled feeling that you may be seeking.
That's how they measure up and SIM enemy aircraft regardless of the mass of the boggy, they reprogram the FCS to mimic the desired aircraft's know perameters and then see how they can out fly it. To SIM a manueverable but much heavier bigger SU27 they reprogram the much smaller F-16.

You have sufficient radio to dial in all that effect but above 3kg you already exceed the retract loads. You comment about bent mains etc, the heavier you are and the rougher the surface will only make all of that more vulnerable. So 50m is even less likely off pavement.

But hey, keep trying.... if you get it to stay in the air and still perform with such a high wing load, which is above the FS wing load at this point, I'll make you an elephant sticker to put on her tail.
Dec 09, 2012, 04:29 PM
Should've, Would've, Could've
v8truckin's Avatar
Well that's the main reason I mention trying to limit weight in that it'll help you get off the ground a lil quicker, being that is your biggest problem so far with this jet. Plus the retracts have a weight rating also so more weight means bent struts and stripped trunnions. Why not add a ramp at the end of your runway like Russian carriers do. And here is another thing I've wondered no american carrier uses a ramp While the Russian carriers use ramps, is guess it's do to the design and weight of their current fighters.

In-depth video: China lands high-tech J-15 jet on new carrier (1 min 31 sec)
Dec 09, 2012, 04:53 PM
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Maxthrottle's Avatar
I already suggested the ski jump as an easier option even if it isn't his park.

Mind you China may just go with the J-31 if their time line has any merit.
Its a better mix for the size decks they are working with if they keep a low number of J-15s for heavy long range/refuel and cap.
Dec 09, 2012, 05:35 PM
Registered User
I won't compromise weight as a fix for take-off run.
It wont even need to. Even the two flights taking off within 22m show it can do that for 3.3Kg approx area fine.... that issue is an AoA issue, not weight at all.
In aircraft this size even 500g is a 'nothing'... I have several other aircraft that treat is it as a 'zero' effect to their take-off... the lift you get off the wings area any jets have is far more than enough for even 4.0Kg. To 'carry' an extra 500g needs about 0.2deg AoA... so that is irrelevant/negligible.

There is no way they can ever mimic an Su with an F-16... just some very rough approximation. And use some fudge of the results to fill it all out. You can never replicate inertia and all the other drag from 'frontal' areas into airflow, of a greatly different shaped and weight body.
The same way these models will never be a 'fully' acting Su.... but all my planes show that notable more weight makes them far closer to correct behaviours. So I won't be changing that strategy, as it is proven to work.

In ratio to real aircraft, our landing gears would be multiple times stronger. They just don't land as poorly as we can, relatively... and if they do, they suffer damages too! And if they crash they also suffer much higher damages than we do!
So there is nothing that more weight will ever take beyond 'reasonable' and valid... if you treat your model like they treat a real aircraft (in all manners) then it will be totally fine too!
Dec 09, 2012, 06:16 PM
Should've, Would've, Could've
v8truckin's Avatar
True on the gear, about if your treat it like the real aircraft yes you'll be fine. However you've already mentioned a problem with bending the oleos on landings and you can't always expect the best, always expect the worse. If anything I would say upgrade to the euro struts which have more dampening, if you insist on flying at 4.0kg.
Dec 09, 2012, 06:18 PM
Registered User
Yes, the main gear will be an ongoing problem to solve..... either a decent runway, or that Euro 'trailing arm' sort of design. One poor grass landing would rip these out... or at least notable damage.
Dec 09, 2012, 06:35 PM
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acesimmer's Avatar
I used the spring instead of a ram for the nose gear. Problem is the plastic rod is to flimsy and bent a couple of times. So I heated it with the heat gun while in the vice and slowly closed the vice until nice and flat. Then I drilled right down the middle from front to back with a 2mm push rod wire and then clipped it off and used CA on it. Never had a problem since.
Dec 09, 2012, 06:39 PM
I did it...
av8ersteve's Avatar
Hey guys, different subject here but I'm having a brain fart and need some advise. I'm trying to get my TV nozzles to follow my ailerons but no luck so far. AUX1 and AUX2, tv up and down. AUX3, tv nozzles left and right. How do I program my tv's to my ailerons? I think I'm over thinking this as it seems it shouldn't be this hard. Everything else works great. Anybody.....?
Dec 09, 2012, 07:02 PM
Should've, Would've, Could've
v8truckin's Avatar
My plastic trailing arm cracked on a hard landing. I ended up using a fiberglass rod that is the same diameter as the plastic arm and cut it to the same length and then drilled holes in it to lighten it up, results are a stronger and 8g heavier arm.
Dec 09, 2012, 07:58 PM
Registered User
My arm has survived... but it is probably is better to make up a proper piston/ram thing... like I think Max had done. Then have the spring in that, and just have a solid stop on the fuselage rail.
I will let the stock plastic arm do its job until it breaks one day - if it ever does - it has survived through a LOT so far! LOL.
Dec 09, 2012, 10:11 PM
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Maxthrottle's Avatar
Pete They do reprogram the flight control systems to mimic other aircraft. Maybe not every nation but the US certainly does. They even had that on discovery channel! The reason why they use smaller aircraft is the obtain the same manueverability which the SU35 are, that their aircraft of the same weight class can't achieve. They set +/- g load turn radius rates etc limiting the boggy flight profile to similar perameters.
They also did the same when the shuttle program was running, reprogramming the FCS of a Citation or other aircraft to mimic the shuttle flight character. In the end its just roll and vector rates that are being matched.

But you're funny, just fly it like the full scale and all will be fine.... So a shorter 22m takeoff from grass, works out to shorter than the recommended takeoff length, basically through a wheat field being the equivolent of grass and then finally running it into a fence, we'll call that a building, isn't exactly scale now is it

And AoA, I don't think you understood my meaning, on the ground, push it on its tail and thats as far as your profile can go. Unless you're talkiing trying to alpha hover on thrust and last second pull level with a decent rate that won't harm the gear.... that's harder than not jackrabbiting off the ground.

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