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Old Dec 07, 2012, 01:17 PM
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Thomas Nelson's Avatar
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Thin wall aluminum tubing is surprisingly resistant to torsion. The largest diameter you can fit, glued along the entire length of the false trailing edge of the flap will help. Insert it into a groove. Drill a hole to insert & glue a ball link. I did this very thing with my design ... my avatar Su-27.

Some arrow shafts are aluminum tubes sheathed with a thin layer of CF tow on the OD. Super stiff, resistant to twisting ... and light. I bought some exclusively for torque tube applications (hiding linkages in fuselage, etc). Archery ranges sometimes have these kinds of broken arrow shafts in the garbage. Usually only the head breaks off, leaving lots of good stuff for RC use.

tn

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Originally Posted by PeterVRC View Post
I am still not happy with the 'visualisation/thought' over the LEF's with a Carbon Fibre strip face, or made from a balsa block. Neither way seems truly 'twist free' enough - versus the fact that the outer regions are getting smaller quite fast, so 'twist' beyond about the 2/3 point is not likely anyway. But I want something assured to remain rigid... to at least "6.3 on the twistigidy scale".

I am more leaning towards 2.5mm plywood LEF face, because that will glue 'properly' to the foam and thus make a very rigid 'ply' structure of the two. But.... all 2.5mm sheets I ever get are bowed anyway! And that is enough 'inbuilt force' to distort the LEF - unless jigged in some manner to assure it 'wins' over the ply's bow while the glue dries.

So... a dilemna over what to do for it still.....

I could make totally new ones from beech, or pine..... LOL
Or.... use a CF LEF face strip, then with the whole LEF glassed (GF sheet and WBPU) to get assured rigidity.
I aim to do it over this weekend, so whatever I come up with as 'acceptable' tomorrow will be it..... (I wonder how much Pine would weigh......??? A bit of a nuisance to work with! Especially a reasonably complex shape in total.)
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Old Dec 07, 2012, 02:44 PM
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Morganton, NC
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Originally Posted by Maxthrottle View Post
Personally, I would invest in a 12 channel RX for any jet if or when I pickup the DX18.
I notice the difference using scale features and would still like to separate the TV YAW etc along with Taileron and Flapperon. I'd even play with differential thrust and ruddervators.

I should add re tailerons, the way SU and I did it both because of radio limits as well as use of gyros was with an external mixer off an aileron channel and Elv channel. By doing it externally, a gyro can be placed on the desired axis. I haven't used this on gyro yet but I have a KK2 board that I'll likely reprogram and add some where down the road; more likely if I crash it I can fit it in during a redo.
Yea, from here on when I buy a receiver, it will be a 12 channel minimum. I guess I wasn't thinking. Whats the point of having all these channels if I limit myself by the receiver. Doesn't make any sense.
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Old Dec 07, 2012, 08:28 PM
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How much elevator control throw? Manual doesn't say. Just from center to max up and down. What you guys use?
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Old Dec 07, 2012, 09:25 PM
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Originally Posted by av8ersteve View Post
How much elevator control throw? Manual doesn't say. Just from center to max up and down. What you guys use?
The manual doesn't say but shows it.

Pics have been posted so look in the attachment catalogue if you're interested. You don't want pitch up any further down as the LE tip of the stab could catch ground with deflection below the underside of the engine tubes (assuming that the lower strakes broke away. This is the same as the full scale.

The DR/Expo is per the manual and you adjust to your skill set. The one thing I posted was the servo linkage setup in the manual is for all out 3D, high on the servo arm which makes it sensitive for some. I'd suggest going mid on the servo arm and add expo if you are not used to it. I've watched 5 videos on youtube from 4 pilots that crashed on or shortly after take off from oversteer (Non posted here).
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Old Dec 08, 2012, 09:41 AM
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United States, AR, Jacksonville
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I rigged my elevators as the manual suggested: Outer servo arm, mid elevator control arm and 100% end point adjustment on the transmitter.

Still only 4 flights total, but I'm always over correcting on the takeoff after it leaps into the air. Even with the recommended low dual rate selected. (This why I haven't posted any videos, lol)

No crashes so far, I'd use that set up again though. Just keep in mind to not over correct too much on take off.
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Old Dec 08, 2012, 10:18 AM
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Whiskey are you using any expo at all if any?
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Old Dec 08, 2012, 12:03 PM
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Morganton, NC
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Originally Posted by Maxthrottle View Post
The manual doesn't say but shows it.

Pics have been posted so look in the attachment catalogue if you're interested. You don't want pitch up any further down as the LE tip of the stab could catch ground with deflection below the underside of the engine tubes (assuming that the lower strakes broke away. This is the same as the full scale.

The DR/Expo is per the manual and you adjust to your skill set. The one thing I posted was the servo linkage setup in the manual is for all out 3D, high on the servo arm which makes it sensitive for some. I'd suggest going mid on the servo arm and add expo if you are not used to it. I've watched 5 videos on youtube from 4 pilots that crashed on or shortly after take off from oversteer (Non posted here).
Thanks Max. Makes perfect sense. I am going to move the linkage rod to mid as well. Thanks for the suggestion. I have figured out how to set up TV on and off with a switch now. Do you ever turn them off? It looks like you would always want them on as you would have more control in low speed and high.
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Old Dec 08, 2012, 01:28 PM
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Originally Posted by av8ersteve View Post
Thanks Max. Makes perfect sense. I am going to move the linkage rod to mid as well. Thanks for the suggestion. I have figured out how to set up TV on and off with a switch now. Do you ever turn them off? It looks like you would always want them on as you would have more control in low speed and high.
I tend to leave them on except on landing particularly because I have flapperons and because I control altitude with thrust and attitude with surfaces. Sudden thrust input at angles starts changing the attitude when I don't want it to.

Just so you understand the difference to the preceeding comments;
Some still hold to doing the linkage full 3D but in conversation with the manufacturer they intended that to be pilots choice but as you know with the Euro manual they don't republish corrections.
Why I suggested changing the position as said before is full 3D high on the arm mid on the horn, the servo doesn't move through its full swing so you immediately remove control resolution by that setup. The stab surface is thus less fine when you need it no matter how little you move the stick; I demo'd this even using min trim increments, the servo moves the surface too much when you need just a little.
Instead with low on the arm mid high on the horn I increase the throws to get the same end points. So I still have full movement, with more steps with the movement of the stick. When you compare it to the full scale, the pilot/FCS input to the stab is in centimetres, where as our input is several centimetres. By increasing your min movements you start encountering things like jackrabbiting off the runway, porpoising, comments about twitchy etc etc.

This goes again even 3D setups where you want deflection via maximum swing of the servo arm. Expo only dumbs down pilot over steer by ignoring more of your stick input but never gains you back the fine resolution that many spend money for in their TX and servos to get; undone by too a high ratio linkage setup. Spektrum even says this on their site regarding resolution.

The reverse to this is if you want the same over responsiveness as high on the arm low on the horn you can set expo on a switch the other direction to make it more responsive if you think you can't position the stick fast enough.
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Old Dec 08, 2012, 04:16 PM
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Yep, I read about the resolution on Spektrum's web site That and reading what you posted earlier about the servo rod location on the servo horn is what convinced me on dialing down the 3D a little by using a hole closer to the servo output shaft. I like full travel on my servo's as I can take more advantage of the servo it's self and I hate having a "over responsive" model. You do more fighting than flying and that's just no fun. You know your stuff Max. Thanks for sharing with us.
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Old Dec 08, 2012, 06:52 PM
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Hello all, I've been lurking on this thread for about 2 weeks. My SU-35 arrived yesterday and it's all together today. No issues during the build. All went together very well. My one issue is the under wing air intakes seem flimsy. I'm looking around for some way to re-inforce that area. Any ideas?
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Old Dec 08, 2012, 07:23 PM
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With the Arielrons versus LEF situation... they are very different.
Even though the flaps are 'larger' they have very little torsional twist - but the seemingly 'much chunkier', at the root end anyway, LEF, can twist notably more - just testing by hand.
So I have zero worry about the ailerons capabilty, but many times more worry about the LEF!

I decide on 2.5mm ply faces.
It will end up overkill, but will also supply what is needed (plus that more) in an easy manner, with very workable material - just slap it on flat! No slots etc required.
Once you laminate a face that is a huge surface area, so you add a huge amount of strength.
It even provides a 'bonus' in that it allows a fully rigid hinge mounting support - versus otherwise just foam slots etc.
So all in all, ply facing won the 'competition' hands down.....

Though I only have 2.5mm here.. and really 1.5mm would do fine, and be lighter and even easier to work with. So That is the current toss up.... as I would have to wait till a weekday to get some!
I will make one 2.5mm soon today and see what I think about makign do with that excess....

All yesterday was "Fix up the Su-35 landing gear day".... well, it was supposed to be an hour or so.... and totalled over eight!!! But I guess I ended up with a notably improved total.....
I covered from "go to whoa", so that will go into my Blog, maybe a bit posted here too later.
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Old Dec 08, 2012, 07:58 PM
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Originally Posted by PeterVRC View Post
...I decide on 2.5mm ply faces.....
That should be more than enough Pete. Seeing that the entire model is made of the same foam, thinner will have less strength, like the LE of the tailerons at the tip. But the foam does twist, just not enough to be concerned about. So the ply is more than enough added assurance flat slotted or just about any which way to add it.
I don't recall but where did you place the servo arm with respect to the full span of the LEF. I usually add the arm at what ever happens to be the surfaces MAC. Since it tapers the horn mounted a 3rd of the span from the root. Yours may be different since its a few inches short of the full span but you likely know what I mean.

Any new numbers on the CS70/12? Motor/Batt/Amps/thrust/RPM/Efflux.... Been meaning to ask Mark/ExtremeRC what he thinks of them. My guess is they are optimized for thrust not speed with similar drive trains applied.
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Old Dec 08, 2012, 08:07 PM
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Originally Posted by biuppa View Post
...My one issue is the under wing air intakes seem flimsy. I'm looking around for some way to re-inforce that area. Any ideas?
Only if you intend to land on it. As long as it doesn't cave, the thinner the better. But if you must then glass it or straight thinned epoxy with fine glass milled fiber mixed with light spackle. WBPU is a good top coat but isn't structural.
But really there no need.
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Old Dec 08, 2012, 09:27 PM
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Yes, I put the servo at that "average LEF stress point"... or "MAC" as you called it.
I would just like to be able to KNOW there is zero twist possible... not find out via an "Air Crash Investigation" after the fact!! LOL

Speaking of which... I think I found out why my last "Refusal to take-off" occured!! hard to prove 100% though.....
When doing my main gear oleo final finishing off job, and AoA Stance 'tuning', I saw that my main gear leg was now leaning 5deg sidewards. On investigation the entire intermal 'floor' for the whole retract area was collapsed, fractured, loose and flexing notably!!
It wasn't like the before the last 'smaller' flight/crash - but could have been close to reaching that!

The long ago "Crash 2" pancake landing might have weakened it all, but in repairs that was not to be seen.(?)
Then the recent "Two flight of great take-offs within 22 metres", which all went totally fine, BUT landing on grass could have over-stressed that floor area and begun the greater damage process.
THEN, that final "Refuses to take off" day, could very well have been a combination of not getting airborne in 22m of hard runway.... hitting the grass, and that shock finsihing off the floor damage.... so then the leg flops X amount sideways and all 'whacko' in operation, and then lowers the AoA Stance that bit more too.... all equalling "No way it will take off then".
OR.... the final wing hitting the fence post and throwing it into the airborne-ground-spin, was the real finishing sidwards punishment to collapse the floor as it ended up (This explanation sounding highly likely!).
Maybe a mixture of those above sequences....

But now I have a rock solid nose gear setup... LOL (more in my Su-35 Blog).
First I epoxied it all up - that was pretty strong an end reuslt, but still leaves FOAM weakness in the design.
So I made an alloy plate that bolts to the plywood 'box-frame' side rails.... so now it is all ROCK solid! LOL
Just don't crash it!! Or have a stress level that is higher than the stronger assembly can take!! Or then other things will suffer mroe than ever too!

I am thinking I will be buying a new Su-35 ARF sooner or later.... so I will shift/do all these mods into a brand new NICE Desert Camo plane!! hehe
At $176, it is probably worth that to save the TIME of ever getting this one to be pristine again!

...
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Old Dec 08, 2012, 09:54 PM
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You were a tank builder by trade I take it
So now that the mount doesn't give at all, all the impact energy is on the retract and strut. Beating every obstruction into submission Just wish you could do some flight vids. Your wing load must be through the roof!
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