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Apr 27, 2014, 07:29 AM
Registered User

Su-35 Current tests


In the non-flying day on between Friday and Sunday (hmmm, that must have been Saturday!) I had a thought to check/test the current used by all the RC gear.
The Maximum ever seen was 2.5 Amps!!
That was moving all surfaces and also the retracts! And that was only because of the peak/surge the retracts cause.
Outside of that it is under 1.5 Amps.

That was an interesting number.. so LOW!! A 5 Amp SBEC would still have 100 % leeway!
And that number is the quiescent current of items - like the RX, and the SBEC(s) - and then the servo motions on top of that.

Sitting static it is 300mA. (Digital servos buzzing or not)
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Apr 27, 2014, 07:37 AM
You win again gravity!
SMorrisRC's Avatar
But that is with the surfaces unloaded? Under air loads in flight it could be a lot higher, right?
Apr 27, 2014, 07:55 AM
Registered User
Well, probably much the same total at most. You wouldn't use them ALL to their maximums ever (almost ever?). Plus not the 1Amp peak of the retract in there.
So I doubt you would ever see over 3 Amps at most.
I can actually log just the RC stuff in flight too. (Never have done that).
Apr 27, 2014, 07:59 AM
Registered User

Altitude-Current plot for Test Flight 14


It would be nice if the Unisense Altitude Telemetry was STABLE!
The Sine Wave makes it a bit hard to decipher, or Reverse Engineer, the path accurately.
eg The fall off the peak Altitude at 180secs approx was a pure fall - the step part way down is the offset of the Sine Wave occurring at that section.
(You can see the Sine Wave cycle/frequency pretty clearly across the whole flight/plot.

...
Apr 27, 2014, 08:21 AM
You are a "go" for reentry
Maxthrottle's Avatar
So for the last flights what we're the particulars.
Stab angle neutral, thrust line position, cg and when you flew to trim set that was in clean mode or was that with another flight mode?

And have you arrived at an idea takeoff configuration yet.

No disrespect but my heads starting to hurt trying to remember your salient details picked from books of posts. I know I sometimes do it to but wing config of, stab angle, cg, thrust line X resulted in while doing Y maneuver would make it easier to folllow.

And SMorris is correct. Everyone seems to test no load, go fly but many still get shot down with them. The amount of cells the bec taps off of changes the amount of amp out put. And as a models battery unloads the amps decreases; still shared with motor duty. It's my guess why those who do a reading find that it's plenty but you still hear others shot down by power issues that seemed ideal..
Apr 27, 2014, 08:31 AM
You are a "go" for reentry
Maxthrottle's Avatar
Quote:
Originally Posted by PeterVRC
Well, probably much the same total at most. You wouldn't use them ALL to their maximums ever (almost ever?). Plus not the 1Amp peak of the retract in there.
So I doubt you would ever see over 3 Amps at most.
I can actually log just the RC stuff in flight too. (Never have done that).
And that's when they cycle clean. If they jam even at end as they cycle the overload amp load is where the concern was. But you have a telemetry set up so you can read the BEC under load at the end of the flight.
It's consistent with comments made from many who have now gone to telemetry. They never realized how close they were boarding on insufficient amps with a number of their set ups.

E.g. it was surmised that Jandro's Euro went down because he switched to 8S with the same set up. The gear cycle and funky chicken dance happened as we all know at the end if the flight and appeared to be all a RX power issue.
Apr 27, 2014, 09:01 AM
Registered User
Yeah but 80% of RC flyers don't even know what they are doing, so 'everything' was an 'RC failure', or a 'brownout'.... as far as they are concerned (because of little true knowledge). Thus 80% of info is useless to utilise. (I do tests of ALL things myself.... relying near 0% on any others info).

I could just grab some surfaces to put more load on them than they ever would have when flying, LOL. I will give that a go....
(I have 10 Amps of SBEC).

----
TV angle - I have not measured it yet.
"20 units" of "OpenTX"... They use 100% as what most TXes use 125%. 20 units is 20%... so on most other TXes that would be about 18% approx.
I have to measure that TV GAP in millimetres, but it is a clearly visible difference from top to bottom gap. For now, at a guess, if the top was 10mm the bottom is 15mm. (But I will measure it tomorrow)
I don't think mine can act/fly any different than any other in these terms, so I expect ALL Su-35's with 'neutral' TV's will flare up on power reduction. Even more so than a 4Kg one...

Rolls are also extremely axial, suggesting the thrust line and elevators are at very good positions - or else the inverted 'half' would fall away. Though some Taileron aspect might assist that - it could have been a worse, or better, factor... or no change at all due to them.
That was another test to do eventually..... asymmetrical Taileron operation - to tune in for optimal 'balance' of them. But it seemed fine with them symmetrical really.

I use 150mm CofG. I will move it and try 155mm and then 160mm... though maybe after some more 'manouverability tests so I have a 150mm Reference of behaviours first.
It is extremely stable as it is, so it would seem it could go a lot more rearwards before issues turn up. Though... the F-4 flew pretty well "totally fine" until it 'found' the hidden point of issue. At least the Su-35 has 'extreme' surface authorities available if needed.

My Elevator is 4mm BELOW the advised neutral point. But that is WITH UPWARDS TV offset too!! (upwards TV = UP elevator)
4mm of elevator makes a very large difference to flight path - a dramatic turn downwards if it is at the advised Neutral elevator point. (eg no Up Trim)
But interesting that the UP Elevator, AND UP TV, does not mess up a roll at all. That suggests the points I am using ARE the correct ones for the plane (mine at least).
Next time(s) out I will test inverted flight also. Which you would THINK must suffer and 'dive' - but if a roll does not.....
(tho inverted flight lasts a bit longer than a roll... but a typical plane is not supposed to fly inverted totally fine and equally to upright, without Pitch control needed anyway - and I doubt the real Su-35 does either)

The last flight was 4.0 Mins of air time. 3600mA used. And had the 4 shortish "WOT runs/bursts" in there too - on top of the take-off longer one. So that was a pretty good flight time, for batteries that came down only 'slightly warm'. (3.75V on recharge for those). But it is not that high a current for most of a flight really.
If that is all it 'needs' then that is all it needs... (averaging 50A to 60A)

At the moment I "Can't be bothered' rewiring for the HV ESCs and 8S - I want to fly it more and fully test what it does with 7S. But I could see it could use the extra power/thrust for more "extreme manoueverability authority" (I have no interest in hovering at all - but it would exceed 1:1 on 8S)
Apr 27, 2014, 10:14 AM
Diverted by planks
tracknoob's Avatar
Quote:
Originally Posted by Maxthrottle
my heads starting to hurt trying to remember your salient details picked from books of posts...
I think I have compressed dozens of posts, consisting of thousands of words each, into a pretty short synopsis:

"I had my TV channel mix programmed to go the wrong way."
Apr 27, 2014, 10:32 AM
Corsair Captain
That's awesome Peter. I knew you would get it figured out. But yes, if you look at the pics of my VT gap measurements, you can see there's a big difference between upper and lower gaps. Before that adjustment you can see in my maiden flight landing that when I applied power after leveling off, she pushed the nose down. You can even hear me say right away what the problem was on the video.
Freewing SU-35 Maiden flight (3 min 51 sec)
Last edited by garryk; Apr 27, 2014 at 04:38 PM.
Apr 27, 2014, 12:00 PM
You are a "go" for reentry
Maxthrottle's Avatar
Petes already picked out that he'll have to see how it does inverted.
No idea what 4mm from recommended neutral is since the stabs recommended neutral was 10 - 17 mm from the stakes seam line. So 4mm from what and which way is still foggy.

If both the thrust angle and stab are increased rather than both coming closer to each other then inverted it may dive as you state.

As for him getting anything wrong. .. we all do.
It's the cg, stab angle mm down from the strake seam line, and thrust line that is needed to tell you what's happening to extrapolate what might happen under other conditions or for consistency with understanding.
Apr 27, 2014, 05:25 PM
Registered User
Quote:
Originally Posted by flylow2011
Quote:
Originally Posted by okke dillen
Yes, they have to move outward!
For brake use only, it has no influence but, as they are actually the rudders they will only continue working when moved outwards, not inwards!

I fly all my jets with the rudders acting as an air brake while they keep their functionality as rudders (you'll be happy about working rudders when crosswinds are blowing) .

There is just one thing you should take care about: the actuation speed! In Peter's video they go the right way but way too fast! Setting them so fast will surprise you with a heavy nose lifter! Do it slow, let it last for 2 or even 3 seconds and you can deal with it easily. I did not program any mixer to compensate it, I dont need it - as long as it acts slowly!! Slowly out, quickly in. That's it. You'll love it!
the red part...
rudders move outward as airbrakes??
are you talking about the su 35 only?

because in real life, the superhornet f-18 has
rudders move inward as airbrakes ... look for yourself in this video
when the superhornet lands on the aircraft carrier
http://www.youtube.com/watch?v=RGQy5ImbnNI

rudders move inward during taking off
http://www.youtube.com/watch?v=Kf1N-PyJddk
Alright, the FULL version - but, first let me mention, they land on an aircraft carrier and these use to point the bow into the wind, while it is hard to rotate your street into the wind all the times

Scenario: rudders inwards
this results in compressing the airflow right in front of the rudders while creating drag at the same time. The compressed air applies pressure onto the area of the plane's back fuselage and thus pushes it down as the push happens behind the CG the nose will be lifted --> strong pitch-up.
Now you want to compensate crosswinds and you'd wanna use your rudders to do so, right? Especially at low altitudes when you risk to smash your wingtip into the ground you don't want to perform a roll-maneuvre.
Further, when flying a flat curve the curve-inner rudder experiences lower airspeed (smaller curve radius but same angular speed) while the curve-outer rudder experiences higher airspeed (due to the the bigger curve radius). Compare it with the stearing of a car's frontwheels.
Therefore you have to open or straighten the curve-inner rudder. But, while doing this you decrase dramatically (!) the drag component of this curve-inner rudder.
The stearing function and the drag distribution fight eachother. This is not exactly what we want!

Same story now with rudders outwards:

the airflow is decompressed behind the rudders and the thereby the plane is kind of suckedback instead of being pushed back by a compression of the airflow in front of the rudders.
As the decompression happens to be behind the airframe, it cannot pull the plane's back upward (which would result in a nose down), as no airframe is present there, which is the reason that the inwards position creates a higher pitch-up effect. Aha, so far so good.

Abstract/conclusion:
both positions have (roughly) the same effect on the drag (as I wrote in my above quotet post). But, they have a different effect on the pitch-up!
And, they have a different effect on the stearability around the yaw-axis.

Rudders inwards: drag and airflow direction fight eachother --> not good!
Rudders outwards: drag and airflow help eachother --> very good!

As long as you keep the landing approach as a controlled stall, you'd possibly favourise the pitch up effect prior to the ability to yaw... especially when you have tilted outward rudders like the F18 or even worse the F22 where moving the rudders outward will also result in having a component of an elevator down!!
The SU has upright rudders, standing perpendicular on the airframe, not tilted. That makes much of a difference!

Hope this explanation clarified a bit the difference - or created even more confusion...?
Apr 27, 2014, 05:42 PM
Registered User
I have 'dots' at the 13mm mark outlined in the maual for approx Neutral.
Then add 4mm MORE downwards from those Dots (more downwards from that seam line) and that is where I need them now.
That is WITH the "5mm" (whatever it exactly is) of "TV to Fuselage gap differential tilting the TV UP.
But when I look at the Elevator to Wing Incidence line that looks GOOD and right to me, approx!! The Elevator has a bit LESS Positive incidence than the wing - and so it should. If it was at that 13mm Dot area, it would have very little or none (or so it seemed from memory).

I was thinking about it last night.... I HAD always noted this issue since day 1, but just never thought about it much. I just thought "Gee, this glides amazingly well for what it is" and just controlling through the issue. I also just took it as "It flies great (other ways) and the plane is therefore well designed" so I totally erased even THINKING they may have done something 'wrong/poorly'. It was just "how it is"....

Now I think it is just bad design, or a "bad idea", that they did that.
It is fine if the main ducting line has to be angle X, to suit the scale looks and construction, but the EXHAUST should have corrected that (tilted up) - but then not as clean looking as dead straight.
I don't even think they meant it!! I bet they just stuck it all in IN-LINE with the ducting (the TV) and just said "Make sure the TV's are 'straight' relative to the ducting/fuselage ends".
And they just flew it like that and never even applied any proper thought/effort to the issue - but they HAD to see it occur too.
(The Freewing Me-262 has a 'Power-On' issue too, and I bet that is a thrust line issue too! NOT just the underslung nacelles, which would cause that - you can OFFSET that. Even without messing up scale looks.)
Last edited by PeterVRC; Apr 27, 2014 at 05:47 PM.
Apr 27, 2014, 05:45 PM
Corsair Captain
Here's my 2nd maiden with a discussion of thrust angles at the end.
Garys Freewing SU-35 2nd flight twin 70mm EDF Jet (6 min 40 sec)
Apr 27, 2014, 05:51 PM
Registered User
Gee... another test to do.... I forgot..... the Airbrakes. Sheesh.
Those should be good for even more "Tension" in the airframe at slow speeds. They are more use for that than for actually a slowing a plane down. (but slowing it down is a sub-set of what they must cause too).
Apr 27, 2014, 06:37 PM
Flying Hazard
SU-4ever's Avatar
Quote:
Originally Posted by PeterVRC
Tailerons: After some Taileron tests, I will most likely LEAVE them on all the time!
It rolls cleaner - more axially. There is no 'negative' aspect to them, so no real need to even turn them off really.
I forget what 'ratio" have have them set for, but it not too much. (30 units?)
Good, that you find out for yourself something that we've been reporting all the while

Quote:
Originally Posted by PeterVRC
Flights 2,3,4 explored Rolls, vertical stalls (seeing how far it can run vertically), some 'tumbles' - just hammerhead type moves with full rates and Power variations. The stalls/tumbles were a BIT scarey at first as I was worried about STRESS and something breaking on it! That is all I would need next.. to crash from something breaking!!
But it survived the first few, so I kept doing them (and variations) to see how it acts.

Don't worry about that. This plane was THOUGHT to be pushed far. I've done cobras at such high speeds to the point that you could hear the wings crack and nothing detached so I can assure you're good to go with some less strainful aerobatics. Jandro's seal of approval → This airplane is High G-loads certified.

Just mind the ground and not loosing too much speed when flying low until you feel more confident!

Quote:
Originally Posted by PeterVRC
Quite different to my Sbach342, so not a lot of that plane's 'move processes' applied to the Su-35! I think the difference of a prop pulling it, versus 'jet thrust' not being as 'strong a bite', plus TV angles, make the Su-35 quite a different animal. So that will be something to learn.....
The flight dynamics are really different. Don't fly your jets as if they were propeller craft. It won't look good

Quote:
Originally Posted by okke dillen
Scenario: rudders inwards
this results in compressing the airflow right in front of the rudders while creating drag at the same time. The compressed air applies pressure onto the area of the plane's back fuselage and thus pushes it down as the push happens behind the CG the nose will be lifted --> strong pitch-up.
Well, I have to disagree on that.

For a subsonic airflow, just need to apply Bernoulli's principle and you see that when rudders are turned inwards they restrict the area that the air has to go through, thus making it accelerate and loose pressure, pretty much like a wing profile would do or a pipe with a neck.

This means they most likely create some suction on the back of the airplane when turned inwards that fights with the pull-up leverage they exert.
rather than compressing the air, "rudders in" will decompress it.

Look at the problem as if it was a nozzle:

Convergent subsonic nozzle: Accelerates flow, decreases pressure.
Divergent subsonic nozzle: Slows airflow, increases pressure.
Convergent supersonic nozzle: Slows airflow, increases pressure.
Divergent supersonic nozzle: Accelerates flow, decreases pressure.

Might be counter intuitive though. Aerodynamics usually are.

Cheers!
Jandro.


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