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Old May 10, 2012, 10:12 PM
Should've, Would've, Could've
v8truckin's Avatar
United States, CA
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Quote:
Originally Posted by sfactor1 View Post
from a torque roll standpoint, having 2 counter rotating fans, it should not matter which is mounted left or right. as long as they rotate in opposite directions, the gyroscopic effects cancel each other
I beg to differ as you would think that. However from a thrust standpoint only, when I switched the rotation of my fans from rotating inwards to outwards by accident the trust dropped. This may not effect torque but it did effect thrust dramatically. I know it shouldn't matter, but it DID... So I make sure they rotate inwards.
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Old May 10, 2012, 10:39 PM
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Yeah, but you had them wired and running in reverse V8 !! LOL
Sucking air..... (joke)
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Old May 10, 2012, 10:55 PM
Should've, Would've, Could've
v8truckin's Avatar
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Lol! Nope! I had them wired correctly. All I did was flip flop the motors and the thrust increased when I put them with rotation inwards. I did it twice just to make sure I wasn't seeing things.
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Old May 10, 2012, 11:14 PM
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Unless something in the inlet, or exhaust, path is non-symmetrical (per side) then rotation direction should not alter a thing.
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Old May 10, 2012, 11:22 PM
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My guess is it may have something to do with the cheats. The cheats likely establish a rotation in the intake and if the fan is chasing the air rather than cutting through it and directing it to the stators there could concievable be a loss that the motor can't make up.
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Old May 10, 2012, 11:38 PM
Should've, Would've, Could've
v8truckin's Avatar
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MAX, that's a great analogy. The cheats are on the inside of the ducts so with inward rotation thrust was fine. However with outward rotation and no cheats on the outside that may have played a roll into why the fan rotation had an effect on thrust. I guess that's what the case was. If there was cheats on either side it wouldn't make a difference on rotation. I won't know until someone else flips the rotation of the fan.
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Old May 11, 2012, 12:12 AM
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LOL.... I was thinking "What I have seen non-symmetrical.... hmmm, nothing".
And totally forgot about the cheaters!!
Have to have a look at their exact design.....
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Old May 11, 2012, 12:17 AM
Ugly planes do not fly
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The lost in thrust may be due to wrong shroud for fan. If you look inside the shroud motor mounts have angle along the fan rotation. Left shroud is different from right one.

There is difference which way fans rotate - inwards or outwards -- when there is difference in RPM. Especially when one engine quits. When they are perfectly synch'ed there is no difference.

I had to add 35g of weight to the nose to balance her at 150mm. Is this good CG for the first flight?

I think I am ready for maiden
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Old May 11, 2012, 01:01 AM
Should've, Would've, Could've
v8truckin's Avatar
United States, CA
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Quote:
Originally Posted by _Sergey_ View Post
The lost in thrust may be due to wrong shroud for fan. If you look inside the shroud motor mounts have angle along the fan rotation. Left shroud is different from right one.

There is difference which way fans rotate - inwards or outwards -- when there is difference in RPM. Especially when one engine quits. When they are perfectly synch'ed there is no difference.

I had to add 35g of weight to the nose to balance her at 150mm. Is this good CG for the first flight?

I think I am ready for maiden
Sergey,

When accidentally flped the motors thus counter rotating outward it was fan, motor, and shroud. When I swapped back to normal inward rotation it was also fan, motor and shroud. So I don't think shroud had a part in it...???
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Old May 11, 2012, 01:41 AM
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Me too Sergey.... out tomorrow if the weather is suitable.
I haven't decided on a CofG. But 150 sounds good, lol.

CofG doesn't really seem to bother me, so far, in any plane. I get it roughly 'right' but it has to be quite a way out of expected range before it is apparent to me, or bothers me. So I tend to think "What's all the fuss with CofG?" lol.
The aim is to have it 'fly right' with it best tuned at some point eventually. But no maiden (of 14) has come to grief because of a CofG issue so far.

I note that I do tend to end up happy with a more nose heavy aircraft than others typically suggest, and that it is safer to err on that side anyway. Well, at least based on the fear instilled by people's comments of disasters of being tail heavy....

I was testing accel/thrust today, on ground from a standstill. Boy does it leap out of the box! I am getting around 2.9Kg peak from initial battery use, which this was. So it has a lot of get up and go on tap and I reckon it would still fly very well - normal flying around - even on 2.5Kg thrust or probably even down towards 2.0Kg. My AUW is a bit under 3100g.
But this is the first plane that I feel any concern over maidening - probably because it cost more than any other so far! hehe. It is not my biggest, and probably not the best, and didn't take anywhere near the longest time to build or get ready, but it cost the most. And maybe that I love the look of Russian Mig/Su, so it is visually my favourite too.
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Old May 11, 2012, 01:51 AM
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That reminds me of the "All videos have people slamming the nose (wheel) into the ground on landing".....

The stock oleo's are so bad!!! Graunchy, 50% efficient motions. So on landings the mains aren't going to be overly great use above what a fixed landing gear leg would do. Certainly not enough to help absorb typical landing 'error margin'.
And on top of the lack lustre motion ability I also think they are too strong/stiff (springs) anyway.
So that is a big input to the "Wham, down goes the nose" on landings.

I forgot that I was going to strip mine down and see what could be done to improve them. But a large part of it is not going to be curable - it is just poor tolerances. Sloppy alloy on alloy graunching away.....
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Old May 11, 2012, 02:24 AM
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Fan rotation direction.....
I just realised. I have dual CS10's... so they both rotate the same direction. And in the thrust tests they were both so close it was negligible difference.
So the rotation direction of the fan does not look to truly matter at all in power/thrust terms.

I guess there would be "swirl" ahead of the fan (which has to be created by the fan's motion).... the closer to the fan I assume there would be more. But in my thrust results it doesn't seem to come into play.
I notice that the cheaters DO have a 'curve' to their 'gills', and you would assume that someone either knew something about that aspect and its possible benefit, or they just parrot fashion (or lack of true knowledge) added it but it really didn't matter anyway.

So whilst I would guess it should do at least SOMETHING, it doesn't really seem to be anything of great importance/result.
And maybe CS10's are less worried about what the inlet side is doing. Seeing they seem more fussed over exhaust side restrictions. ??
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Old May 11, 2012, 04:54 AM
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Joined May 2010
381 Posts
Apologies if this has been mentioned before, but I'm reading that the stock power systems are pretty good out-of-the-box and other options mentioned are upgraded motors (say HET 2W25) with upgraded fan units (Wemo / HET 6904 / CS10).

Has anybody who has installed upgrades really noticed a material difference i.e. does the increase in performnce justify the cost / time in upgrading.

I guess I'm looking at this from a cost / benefit point-of-view.

I'm now looking at HET Aluminium 6904 fans and 2W25 fan units but if others have tried similar and haven't noticed much difference I'll not bother.

I've discounted CS10 fans (despite having bought a set!) as being too inefficient, last thing I need is shorter flight times with no real advantage other than a "whoooooosh".

Comments most welcome!

Andy
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Old May 11, 2012, 08:12 AM
Should've, Would've, Could've
v8truckin's Avatar
United States, CA
Joined Dec 2010
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Hammer,.

As for the stock power system it provides enough power for good flight and time. You are correct on the CS10, as there are not efficient enough on this bird yet. I have to sets sitting in the closet waiting for the right motor and airframe. I installed and removed it from my plane, I believe there are a few trying the wemo setup and believe someone is trying the RCL metal shroud counter rotating fans.
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Old May 12, 2012, 05:44 AM
Auxerre - France
toubab's Avatar
France, Bourgogne, Auxerre
Joined Dec 2011
119 Posts
Hi everyone !

I am new in this thread !
I just got my SU yesterday and as everyone said it's a really nice plane !!

Can someone help about the 17 g servo elevator that will feet the best for this plane ?

Thanks
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