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  #1  
Old 06-13-2006, 04:48 PM
flaXen flaXen is offline
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Engine instead of Tail Rotor for a Heli?

I'm trying to setup a simulation of a micro heli (the Blade CP -- see attached pic) that uses a separate ESC+motor and fixed-pitch fan on the tail instead of the usual belt/gear-driven variable-pitch setup. In all my attempts so far, replacing the tail rotor component for a rotated engine at the end of the boom has failed horribly. The engine-driven fans just don't generate any power (rarely even 1lb of thrust) -- never enough to fly straight... what could I be doing wrong?
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  #2  
Old 06-13-2006, 11:12 PM
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L0stS0ul L0stS0ul is offline
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Comeon? Can anyone help here? I've no clue. This is one of the deperatly needed models in realflight IMHO.
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  #3  
Old 06-14-2006, 02:11 AM
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opjose opjose is offline
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Have you actually done the 3D model for the Blade?
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  #4  
Old 06-14-2006, 11:21 AM
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vitek vitek is offline
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I honestly don't believe that the tail on a blade would provide 1 lb of thrust.

I'll have a look at it. Obviously your other choice is to just leave the tail setup working like a conventional R/C helicopter.

Travis
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  #5  
Old 06-14-2006, 09:54 PM
flaXen flaXen is offline
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opjose: Yes, the screenshot up there is of my actual to-scale model of the BCP flying in G3. I've refined the spinning hub mesh a bit but still need to texture everything.

About thrust, the BCP probably does make more than 1lb of it. I've held it (w/o the main motor running) with full rudder stick and that tail fan is quite forceful. My problem with G3 is that even if I do get some amount of thrust, whatever quantity, it's never enough to counter-torque the main motor.

I've tried it all: I used crazy motor KV/R values but never got more than 1/3rd lb thrust, maxing-out the torque modifier didn't help either 'cause the whole heli starts twisting around the tail, and no combination of those plus gear ratios and prop pitch could ever get me more than about 1lb of thrust....

The only factors I really care about are prop diameter, weight of the motor, and mainly thrust. Using the default tail works fine for me, but it doesn't faithfully simulate these types of helis and requires some other work-arounds to make it fly something like them.
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  #6  
Old 06-15-2006, 11:03 AM
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opjose opjose is offline
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Quote:
Originally Posted by flaXen
opjose: Yes, the screenshot up there is of my actual to-scale model of the BCP flying in G3. I've refined the spinning hub mesh a bit but still need to texture everything.
Excellent!

Quote:
Originally Posted by flaXen
About thrust, the BCP probably does make more than 1lb of it. I've held it (w/o the main motor running) with full rudder stick and that tail fan is quite forceful.
Yes it's forceful, but it's not 1lb.

Turn your real heli sideways so that it thrusts the tail downward and place it on a scale.

At full throttle you'll see that the thrust is about 1/2 lb.

Quote:
Originally Posted by flaXen

My problem with G3 is that even if I do get some amount of thrust, whatever quantity, it's never enough to counter-torque the main motor.
That's a completely different problem!

On the stock helis, this is usually (assuming it's not a tail airfoil problem) because of the gearing ratio between the main rotor and the tail rotor, coupled with the inertia of the main rotor.

You may need to increase the spin of the tail rotor and/or use a different "wing" with more lift.

Quote:
Originally Posted by flaXen

I've tried it all: I used crazy motor KV/R values but never got more than 1/3rd lb thrust, maxing-out the torque modifier didn't help either 'cause the whole heli starts twisting around the tail, and no combination of those plus gear ratios and prop pitch could ever get me more than about 1lb of thrust....
I think you have the right idea but wrong approach.

I'd give it a shot, but I can't do so for at least a couple of weeks.


Quote:
Originally Posted by flaXen

The only factors I really care about are prop diameter, weight of the motor, and mainly thrust. Using the default tail works fine for me, but it doesn't faithfully simulate these types of helis and requires some other work-arounds to make it fly something like them.
This all sounds fixable.
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  #7  
Old 06-15-2006, 02:16 PM
flaXen flaXen is offline
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Hey opjose,

Oh ya, you're absolutely right. Without any measurements we can be pretty sure that tail fan doesn't do anything like 1lb of thrust -- the whole heli's flying weight is less than 3/4ths lb anyway.

So thrust isn't the issue, the engine seems to be working and responding to rudder inputs via the gyro. I've also tried direct rudder inputs to make sure it's not a goofed gyro setting, but no change in counter-torque strength...

Quote:
On the stock helis, this is usually (assuming it's not a tail airfoil problem) because of the gearing ratio between the main rotor and the tail rotor, coupled with the inertia of the main rotor.

You may need to increase the spin of the tail rotor and/or use a different "wing" with more lift.
heh yeah.. Avoiding all involvement with the main rotor is my goal with this tail setup. I think it accounts for most of the "unrealistic" behavior in my attempts to model this thing's physics so far.

Gear ratios only helped so-much in my case, same with pitch and other basic parameters. After all, thrust isn't the problem since the engine is making plenty. Something else is wrong..
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  #8  
Old 06-15-2006, 02:46 PM
boarderboy1593 boarderboy1593 is offline
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a blade cp would be amazing in G3
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  #9  
Old 06-15-2006, 03:01 PM
rjm1982 rjm1982 is offline
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Now if we could only simulate the battery drain and resulting taildrift you get as the flight goes on...
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  #10  
Old 06-15-2006, 04:08 PM
boarderboy1593 boarderboy1593 is offline
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hahaha true enough
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  #11  
Old 06-15-2006, 04:47 PM
boarderboy1593 boarderboy1593 is offline
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battry drain is less if u have lipo battries and haveing a bcp on G3 would be still amazing. and amazing model flaXen how long till your finished?
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  #12  
Old 06-15-2006, 04:53 PM
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opjose opjose is offline
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Quote:
Originally Posted by rjm1982
Now if we could only simulate the battery drain and resulting taildrift you get as the flight goes on...
Eh, it's already modeled in G3, as is fuel consumption and other factors.

People have been historically choosing overly powerful batteries though.
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  #13  
Old 06-15-2006, 04:58 PM
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Quote:
Originally Posted by flaXen
Hey opjose,

Oh ya, you're absolutely right. Without any measurements we can be pretty sure that tail fan doesn't do anything like 1lb of thrust -- the whole heli's flying weight is less than 3/4ths lb anyway.

So thrust isn't the issue, the engine seems to be working and responding to rudder inputs via the gyro. I've also tried direct rudder inputs to make sure it's not a goofed gyro setting, but no change in counter-torque strength...


.
I find the best way to correct this is to TURN OFF heading hold, so that the heli is using purely rate gain at first.

Often the heading hold feature will hide what is really to blame.

Ever see those helis which spin as they start up in G3?

Turn off heading hold and you'll find that they are impossible to stabilize.

The reason is G3 is modeling the tail pitch being turned waay too far by the HH gyro....

In effect the gyro is trying like crazy to stabilize the heli when the ratio between the tail and the rotor head is just too far off.

Turning off HH reveals all of this quickly, and also lets you spot when you are in the correct ratio zone.

Once you can somewhat stabilize the heli with no spin with the controls not at their extremes, then if you flip on HH, all that power up spin STOPS cold.

Anyway it sounds very fixable.

But I will be unable to look at the physics for about two weeks, to help you out.
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  #14  
Old 06-15-2006, 04:59 PM
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opjose opjose is offline
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Excellent job on the model BTW...
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  #15  
Old 06-15-2006, 06:39 PM
boarderboy1593 boarderboy1593 is offline
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ya it is
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