Engine instead of Tail Rotor for a Heli?

[flaXen]

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?

[L0stS0ul]

Comeon? Can anyone help here? I've no clue. This is one of the deperatly needed models in realflight IMHO.

[opjose]

Have you actually done the 3D model for the Blade?

[vitek]

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

[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.

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.

[opjose]

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!


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.



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.



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.




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.

[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...

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..

[boarderboy1593]

a blade cp would be amazing in G3

[rjm1982]

Now if we could only simulate the battery drain and resulting taildrift you get as the flight goes on... :)

[boarderboy1593]

hahaha true enough

[boarderboy1593]

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?

[opjose]

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.

[opjose]

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.

[opjose]

Excellent job on the model BTW...

[boarderboy1593]

ya it is

[boarderboy1593]

it would be nice to have a good blade cp in G3 cuz there hard to learn to fly and u go through blades fast cheaper to pratice on the computer

[boarderboy1593]

i m trying to get in to modeling whats a good way to start like programs and what not

[flaXen]

Here's an updated pic of it flying w/ improved hub motion blur models and one w/ the canopy off. I really really wish I could create custom blade types 'cause I modeled the main blades, paddles, and tail fan too but it doesn't seem possible (or at least not documented). I've still got to texture it, all of its coloring is just materials.

boarder: I used the little Wings3D (http://www.wings3d.com/) program that was linked to in the useful links (http://www.knifeedge.com/forums/showthread.php?t=11067) sticky post to model my BCP. I already had experience with sub-division modeling so it only took me about 30 minutes of warm-up, practice, and hot-key setup to get started on the canopy, which I did first. Then I used a digital caliper to build the frame & components to-scale.

The KE tutorials became useful once my model was pretty much done and was ready to run in G3. Fortunately, my bro is developing a game and has a copy of 3DS Max so I had no problem getting my model imported there and exported again to a KEX for import into G3. Honestly tho, Wings 3D is easier to model with since it's specialized and not cluttered with so so many features, but I had to setup all the hierarchy and pivots in 3DS. Still, I re-import changes to the model from Wings 3D since I can't stand the 3DS UI.

[boarderboy1593]

thats going to be one amazing model, and thanks for the addvice flaXen.

[boarderboy1593]

dude u ever finish that

[WingsWest328]

Ya, Is it done or are you gonna keep it for yourself :confused:

[ScottyGraham]

How can we get this model? Is it going to be on the aircraft page soon?


Is it going to be free? :)

[opjose]

Me detects the smell of fish!

Hub motion blur?

You do not "make" it, it is generated by G3.

[boarderboy1593]

i want that cp

[Larry A.]

Here's an updated pic of it flying w/ improved hub motion blur models and one w/ the canopy off. I really really wish I could create custom blade types 'cause I modeled the main blades, paddles, and tail fan too but it doesn't seem possible (or at least not documented). I've still got to texture it, all of its coloring is just materials.

boarder: I used the little Wings3D (http://www.wings3d.com/) program that was linked to in the useful links (http://www.knifeedge.com/forums/showthread.php?t=11067) sticky post to model my BCP. I already had experience with sub-division modeling so it only took me about 30 minutes of warm-up, practice, and hot-key setup to get started on the canopy, which I did first. Then I used a digital caliper to build the frame & components to-scale.

The KE tutorials became useful once my model was pretty much done and was ready to run in G3. Fortunately, my bro is developing a game and has a copy of 3DS Max so I had no problem getting my model imported there and exported again to a KEX for import into G3. Honestly tho, Wings 3D is easier to model with since it's specialized and not cluttered with so so many features, but I had to setup all the hierarchy and pivots in 3DS. Still, I re-import changes to the model from Wings 3D since I can't stand the 3DS UI.

If you ever get that model corectly to simulate tail motorized driven helis, I'd love to see any of these, the white canopy one as my favorite.

[boarderboy1593]

the blade cp i way better the your white krap

[Larry A.]

the blade cp i way better the your white krap
:) Sounds like you have tried both of them. Can you talk about their major differences besides the obvious size? ;)

[remyrw]

I am also working on a blade cp so if you want some help I need the basic g3x file you're working with.

I was just going the route of manipulating an MX400 to be close, rather than try to build up from scratch. Mostly because my 3d design skills stink and I was more concerned with just a reasonable simulation of Blade CP hovering rather than more complete accuracy.

Heck, even just that 3d model with the stats from my MX400 mod would be great :)

[opjose]

Please note that "Flaxen" has not posted in a long time.

Don't hold your breath for his model.

[mcomet]

Hmmm i just joined in... I need to see what the process is like to get teh model from something like Maya into G3.... seems like it needs a .3ds convertor... and then what? The sticky docs at the top didn't seem to have info on that...tho maybe i missed it?

I would like to model a CP as well...
At least if this one doesn't make it public...

[ScottyGraham]

take a look it has no tail rotor it has an electric motor instead

[boarderboy1593]

please do

[remyrw]

well, it's not using that pretty 3d model he had shown but it's a couple versions of a working CP and CPP, just check the regular swap pages, CP first Try or somethinglike that. Make sure you get the recent version of each, not older ones. I keep improving them. The current version of the CPP doesn't require the expansion pack and I've got a standard CP coming out shortly that won't either. They're not perfect but pretty close and good enough to practice with unless you're doing advanced 3D and want it to be just like the real thing. Since I can't fly 3d I have no clue how to judge what's off.