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HomeAircraftHelicopterHelicopter Main Discussion › Tail blades Max pitch?
10-12-2010 09:13 PM  8 years agoPost 21
GetToDaChopper

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Las Vegas , NV

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What ever lol
unless ya must get really picky with words. of course i know there different
because blades loose effectivenes, due to turbulent flow instead of laminar flow
all i want to know is at what PITCH does this happen on a 450 heli ruffly speaking ??? thats all , is that so hard to answer with out getting off the beat-n-trac ???

so i'll ask it one more time at what PITCH do blades loose effectivenes due to turbulent flow on a 450 heli ???

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10-12-2010 09:23 PM  8 years agoPost 22
hornet dave

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Cedar Rapids, IA USA

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I got a fever! The only prescription is MORE 6HV

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10-12-2010 11:48 PM  8 years agoPost 23
Rafael23cc

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Junction City, KS

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so i'll ask it one more time at what PITCH do blades loose effectivenes due to turbulent flow on a 450 heli ???
Although you have a very interesting question in your hands, nobody cares to what the answer is. We all just set up the helicopters so that the total travel is just before the servo binds, and just fly.

As an engineer, I would be interested in the answer, and how did anybody arrive at the solution. I still remember my fluid dynamics class in college. It was one of the most interesting subjects.

I not only hang out with RC pilots, but also with kitplane builders. They have two kinds of people. The ones that like to experiment while building the kit, and the ones that want to finish their aircraft to be able to fly. One group thinks that they can do better than the engineer that designed the plane. And the other is just happy with the design and want to fly as soon as possible. Which one are you?

Rafael

Keep your feet on the ground, but your eyes on the sky.
Team Heliproz.com

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10-13-2010 12:21 AM  8 years agoPost 24
Heli_KV

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Ottawa, Canada

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BTW, the angle of attack of the tail blades will be considerably different from their pitch angle when the heli pirouettes rapidly. The difference is caused by the sideways component of relative wind induced by the yaw rate.
Ok. Let's roughly calculate. Very roughly. What can be fast piro rate? Let's exaggerate and say 10 rpm per sec. Isn't it too much? I think so, but let's take this number. This results in 600 RPM.
Tail rotor has around 12000 RPM. I am a bit lazy to remember linear speed of blade tip at the end of tail rotor, but let's do simpler. Let say, tail blade is 10sm. Linear speed of tip is linear function of rotation and radius. Let's say it is some function alpha(RPM, Radius). So for 12000, we have alpha(12000RPM, 0.1sm) for tail blades. Rotation of heli itself with 10 RPM, having boom of 1meter will be alpha(10RPM, 1M). Do I need to continue or it is obvious enough, what I am going to? it is order of magnitude difference, even having these numbers.

Actually: Velocity = Omega*Radius, i.e. linear.

A while back ago and for a long time, people believed that Sun rotates around Earth and more over it was written in a number of 'manuals' and were taught at schools. In different countries with different religions, it was slightly different, but nevertheless, that was a given and even ship navigation used that fact and quite successfully. This fact, by the way, was a real cornerstone of belief above. More over, church strongly supported this and as we all know even burn people on fire for distribution of 'false' knowledge (Giordano Bruno). Then there was Nikolaus Copernicus, who was forced to accept that Sun around Earth. So story was even more dramatic, then seemingly simple question of OP.
Do I need to continue about manuals?

Are there numbers of proof, instead of religious: use manual?

Thanks for reading and do not take it all personally.

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10-13-2010 12:32 AM  8 years agoPost 25
RCSavager

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Topeka, KS

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Amen and haloooooyah!!

If you have to ask then you need a better tail gyro. Set it to max limits and let the hard-earned coin you spent on your gyro cover the rest.

Once you try steak, is hard to go back to hotdogs.

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10-13-2010 12:50 AM  8 years agoPost 26
Heli_KV

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As for proper computations, it is enough to take Navier-Stocks equations for gas dynamics and to solve then numerically. It is enough to have two-dimensional model, which will significantly reduce computation time. The only problem is that equations cannot be solved analytically in general case, so numerical approximation is required. For example using finite differences (or finite elements) methods. If to get rid of viscosity, it is possible to take equations of ideal gas dynamics, which does not count viscosity. It will be close enough or for that matter, if taking into account, that Mach number having our speeds is less then 1, it is possible to take linear approximation of such equations, which will significantly reduce computational and algorithmic efforts and maybe will allow analytical solution. I was not specialized in linear approachs, so maybe it is way simplier then it seems to be and does allow analytical solutions. Btw, for a number of cases even nonlinear equations can be solved analytically and that's used in hyperspeed flow engine creations (kind of jet engine, where it is nesessary to heat gas (air) to most possible temperature to get desired effectiveness). But that's completely different subject for hypersonic flows.

All we need to look at what speed vortexes after the blade start to appear and at what speed and what angle of attack. I think, that approximation of blade as an infinitely thin plate will be good enough. I may be mistaken in my latest assumption. Let specialists in gas dynamics linear approximation say their word and give us a light.

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10-13-2010 01:05 AM  8 years agoPost 27
Heli_KV

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If you have to ask then you need a better tail gyro. Set it to max limits and let the hard-earned coin you spent on your gyro cover the rest
Sorry, but no. It is not good enough. Let's take a look at this scenario: You have a gyro, fast enough, but not infinitely fast and fast but not infinitely fast servo. Let's say we fly tail forward with high speed. Ok. So, tail starts to deviate from desired direction. What will gyro + servo do? Right, it will deflect tail blades to compensate for rotation, keeping heli heading. But, look, speed was not enough to compensate at the very beginning of started deflection (Gyro/Servo has finite speed), so task now is more complicated, we need more force to apply. So, what will gyro do? Right. It will continue to increase tail pitch and ahh, unfortunately up to the level of loosing effectiveness of blades. If having max pitch as recommended in 'manual' and having long enough tail shaft, gyro will keep going and going, increasing pitch (btw, at the same time increasing load on motor), but it results in further and further non effectiveness of gyro efforts. So what is the limit for gyro then? That's exactly what OP asked. But gyro does not know, but it can be limited (and as we saw speeds we are talking about are way less then tail rotation speed). So what do we need to tell to gyro? Well, depends on blades, their shape, size, flexibility, etc. Let's forget of fexibility of material (important, but hard to take into account). Maybe some rough numbers will help? That's exactly what OP was asking and I agree with him.

Sorry for spelling mistakes and once again, please no offence. The topic seems to me quite interesting.

In a nutshell, I think, gyro has to know of max angle of tail blade attack and we can set it by limiting gyro deflection. Simple enough, but the question is still unanswered: What is max angle of attack, let's say having blade like we have. At least an idea: 5 degrees, 10, 40?

Max angle is not good enough, at least for theoretical subject. Isn't max angle is too big, that we shoot ourselfs with this max angle and then horrible stories heard, that 'tail blows'?

Too much postings for today. Probably after Thanksgiving day.

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10-13-2010 01:06 AM  8 years agoPost 28
Eagle2bravo

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You DID try to help Hornet Dave...lol

T-rex 600n super pro , Trex 450 se, Gaui 200, Trex 500, Blade cx, . "If ya plant corn, ya get c

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10-13-2010 01:17 AM  8 years agoPost 29
Heli_KV

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You DID try to help Hornet Dave...lol
Not sure I understood , if post was directed to me

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10-13-2010 01:47 AM  8 years agoPost 30
Eagle2bravo

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not at you...

T-rex 600n super pro , Trex 450 se, Gaui 200, Trex 500, Blade cx, . "If ya plant corn, ya get c

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10-13-2010 01:59 AM  8 years agoPost 31
RCSavager

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Topeka, KS

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"So I fly my heli backwards at the ground at &&&mph/kph and I'd like to know at what point will my tail blades stall?"

Impossible question to answer. Great food for thought but it would depend on speed of drop, bird in question, blades used, servo used, gyro used, direction/speed of the wind, moon phase, president in office, blah, blah. Any more questions?

Once you try steak, is hard to go back to hotdogs.

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10-13-2010 02:09 AM  8 years agoPost 32
Eagle2bravo

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LOL!! I would not worry about stalling the tail blades. Never happened to me after all these years...don't know why and don't care.. I just fly the darn thing..lol

T-rex 600n super pro , Trex 450 se, Gaui 200, Trex 500, Blade cx, . "If ya plant corn, ya get c

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10-13-2010 02:27 AM  8 years agoPost 33
GetToDaChopper

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Las Vegas , NV

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Thank You Very Much Heli_KV you completely understand what i'm asking, i guess i'll just have to experiment until i find out what i want to know. i just thought i'd get more help than "do what the manual says" and i really didn't have a problem with that, i just wanted to know the pitch angle that tail blades basically stall at and load up the motor and begin lose tail authority.

P.S. And i'm not worrying about anything, i just wanted to know and thought some one here mite know, geeeeeesssss Toooooo many asumptions not enuff thought.

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10-13-2010 02:30 AM  8 years agoPost 34
hornet dave

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Cedar Rapids, IA USA

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You know, if you're going to go through the trouble of limiting the pitch of your tail blades so that they never stall, you may as well limit the pitch of your main blades too. They probably stall at around 10 degrees, so figure give yourself 6 degrees of collective pitch and 4 degrees of cyclic for a combined 10 degrees max and you should be safe.

Let me know how it works out, I'm sure it's a lot better than my +/- 13 and ~7-8. Or should I be worried about my main blades stalling on me?

Next someone is going to tell me that the main blades and tail blades are different. I'm waiting for it, really I am.

I got a fever! The only prescription is MORE 6HV

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10-13-2010 02:31 AM  8 years agoPost 35
RCSavager

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Topeka, KS

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i just wanted to know the pitch angle that tail blades basically stall at and load up the motor and begin lose tail authority.
At the point your speed exceeds the tail blades' ability to correct as needed.

Once you try steak, is hard to go back to hotdogs.

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10-13-2010 02:38 AM  8 years agoPost 36
GetToDaChopper

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Las Vegas , NV

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If having max pitch as recommended in 'manual' and having long enough tail shaft, gyro will keep going and going, increasing pitch (btw, at the same time increasing load on motor), but it results in further and further non effectiveness of gyro efforts
That is exactly what i was thinking about, +1 Heli_KV

i'll find one what i want to know on my own, (par for the corse)

And Thanks one more time to Heli_KV for your help !

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HomeAircraftHelicopterHelicopter Main Discussion › Tail blades Max pitch?
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