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Fast Lad Performance . Ace Hobby . Esprit Model

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Main Discussion > elevated tail rotor design
 
 
avatar71
Senior Heliman
Location: East Amherst, NY

has there ever been a heli (model) that has had an elevated tail rotor? Elevated enough to be inline with the main blades?

If there were, it would be interesting to see how it cancels out the induced roll from the tail rotor.

I would imagine it would increase the complexity of tail power delivery and control but I can imagine its never been done!

I would think the heli would need no mixing (pitch to aileron).

Sharkbait! hoo ha ha
07-16-2008 11:43 AM
 
 
Bruce Naylor
Senior Heliman
Location: Swindon, Wiltshire, UK

Google "Heim Lockheed 286" and "Schluter Cheyenne" for a starting place for historic designs.

I believe "Maxi Joker 2" is still available.

Enjoy.

"If you know what you're doing, you're not learning much"
07-16-2008 01:03 PM
 
 
cfranks
Veteran
Location: Adelaide South Australia

Maxi Joker 2
07-16-2008 01:03 PM
 
 
dkshema
rrProfessor
Location: Cedar Rapids, IA

One oldie comes to mind -- the Schluter SX-81 from the early/mid 80's. I think the Horizon also had one.

These were both pre-aerobatic helis, so it's hard to say what the effect was.

-----

* Making the World a Better Place -- One Helicopter at a time! *

Dave
07-16-2008 01:05 PM
 
 
Yug
rrProfessor
Location: UK. Herts





Vegetable rights and Peace
07-16-2008 01:34 PM
 
 
Brokenlink
Senior Heliman
Location: Oakdale,Ca.

this is horizons

07-16-2008 01:58 PM
 
 
kangarooster
Senior Heliman
Location: Orlando Fl-USA

The translating tendency actually increases when the tail rotor is raised.
07-16-2008 02:19 PM
 
 
J2M
Senior Heliman
Location: UK

"The translating tendency actually increases when the tail rotor is raised."

Why is this statement true?
07-16-2008 02:29 PM
 
 
kangarooster
Senior Heliman
Location: Orlando Fl-USA

As background, I tried this mod on a 30 size Hirobo.
It didn't work as I had expected.
I ended up making a vector diagram and the answer was clear
In the normal position the tail rotor creates left thrust on the tail to countrer the main rotor's torque.
Since the line of thrust is outside of the main rotors path,the thrust needs to be greater than the rotor torque and at a different angle. the excess thrust causes the left drift.
Since the thrust line is below the rotor path it causes a roll to the right which partialy counteracts the left drift. Right cyclic is used to counter any drift remaining.
With the raised tail rotor roll is not caused,so all correction is done with cyclic.

EDIT: The above statement is wrong. Further experimentation and computation leads me to believe that roll is dependent on rotor torque only and tail rotor position is unimportant.
The only purpose of an elevated tail is to reduce groung strikes altho it might increase the chance of bird strikes from low flying birds.
Ben
07-16-2008 03:08 PM
 
 
avatar71
Senior Heliman
Location: East Amherst, NY

Quote 
With the raised tail rotor roll is not caused

that is exactly my point! I makes sense. why would we not want to eliminate this roll factor?

Sharkbait! hoo ha ha
07-16-2008 05:07 PM
 
 
kangarooster
Senior Heliman
Location: Orlando Fl-USA

By raising the tail the partialy self compensating effect is eliminated.
The side thrust is still aproximately the same ,so cyclic is used to roll the heli to stop the drift.
The apparent roll still seems to be the same.
Building in some mast angle will keep the body level at a given power level.
At the time that I origionally tried this mod, my flying skill level was not good enough to evaluate the rolling and piroetting performance.
I would welcome any input on this subject,
I am tired of leaning hovers,sloppy rolls and hours spent getting the mixes just right.

Visual aids will earn extra credit.

07-16-2008 05:55 PM
 
 
avatar71
Senior Heliman
Location: East Amherst, NY

i would think that if the rotor was inline with the mains, I'd imagine the roll input would be gone. Now, roll would be translated to yaw thrust and this should be eliminated by a heading lock gyro. A verticle "take off" would likely then see some right thrust. So, i guess right roll would be replaced with a heli moving left on you... perhaps.

Sharkbait! hoo ha ha
07-19-2008 01:26 AM
 
 
Yug
rrProfessor
Location: UK. Herts

Indeed, the physical benefits of a raised tail rotor in line with the perpendicular axis of mains is beneficial when considering the perpendicaulr moments of the two syetems as well as considering the interaction of the TR in the main wash when flyng inverted as opposed to non inverted. But all said and done, go flybarless and let the gyro stabalisation sort this all out.

Vegetable rights and Peace
07-19-2008 01:48 AM
 
 
avatar71
Senior Heliman
Location: East Amherst, NY

flybarless... yes, I am awaiting that logo 400 for my 1st one.

Sharkbait! hoo ha ha
07-19-2008 12:04 PM
 
 
kangarooster
Senior Heliman
Location: Orlando Fl-USA

avatar71,
You are correct.
The heli would drift left which would be corrected with right roll.
Right back where we started.
To eliminate the drift the tail rotor not only needs to be raised to be in vertical alignment, it also needs to be moved into horizontal alignment,which would be about 2/3 out from center in the main rotors swept area.
Not a good place to be.

Yug,
A flybarless has all the same thrusts.
It leans to the right also.

Ain't no free lunch.
But, lunch is not what it used to be since you vegtable rights activists won't let us have potatoes with our meat.
07-19-2008 01:43 PM
 
 
avatar71
Senior Heliman
Location: East Amherst, NY

great point! thanks for thinking that out for me... interesting at the very least.

i guess my plans for a revolutionary new heli just went out the window.

Sharkbait! hoo ha ha
07-19-2008 03:02 PM
 
 
Damper
Senior Heliman
Location: Point Blank TX USA

Avatar71

Take a look again maybe you tilt the tail on the other
axis it might work! Just thought. I think the UH-60
works like that! I am just thinking out loud here.
So please excuse this way of thinking about that.

Full Throttle Spooning Leads To Forking
07-19-2008 11:17 PM
 
 
Roscoe
Heliman
Location: northfield,ohio - USA

The new mini-titan AH-1W Super Cobra scale fuselage comes with a elavated tail rotor mechanism in the kit; [[www.acehobby.com/ace/TTR3870_G.htm]] I'm thinking of picking this up myself. I always thought it would be cool to do, but now you can buy it already pre-built.

"Knowledge speaks, but wisdom listens. "~ Jimi Hendrix
07-19-2008 11:59 PM
 
 
Bad Karma
Veteran
Location: UK

Simple solution, not so simple mechanics...... coaxial
07-20-2008 12:42 AM
 
 
jgunpilot
Heliman
Location: Pollock, LA

"Avatar71

Take a look again maybe you tilt the tail on the other
axis it might work! Just thought. I think the UH-60
works like that! I am just thinking out loud here.
So please excuse this way of thinking about that."



Nope, the Uh-60's tail rotor is canted 20 degrees to add 3% of the total vertical lift due to it having an aft CG. Some helicopters like the BO-105 have a tail rotor that is raised up to the level of the main rotor, but it also has a rigid rotor system. It still hovers a little left skid low like most Western designs.
07-20-2008 12:51 AM
 
 
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