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Old 04-24-2012, 03:51 AM   #1
JohnnyCrash
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Question Purpose of horizontal tail surface on model helis?


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Howzitgoin' eh!

Just curious if anyone has a definitive explanation of the role of the small horizontal tail surface on model (or full scale) helicopters, usually just in front of the tail rotor disc, usually bolted to the top of the clamp that the tailboom braces attach to. I can't see it doing anything but causing turbulence in the rotor downwash and absorbing some power doing so, reducing overall flight performance (mind you, I have a far less than complete understanding of heli aerodynamics!). Every model heli seems to have one, and full-scale helis often have them too. I busted the one on my EXI 450 in a tail-down crash and haven't replaced it--not good enough of a pilot yet to notice any difference!

Any takers?

Peace

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Old 04-24-2012, 05:31 AM   #2
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Re: Purpose of horizontal tail surface on model helis?

I have often pondered this quesiton myself...and have flown some heli's without one with no appreciable difference in flight characteristics...I am leaning more towards asthetics than true functionality. Other than the tail boom support clamp where youre tail support rods connect to to stiffen up the tail and make it more rigid...

Anyone else want to weigh in on this one?

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Old 04-24-2012, 06:26 AM   #3
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Re: Purpose of horizontal tail surface on model helis?

The theory is that it makes the heli track better in fast forward flight (when they tend to become pitchy). In all practicality, they don't actually end up doing much. Most horizontal stabs on model helis today have virtually no surface area (big ol' holes in 'em) to keep them light for 3d guys. No airfoils on 'em either.

On full scale helis, I would imagine they actually do some good.
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Old 04-24-2012, 06:40 AM   #4
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Re: Purpose of horizontal tail surface on model helis?

Quote:
Originally Posted by Gizmodude View Post
I have often pondered this quesiton myself...and have flown some heli's without one with no appreciable difference in flight characteristics...I am leaning more towards asthetics than true functionality. Other than the tail boom support clamp where youre tail support rods connect to to stiffen up the tail and make it more rigid...

I'm with you on the first point, but not all that experienced with flying these puppies yet, so I don't notice any difference in handling (strictly a softcore/sport flier).

Because of the way I look at the model as a whole system, I don't see the aesthetic value of anything that adds weight and decreases flight performance, although unless I'm testing something I usually fly with a canopy installed If anything it provides some crash protection, and the rotor wash speed is very low near the hub, so it has minimal effect on aerodynamics. The horizontal tail seems, to me at least, to have only a detrimental effect.

Anyone else?

Ian
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Old 04-24-2012, 06:50 AM   #5
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Lightbulb Re: Purpose of horizontal tail surface on model helis?

Quote:
Originally Posted by rotormonkey13 View Post
The theory is that it makes the heli track better in fast forward flight (when they tend to become pitchy). In all practicality, they don't actually end up doing much. Most horizontal stabs on model helis today have virtually no surface area (big ol' holes in 'em) to keep them light for 3d guys. No airfoils on 'em either.

On full scale helis, I would imagine they actually do some good.
RM,

Gotcha on the FFF handling improvement, models probably don't benefit much from them because of the flybar/FBL gyro which holds a constant attitude regardless of speed.

On full scale helis, they cost a bit more than $2.49 to design, fabricate and install, so I'm sure they do more than give the mechanic a place to park his beer when wrenching on the tail!

Cheerz

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Last edited by JohnnyCrash; 04-24-2012 at 06:58 AM. Reason: to change stuff
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Old 04-24-2012, 07:53 AM   #6
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Re: Purpose of horizontal tail surface on model helis?

For the look and maybe a point of reference to see how level your tail is by "eye" ?
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Old 04-24-2012, 09:47 AM   #7
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Re: Purpose of horizontal tail surface on model helis?

Very few Canadian pilots are engaged in competitive FAI F3C flying.
For straight-line FFF, the solid horizontal fin is essential; it's size, e.g., 27 sq. inches, and position on the boom is very important to prevent the heli from pitching up or down. Here's the same question on another message board:

http://rc.runryder.com/helicopter/t5.../?p=4457002#RR

As an aside, 3D fliers can also rid the heli of the vertical fin too - lessening the job of the HH gyro in backwards flight, but leaving the t/r vulnerable to the ground.

Last edited by tskca; 04-24-2012 at 02:23 PM.
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Old 04-24-2012, 11:36 AM   #8
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Re: Purpose of horizontal tail surface on model helis?

When FAI/F3C first started being flown regularly by more flyers, the blades of the time ALL had severe design problems by today's standards. Even the best, would lead excessively. This would cause the pitchiness to change as the flight speeds increased.

We did many things to help minimize this, from playing with the rotor and flybar systems, changing the length of the flybars, changing the weight and shape of the paddles, adding more lead weight to the blades, changing the bell/hiller ratios, etc. Of course, all of this would help the stability in windy hovering conditions and in forward flight, but they would also slow the cyclic response which was becoming an issue as newer maneuvers where incorporated into the schedules.

One of the things that could be done which had minimal effect on the overall maneuverability, was to use larger horizontal tail stabilizers and experimenting with the distance of them from the mainshaft.

Today, with the great FAI and FBL type of blades now available that can literally have no lead or lag issues, the importance of the tail fins has diminished drastically in FAI and is relatively a non requirement in 3D, specially with the current use of FBL gyro systems.

But there are still some pretty badly designed blades out there, and if you are using some of them, you would still find some undesirable pitchiness in hovering on gusty days and in FFF or FBF, so a bigger airfoil shaped fin (with no holes) would be advantageous.
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Last edited by Phil Noel; 04-25-2012 at 01:32 PM. Reason: spelling
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Old 04-24-2012, 02:18 PM   #9
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Re: Purpose of horizontal tail surface on model helis?

Very nicely done, Phil.

Now I know how far behind I am. Perhaps I won't buy a JR Sylphide "C" after all. LOL
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Old 04-24-2012, 02:49 PM   #10
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Re: Purpose of horizontal tail surface on model helis?

I have also heard that some hard 3D guys remove the fin and just use a wire in the shape of a fin bacause a rule of the competitions are "You must have something in its place".

More tail maneuverability I'm assuming. I actually broke one side of my Horizontral Fin off and decided to break the other side off to make it even. I never noticed any flight changes with the B400.
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