Torque tube

[wlfk]

How much does it actually matter if the tail rotor spins the opposite direction? So long as the blades are reversed and any settings on the gyro are correct, it should fly more or less correctly, no?

[JoeW]

You won't get as much 'lift' out of the tail blades if they're reversed.

The blades need to go up in to the main rotor otherwise the rotor wash will take lift off the blades.

It will work... but you won't have as much power at the tail. (ask me how I know )

[glarepro]

It does matter dude!

Helis always want to turn faster in one direction than the other (talking about rudder here). Its the natural behavior of having one main rotor spinning in one direction. The heli will always have quicker rudder to the opposite direction of the way the mainblades are spinning.
This means you have to have more degrees of pitch on the tail rotor to turn the same direction as the mainblades (as opposed to how much pitch you have going opposite the main rotor) so that the rate going same direction as the mainblades matches the rate turning opposite the mainblades. If the tail rotor is blowing air in the direction of the tailboom to turn in the same direction as the mainrotor this could be a problem. I'm not saying it definitely is a problem, but in theory, it could be a problem. You dont want the tail boom obstructing or redirecting air-flow from the tail rotor when youre turning in the direction the heli doesnt like to naturally turn into. Which side you mount, or which way the tail is spinning will make a difference. How much difference is yet to be determined. My guess is it would make a slight but notable difference between the 2 different conifigurations. Just some food for thought.

[Newfie Pilot]

Would like to convert my Trex 250SE to TT...has all the issue been resolved re: tail rotor direction, and if so, what do I require to complete? I am still a little confused. Do I just need the Tarot 250 Shaft Driven Set : http://www.oomodel.com/tarot-250-spa...1-p-62397.html

or do I also need the TT tail: http://www.oomodel.com/tarot-250-par...0-p-62112.html

or do I just use the pieces from the Align belt tail with the Shaft Driven set? I would hate to order it and then wait, only to discover upon delivery that I require something else and have to wait longer.

Jim

[mhills51]

Yes oomodel has it fixed. I also ordered the gear box and it also included the extra shaft and spacer.

[noddyflyer]

the only thing you need is the bottom part of the tail gear(belt) box everything else is in the kit, use the side plates off the old tail

[wlfk]

JoeW
I looked up the issue in my helicopter textbook (Leishman), and the only thing mentioned was that you get more rotor noise and vibration due to interactions between the main rotor vortices and the tail rotor, if it turns in the 'wrong' direction. It doesn't mention efficiency at all, so presumably there are no strong theoretical reasons to believe it should be an issue.

Is the problem perhaps mechanical rather than aerodynamic? On the 250 the throw on the tail is not symmetrical so if you reverse the tailblades you end up with the reduced control throw in the direction where you need it most. Could perhaps be overcome by reversing the tailgrips so that they lead rather than lag.

glarepro:
It's true that mounting the tail rotor so that it's blowing air away from the fin and boom is more efficient than blowing air over the fin (by about 10%) but this shouldn't be an issue in this case, as all we're talking about is the direction of rotation of the tail rotor. The torque from the main rotor is still causing yaw in the same direction, so we still need to push air away from the fin.

[JoeW]

Originally Posted by wlfk

JoeW
I looked up the issue in my helicopter textbook (Leishman), and the only thing mentioned was that you get more rotor noise and vibration due to interactions between the main rotor vortices and the tail rotor, if it turns in the 'wrong' direction. It doesn't mention efficiency at all, so presumably there are no strong theoretical reasons to believe it should be an issue.

Is the problem perhaps mechanical rather than aerodynamic? On the 250 the throw on the tail is not symmetrical so if you reverse the tailblades you end up with the reduced control throw in the direction where you need it most. Could perhaps be overcome by reversing the tailgrips so that they lead rather than lag.

glarepro:
It's true that mounting the tail rotor so that it's blowing air away from the fin and boom is more efficient than blowing air over the fin (by about 10%) but this shouldn't be an issue in this case, as all we're talking about is the direction of rotation of the tail rotor. The torque from the main rotor is still causing yaw in the same direction, so we still need to push air away from the fin.

It's basic flight theory... A wing with a head wind will generate more lift than a wing with a tail wind.

On the 250, the forward blade is coming in to the dirtiest air from the main rotors down wash. If the forward blade is going down, that blade essentially has a tail wind and will not generate as much lift as it could if it was going in to the rotor wash. That dirty air would also make the tail the most unstable if it was coming at it from behind.

Because of that basic fact, the tail is designed to rotate with the forward blade going up in to the rotor wash, and the pitch is offset in the required direction.

If you reverse the rotation of the blades, you suffer on both fronts. You will not have enough pitch in the direction needed for maximum torque compensation, and the tail won't be generating as much lift as it could because it's not 'flying in to the wind'

It's the same reason we take off in to the wind with a plank.

The rear most tail blade has the least interaction with this dirty air, so you have more possible to gain from the forward one going up in to the rotor wash than the back.

Hope that helps

Joe

[wlfk]

Yes, I see where you're coming from. Thanks.

[mhills51]

You need the side plates off a Tarot tail, I have tried HK and align. Both put the end support bar too close to the bevel gear to work.

[glarepro]

I think I'm going to wait for ALIGN to sort all this TT tail stuff out before I buy an aftermarket kit. ALIGN's TT should be out by June.

[JoeW]

Originally Posted by glarepro

I think I'm going to wait for ALIGN to sort all this TT tail stuff out before I buy an aftermarket kit. ALIGN's TT should be out by June.

I've got enough belts to last me until then for sure!

[walkera4g3]

mhills, how's the 250 TT going?

[noddyflyer]

Originally Posted by mhills51

You need the side plates off a Tarot tail, I have tried HK and align. Both put the end support bar too close to the bevel gear to work.

i cut down the tie bar from a boom holder loads of clearance all round

[mhills51]

Big set back. I thought my boom was mounted solid, but at speed it pulled out breaking my tail servo and bending the tail shaft. I used a Align boom mount and tarot tail boom. Next I got some align booms and if that don't work I will throw the boom mount on the belt sander and take it a little bit down

[Vinger]

Originally Posted by glarepro

It does matter dude!

Helis always want to turn faster in one direction than the other (talking about rudder here). Its the natural behavior of having one main rotor spinning in one direction. The heli will always have quicker rudder to the opposite direction of the way the mainblades are spinning.
This means you have to have more degrees of pitch on the tail rotor to turn the same direction as the mainblades (as opposed to how much pitch you have going opposite the main rotor) so that the rate going same direction as the mainblades matches the rate turning opposite the mainblades. If the tail rotor is blowing air in the direction of the tailboom to turn in the same direction as the mainrotor this could be a problem. I'm not saying it definitely is a problem, but in theory, it could be a problem. You dont want the tail boom obstructing or redirecting air-flow from the tail rotor when youre turning in the direction the heli doesnt like to naturally turn into. Which side you mount, or which way the tail is spinning will make a difference. How much difference is yet to be determined. My guess is it would make a slight but notable difference between the 2 different conifigurations. Just some food for thought.

Old wife's tale, the TDR has the tail rotor turning CW if viewed from the right, NO problems and NONE of the symptoms you describe are present. Just fit the tail blades the other direction, make sure of gyro direction and rudder direction and fly it.

[Ah Clem]

I have no desire to convert my 250 to torque tube.

The belt is reliable and, when set up properly, low drag. I have any desire for the added complexity, extra parts and repair costs, and increased drag of the torque tube (five additional bearings, two sets of gears, changing the direction of the power transmission 90 degrees-twice).

[walkera4g3]

Originally Posted by Ah Clem

I have no desire to convert my 250 to torque tube.

The belt is reliable and, when set up properly, low drag. I have any desire for the added complexity, extra parts and repair costs, and increased drag of the torque tube (five additional bearings, two sets of gears, changing the direction of the power transmission 90 degrees-twice).

give it a go first ah clem, a 250 TT may have potential???

[noddyflyer]

i have one of each (tt and belt) and find the tt to be more solid, quieter less vibration (same giro settings)

[glarepro]

Originally Posted by noddyflyer

i have one of each (tt and belt) and find the tt to be more solid, quieter less vibration (same giro settings)

Exactly!