Auto rotation, driven tail ??

[Farmer Giles]

Hi,

all this talk of people doing their first auto's made me think about my own heli's.

I have a T500 and a Raptor 30 and they have different tail rotor drive systems.

The T500 is perminantly driven and the Raptor is on a one way bearing so I would like to know what the characteristics of autoing each of these helis is so I know what to expect when I eventually get back to flying and have a go.

thanks

[Tim Procter]

The T500 is perminantly driven and the Raptor is on a one way bearing

You have a problem with your 500 because they are certainly fitted with a one way bearing just the same as your Raptor.

Check it out and see it hasnt siezed up.

As for the differences the torque tube tail certainly has more "hang time" and runs free where as the belt tail obviously has a little drag chewing the belt round.

Hope this helps.

[Steve]

On the Raptor 30, when the engine stops, so will the tail. The main blades will keep spinning for a while and you will have some limited success at autoing it down. When the tail blades stop, the heli won't piro violently because the engine has stopped so there's no torque being generated, but the heli will weather-**** into wind.

On the 500, the tail blades will keep spinning for as long as the main rotor disc is spinning. Disadvantage of this system is that the tail blades are sapping energy from the main rotors and the more you use the tail control during the auto, the more the main blades will slow down. Also, the heli is even smaller than the Raptor, so the blades will slow down very fast anyway.

Edit: - just read Tim's post - I was assuming the 500 had a constant drive tail.

That's why 90s auto so well - the blades are big and heavy so carry a lot of momentum which allows the pilot to do fancy things with the cyclics, collective and tail all the way down to the ground. 30s and smaller hardly auto at all.

[Dedcalm]

I thought Raptor 30/50v2's had driven tails, certainly my 50v2 does and so while the main rotors are turning so is the tail thus giving you tail authority during the auto.

[Steve]

50 does, 30 doesn't

[Andy from Sandy]

T-Rex 500 has a fully driven tail auto rotation system. All this means is that the tail rotor is fixed to the main rotor and continues to turn when the power is removed. Therefore when autoing the 500 you will still be able to input rudder commands and turn or piro the model whilst it is autoing.

The Raptor 30 does not have a fully driven tail and will stop turning when the power is removed. To auto the Raptor 30 therefore you should always point the model into wind before hitting throttle hold.

Remember the tail rotor is primarily to combat the torque reaction of the motor/engine. Once the power is cut you no longer need the tail rotor to stop the model from piroetting.

Out of the two model use the Raptor 30 as it will have more inertia (or is it kinetic energy) in the blades to keep them turning longer.

[trillian]

With the Raptor 30 you can practise the start of an auto just by cutting the throttle in normal flight mode. Keep some forward cyclic so you have the heli pointed in a predictable direction.

I haven't done a complete auto with the 30 but have done some descents with the throttle cut and it's no biggie.

[Farmer Giles]

You have a problem with your 500 because they are certainly fitted with a one way bearing just the same as your Raptor.

Check it out and see it hasnt siezed up.

When the mains are in the blade caddy on the 500 I cannot turn the tail rotor in either dircetion but I can rotate the main gear one way so I don't think the bearing is seized. With the mains in the caddy on the Raptor I can turn the tail rotor one way.

The 500 has alway been like that, I think this is 'normal' isn't it ? don't think anything is seized.


Actually it might have rusted up through lake of use over the last 4 weeks LOL...

[Farmer Giles]

one other thing....

if I select the 500 or Raptor 30 for practicing autos on Phoenix I presume all these characteristics are programmed into the SIM and as realistic as the rest of it ?

[Holst]

When the mains are in the blade caddy on the 500 I cannot turn the tail rotor in either dircetion but I can rotate the main gear one way so I don't think the bearing is seized. With the mains in the caddy on the Raptor I can turn the tail rotor one way.

The 500 has alway been like that, I think this is 'normal' isn't it ? don't think anything is seized.


Actually it might have rusted up through lake of use over the last 4 weeks LOL...

Thats how it should work

The tailblades are fixed to the mainblades and the one way bearing is on the motor only.

On the raptor (if I understand properly) the one way bearing only works on the mainblades. So if you have the mainblades in the caddy you should be able to turn the tail (and engine) one way and not the other.

[Farmer Giles]

should have been clear at the start, I am still using a belt driven tail on the 500.

thanks guys..

[Rotormotor]

The Raptor 30 does not have a fully driven tail and will stop turning when the power is removed. To auto the Raptor 30 therefore you should always point the model into wind before hitting throttle hold.

Evo Andy,

I agree wholeheartedly with most of what you said except the part about always starting with the nose pointed into the wind. This is true of any heli as a good way to start to practice one's autoing proficiency. Unfortunately this may lead many to believe one must always be pointed into the wind to auto such a heli, so one would not be able to change directions while in the auto with one that does not have a driven tail.

Just to clarify, I would like to let them know that even with a auto system that does not have a driven tail one can start downwind and still do a 180 degree turn and even a 360 degree turn to the landing. As there is no torque to counter, the tail fin will always keep the tail following the canopy as long as one maintains forward flight.

I have done thousands of such autos with helis that do not have driven tails in their auto drive system. We used to have to do 180 degree autos in the FAI competition schedules long before driven tails came onto the scene...they all had to be started while facing downwind.

Myself and some of my flight mates, also regularly (at least 3 or 4 times per flight) perform 180 & 360 autos with our Century Hawk Pros. I even do so with the 30 Hawks that are installed in an A-355 Squirrel and Long Ranger fuselages.

Due to the heavier weight (disc loading) of the Rappy 30, relative to the Hawk, and the extra drag of the Rappy's belt drive relative to the lesser drag of the Hawks' shaft drive, more energy from the main rotor is required to auto properly with the Rappy, but I agree that it is still a better auto practice platform then the heavier disc loaded and tail driven T500.

[Holst]

Evo Andy,

I agree wholeheartedly with most of what you said except the part about always starting with the nose pointed into the wind. This is true of any heli as a good way to start to practice one's autoing proficiency. Unfortunately this may lead many to believe one must always be pointed into the wind to auto such a heli, so one would not be able to change directions while in the auto with one that does not have a driven tail.

Just to clarify, I would like to let them know that even with a auto system that does not have a driven tail one can start downwind and still do a 180 degree turn and even a 360 degree turn to the landing. As there is no torque to counter, the tail fin will always keep the tail following the canopy as long as one maintains forward flight.

I have done thousands of such autos with helis that do not have driven tails in the auto drive system. We used to have to do 180 degree autos in the FAI schedules long before driven tails came onto the scene...they all had to be started while facing downwind.

Myself and some of my flight mates, also regularly (at least 3 or 4 times per flight) perform 180 & 360 autos with our Century Hawk Pros. I even do so with the 30 Hawks that is installed in an A-355 Squirrel and Long Ranger fuselages.

Due to the heavier weight (disc loading) of the Rappy 30, relative to the Hawk, and the extra drag of the Rappy's belt drive relative to the lesser drag of the Hawks' shaft drive, more energy from the main rotor is required to auto properly with the Rappy, but it is still a better auto practice platform then the heavier disc loaded and tail driven T500.

So how to you change directon?

Maintain forward flight and then turn the heli like you would a plane?

As without any drive to the tail your rudder inputs wont work.
I think this was Andy was getting at rather than implying that a turn would be impossible... you just have to use a different method

Where as with the 500 the rudder will still operate as normal as long as you have sufficent headspeed to control the tail.

If anything its more important to get the 500 pointing into the wind to auto, otherwise the gyro will sap some power holding the tail across the wind

[electricsceadu]

to turn a non-driven tailed model in an auto use the left/right cyclic controls

with a driven tail you can use the rudder or cyclic to turn the model

the non-driven tailed model will have more energy available on the head than a driven tailed model of the same type

if you want a driven tail on the raptor 30 put the 50 main gear set up on it
if using the 50 gear on a 30 check that the gear has the same number of teeth to keep the gear ratio the same

[David Drew]

if you want a driven tail on the raptor 30 put the 50 main gear set up on it
if using the 50 gear on a 30 check that the gear has the same number of teeth to keep the gear ratio the same

I converted my 30 into a 50 but I can't remember what I changed. I did change the main gear & pinion (gearing) but can't remember what I did to the one-way bearing

Must check this out

David