Align Trex 700 turbine build

[torque to twist]

I have made good progress this week designed a mount for the turbine and printed the first off.
also got a Pr of servo mounts done

I will post some more tomorrow- Looking good.

[torque to twist]

Coolice
Great photo's just love the inverted one.

[torque to twist]

Is anyone running a wren turbine with a gov. If so does the turbine react slow?

[coolice]

Coolice
Great photo's just love the inverted one.

Is anyone running a wren turbine with a gov. If so does the turbine react slow?

Thanks buddy, although they've never been mine as such I've always enjoyed the turbines.
I have loads of other photos of me with the CenturyUK/Wren Predator turbine as I did a lot of R&D test flying of the MW54 setup in a helicopter.

Sadly as you've guessed a govenor doesn't work well with the turbines, only due to the fact of the turbine takes a few seconds to change rpm. The MW44 is better than the bigger 54 I will say at rpm changes.
All the models I setup and flew I used throttle curves tuned to keep as constant rotor rpm as possible, while the slow rpm change effects spool up times it kinda helps a little on slowing down to. Not much I'll admit but a little.

The only governor'ish unit that worked was the Throttle Jockey PRO that just guarding an upped limit on rotor rpm only and not provide a full on governor.
Basically if the rotor rpm went over a set point, usually around 1750 rpm with the big 800mma blades, the TJpro would slow the throttle to stay with safe limits.
I never used one but Bob Johnson did in his Quatro from memory.

Ian

[mgt4fun]

Hi mgt4fun
I'm still learning how to use this forum, how do you get the blue bubble of my text up?

Thanks for the advise on running out of fuel and cooking the bearings. I have bought 2 msr fuel bottles to have a similar set up like bergen.

just hit the 'reply with quote' button, works a treat.

ian is right re the governor, I just run almost flat curves to keep the headpseed sensible and in range with pitch changes. Old school works sometimes.

[Grumpy]

Sadly as you've guessed a govenor doesn't work well with the turbines, only due to the fact of the turbine takes a few seconds to change rpm.

I appreciate that turbines have a slight lag in changing RPM but surely with a governor your aren't changing RPM.. That's kinda the whole point of a governor, to avoid any change in RPM. All a gov does is change throttle position such as to maintain constant RPM... No?

[torque to twist]

Thanks Ian, for sharing you experiences with us
I don't mind old school did it for years we just didn't have the over powered motors we have today.
Do you have a pic's of airframes?

Cheers

[torque to twist]

One problem with governor is keeping the set point RPM if the motor has slow reaction time the electronics will ask for more and more throttle and so will cause over speed, then add in a bit of unloading on the blades and you will have megga over speed. I am going to try a gov I will wind the gains way down to start see if i can get a steady head speed.

[coolice]

Thanks Ian, for sharing you experiences with us
I don't mind old school did it for years we just didn't have the over powered motors we have today.
Do you have a pic's of airframes?

Cheers

Hey buddy.

You're very welcome. I have fond memories and the odd brown trouser moment to of my time with turbines.
I was hoping to still be around them, but Wrens personality changed and some comments they made upset me. The 700 conversion was a fellow club members, who was sadly quite ill and couldn't complete the conversion himself, so with my previous experience I was asked to help........ I didn't need asking twice :-) The owner managed to get a go on the buddy lead and enjoy seeing the model put through its paces before passing.

I'm sure I have better photos somewhere of the mechanice, when I am next on the pc I'll have a look and post them.

Ian

[torque to twist]

Turbine mount trial fit session

It all fits well but I may go to plan B

[coolice]

I appreciate that turbines have a slight lag in changing RPM but surely with a governor your aren't changing RPM.. That's kinda the whole point of a governor, to avoid any change in RPM. All a gov does is change throttle position such as to maintain constant RPM... No?

Hey buddy.

In reality you are changing the rpm, as any collective pitch input (and cyclic for that matter) is going to load up the head and thus drag down the rotor rpm.
Unlike an IC engine or electric motor, not only do you have to change the turbines rpm by thousands of rpms, rather than hundreds, the turbine gas generator is also not physically connected to the main rotor/main gear.
The turbine, called a gas generator in most heli's case, is actually there to provide air flow to drive another turbine wheel which is then connected to the OS91 crankcase style 90 degree gearbox assembly. Hence the term free air turbine as the engine isn't physically connected to the driven parts of the mechanics.

So what this means is you are waiting on two areas to spool up;

1. The actual turbine shaft, the ecu throwing more jet A1 into the chamber to burn more and create more rpm on the turbine shaft and thus more thrust. And

2. The free air turbine wheel that is in the turbines exhaust air flow to now be driven round faster by the now quicker flow of air coming out the back of the turbine.

As above you can't dampen the govenors response enough to allow for this additional time from speed dropping detection to govenor compensating throttle increase.
So you get into a catch 22 situation, rotor rpm drops, govenor throws in more throttle, turbine takes its time to respond and then when it does it over shoots. Govenor now cuts the throttle and it then dips too low and is commanded to increase and so we start again.

Another link in the chain is the fuel pumps, turbines are essentially fuel injected, so the ecu tells the fuel pump to flow more fuel.
It all adds up to the reason why most govenors just do not work on a turbine, we've been there and tried it to make our lives easier.
The ones that do are on more scale orientated turbine mechanics that do not get stressed so much in flight.

Ian

[Grumpy]

Thanks Ian, I should have known that (the gas generator is not connected to the power turbine).. thanks for reminding me!

[coolice]

Thanks Ian, I should have known that (the gas generator is not connected to the power turbine).. thanks for reminding me!

No worries buddy.

I've not kept up with Wrens latest ECU changes, but I'm sure they haven't added a govenor yet still. However I could be wrong.
Inbuilt/programmed with the ECU would be the best bet, as it could be more reactive based on throttle inputs received.

Ian

[Grumpy]

Ian, So on this basis i guess that you just have to accept that on a turbine heli RPM will bog when you apply collective. I'd imagine that even if using a V shape throttle curve you would have the same problem of lag of response of the gas generator following aggressive collective input.. So I'm guessing not to good for aggressive aerobatics?

Also.. i wonder, would the turbine's bearings cope with the loads from gyroscopic procession caused by 3D type flying?

[coolice]

Ian, So on this basis i guess that you just have to accept that on a turbine heli RPM will bog when you apply collective. I'd imagine that even if using a V shape throttle curve you would have the same problem of lag of response of the gas generator following aggressive collective input.. So I'm guessing not to good for aggressive aerobatics?

Also.. i wonder, would the turbine's bearings cope with the loads from gyroscopic procession caused by 3D type flying?

Evening Mate.

Yes, as expected RPM will fall slightly. However, there is half a cure. With some nicely setup throttle curves you can remove most of the rpm drop, as the throttle curve will be set to increase throttle/turbine rpm alongside collective pitch changes.
In this case, as you command a climb out main blade pitch will increase and thus load up the disk, but the throttle curve is also advanching the throttle output signal at the same time, so unlike a govenor that is waiting for the rotor rpm to decrease before it reacts, you're actually giving the turbine the heads up almost to add more power. It's by no means perfect, but it works well enough in this sort of setup.
It's a bit like the old transmitter mixing trick before govenors came along for IC engines, we'd setup the spare mixers in the Tx to throw an additional 10% throttle on any cyclic inputs, thus anticipating the load imposed on the rotor disks rpm as we performed a flip or roll.

While turbines are surprisingly nimble, aggressive 3D isn't their strong point sadly. It's not that they can't do it, but it's just the sheer mass of that turbine underneath having to be hauled up & over/around the rotor disk that blighted their flight performance. I remember the very first Turbine Predator being flown at Sanddown park by Perry Kavros, his death spiral was just that as he misjudged the height at which he had to pull out with the much heavier turbine compared to the IC model :-/ I think CenturyUS even got charged to repair the horse racing fence

Having said this they do darn well at 3D, back in the day Bob J was much more advanced in his 3D flying skills than I was (back then I was more F3C orientated than 3D) when I first started flying a turbine and he certainly threw his Quartro around very spritely. His was always an 800mm main blade model from memory, which helped ligthen the disc loading, the Century Predator I flew started life on the stock 720mm main blades before I saw the light and changed to 800's. My Predator was near enough (or a bit more) than 15 lbs. fuelled so no shrining violet as they say.
As confidence grew on the machine I was flying, I followed suit and flung the model around a lot more, but I was always reminded by Dean Smith (general manager of CenturyUK) that the ground was at head height :-) lol

The turbine shaft didn't seem to mind being spun in all directions while it turned at over 140,000rpms, whether there was any gyroscopic effects I do not know for sure and can't say I felt anything.

It's old, but here is the Predator Turbine;

It did it, but the nose weight always wanted to try and catch me out as flick out of any backwards manouvers. This was why I was chomping at the bit to get hold of Wren's MW44 heli setup, as it was smaller, lighter and more than powerful enough.

Ian