Turbine cool down - pulsating vs. constant
 

Hello guys,

I have an air start turbine which i converted to electric start (semi auto) for a friend, and im building an external start box to operate the glow plug \ starter with switches.

Im thinking about the cool down procees - do you think it is better to pulsate the starter motor (like most ECU's do today) or just run it constantly at a low RPM until the turbine cools down ? i hear some turbine manufacturers (i.e. Jetcat P-20) are changing to the latter with good results ?

Please express your thoughts.
thanks.

RE: Turbine cool down - pulsating vs. constant
 

Merlin turbines have a continuous cool down cycle. I prefer this, as I think a pulsating cycle will cause more wear & tear on components (all that switching on & off).

RE: Turbine cool down - pulsating vs. constant
 

wren 160's have a constant cool down cycle

RE: Turbine cool down - pulsating vs. constant
 

I didnt realize it was that popular already :)
can you guys please tell me which RPM do they spin until they cool down ?

RE: Turbine cool down - pulsating vs. constant
 

Doesn't really matter.

I think that the pulsating cooldown is easier to achieve electronically. Anything between 1000 rpm and 5000 rpm should be fine. All it does is prevent the rear bearing from soaking up too much heat and gumming up the oil on it.

Make sure you have the pump switched off so you don't accidentally spill fuel into the cc while cooling down.

RE: Turbine cool down - pulsating vs. constant
 

I would think that a constant cool down would be easier on the "O" ring in the Bendix...

Pins for the Flash gear are on the way - the fan looks good! ;)

Bob

RE: Turbine cool down - pulsating vs. constant
 

Also (assuming that u have whatever the minimum airflow should be) a slower rpm over a longer period will be a lot easier on the battery than a fast rpm for a shorter period.

RE: Turbine cool down - pulsating vs. constant
 

You guys are all right. i will go with the constant low RPM method.
the only question is now - which RPM are these turbines spinning at cool down ? i will design a circuit that allows me to change the RPM to which ever RPM i choose.

RE: Turbine cool down - pulsating vs. constant
 

if i was you i would go for a slower cool down rather than fast cool down just to keep the stress from thermal expansion/contration down don't want something to develop a crack, i dont know if it could happen but as a welder/engineer i have seen the damage it can do

RE: Turbine cool down - pulsating vs. constant
 

Anybody know if jetcat has an 'update" to change from pulsating to constant rpm cool down.?

RE: Turbine cool down - pulsating vs. constant
 

We done some tests in our factory as one of my guys decided to build his own ECU as part of his sons collage project, and constant rpm was the best, one thing though you must think about is the lack of lube so rpm should'nt be too high.

RE: Turbine cool down - pulsating vs. constant
 

Thanks everyone for the help ! it does sound like constant RPM is the best way to go. :)

does anyone have any idea which constant RPM do most manufacturers use for cool down ?

RE: Turbine cool down - pulsating vs. constant
 

I guess it all depends on the size of the engine. Your best bet is to use a variable power supply on the starter and adjust the motor speed while checking the air flow at the tail cone. Then use that data I'm guessing your are using electro
dynamic ecu?
Xicoy.com fad06

RE: Turbine cool down - pulsating vs. constant
 

I would think one could shoot for the best rpm to power draw ratio...
to get the most rpms out of the least amount of battery power
That could also change from starter motor to starter motor.

You could also use an "external booster battery" for constant starter cooling as not to drain the onboard ECU battery.
There a thread here on RCU about that as well.

RE: Turbine cool down - pulsating vs. constant
 

i am using an external start box for the starter and can use any size of battery that i would like. i dont care about current draw at all - the only thing i care about is what is the healthiest approach as far as the turbine goes, i.e. cool it quickly enough yet not kill the bearings by spinning it dry for a long time.

RE: Turbine cool down - pulsating vs. constant
 

Lukey made me this nifty blower for my Tucano.

It uses a 3" bilge blower and a 7ah gell cell battery. The blower "moves" air instead of "blowing" like a leaf blower would so it sets up a breeze that spins the turbine at about 1500 RPM. It's nice to have on the Turbo Prop because it takes longer to cool off because of the gear box. I don't have to kill the ECU battery anymore with the cool down cycle...I just park the plane, shut it off and hook up the blower.

Beave

RE: Turbine cool down - pulsating vs. constant
 

One thing to keep in mind is that the rpm must be high enough to allow centrifugal force to keep the starter bendix engaged. If your circuit allows you to vary rpm you could conduct some experiments to see what the minimum engagement rpm is. Then you could generate some EGT vs. time cool down curves at various rpms to determine the optimum rpm for your engine. My guess is that you will have to give it a short burst of higher rpm to engage the bendix, then slow it down somewhat to the cooling rpm.

That would be an interesting experiment. Please post your results if you decide to do that.

Joe

RE: Turbine cool down - pulsating vs. constant
 

I will do some tests either way for sure, just interested what other manufacturers are doing to get in the ball park.
This is going to be one awesome DIY startbox - i will post it once done.

RE: Turbine cool down - pulsating vs. constant
 

luckey still flying that trainer jet that made from a trainer:D.

RE: Turbine cool down - pulsating vs. constant
 

Bas,

Yep. This weekend he's removing the P-70 and installing his extra RTI-2800 in it's place.

Yahooo!

Beave [X(]

RE: Turbine cool down - pulsating vs. constant
 

[X(] omg :)man I sure miss markham park [&o]

RE: Turbine cool down - pulsating vs. constant
 

I am running a constant low rpm cool down with my P160, P200 and P80. The newest software update has this feature.

RE: Turbine cool down - pulsating vs. constant
 

Seems like i need to update my Jetcat ECU's ! good info :)

RE: Turbine cool down - pulsating vs. constant
 

Next time you run it plug in the GSU and note down what rpm