First turbine : Which one ? Why ?
 

Does anyone have experience with Simjet turbines?

First turbine : Which one ? Why ?
 

If you do a search here on RCU you will find a lot of feedback on the Simjets.

One word of warning though - be careful to look at the dates of any feedback you read. Originally (18 months + ago ??) Simjet got a fair amount of adverse feedback. Then Kevin & Ed (Great Northern Models) got involved - they invested a lot of time & effort (& probably money !) and managed to make a terrific turn-around (no small feat - once a brand name gets some bad press, it takes a heck of a lot to turn that around). So - if you see recent feedback being good, and older feedback being bad - that's not a contradiction - it's a testament to the work of those two guys.

Gordon

First turbine : Which one ? Why ?
 

As Kevin East said, I think the best way is to look around yourself at the airfield, and try to mimick jet addicts.

But when there is absolutely no jet addict around at your airfield, you have to make the right choice ! This is actually what I'm facing today...

Wren manual
 

I think something which would convince me at buying a Wren would actually be reading the detailed manual. Has anyone a pdf version of this manual or something which may be downloaded ?

Thanks

First turbine : Which one ? Why ?
 

That's not why you cool down the turbine after a flight. The main reason you cool the turbine is to keep the bearings inside the engine from getting too hot.

First turbine : Which one ? Why ?
 

WRONG do your research before you QUOTE someone. If bearing heat is a factor for cooling down, remember the bearing is alot more hotter during running condition.

First turbine : Which one ? Why ?
 

Um, actually that is correct (about cooling post run in order to keep the bearings from overheating).

Here is why (from many of my home-builders sources).

When the turbine is running, the steady stream of cool air that passes through the bearings and down the shaft tunnel (and around it) rapidly remove heat away from the bearings and around the shaft, while the "other" parts like the NGV and combustion chamber get quite hot.

Now, when the turbine is stopped, the stored heat can rapidly migrate to the other parts, since the source of cooling (the airflow) has stopped. It is at these times when the bearings actually can sustain damage.

If you read Kamp's books thoroughly, and all that is contained in the newsletters of the GTBA, the information is there.

Regards,
Andrew Coholic

First turbine : Which one ? Why ?
 

Lets look at this logically. auto start ecu only pulse the starting motor 3-4 time in a 3 second burst. Thats not enough to seriously cool the bearing down. In fact during the cooling down process there is no oil present. Also companies building and assembling turbine after test running the engine. they simply put it down to cool without cooling runs. But every body has there own theory.

"dats only in da mo nin"
 

Matt
can you PM me why brand X motors suck. I just dont understand. I only cool my engines down "in da mo nin."

Whoooooo whooooo

LOL!!
 

those turbines, we do it fo da dekarayshunz, dats it an dats all man.

First turbine : Which one ? Why ?
 

Gotta agee with Ajcoholic and Doug here Unknown. Ya wana cool the bearings man, DA BEARINGS!!!

its official like a ref with a whistle
 

FO SHIZZLE MY NIZZLE!

laymen's viewpoint
 

hmmm....I'd be suspicious of listening to anyone who says "a lot more hotter".

First turbine : Which one ? Why ?
 

Unknown, during the cool down there IS definitely oil present. The oil doesnt just "dissapear" when you stop the engine, and a film of oil remains on them. I have taken my engine apart many times (Wren and KJ66 homebuilt) during my first few hours running for inspection, and the bearings were definitely oiled up.

I know with my Wren, which I am running in a semi auto start, with an attached electric motor for starting and cooling, when I stop the engine, the temps quickly drop to about 300 degrees C. When I hit the starter motor on and off in 5 or 10 second bursts, a half dozen times, it quickly cools to below 100 C where I like it to be.

We can all do what we want, but I think a cool down is too easy NOT to do it, not wanting to take the chance myself.

AJC

First turbine : Which one ? Why ?
 

It's not theory. It's called Thermodynamics. Heat soak specifically. In fact, all engines display some of this following shutdown without forced cooling. Cylinder head temperatures of reciprocating engines all rise following shutdown for a brief period of time but since they're not running at the same temps as turbines there is less chance of damage to the bearings.

SIMJET
 

mnmills,

You bet.

Please check your PM.

Regards:

First turbine : Which one ? Why ?
 

If the main problem is that enclosed engines cause hot air to rise up and damage paint - the solution is simple !!

Build a stand to hold the plane vertical after you stop the engine... then the hot air rises up out of the tailpipe, not up through the bypass and fuselage to damage paint. Simple ! now the engine gets to cool down without risking damage by spinning it over with no oil, and the paint gets protected since hot air goes up, not sideways. Perfect solution.

YMMV,
Gordon

Turning engine without oil
 

A couple of things need to be said here:

a) There is usually enough oil left in the bearings after a run.

b) The ceramic bearings we use are incredibly wear resistant. How would you compare running at 120-160krpm with oil mist lubrication to running at 10krpm with a film of oil? What would generate more heat? More wear?

Turning the engine over with a starter will not damage the bearings!

Having said that I must say that I do not see a good reason to spin the engine other than to purge it from unburnt gas and to prevent the heat from going up ito the fuselage.

I don't think that heat soak is too much of a problem for the engine in general. It isn't a problem for the bearings since they are built to withstand much worse punishment.

Pulsing seeme like something that would cause unwanted wear on the starter motor and the bendix assembly. I run my motor on 3v to spin it more gently.


BTW, at running speeds the oil is too viscus to lubricate properly. The lubrication is actually done by the fuel itself. The reason we add oil to the fuel is for startup, idle and cooldown mostly.

First turbine : Which one ? Why ?
 

I agree with erazz %100... I was told 10 years ago by
an AMT desiginer that you can run at low RPMs (1-3K)
all day long.. That is nothing compaired to 115K.

Eddie Weeks

First turbine : Which one ? Why ?
 

It's obvious that all you grammar specialists have run out of arguments for my theories or your mechanical background is limited.
Therefore you choose to focus on my grammar. I originate from a Spanish speaking country and i learned to speak, read, and write
English in this country. at least i am one of the few who made the attempt to learn the language which is not easy. In my country
Americans speak Our language.

Now can we get to the topic.

Remember this post is only for the (GRAMMAR SPECIALISTS) CHECK THIS POST WITH A MICROSCOPE. :D

Heat on bearing
 

ajcoholic

Thats all i am saying.

First turbine : Which one ? Why ?
 

Finally time for my two cents- I cant speak exactly to model turbines as I, as most of us, am not an expert there. My experience is with auto turbo-chargers. In cars heat soak is a problem. In auto turbos the bearings are lubed by circulating engine oil. The turbos have much more mass than our models-the radial turbine wheel is heavy and also the turbine housing is quite heavy and can retain MUCH heat. The turbos can operate at 11-1200 deg Farenheit. When you turn off the engine the oil stops circulating to the bearings-the 1200 deg. heat from the mass of the turbo "heat soaks" via the shaft to the bearings and can cause harm. The harm can take the form of damage to the bearings, but mostly the harm is from cokeing of the residiul engine oil left on the bearings. Autos address this in different ways (oil pressure canisters, electric pumps, idle down etc.)
Now all that being said-I dont know if ANY of it applies to our models. Reason being is the MUCH smaller masses we are dealing with. (light axial flow turbine -vs- heavy radial turbine, cast iron housing-vs-light weight inconel chambers. and very small amounts of special TURBINE oil left on bearings, etc). As stated earlier, they cool down WAY quick. 400C to under 100 C in less than a minute. Anyway-It cant hurt to cool them down. Scott

First turbine : Which one ? Why ?
 

Unknown,
I dont care how bad your english is, that to me is unimportant - both my parents come from foreign countries and had to also struggle to learn English - I understand how it is (from grouwing up with them) to have to deal with people making fun of you because you cannot speak or write as good as them. That really has NO place here...

Basically, I think it is a good idea to cool the engine a bit (I bring it to under 100 C) after a run. It isnt hurting anything, and if you dont want to, thats fine too! You paid for your engines and heck, you can do whatever you please. :)

I am just glad to be able to have discussions like this - since where I am I am the only one with a turbine.

AJC

First turbine : Which one ? Why ?
 

Hey ajcoholic

May be someday you will say i am right or i might say ajconholic was right all along. The bad thing about SOME Americans are if they cant't find A PROBLEM WITH SOMEONE THEY MAKE ONE.

I love this kind of discussion because i learn from it and some one out there will learn something also.

TRU DAT...... TRUE DAT
 

you are the great CORNHOLEO