HI all, I sent my Ram 1000 in to get new bearings and balancing, as their was a slight vibration at 60 tho.
Was told before the work was started at the compressor wheel looked like it might cause the turbine to cavatate.
Bearing where put in and when the turbine was ran to over 100tho, it cavated and the compressor let go.
The purpose of this tread, is to find another compressor and see if any one else has ever seen a compressor wheel let go like this one.
Rcpete

I have a used Ram 1000 compressor wheel for $ 55 if you are interested.
Email me @ [email protected].


Johnny

RE: Compressor stall?? Help! - 7/5/2006 8:56 AM


Shogun








Posts: 931
Joined: 7/27/2002
Last Login: 8/15/2008
From: Omaha, NE, USA
Status: offline I spent my military time as a turbine engine mechanic and have witnessed compressor stalls in full scale aircraft(US ARMY Heli's). A turbine engine is a precarious balancing act of RPM/temperature/pressure that has to be maintained within tight parameters or you can get a compressor stall. In the case of the full scale aircraft this is done electro-mechanically with ECU and/or a mechanical fuel control, depending on the vintage and type of the engine we are talking about.

Essentially a compressor stall occurs when the combustor pressure rises beyond that being created by the compressor (cold)section of the engine. Since the internal pressure is always attempting to find it's way out of the engine and when everything is working properly it exits to the rear. If, for any reason, the pressure in the combustor(hot) section rises beyond that being created by the compressor you get a pressure reversion that flows backward toward the spinning compressor(rear to front of the engine). Since these engines are designed to flow in one direction only, inlet to exhaust nozzle, the reversed flow of air essentially acts like a brake and tries to stop(stall) the spinning compressor. Now when you consider that these compressors are spinning upward of 120,000 rpm you can imagine the catastrophic results that can take place when such things happen.

Stalls usually occur when throttling up quickly or rolling off the throttle quickly. In full scale aircraft the causes can be many but usually are the result of an improper rigging of the inlet or variable stator vane systems, cold section bleed bands that don't open at the right time, a mechanical or electrical fuel control unit that is damaged or out of adjustment or, in many cases, erosion of the compressor blades/vanes that leads to improper(too loose) tolerance of the parts which results in a drastic drop in efficiency(reduced airflow and pressure). Erosion is caused by dirt and debris ingestion(FOD) and can literally thin blades or in some severe cases literally roll the metal back on the leading edge of the blades destroying their aerodynamic properties. In some cases I have seen air density cause stalls when the engines was improperly rigged, ran fine in cold air but stalled in hot(thin) air.

In the case of model turbine s these are basically smaller versions of the old 50's era centrifugal engines(think F-86 or Mig-15). These engines are essentially 2 impellers mounted back to back and connected together on the same shaft. The front impeller draws in air and spins it outward at a 90 degree angle into a duct called a scroll. It's the centrifugal force that is imparted to the air that results in a pressure rise. Next this compressed air is directed into the combustion chamber where the fuel is injected and ignited, once the burning process begins it is self sustaining and will burn as long as there is fuel to feed the flame, much like a blow torch. The gasses created by the burning process expand and are directed onto the aft impeller which causes it to rotate, think of a child's pinwheel and you will have the idea. The rotation of the aft (power turbine ) drives the forward (compressor turbine ). An interesting fact that most people are not aware of is that turbine engines use 70% of the power that they make simply to sustain their own operation, the remaining 30% is what we see as thrust or horsepower that turns a shaft in the case of turbo-shaft engines.

Things I witnessed when full scale turbine s stalled were broken and burned internal parts in the compressor and power turbine sections, 20-30 foot long flames shooting out of the back(usually) or the front of the engine in some cases. In all cases the engines would make a loud banging noise, imagine the sound a machine gun makes but much louder and deeper in tone. In some cases the stalls were so severed that the engines failed completely and essentially came apart with catastrophic results. Have you ever noticed that in pictures of older full scale jets like the F-4 or F-105(among others) that there is a red stripe painted around the fuse about 2/3rd's of the way back on the airframe? What that line signifies is where the turbine wheels will leave the airframe should a catastrophic failure occur. All personnel are trained to never stand beside the aircraft on either side next to that line while the engines are running for up to a 100 feet(or more) from the aircraft. where turbine s are concerned you are safer standing in front of or behind the aircraft than beside it.

I'm not sure this will answer your question but it should be informative to those who have heard the term compressor stall but had no idea what it meant.

_____________________________

Scott

Hide Signatures

Now when you consider that these compressors are spinning upward of 120,000 rpm you can imagine the catastrophic results that can take place when such things happen.
quote taken from Scott

I purchased a ram 1000 ( I was told ) awhile back. It had been sent to modelbau and gone threw, returned and sat on a shelf.. Anyway, went to start it with no luck. Gave to a friend who is used to rams and he couldn't get it to run. He sent it to Carlos and he got it to run but had a 'rumber' around 122,000 rpm and that it was only putting out 22 lbs. Carlos told him it would cost around $1700 to get it working right.. He said that someone had replaced the diffuser with a wren and not the ram, that the combustion chamber was bad and that it needed the new ecu... Too much to spend for a $1500 motor!!!

Shhhhhhh!!! Can't say the S word or the mods will edit it [:-] (previous post)

Rcpete.. i've got a airstart Ram 1000 that has a NGV / turbine disc rub at shutdown after a run.. It literally has 10 minutes or less run time on it. and i've got over $1800 invested in it. I need the tailcone off of it for my autostart ram, so i was going to just used the turbine as spare parts. If your interested, shoot me a pm..

thomas

I have never seen a wheel fail like that. Can you post a better picture of the last one you have posted. Try to zoom in as close as you can. There must have been a void in the wheel.

HI, their is no void.
Rcpete

I've seen a few turbo compressors do exactly this, and it was typically caused by either FOD or over-revving... or a combination of both.

I find it interesting that there is a shiny area on the tear, this material will not do this under normal circumstances, is that really like that or is it just the pic? If there is a void or crack, it could be very tiny and hard to see. I would imagine that this would be close to the leading edge of the blade, as the tear propagates back to the hub, the centrifugal force would make this section rotate as it comes out, the leading edge of the blade would hit the bell mouth forcing the broken section out through the back of the compressor, as you can see in the pic it has the bent back portions on the side . What does the bell mouth and diffusers look like? I imagine there done.
That is a very old style compressor is this what come with a Ram?

I could see over revving but would the fod make it past the inducer?

I had a RAM750 that came apart on me and the compressor had chunks missing that were pretty similar looking to that one. Don't know why it came apart, if the engine had ingested FOD before I owned it or what had happened.

I was on the fourth compressor in nine years and about 600 cycles when my RAM750+ screeched to a halt a week ago. My first thoughts were "not another compressor" gone but this time the rear bearing had failed catastrophically and now the motor is probably not worthwhile rebuilding.

The characteristics of the three failures my Ram compressors had were basically identical except the part of the vane that failed on #1 did not break off. Also interesting to note that the failures happened at approx. 180/360/540 cycles indicating fatigue as the most likely culprit. We used to joke that the next one was expected at about 720 cycles but now I don't think we are going to get there.

Had a great ride with the Ram and all happened on the same Kangaroo.

[img][/img][img][/img]

I should have also added that #2 & #3 failures occurred with a screen fitted to stop FOD. After #2 failure, we set max. rpm at 105,000 from 120,000, and after #3 failure, we set max. rpm to 95,000. So even with the lower max. revs the compressors continued to fail. Kangaroo performance was down a bit but still OK. Flying only off full size bitumen runways was a big help.

Thomas,

What is considered over-revving in a turbo-charger? I have no idea what kind of RPMs they spin.



Pete,

I would say this is pretty good evidence as to what happened to yours and with all exhibiting the same end result. I think jet log's first pic showing the beginning of the failure is very revealing. Just picture that break continuing and leaving you with the half-moon shaped piece missing from the outer hub with bent back edges. And given the fact that his last two occurred with a FOD screen eliminates that cause; leaving the RPMs as a main focus. Maybe these older wheels had a problem or were never designed or intended to be spun that fast.

BTW, I might have a compressor for you, but I think it's from a 750. Are they different? Anyways, I'll have to have my wife look for it since I'm gone. Give me a couple days and I'll see if it can be located, if so, it's yours.

George

George,
the last turbo car i had (97 mustang gt) had a 76mm turbocharger. With it producing 20psi of "boost" it was spinning roughly 85,000 rpm before it came out of its efficiency range. The smaller T3/T4 hybrid turbines which are about the size of a mw44 size turbine, spin around 150k max in their efficiency range. A ram size turbine would probly utiilze a T-4 style compressor and they max about 125k rpm before they get out of their efficiency range. Its hard to say what rpm they would fail at, the few times i have seen it, it was b/c of wastegate failure which allowed the turbine to just keep accelerating past its rpm point.