The Fat Lady ..................FM-1

[racket]

Hi Chris

LOL.............yep , lotsa R and D testing :-)

Good to hear the new comp worked out OK , was it actually a new one or had it been "used" ??

Cheers
John

[Deleted]

Nov 13, 2018 3:23:54 GMT -5 racket said:

Hi Chris

LOL.............yep , lotsa R and D testing :-)

Good to hear the new comp worked out OK , was it actually a new one or had it been "used" ??

Cheers
John

It is brand new, an absolute score
will run in the engine with the old slightly shorter compressor wheel
just in case.....lol
could you lookup which turbine wheel number was used?
have googled the one on the turbine wheel but it comes up with a tv 92 turbine
is this correct?



cheers chris

[racket]

Hi Chris

Yep , the turb wheel is used across a lot of sizes from TV91 to 94 Part Number 442208-0001

That certainly was a good score with the comp :-)

Cheers
John

[Deleted]

Nov 13, 2018 4:27:10 GMT -5 racket said:

Hi Chris

Yep , the turb wheel is used across a lot of sizes from TV91 to 94 Part Number 442208-0001

That certainly was a good score with the comp :-)

Cheers
John

hi John

Yes it was ,thanks again for the tip

The # on the wheel is 407452-50

is that the same as the one you are referring too?

cheers Chris

[racket]

Hi Chris

I have no idea where that 407452-50 number comes from :-(

Cheers
John

[Deleted]

Hi All
just a quick update
have had FM-1 up and running ,even with the gearbox attached (video later ,needs editing)
have had a few oil supply issues which caused the bearings in the engine to fail, a few modifications later she seems ok again
I havnt got numbers as yet still to hot up here
have run into an issue with the freepower turbine bearing
Anders, im wondering how you lubricate the bearing from the cold side and prevent the oil getting to the freepower wheel as your setup is the closest to what i have ,a 3rd stage C20 wheel,have tried to find your old pictures of how you set it up but cant find them
chris

[Johansson]

Just a 1mm oil jet pointing into the bearing and a washer with something resembling a labyrinth seal on the hot side of the bearing. I get some oil leakage into the exhaust duct but not much.

The oil runs back into the bottom drain of the gearbox through a slot milled in the rear pinion bearing housing, the rear bearing has its own 1mm oil jet lubricating it.

[Deleted]

Hi All
Have finished the Hot end shaft and oil seal ,somewhat based on Anders idea
I ended up using a 62mm piston ring (chain saw piston)




so slowly getting there
should be able to assemble for a test run soon

Cheers Chris

[madpatty]

Sept 1, 2014 17:54:32 GMT -5 racket said:

Hi Guys

Looking at the pics, I think I put more effort into the FM-1 than I did subsequent builds , it was a less hurried build .

The diffuser with its large vaneless gap and longer less divergent passageways is I feel a better setup than the smaller diameter engines I made , also the TL92 comp wheel of only 44 Trim gave less inducer problems than the TV94's 48 Trim .

I had enormous bearing problems with the build , wrecking several comps and turbs when the bearings failed , the poor old NGV is pretty battle scared from turb tip shrapnel whilst the comp outer cover has a bit more inducer clearance than original machining produced :-(

She was a good learning tool though, and now that she's equipped with an axial thrust reducing labyrinth seal against the rear of the comp wheel and nice #8 bearings from an Allison C20 engine being squirted with plenty of turbine oil , she's a much more reliable engine deserving " to be put out to pasture " with just an occasional spoolup to keep the bearings happy ;-)

Cheers
John

Hi racket.

I was curious as to what was the reason for the massive ball bearing problems you had with this engine?

Almost all of the rc turbines these days use ball bearings without major problems and none of them uses the brass cup arrangement or anything similar to that. Bearings are normally seated in the shaft tunnel without anything to dampen their radial motion.

Maybe it can help anyone trying to use ball bearings in future builds.

Cheers.

[racket]

Hi Patty

One of the problems with our short shafts compared to the RC turbines "longer between bearings" shafts is bearings, also that big heavy lump of Inco isn't easy to control as the shaft goes through its various "vibration modes" .

"brass bushes" and lotsa oil flow do a good job of controlling things , I think it was Turbonetics that used balls at the comp end and brass at the turb end .

There are large turbos with "balls" only , but theres probably some means built in to damp vibrations out .

Most of FM-1's initial problems were with the lube system using the standard RC turbine arrangement of fuel mix bleed and air bleed to provide lubrication and cooling because I had a reversal of static air pressure between where the air was bled off near the front comp bearing and downstream of the turbine bearing , which caused hot gases to enter the turb bearing .

After adding the snorkels to the air bleed holes and feeding them ram air exiting the comp diffuser, the pressure gradient was reversed and things improved , but I can't remember the timing of when I went to full pressure lube with scavenge, it could well have been at roughly the same time .


Thought I'd better check my notes .............it seems I started using a semi lube pressure arrangement in early 2008 with ~400 ml/min of oil being pumped to the SiN bearings .

In January 2009 I started fitting the Allison C20 #8 bearings to the engine , but still with "restricted" flow of ~300ml/min of 5W-30 oil , I then changed over to #2 turbine oil .................My notes start to fade away after that as I was probably beginning the 9/94 engine build which had "upgraded" mods learnt from the FM-1 dramas, the 9/94 hasn't suffered the same problems .

Undoubtedly I'd be possible to build an all ball race engine , but the costs of development stars getting a bit high once we use big turbo bits :-(

I'll stick with "brass" as shaft tunnel machining requirements aren't as critical.

Cheers
John

[madpatty]

Hi racket,

So did you use the same brass cup arrangement in 9/94 engine or was it simply done as in ‘Regular’ RC engines without any damper arrangement.

Also did you use Allison bearings in that engine as well.

Cheers.

[racket]

Hi Patty

Yep same arrangement , only improved , the bronze cups had O'rings at each end of their ODs , the lube oil was fed to between the O'rings and through a drilling in the bottom of the cup to the "oil jet" that squirted onto the inner raceway of the Allison bearing , the Allison bearings have a lot of axial play in them so needed the "fixed" endfloat arrangement of the cups.

The couple of thou clearance on the cup ODs along with the O'rings and lube hopefully contained any vibration.

When I first started making FM-1 the bearing issue was discussed with Mike Early on the old Yahoo DIY Gas Turbines Site, and Mike being a retired Garrett aero engineer who was in contact with the Garrett turbo guys in Arizona where he lived tried to persuade me not to go the "balls" route as it was fraught with problems ..............but being "young and silly" back then I thought "I can do it " so started on a long road of frustration and despair with lotsa bearing failures.

The original FM-1 bearings were physically larger than the Allison ones , both being 20mm ID , so the 9/94 shaft tunnel could be made a bit smaller in dia , I can't remember how I arranged the lube supply into/through the engine , the 9 inch outer casing was a tad tight for the flametube and is the reason why I went to the 10 inch casing on the 10/98 engine with reliable "brass" for bearings.

Cheers
John

[madpatty]

Apr 28, 2020 21:19:30 GMT -5 racket said:

Hi Patty

One of the problems with our short shafts compared to the RC turbines "longer between bearings" shafts is bearings, also that big heavy lump of Inco isn't easy to control as the shaft goes through its various "vibration modes" .

"brass bushes" and lotsa oil flow do a good job of controlling things , I think it was Turbonetics that used balls at the comp end and brass at the turb end .

There are large turbos with "balls" only , but theres probably some means built in to damp vibrations out .

Most of FM-1's initial problems were with the lube system using the standard RC turbine arrangement of fuel mix bleed and air bleed to provide lubrication and cooling because I had a reversal of static air pressure between where the air was bled off near the front comp bearing and downstream of the turbine bearing , which caused hot gases to enter the turb bearing .

After adding the snorkels to the air bleed holes and feeding them ram air exiting the comp diffuser, the pressure gradient was reversed and things improved , but I can't remember the timing of when I went to full pressure lube with scavenge, it could well have been at roughly the same time .


Thought I'd better check my notes .............it seems I started using a semi lube pressure arrangement in early 2008 with ~400 ml/min of oil being pumped to the SiN bearings .

In January 2009 I started fitting the Allison C20 #8 bearings to the engine , but still with "restricted" flow of ~300ml/min of 5W-30 oil , I then changed over to #2 turbine oil .................My notes start to fade away after that as I was probably beginning the 9/94 engine build which had "upgraded" mods learnt from the FM-1 dramas, the 9/94 hasn't suffered the same problems .

Undoubtedly I'd be possible to build an all ball race engine , but the costs of development stars getting a bit high once we use big turbo bits :-(

I'll stick with "brass" as shaft tunnel machining requirements aren't as critical.

Cheers
John

Hi Racket.

The reason I am curious in this ball bearing arrangement is the 100mm inducer engine I had bought is also a FULL ball bearing design.

BUT it has your “normal rc type” fuel bleed lubrication with a small hole just behind the compressor wheel (NOTE- the hole is positioned behind the compressor wheel thus air from impeller exit is fed to it and NOT casing air) to supply air for air blast lubrication and cooling.

Now regarding the flow reversal in the shaft tunnel, any engine even the rc types will/should have it as any air bleed from behind the compressor wheel (NOT from diffuser exit or casing air) will be at 1/2 static pressure assuming other 1/2 pressure rise is in the diffuser.

THUS maybe when you shifted to snorkels at diffuser exit you had air at max pressure entering the shaft tunnel thus reducing any chances of flow reversal.

Your comments on ball bearing failure are concerning me now as this engine (based on your theory and experience) is essentially the same arrangement which in your case failed.

Do you remember any details on “snorkels” you used in your engine? Any dimensions etc.

Regards

[racket]

Hi Patty

If you checkout this pic postimg.cc/Thtgt2X5 theres 3 holes at the diffuser to shaft tunnel mounting position , 2 holes were for air and the other for fuel/oil .

There was also a piston ring seal behind the comp to prevent lube going "forward" .

I would have thought the holes I had would have passed the right "pressure" air from the position/s they were , but because of the radial inflow turbine stage the hot gases are forced down behind the turb wheel where I feel they "recompressed" to a static pressure high enough for flow reversal .

The 2 snorkels would have been made up from 1/4" OD metal tubing and simply slipped into the two holes with a blob of silicone sealant around them , the inlet ends were bent/curved 90 degrees to accept full total pressure exiting the diffuser passageways , like a pitot tube , and probably simply lockwired into position to prevent them being blown around.

Cheers
John

[ripp]

Hi Patty,

all of this is very interesting.

Could you upload pictures?

many thanks

Ralph

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