Got a "Napier Gazelle" but need help

[TwoGears]

Good idea!

Yes the engine indeed has IGV's.
The IGV mechanic consists of a rod comming from the HP distributor
connecting to a lever steering the IGV's. The scale for the angle is mounted
directly above this lever. The scale reaches from -10 to +50 I think (need to check that, could also be 60).

I treated and cleaned it but the mechanic still moves very bad. I'm not sure if it's
because the HP system is holding against my attempts or if it's still dirty.
I need to check if it moves tomorrow when I try to start the engine again.

However, if the IGV scale reaches to 60, there surely could be a connection between
them and the unknown lever.
I'll go, take a picture of the system and post it here after work today.

[cursorkeys]

Yeah, I really wouldn't try running it without any RPM indications!

If you get a multimeter with a frequency counter mode just connect two of the tacho pins to it (the tachos are three-phase generators basically) and you will get a reading in Hz. If you remove the tachogenerator and spin it with a drill at a known frequency (use a strobe or a laser tachometer like this: www.ebay.co.uk/itm/Digital-Laser-Photo-Non-Contact-Tachometer-Rotational-Speed-Tester-99-999-RPM-/131009601574?pt=UK_Sound_Vision_Other&hash=item1e80c7e026) you can find out how many pulses per rev the tacho has (the number of poles) and so calibrate your display in Hz to the real RPM. I did this with my GTD-350 until I got a proper gauge.

600°C sounds fine, as that's EGT I wouldn't allow it to get much above 700'ish on such an early engine as that will probably be a TIT aproaching 800°C or even 900°C which would likely be the material limit on such an early engine. EGT is a pretty poor measure as it depends hugely on probe placement.

In my experience of IGVs they don't come into play at all until the engine gets to 60-70% or so. But I've only played with 3 engines with IGVs.

Flight global says your maximum output shaft RPM should be 3000 RPM. I found the rated max core RPM! Its 20400 RPM.

So your idle is probably somewhere in the region of 40% I would guess so 8000 RPM.


Edit if your engine is an early one marked 'NGa.13' then the core RPM limit is lower at 17000 RPM: www.flightglobal.com/FlightPDFArchive/1958/1958-1-%20-%200330.PDF

[TwoGears]

Sorry guys...
I was abroad but there is hardly any internet connection in the russian outlands
I'll uplaod the stuff I've made so far later. Here is a small update...

Facts from my last try:

• After trying to swith off the starter much later I managed to get the turbine to a good speed where the engine didn't act like a dragon and blow fire out of the exhaust. But I just reached this state just once out of five attempts (maybe the batteries were to weak)
• The EGT always stood at 900°C (to high and the blades of the power turbine were glowing --> why so high temperatures?)
• Got new and better batteries today
• Got a multimeter, DSO and a tacho for each N1 and N2(like the lasertachometer but mechanical)
• I forgot to give much attention to the oil but the level always were pretty high and it was a little foamy in the control window at the tank (maybe scavenge pump is really faulty --> is there an easy test for this?)

[/ul]

I'll work on the engine this weekend again. Maybe it'll work
properly this time. However, I've got more starting attempts
due to the new batteries

Greets~

[turbochris]

watch the temps!If the pT was glowing the GG was hot! spool it up fast and feed the fuel easy. watch for puddling in the combustor., foam is from scavenge pumps as long as the level is OK u should be good.

[gidge348]

EGT 900°C is a VERY BAD thing DO NOT LET IT GET THAT HOT.

Please do not try and start until you have a way of tracking RPM

Is there a brake on power turbine or is it free wheeling and still glowing???

I am pretty sure you have a hung start it will just sit there and get hotter and hotter, it is basically caused by not enough air passing through the engine to cool it. Normally only a small proportion of the air going through the engine is burnt (20-30%) the rest is cooling and is expanded by the hot burnt gasses. This what keeps the 980°C (controlled burn temp of jet fuel) from damaging the engine. If your EGT was 900°C the gas generator would have to have been at or close to the 980°C a VERY BAD THING.... the only way it will get hotter than that is a thermite reaction starts inside the engine. Have you ever seen a Oxy Acetylene torch cutting steel.... same thing (not good in a turbine engine). Please don't tell me it was spitting sparks out the back...

While it was at "idle" did you have any throttle control? ie. did moving the throttle change the rpm?

Here is a T53 with a hung start www.youtube.com/watch?v=PFblTG8YOCM Note how there is a small increase in speed when the main fuel on but still dumping fuel out the exhaust and not climbing to full idle rpm. Also notice how they shut it off pretty quick.

Remember idle on a turbine sounds like a piston engine way past max revs they are scary things.

Agree with Chris foaming oil is a good thing means the pumps are working as long as the level is correct I would not worry too much.

I am sure that batteries are the problem ..... can you load a video may give us a better idea of what is happening it could be the pump or governor or even the mysterious third lever?

Also try Chris's advice... slow on with the fuel to see if it will catch and start having throttle control you always want a lot more air than fuel.

Ian...

[TwoGears]

Thanks again for all the helpful information!

My engine acts exactly like the one in the video, so it's a hung start.
Even if I didn't change the throttle from almost zero yet, I can tell
from the sound it makes.

So far so good...
I thought so that 900°C is to much so I shut it off very quickly each time.
The glowing was noticed by a friend standing behind the engine but there
were never sparks coming out of the exhaust.

The power turbine doesn't seem to have a break so it was free moving.
The shafts speed (after the reduction gear) looked quite okay, not to
fast for driving a helicopter rotor. However, I've got a lot of appliances
with me today, for measuring the RPM (multimeter, DSO, mechanical tacho,...)

I'll make a video of every start attempt today and upload it when I'm back.

[TwoGears]

Well, there are good and bad news.

Good:

• I made a video of my last start attempt and after several hours of trying to upload it, YouTube finally took the file.
• the IGV-control works properly (reset itself to default angle)

Bad:

• The batteries I got weren't fully loaded and we didn't have the other ones around.
• So I had just enough power for one start. Unfortunately everything which could went wrong actually did so.
• Starter shut-off to early
• Flames out of the turbine
• To hot EGT
• The multimeter didn't measure anything because the plug fell off.
• Oil became foamy but always stood at the same level which was over maximum in the tank

I'll give it another try tomorrow monday. Hopefully the batteries are full and I don't
make mistakes as this time. However, I still think there is something wrong and somewhere
it's getting to hot.

I'll trim the whole engine to zero fro tomorrow and begin completely from the start.
I need to wait much longer until I open th HP-valve but from all my starting attempts
I never managed to not have flames coming out.. NERVER!
That's why I'm not that sure anymore if there really weren't sparks.

Please forgive me for treating this wonderful engine like this.
It also hurts my heart... 

Here is the link to the video: www.youtube.com/watch?v=o4bpaegcNcM

[racket]

Hi Ben

Sounds like you experienced the usual problems we all experience when getting a new engine fired up for the first time.

You can hear the starter slowing down as the batteries lost power, were the batteries cold ?? warm batteries will give more cranking power , heat them up before a start attempt.

Can you think of a reason why the lower exhaust pipes had more flame/fuel than the upper ones ??

It was getting close to self sustain, ......fresh fully charged "warm" batteries and she should get there :-)

Cheers
John

[racket]

Hi Ben

Did you sort out the IGV mechanism ??

The information I have in one of my texts for "small " engines has the angle being changed by fuel pressure .

At idle , and I'd assume also during spoolup, the vanes are set at the highest degree mark , as thats the degrees "closed" from fully open high power setting , generally ~50 - 60 degrees closed , with the vanes pointing in the direction of rotation .

As the engine is accelerated from idle to high power the angle of the vane gradually "opens" up to a more axial direction .

If your vanes are too "open" at spoolup the angle of attack onto the first stage compressor wheel will be wrong , the inefficiency produced will be a "power sucker" and could be preventing acceleration to idle .

Just some thoughts :-)

Cheers
John

[gidge348]

Thanks for loading the video, yes I think a lot of the problem is the batteries.

One thing I noticed is just as you shut the fuel off it started run up nicely (24 seconds) before it ran out.

If you could try opening the fuel a little slower and only open to maybe 1/4 open until you hear it catch

You can close it for a second if you see flames but keep the starter engaged.

I think you are very close with this and sorry if I was a bit harsh with my last comments .... keep at you will get it running

[cursorkeys]

Wow, thanks so much for the vid!

Yes, I think you're very close too. Better/charged batteries and keeping the starter on for much longer should do it

As Ian said closing the HP cock slightly to keep the EGT under, maybe, 850°C is probably fine as this is a standard procedure on my M701c-500 which is an early engine too. The only caveat to doing this is that the engine MUST still be accelerating to idle even if slowly or you've got a hung start.

Keeping the EGT in limits is the most critical thing. This is the problem and these are the TIT temps which will be higher than the EGT:



For your comment on maybe seeing sparks, on blades that have been damaged by over-temperature you can usually see a telltale greenish sheen on the blades. Another check is that the blade tips still have a nice sharp profile.

It shouldn't look like this (these are static vanes but the damage looks the same on blades!)




Nearly there and congrats on the progress so far!

[turbochris]

you have to make sure there's NO fuel in the combustor find the drain. Spool it up as fast as you can, then make sure you hear the ignitor kick and then make sure you know how the fuel control puts fuel in. Put the fuel in slow and watch for heat, when you get heat, add more fuel. Try not to take too long or the batteries/starter get hurt. Sounded like it was a little loaded up w fuel that can run away on you make sure you know where the fuel goes and where/when it burns.

[TwoGears]

Okay, tomorrow is the day for the next try and I'm in cheerful spirits
the engine will work properly

Today evening I prepared everything for the start (plus battery warmers).
Absolute zero throttle and the mysterious lever is also set to zero at it's scale.

When I wanted to leave I had the usual glance on the oil level and recognized
it suddenly sunk to a level between min. and max. When I left after the bad
start it was over maximum, that's for sure.
I don't really know how this happened but it makes me feel a little better
about the oil problem.

racket
Maybe there was to many fuel and most of it was blown around or from the
bottom. Even though the pT should spread it around.

For the IGV mechanism I think it's the same you described in your post. It surely
is controlled through fuel pressure. Before the start you can see in the video I
manually set the IGV's to the highest angle possible. When the turbine began to
spin the angle was reset to minimum (-48°) automatically.

gidge348
This time I'll only concentrate on the HP-pump and throttle management. My buddy
will handle the starter and ignition system. With the new batteries it should be possible
to let the starter run in assistance much longer. And when I can't hear any increase in
speed anymore I'll first open the HP-system with throttle at zero. Then, as you said,
slowly starting to give fuel, always having an eye for flames, the EGT and glowing parts

Don't mind being harsh, I didn't grasp it in a bad way either. I guess I were a little down
because of the bad start. They aren't as easy to run as a bicycle.

cursorkeys
Checked all blades(pT and static vanes behind it) I was able to see through the exhaust tubes.
I didn't notice any greenish sheen on them and also the blades look all the same from bottom
to tip. Maybe I was lucky at this

turbochris
I set everything to minimum or zero if possible. If I open the HP-lever there almost shouldn't
be any fuel getting into the combustors. Then I can slowly open it. The batteries aren't any
problem anymore. If I kill them I can get some replacement from a friend.
I also think it's all connected to the car batteries I used before. They didn't last long enough
to start properly and run the starter long enough.


Hopefully tomorrow will be my lucky day and the Gazelle will run properly
for it's first time since being under my observation.

[gidge348]

Good Luck Ben..... don't forget the video

If you see a spike in temp and shut it down like you did in the last video, I think there is only a small chance of damage.

It is just when it is held at those high temps for 10 or 20 seconds that bad things happen.


Ian...

[TwoGears]

After a huge lock-out I'm back online and finally can bring
you a positive feedback.

It worked! The engine finally ran.

I'll post further details as soon as I managed to uplaod
the video to Youtube.