BBP Diary

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Renegadenemo
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Re: BBP Diary

Post by Renegadenemo » Tue Dec 06, 2016 2:14 am

Seems the Twitterers and a few others got their collective knickers in a twist over the latest rant. Result!
When will they ever learn that I only do it to wind them up? Let's hope they get so annoyed they twatter it all over creation so we do trending and stuff...
I mean - who the hell would ever want to eat badger stew? :lol: :lol: :lol:
I'm only a plumber from Cannock...

"As to reward, my profession is its own reward;" Sherlock Holmes

Voltaire's apology when he wrote a long letter: "I didn't have time to make it shorter."

no1traumanurse
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Re: BBP Diary

Post by no1traumanurse » Tue Dec 06, 2016 9:26 am

It's too chewy and gives me a nasty cough.
Interesting, just found a website with a badger stew recipe. Apparently after skinning and gutting it needs placing in a fast flowing river for 48 hours to de-grease it. Who knew?
Wonder how many badgers it took to find out 48 hours was the key.
Last edited by no1traumanurse on Tue Dec 06, 2016 10:27 am, edited 1 time in total.

Blackplate
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Re: BBP Diary

Post by Blackplate » Tue Dec 06, 2016 9:41 am

In the diary it tells us this, '.

The AFRC spills servo pressure causing the piston pump to de-stroke until the engine catches up at which point it restores the servo pressure and off you go. But we’d never managed to get ours set up so it wouldn’t over-temp the engine on slam-accelerations'.

Now I don't know about jet engines (but I'm reading the diaries closely) ...but with the over-temp does that mean it's running too lean on this set up and you'd need to 'up' the kero (stroking the piston up slightly?) because you can't or don't want to slow down the turbine pick-up?

Thanks in advance. Bp.

Mentallica
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Re: BBP Diary

Post by Mentallica » Tue Dec 06, 2016 11:57 am

Thanks for the update.

Keep up the good work!

the engine information is fascinating, top job

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Renegadenemo
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Re: BBP Diary

Post by Renegadenemo » Wed Dec 07, 2016 2:26 am

The AFRC spills servo pressure causing the piston pump to de-stroke until the engine catches up at which point it restores the servo pressure and off you go. But we’d never managed to get ours set up so it wouldn’t over-temp the engine on slam-accelerations'.

Now I don't know about jet engines (but I'm reading the diaries closely) ...but with the over-temp does that mean it's running too lean on this set up and you'd need to 'up' the kero (stroking the piston up slightly?) because you can't or don't want to slow down the turbine pick-up?
Good question, and if it was your average petrol piston engine you'd be spot on but gas turbines use about 70% of their inducted air for cooling (this is how come afterburners can work - because most of the air exiting the engine still contains unburnt oxygen so chucking in extra fuel and lighting another fire will produce extra thrust without frying the turbine.)
With the limited spilling of the AFRC such as we lft it in the summer there was just too much fuel for the airflow in the summer conditions so it all got too hot. In lean-running petrol engines you get erratic flame-paths, compression-ignition and incomplete combustion leading to too much heat but in our case all we have is too much burning fuel and not enough airflow to carry the heat away.
The trick is to introduce enough fuel to accelerate the engine whilst creating sufficient draught to blow the unwanted heat out of the other end until it reaches that glorious self-sustaining 3650rpm
I'm only a plumber from Cannock...

"As to reward, my profession is its own reward;" Sherlock Holmes

Voltaire's apology when he wrote a long letter: "I didn't have time to make it shorter."

Blackplate
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Re: BBP Diary

Post by Blackplate » Wed Dec 07, 2016 9:44 am

Thanks for that reply, ok I think get that, (I get why afterburners work too now, I should have realised there'd be unburned oxy to do that, bonus!) you'll drop the fuel a 'gnats' then? Yep, that was counter intuitive to my automotive upbringing. Also, this you say is for your summer conditions, I'm presuming ambient air temp too high (not so much ambient pressure) to get enough cooling. May the settings be ok in these colder days and so get better results in the winter because you can burn more fuel without raising the temp too high? I can see that on start up 20deg is a big drop in temp from summer to winter...Just to clarify,this is just for start up isn't it?.. Cheers, and sorry for being a pain with all the questions but I find this fascinating. Bp.

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Renegadenemo
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Re: BBP Diary

Post by Renegadenemo » Wed Dec 07, 2016 11:47 am

Basically, the AFRC was spilling in the summer but not hard enough to perform slam-accelerations in the prevailing conditions - you take the engine to 40%, let it stabilise then slam it wide open and what you see on the instruments is an almost instantaneous drop in servo pressure but it comes after you put the extra fuel in and in response to it so you already have extra fuel in the engine. The fall in servo pressure de-strokes the piston pump so it doesn't throw any more in after it and the engine accelerates on what it already has. Once its pressures are back within limits the AFRC stops spilling and the pump strokes up again but by now the engine is spinning fast enough to cope with the extra fuel. There is a rise in JPT associated with all of this.
What we had in the summer with higher ambient temperatures was the AFRC not spilling enough to keep the JPT within limits as all this went on. But when we ran in the winter we had much more in hand so it allowed us to perform some nice clean slam-accelerations. The AFRC doesn't do anything on startup, that's done by the pump and the CCU. (Combined Control Unit)

The early systems were fitted with simple screw adjusters with a locknut and they are ridiculously sensitive. We have one on our 1959 BPC (Barometric Pressure Control). In fact the only way we found to set it up properly was to instrument the pressure we wanted to alter then watch the gauge whilst applying minuscule adjustments, then try to nip up the locknut without anything moving. Now because some of these adjusters are supposed to be tweaked by mechanics in the field, and because you can be a quarter turn off and your engine won't go, the later systems were fitted with a clicker adjuster and that's the opposite extreme. Six million turns later you may see something happening and this is what's fitted to our AFRC so we never quite got it set up. We will, though.
I'm only a plumber from Cannock...

"As to reward, my profession is its own reward;" Sherlock Holmes

Voltaire's apology when he wrote a long letter: "I didn't have time to make it shorter."

Blackplate
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Re: BBP Diary

Post by Blackplate » Wed Dec 07, 2016 2:58 pm

Six million turns later you may see something happening and this is what's fitted to our AFRC so we never quite got it set up. We will, though.

No doubt about that, I'm sure.

I'll digest what you've written, with many thanks. I'll try not to tie up any more of your time. Bp

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Renegadenemo
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Re: BBP Diary

Post by Renegadenemo » Wed Dec 07, 2016 3:57 pm

I'll digest what you've written, with many thanks. I'll try not to tie up any more of your time. Bp
No problem at all - always happy to natter on about gas turbines.
I'm only a plumber from Cannock...

"As to reward, my profession is its own reward;" Sherlock Holmes

Voltaire's apology when he wrote a long letter: "I didn't have time to make it shorter."

alslad
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Re: BBP Diary

Post by alslad » Fri Dec 09, 2016 8:09 am

Anyone else unable to see the latest diary entry?

The link in the subscriber email goes straight to the homepage/pic of the day and when I click on the diary page, the last entry is the one from February
Treat life's problems like your dog would... if you can't eat it or sh*g it, just pee on it and walk away

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