Pic of the Day

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Engine 711
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Re: Pic of the Day

Post by Engine 711 »

Good to an engine back in place... :)

Surely, Scotland is the place to try the on-board Start System...? By all means have the proven off-board system there as well, but give the on-board system a go as well...? :?
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Renegadenemo
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Re: Pic of the Day

Post by Renegadenemo »

Surely, Scotland is the place to try the on-board Start System...? By all means have the proven off-board system there as well, but give the on-board system a go as well...? :?
If you want to decant gas at 200bar into it you're very welcome. Personally I'll hang on until it's had a thorough strip, rebuild and hydrostatic test on the bottles. Also, the LP starter is more hungry than the HP one it was designed for. We'll get it working, just not this time.
I'm only a plumber from Cannock...

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Engine 711
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Re: Pic of the Day

Post by Engine 711 »

Renegadenemo wrote: Thu Jun 21, 2018 10:57 am
Surely, Scotland is the place to try the on-board Start System...? By all means have the proven off-board system there as well, but give the on-board system a go as well...? :?
If you want to decant gas at 200bar into it you're very welcome. Personally I'll hang on until it's had a thorough strip, rebuild and hydrostatic test on the bottles. Also, the LP starter is more hungry than the HP one it was designed for. We'll get it working, just not this time.
I thought I had read (on here) that the on-board spheres had been hydrostatic tested, some time ago - albeit to a reduced pressure...? Wrong again, obviously. But still happy to decant to whatever the current working pressure is.... :)

Am pretty sure K7 must have a pressure regulator for the air start system, to drop the pressure from 3000psi to say 250psi (for the HP starter). There could be potential to adjust and/or mod this reg (perhaps re-spring it..?), so as to deliver less pressure, to suit the LP starter.
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Renegadenemo
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Re: Pic of the Day

Post by Renegadenemo »

The bottles were tested to their old working pressure, 3200psi, then given a new working pressure of 2000psi, which isn't enough for a good start with our current setup. The LP starter needs a large volume of LP gas but we have to get that volume down the narrow plumbing of the original HP delivery system and so the problems multiply, hence exploring the gas delivery methods embodied in the old HP starter by nicking one from a museum engine then adapting one of the LP starters to take advantage of what we learned. We'll get it going with a methodical approach but HP gas is lethal.

What's a truck tyre inflated to? 100psi, maybe? Anyone want to be near a pair of quarter-inch wall thickness spheres with 2000psi inside if one chooses to let go?

I'm only a plumber from Cannock...

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'Sometimes you gotta be an S.O.B if you wanna make a dream reality' Mark Knopfler
Vernon
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Air start

Post by Vernon »

Hi
Regarding yesterday's pic of the day ( air start ) it was mentioned this will be carried out externally at Scotland. What is the reason behind this ?
Many thanks
Vernon

Post moved to where the answers are- see above! -Mike
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Engine 711
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Re: Pic of the Day

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Renegadenemo wrote: Fri Jun 22, 2018 12:58 am The bottles were tested to their old working pressure, 3200psi, then given a new working pressure of 2000psi, which isn't enough for a good start with our current setup. The LP starter needs a large volume of LP gas but we have to get that volume down the narrow plumbing of the original HP delivery system and so the problems multiply, hence exploring the gas delivery methods embodied in the old HP starter by nicking one from a museum engine then adapting one of the LP starters to take advantage of what we learned. We'll get it going with a methodical approach but HP gas is lethal.
Ok, thats what I recall, re WP.

Reading up on the K7 air start system (in Neil Sheppard's book), the system was adapted by Rotax, using parts from their Gnat system - '... comprising two spherical air bottles containing 39lbs of dehumidified air, compressed to over 3000psi.' I reckon thats 39lb per sphere - as the volume of 39lbs of air at 3200psi should be about a 500mm diameter sphere - which the Mk1 eyeball suggests is about right... ;)

Yes, blowing them to only 2000psi doesnt exactly help. But if the original set up gave 6 starts - which it did (tested at Norris Bros, before going North), then 2000psi potentially could give 4 goes. But only if the air consumption (so mass flow) of the LP starter can be got to be similar to the HP one. Do you know if the LP & HP Orpheus Starters look similar - could the guts be common...? Or are they totally different sizes....? The pressure drop is dramatically different (250 psi versus 40psi) - and its the drop in pressure across the turbine which creates the energy.

Found a bit of info, online. The HP Orph starter ran at 250 to 320psi, using 0.8 to 1.0 lb/sec of air - and could get the engine lit in 4 seconds using 6 lb of air...! (yes, that doesnt add up). THe LP starter is mentioned, but no detail is given.

https://www.flightglobal.com/FlightPDFA ... 200449.PDF

I agree HP air is scary, but check the speed Air Starter Turbines run at - 100,000rpm or more. (I mean the actual Turbine rotor - not the output which is geared down a lot - typically by around 20:1, to spin the compressor up to say 5000rpm.)
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Engine 711
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Re: Pic of the Day

Post by Engine 711 »

Mike Bull wrote: Fri Jun 22, 2018 3:04 pm
The air start installation on Bluebird came from the uncompleted second Hunting H.126 aircraft, not the Gnat.
https://en.wikipedia.org/wiki/Hunting_H.126

I see that had an Orpheus 805.
conistoncollie
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Re: Pic of the Day

Post by conistoncollie »

Do you have to have the air start system (bottles/pipes/hoses/relief valves etc) independently inspected/tested under hydraulic and air pressure, as with steam boilers/pressure vessels. Will it require a valid test certificate and insurance to be operated in a public place?
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Richie
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Re: Pic of the Day

Post by Richie »

What a very strange question ?
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Re: Pic of the Day

Post by Renegadenemo »

The bottles have to be tested and they are - they were brand new in 2016, as were all the delivery hoses, fittings, gauges, etc.

The onboard air system I reckon is, and always was, good for no more than three starts. You can't use the last 700psi anyway because it simply will not accelerate the engine to start speeds. The bottles were previously rated to a working pressure of 3200psi with their life limited to 400-odd cycles, but we have no way of knowing how many cycles had been completed by the time we came along. A cycle was deemed to be any event that dropped the bottles below 2000psi from full. So, having carried out all kinds of hot-work on them, we tested to 3200psi and imposed a new WP of 2000psi
Unfortunately this just isn't enough for a clean start with the LP starter. Interestingly, we saw similar gas consumption figures in terms of pressure drop in the storage cylinders to those seen in 66 at Haywards Heath but we were using 100litres of storage and they had 32 - 16 per sphere - so the HP starter seemed notably more gas-efficient. That said, the log from Norris Bro's also shows that they kept stopping to charge the bottles so they weren't going to ever get six starts from them either. They also sailed close to the wind with the JPT and had to shut down on one occasion because the temps went out of limits.
So next we snaffled a HP starter from a museum engine but no way was it going onto the 101 Orph' - the gearbox is totally different on the front of the engine, so instead we set about discovering the difference, which turned out to be a plate ahead of the start turbine with a series of converging nozzles such that compressed air impinges directly onto the turbine blades. It's far less wasteful so with just such a plate made up and tested we saw our gas consumption halved to achieve start speed (1000rpm approx) Now we were getting somewhere but much development work is still needed.
We need more NDT on the bottles and another test as they've been used a bit since. If all is well we may test to a higher pressure and give ourselves a higher WP but only if this is agreed by those who know in the world of pressure vessels and materials. We also need to get some hard data on what the hybrid LP/HP starter is doing with its air to see what we realistically have to do to make the system work. Even if we could safely life it for maybe 30 starts that would see us through a proper proving trial. But for Bute we are simply going to plug in our offboard supply and hit the go-button.
I'm only a plumber from Cannock...

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

'Sometimes you gotta be an S.O.B if you wanna make a dream reality' Mark Knopfler
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