Orpheus Conversion/Lip Thickening

f1steveuk
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Orpheus Conversion/Lip Thickening

Post by f1steveuk »

There has been some discussion regarding the need to thicken the intake lip for the Orpheus conversion for 66/67, and a thought has occured to me (a rare event in itself). The yellow intake transit plugs, would they have fitted after the lips were thickened? Just trying to date exactly, when the work was done!!

There appears to be several pictures of the plugs in place, before the intakes were removed, after their collapse, and if there are any of them after re-installation, it might show if they had been reduced in size to fit. Like I said, just a thought!!
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Renegadenemo
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Re: Orpheus Conversion/Lip Thickening

Post by Renegadenemo »

There's a chance the plugs would fit just the same. They'd need a bit of jiggling but they'd likely go if they were pushed beyond the lip.
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f1steveuk
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Re: Orpheus Conversion/Lip Thickening

Post by f1steveuk »

Ok. Where are the original plugs today!!??
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Renegadenemo
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Re: Orpheus Conversion/Lip Thickening

Post by Renegadenemo »

No idea. But I remember Robbie Robinson telling me about, I think it was Clive Glynn, sitting on the silpway on the 5th messing with the plugs and saying how they'd not be needing them again. Maybe Robbie knows where they went.
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Renegadenemo
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Re: Orpheus Conversion/Lip Thickening

Post by Renegadenemo »

That sounds about the same. Best ask Robbie. He's a chance to have them stashed away somewhere.
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klingon
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Re: Orpheus Conversion/Lip Thickening

Post by klingon »

Mike Bull wrote:That's poor Robbie fending off anoraks left, right and centre then!
Save him that!-I got a bunch of plugs down in the hangar-send me sizes and profiles and I'll see what's lying around-never know-sides they're all probably as old as the engine so don't contribute to the "new metal" score! :mrgreen:
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Russ
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Re: Orpheus Conversion/Lip Thickening

Post by Russ »

f1steveuk wrote:There has been some discussion regarding the need to thicken the intake lip for the Orpheus conversion for 66/67
Apologies if I've missed the discussion elsewhere on the forum, but what was the conclusion about the need for the lip thickening?

Without knowing anything other than quote above, then what was the reason for mod? Was it to improve the airflow into the Orpheus; postings elsewhere on the forum from Keith (Pic of the Day, 29/04/09) note that the inlet cross-sectional area is the same as the face of the compressor, so was the lip thickened to create this configuration, or was there another reason?

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Re: Orpheus Conversion/Lip Thickening

Post by KW Mitchell »

Russ - jet engine intakes with very sharp lips perform very poorly at low speeds. The reason for this is that air which is entering around the lip itself - particularly around the sides of the cowling and indeed behind the front of the orifice - suffers turbulence as it cannot flow smoothly around the lip itself.

Have a close look at the intakes to a modern airliner- they are beautifully rounded to promote smooth flow around the lip. That is why Bristol Siddeley's engineers recommended the mod's to Bb.

At very high speeds approaching Mach 1 and above, the situation changes and sharp lips are advantageous - together with some very complex ducting devices modifying the inlet passages and their area e.g. Concorde. Indeed, the latter was said to be one of the most complex and costly problems to get right on the entire Concorde development -------.
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Renegadenemo
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Re: Orpheus Conversion/Lip Thickening

Post by Renegadenemo »

There were good aerodynamic reasons for thickening the lip but its primary function, I suspect, was to keep the inner skin from tearing away from the formers when it was discovered just how hard the Orph' could suck.
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Re: Orpheus Conversion/Lip Thickening

Post by Russ »

All, thanks for the replies - interesting point about the sucking power of the Orpheus, there's a posting elsewhere about rivets being sucked in following the Orpheus being fitted, I should have remembered that.

Keith, yes I'd spotted the difference between air-intake profiles, and now you've mentioned it, supersonic aircraft show the narrow intake lips - Concorde as you point out, Tornado, Typhoon, F-15, Mig-25 and all the rest.

Interestingly, I did once see a film of a Harrier with an annular ring of ducts just behind the intake snapping open and shut very rapidly to cope with the pressure changes, presumably the aircraft was changing speed by a large amount during the filming. Although the Harrier was not supposed to be supersonic, it was capable of Mach 0.9+, so the air intakes had to cope with full range of controlled flight speeds from 0 to max, unlike everything else, which copes from take-off speed to max. The Harrier intake lip is more like that of commercial sub-sonic aircraft, though the ducts I mentioned above seem unique to it. Any further info on these is welcome.

I was also even more impressed by the whole Concorde programme when I learned that the air entering the engine has to be sub-sonic, no matter what speed the aircraft is flying. To make that happen the air intakes then have to, I guess, create and maintain an area of compression where the air is slowed down before getting to the compressor. Without knowing the ins and outs of these things, I assume that once you have a steady state then it's not too difficult to manage, but the trans-sonic stages might be an interesting design exercise.

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