Hedgehog Exhaust

Greg87 · **Posted:** Wed Mar 26, 2008 8:44 am

Hi all. Just wondering if anyone knew about the "Hedgehog" exhaust used on aircraft such as the Beaufighter, Halifax and CAC Boomerang. I haven't been able to find any reliable information through online searches, and just thought someone here might know.

JDK · **Posted:** Wed Mar 26, 2008 8:49 am

What do you want to know?

They were made of specially trained fire-breathing hedgehogs who could grasp a red-hot exhaust with their little pink feet, breathe in the fumes and excrete the efflux to achieve a significant increase in the mach number.

Or not.

The short, serious answer to the presumed 'why' or 'what for' was they were flame damping exhausts.

Greg87 · **Posted:** Wed Mar 26, 2008 10:32 am

Haha, sorry about that, guess it would have helped if I worked a question into there! Yes I wanted to know what they are for. Is there an easy description of how they work? We stumped our aircraft engines teacher by asking him about them, he'd never seen or heard of them before.

Tillerman · **Posted:** Wed Mar 26, 2008 10:58 am

As seen on a Beaufighter:

I didn't know about the hedgehog name. Learned something again!

Tillerman.

Swiss Mustangs · **Posted:** Wed Mar 26, 2008 11:03 am

Martin

Kdmoo · **Posted:** Wed Mar 26, 2008 11:51 am

From a Boomerang:

JDK · **Posted:** Thu Mar 27, 2008 1:46 am

Greg87 wrote:

Haha, sorry about that, guess it would have helped if I worked a question into there! Yes I wanted to know what they are for. Is there an easy description of how they work? We stumped our aircraft engines teacher by asking him about them, he'd never seen or heard of them before.

Good one, bet he loves you.

I don't think there's anything 'clever' it's just a selection of slots sticking out, rather than a single port. Bear in mind that most of the examples above were a single exhaust that ran off a collector ring, which (I presume) suppressed most of the visible flame at night. I'll ask next time I'm talking to a Boomer expert. The Beau and the Hali were Bristol powered, with the collector ring at the leading edge of the cowling; common British practice, unusual, I think, in the US. Bristol engine data will give you more.

Cheers,

ausflyboy · **Posted:** Thu Mar 27, 2008 2:42 am

from Australian National Archives file

DTS [Directorate Technical Services] - Boomerang aircraft - cowlings and [engine-airframe] fittings
Series number A705
Control symbol 9/49/32

airnutz · **Posted:** Thu Mar 27, 2008 2:45 am

JDK wrote:

Greg87 wrote:

I don't think there's anything 'clever' it's just a selection of slots sticking out, rather than a single port.

I wouldn't underestimate the engineers of the day, James. I think the design is
is quite clever! The exhaust exits from the ring, hitting the capped-off stack and possibly exit back forward thru the
porcupine vents...They would have to figure what the volume of exhaust to exit and account
for effects on engine performance...an interesting compromise for an engine tuner.

EDIT:
I'd be interested to see what the stack looks like internally coming out of the collector..is it a solid tube, or is it
"drilled" with holes like a silencer on a gun?

JDK · **Posted:** Thu Mar 27, 2008 3:18 am

Fair point Airnutz; I wasn't meaning to under-rate anyone's ideas; perhaps I should have said there's nothing 'fancy' inside the design. Like lots of effective solutions and ideas, it's quite simple! I should also have added I'm no expert on the topic.

Ausflyboy - thanks, most 'illuminating'.

airnutz · **Posted:** Thu Mar 27, 2008 3:35 am

JDK wrote:

Fair point Airnutz; I wasn't meaning to under-rate anyone's ideas

I tweren't implying you were Mr. Tweed..

...just suggesting an alternative, and asking a
"wrench-bender" question for the group on the same stroke..no worries here, Amigo! :wink:

I did think about it abit and edit my original reply...

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