Helicopter Museum, Weston-super-Mare (not for 56k)

VEGAS · Post by **VEGAS** » 10 Feb 2007, 10:11

kit wrote:My wife and I went to the Museum the day that Hind D was delivered. She asked 'What are those black rod things sticking out from under the cockpit for?' :roll:

Ah, you must mean this, I had to take a picture!...

Callum · Post by **Callum** » 10 Feb 2007, 11:31

The smell inside the Cockpit on those things is quite addictive. I can only aliken it to shipping oil

Pringle · Post by **Pringle** » 10 Feb 2007, 11:46

Great shots, love the look of the Hind. The one at the midland air museum is in really strange colours compared to what i'm used to seeing the hind in.

Link for the Midland Air Museum Hind

TobyV · Post by **TobyV** » 10 Feb 2007, 12:09

kit wrote:They have a Rotodayne rotor blade there too. The last time I was there, maybe 2 years ago, it was lying on the floor between the fuselage section and the wall. The tip jet is surprisingly small for something that made such a DIABOLICAL noise!

The fact that they are small is precisely why they were loud. Basically for a given mass flow, you have a trade off between the area of the exhaust nozzle and velocity. The smaller the hole the higher velocity. Since thrust is mass flow multiplied by velocity, thats why they went for a small hole (that and the size constraints of the blade). As you can imagine, the faster flowing gases make more noise! I believe I am right in saying the Mach numbers involved were transonic so there would be a few shocks in there for good measure. All in all, not good news for your ear drums!

Post by **Garry Russell** » 10 Feb 2007, 12:19

Hi Toby

Is that why in the early days biz jets were so loud

It always seemed the smaller jets made more noise or at least far more noise that they seemed they should have done.

Early Lear Jets, JetStars and HS.125 certainly made themselves known

Garry

TobyV · Post by **TobyV** » 10 Feb 2007, 12:41

Thats precisely it Garry. Its more efficient to achieve your thrust by moving lots of air more slowly than a small amount very quickly. The noise comes from many different sources, but in general if you consider the worst offender to be the exit nozzle, the noise is sort of proportional to the exit velocity.

The only thing we suffer from these days is that at the tips of the front fan, which has the largest diameter of any stage, you havea tangential tip velocity on or about the speed of sound, especially on t/o. Thats the "buzz saw" sound you get as an aircraft with high bypass ratio fans goes past you - lots of little shock waves produced by the tips of the fans.

Post by **Garry Russell** » 10 Feb 2007, 13:00

Cheers Toby

The buzz off the fan you mention is similar to the prop "Rasp" on most notably the Harvard.

The Herald used to "Chop" in certain conditions, one of the things that made the Herald sound different to other Dart powered types.

All due to over or near supersonic

Garry