Fairey Rotodyne

[kitnut617]

Another 3-view of the Type Z, from Fairey Aircraft since 1915, H A Taylor, Putnam 1974 (1984 NIP reprint).

Taylor has the following to say about the Z and noise levels:
"With the power planned for the production Rotodyne the noise level for the existing
tip-jets would have been about 113 db. To achieve the necessary 17-db reduction in
noise level a complete redesign fo the pressure jet was planned. This would have been
in two-dimensional form, occupying the last 48 inches of each blade, with nine circular
flame-tubes in a combustion chamber submerged within the blade profile."

Jon

There's also a photo of a model of the 'Type Z' in BEA colours on page 411 in my copy Jon (1974 issue), apparently this model was made for a sales pitch to NYA and was originally painted in that airline's colours

Robert

[Mossie]

I remember how loud the Darts were on the F.27 Friendship. I used to hang around the civil airport a lot and the Australian airlines used to operate them on short-haul routes.  They were, to me as a child extremely loud.  I wonder though, how they do in comparison to the Rotodyne?

The program target for noise to bring it within CAA regulations was about 96 decibels, (it depends on how far you are away).  It was at least 16db higher than this initially so this puts it around 112db.  According to Wikipedia, 100db is the level of a jackhammer 1m away & hearing damage due to short term exposure occurs at 115db (explains Kits experience).  So even at it's target level, it was damn noisy & could damage your hearing long term.

Another problem was not so much the noise, but the repetetive sound from the tip jets.  This won't have helped passenger comfort or crew fatigue.  You can get an idea of this from the Fairey promotional video available on YouTube:
http://www.youtube.com/watch?v=y9633v6U0wo

[PR19_Kit]

Compared to the twin Darts on an F27 the 'dyne was in a different league.

While the Eland main engines whine was quite similar to the Dart's the major noise came from the tip jets themselves. They started the rotor turning just on the 'cold air' and you could hear an extra whistle above the main engines as each blade came past you, but when they lit off the jets the noise level rose alarmingly, with a massive roar to start with.

Then the roar increased as the rotor speeded up, and there was a distinct 'whumph' every time a blade came past. At 140 rpm, the designed take-off rotor rotation speed, the 'whumphs' were running at about 10 hz, quite quickly really.

[Mossie]

That's what comes across in the promotional film.  You can't hear any engine noise, it's almost all drowned out by the 'wumph'.  It's difficult to get an idea of real noise levels on a recording, so I turned up the volume pretty high to try & get an appreciation for the noise.  It's pretty off putting, especially with the continued 'wumph'.

[rickshaw]

My understanding is that the tip jets were only lit just as the aircraft began its descent into landing and during the take-off.  These are relatively short periods of time (if the pilot's doing what he should) whereas the other turboprop aircraft that have been mentioned - the F.27 and the V-22 have their motors running continuously.   Another turboprop I'm familiar with is the Hercules.  Now, that was noisy!

[Mossie]

Yes, the tip jets were only at full power in the hover, being idle in normal flight.  It was still excessively noisy before the noise reduction measures were introduced, enough to damage your hearing at close quarters (as Kit can attest to).  Ground crew would have been especially at risk & those living near airports would be less than happy.  The Rotodyne was expected to operate from heliports & city airports, so it would have been hovering in built up areas.

It'll still have been very loud once the reduction measures were in place, similar to standing next to a jackhammer, although many contemporary aircraft would have been as noisy.  The regulations have got tighter over the years & this may be a concern for companies like Groen Brothers trying to resurrect the concept.

Hercs & other military aircraft are often not subject to the same regulations as civil aircraft.  If you've ever heard a Herc or especially Tornado in thrust reverse at an airshow you feel it as well as hear it!  And a Harrier in hover usually has the obligatory crying kids & car alarms blaring!  The main market for the Rotodyne would have been civil aviation, had it been purely military the noise problem would have been less of a concern, if not for the poor old Erks working a few yards away!

[jcf]

Simon's comments about the repetitive noise and Kit's observation that it was about 10hz points out the problem,
it is not just a matter of volume but frequency.

From all accounts the XF-84H Thunderscreech produced an unholy noise, but the bigger problem was the frequency of
the soundwaves produced by the propeller, evidently they were capable of producing instant nausea in bystanders.

I have personal experience with a milder version of a similar phenomenon with the soundwaves generated by a Bell 214B BigLifter (T55 engine, larger rotors) during some post electrical work testing. The machine was on the tarmac in front of our hangar, as part of the test the pilot (Tommy who owned the machine and pretty much lived out of it during the fire and logging season. He had a big Rottweiler that flew with him everywhere), had to take the rotor to about 80% power and hold it there. At that speed with the rotors in flat pitch the noise was loud but tolerable (we had attenuators and headsets) but the soundwaves were something else, your whole body felt like it was rippling and your guts like they were turning to jello. Very weird and extremely unpleasant. We actually thought the office windows were going to flex right out of their frames and the resonation within the hangar made the whole effect worse. Luckily we only had to endure for less than five minutes (it felt far longer I'll tell ya), everything checked OK so Tommy sped up and flew off. He of course felt none of the effects being at the relative center of the source.

Jon

[kitnut617]

My understanding is that the tip jets were only lit just as the aircraft began its descent into landing and during the take-off.  These are relatively short periods of time (if the pilot's doing what he should) whereas the other turboprop aircraft that have been mentioned - the F.27 and the V-22 have their motors running continuously.   Another turboprop I'm familiar with is the Hercules.  Now, that was noisy!

I think that the noise you hear from the turbo-props is actually just the prop tip noise, whereas on the Rotodyne this was amplified by the tip jets.  There's a lot of Dash-8's operating around Alberta, working out of regional airports and one of these is about 70 kms north west of my place and the flightpath to Calgary is about 50 kms due west, the throb from the props can be heard very well when they pass, even more so when the wind is blowing towards our house. C-130's come through occasionally and they are the same along with the ATR-72's which are getting more popular here.  I mentioned this to airplanedriver as he flew Dash-8's and he didn't believe me, but living at 3000ft above sea level and on the open prairies (there's nothing between our house and the flightpath other than a few farms), sound travels a long way. 

Then I was quite surprised with the US Army' choice for it's new observation helicopter, the Lakota, the Alberta Stars Air Ambulance service used a number of the medi-vac version of these and this is one of the noisiest helicopters around (rotor tip noise), you can hear these for quite a number of minutes before they actually become visible, same with the multitude of Hueys that operate around here.

[jcf]

Then I was quite surprised with the US Army' choice for it's new observation helicopter, the Lakota, the Alberta Stars Air Ambulance service used a number of the medi-vac version of these and this is one of the noisiest helicopters around (rotor tip noise), you can hear these for quite a number of minutes before they actually become visible, same with the multitude of Hueys that operate around here.

The UH-72A Lakota performs the LUH (Light Utility Helicopter) role than the LOH role,
the OH-58 is still the LOH aircraft. The UH-72A is currently only issued to domestic US
Army and National Guard units, supposedly it will not be deployed to overseas combat
zones.

The OH-58 was to be replaced by the ARH-70, that project was canceled in 2008,
EADS and L-Mart have proposed an armed version of the basic EC-145 as the
Armed Scout 645 for the still nascent Armed Scout Helicopter (ASH) program.
http://www.armedscout.com/index/index.asp

Boeing is proposing a stretched MD-500 with a six-blade main rotor as the
AH-6S, evidently the machine will be field convertible to a UAV mode.

Jon

[AeroplaneDriver]

My understanding is that the tip jets were only lit just as the aircraft began its descent into landing and during the take-off.  These are relatively short periods of time (if the pilot's doing what he should) whereas the other turboprop aircraft that have been mentioned - the F.27 and the V-22 have their motors running continuously.   Another turboprop I'm familiar with is the Hercules.  Now, that was noisy!

I think that the noise you hear from the turbo-props is actually just the prop tip noise, whereas on the Rotodyne this was amplified by the tip jets.  There's a lot of Dash-8's operating around Alberta, working out of regional airports and one of these is about 70 kms north west of my place and the flightpath to Calgary is about 50 kms due west, the throb from the props can be heard very well when they pass, even more so when the wind is blowing towards our house. C-130's come through occasionally and they are the same along with the ATR-72's which are getting more popular here.  I mentioned this to airplanedriver as he flew Dash-8's and he didn't believe me, but living at 3000ft above sea level and on the open prairies (there's nothing between our house and the flightpath other than a few farms), sound travels a long way. 

Then I was quite surprised with the US Army' choice for it's new observation helicopter, the Lakota, the Alberta Stars Air Ambulance service used a number of the medi-vac version of these and this is one of the noisiest helicopters around (rotor tip noise), you can hear these for quite a number of minutes before they actually become visible, same with the multitude of Hueys that operate around here.

I'd be very surprised if you can hear a Dash 8 in cruise flight from 50km...it's really a very quiet aircraft.  At takeoff the props are only turning 1200 rpm, and in cruise they are brought back to 900.  I work at CLT, a USAirways hub with a lot of DHC8 traffic, and even on takeoff they are barely audible once they get a few miles away and the props come back to 1050 for the climb.  Where I live is directly between two routes that the USAirways Express Dashes take about 10 times a day each (I know the routes well, I used to fly them in Dashes).  I'm less than 20 miles off each route and I never hear a Dash unless there's weather around and they are diverting overhead. 

[kitnut617]

I'd be very surprised if you can hear a Dash 8 in cruise flight from 50km...it's really a very quiet aircraft.  At takeoff the props are only turning 1200 rpm, and in cruise they are brought back to 900.  I work at CLT, a USAirways hub with a lot of DHC8 traffic, and even on takeoff they are barely audible once they get a few miles away and the props come back to 1050 for the climb.  Where I live is directly between two routes that the USAirways Express Dashes take about 10 times a day each (I know the routes well, I used to fly them in Dashes).  I'm less than 20 miles off each route and I never hear a Dash unless there's weather around and they are diverting overhead. 

Hi Nick,

I thought you might answer, if only I could record what I hear and post it here but I do hear them very well.  But to check that the flightpath is where I say it is, maybe you could check your flight maps (I don't know where to look for them) and tell me if it goes from Red Deer Alberta to Calgary Alberta and it passes right over a town called Olds.

Cheers,
Robert

[AeroplaneDriver]

Robert,

I dont have any Canandian charts, but I'll see if I can access some at work this week so we can figure out what you're hearing.  Are you sure it isnt just the voices telling you to go build a whiffed Dash 8 gunship???   

[Mossie]

Stretching my memory back to Physics 101 at college, but IIRC there is a physical effect that explains why Robert is hearing the Dash 8's from 50km away.  Sounds can often be heard over long distances with certain wave lengths, as long as there is nothing in between.  I think it can only be heard at cetain spots, ie the Dash 8's won't be heard all the way along those 50km's.  Sorry for the vagueness, but it's a long time since I did that module!

[PR19_Kit]

Dragging this kicking and screaming back on thread  I should think you could hear a Rotodyne 500 km away!

[Mossie]

Okay!  How about operators?  I dug into this a little bit with the profiles I did.  The first customers would have been BEA, JAL, Okanagan Helicopters & New York Airways, with the RAF being the first military customer.  For civil customers, it would have been a direct competitor to types such as the Fokker Friendship & the Avro 748.  For military customers, it would have been up against the Chinook, CH-53, as well as types like the Andover & Troopship.  Kaman might well have made inroads in the US too with the licence built version.