It's those Bear necessities...

[Chris Trott]

Sorry, it wasn't meant as a dig, I was just picking up on a piece I saw about unducted fan engines and an Airbus proposal for a short haul airliner with the fans out the back.

http://www.ainonline.com/aviation-news/ ... rd-avenues

Yeah... it was tried before. It failed for 2 reasons - 1) It was louder, 2) the public didn't like the sight of that many fan blades whirring around.

http://en.wikipedia.org/wiki/General_Electric_GE36

Now, the propfan might have a chance because at least it looks like a prop (and it won't be placed on the aft fuselage like it was with the MD80 UDF test aircraft), but I still think there's going to be a problem convincing too many companies to buy the UDF or Propfan concept anytime soon. Turboprops are significantly more efficient and you can get jet speeds out of them (like on the Q400), but the flying public still has a problem with them and until that is overcome, it's gonna be one hard sell on anything bigger than a small regional aircraft that seats less than 75.

[Garry Russell]

Boeing also flew and unducted fan on a 727

Truth is the props are a lot more economical but people want jets. This leaves the airlines trying to satisfy the econimics and the pax demand.

On the Southampton to Guernsey route, according to a pilot freind of mine who few both the 146 and Dash Eight for Flybe, the Dash burnt about the same fuel on the trip as the 146 did on the climb out.

[Dev One]

Not sure about open props being more efficient than ducted ones....I hear C130's going overhead & they are noisy when at altitude & I believe the Bears props are worse than a Shacks, so there must be losses in making that level of noise. Tip speed is also a limiting factor although the latest Dowty designs seem to have overcome some of that problem. Not only that, think of the fatigue to the airframe from that noise!
I'm being Devils advocate again!
Keith

[Chris Trott]

The GE36 was engine that flew on the 727. It was flown initially on a 727 then on the MD-80 that later flew the Pratt & Whitney/Allison UHB engine.

Also, consider this, the Convair 580, as big as it is (and with as big as those engines "are") only requires ~7000 pounds of fuel for a 3 hour flight. The only reason the Convair 580 was replaced was speed. Nothing more, nothing less. You can fly a Convair 580 for 1/3 the price of a CRJ-200 even today and you're still carrying 52 passengers, but you're doing it a 1/2 the speed. Funny thing is that Lockheed recently said they want to get back into the civilian airliner business. I suggest that they start by pulling the Convair 580 plans out of the archives, putting a new tail on it to fix the MMO issue, put a pair of AE2100's on the wings, and see what they get. I'll bet it'd be faster and more economical than the Q400 at 75% the cost.

[Chris Trott]

Not sure about open props being more efficient than ducted ones....I hear C130's going overhead & they are noisy when at altitude & I believe the Bears props are worse than a Shacks, so there must be losses in making that level of noise. Tip speed is also a limiting factor although the latest Dowty designs seem to have overcome some of that problem. Not only that, think of the fatigue to the airframe from that noise!
I'm being Devils advocate again!
Keith

Modern turbofans are quieter simply because the bypass fan is its own silencer, shielding the very loud hot gas stream from the outside world and making it appear quieter. If you remove that stream, they'd be as loud or louder than turbojets. However, there is a phenomenon that turbofans have to deal with - interference drag and flow disruption. Because each blade is its own wing, it leaves an area of turbulence behind it. As such, the most efficient propellers have 1 blade. However, due to issues with ground clearance, you can't have just 1 propeller on most planes because they'd have to be massive to also absorb the engine power and provide enough thrust to fly the airplane.

For example, the 501D on the Convair 580 is flat-rated to 4100 SHP and drives a 13.5 foot (4.1 meter) diameter prop turning at 1040 RPM (although the turbine is running at 13,500 RPM). This produces ~24,000lbs static thrust, at a fuel consumption rate of 1200 lbs/hr. The CFM-56 consumes ~4000 lbs/hr for the same power output.

[airboatr]

Sorry, it wasn't meant as a dig, I was just picking up on a piece I saw about unducted fan engines and an Airbus proposal for a short haul airliner with the fans out the back.

http://www.ainonline.com/aviation-news/ ... rd-avenues

It is variously suggested that the unducted fan or open rotor concept would save about 25% on fuel and only be about 10% slower than the pure jet variant - which probably explains why Bombardier are still churning out Q400s!

The short haul airlines are constantly swithering between pure jets and props as they react to the opposing pressures of passenger perception that jets are more "modern" and the fuel economics. When Mcdonnell tried the idea out in the 90s noise was held to be a drawback. That probably explains why the Airbus fans are hanging out the back.

Nowt wrong with the Lancaster, it has been suggested that the BBMF one is the only dedicated long-range strategic bomber that the RAF have these days.



Ironic that the Russians still have rear-gunners given Putin's views on gays.......

I'll get my coat.

Hello Allan,

Naw mate I didn't take it as a dig.


Re: tail guns
Funny ... you'd think Putin would know the gun is sticking up in there the wrong way to be seen as a " " thing..

That machine gun?! ...It is a outie , not an innie!



.... just sayn'

Cheers

[Herkpilot]

Having spent many hours being hauled around by the magnificent T56/501s, I would suggest that most folks miss the most important issue with the turboprop. You can look out the window and tell if everything's still running! Really reassuring to the pilot. Do that with your typical bug-sucker!

[Dev One]

Surely not if the gearbox has gone & the prop is windmilling!
Keith

[Chris Trott]

No, it's still a good way to tell the passengers the engines are "working".

Back in 2001 Air Wisconsin had a Do-328 shutdown an engine inflight at the top of climb. The crew (smartly) left the prop just slightly unfeathered so it would windmill. We had a whole crowd of managers, senior gate and ramp agents, and even Airport Reps on hand when the plane taxiied into the gate because the crew had declared the emergency but made the decision to proceed from Rapid City to Denver due to the short flight and the fact the 328 cruises just fine on one engine.

Every passenger got off and not a one was aware of the problem. The bearings on the engine were working so well that the prop didn't finish spinning down until they were less than 100 yards from the gate, so the passengers thought the crew had done it as part of a normal procedure arriving into the crowded Denver gate area.

[Dev One]

Jolly good show then! You can fool some of the people.......
Keith