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A400M - why the props ?

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A400M - why the props ?

Old 16th May 2020, 12:13
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In the early 80's when the" Future Large Aircraft" (FLA) was being considered , weren't Un Ducted Fans (UDF) also being developed in the USA and Soviet Union?. Might this approach have the attraction to European Industry of also assisting UDF development costs for an anticipated Civilian Market?
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Old 16th May 2020, 12:33
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Could be.
I guess an ATR with two of those (detuned) engines might be an interesting proposition...
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Old 16th May 2020, 14:36
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I always thought the RR Dart was a high-bypass unducted fan
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Old 16th May 2020, 15:01
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Slight aside, but talking of the engine blue note, there is a weird effect if you stand immediately below one on approach. A few seconds after the a/c passes overhead you get this odd sound effect, difficult to describe but like a threshing sound. No silly jokes please, and no, I wasn't imagining it.
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Old 16th May 2020, 15:33
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d_p, I think I've heard this described before and if I remember correctly it is something to do with the interaction of the prop-wash (opposite turning engines)?
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Old 16th May 2020, 15:52
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Originally Posted by Green Flash View Post
d_p, I think I've heard this described before and if I remember correctly it is something to do with the interaction of the prop-wash (opposite turning engines)?
Might indeed be the case.
How are does birds categorized when it comes to wake turbulence?
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Old 17th May 2020, 11:06
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Unductec fans have been put aside because they produce a huge amount of noise, not compatible with EU regulations.
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Old 17th May 2020, 12:54
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Originally Posted by atakacs View Post
Having some time for musing I was wondering about the advantages of the turboprop vs. using more conventional turbofans for the A400M.

Designing a completely new engine was obviously a very expensive proposition (and turned out to be even worse than that...) so what are the expected gains ?
It was the nation's who defined the specification.
And we must not loose sight of the fact that the TP400 is actually a very efficient power plant indeed.
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Old 17th May 2020, 14:31
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Originally Posted by dead_pan View Post
Slight aside, but talking of the engine blue note, there is a weird effect if you stand immediately below one on approach. A few seconds after the a/c passes overhead you get this odd sound effect, difficult to describe but like a threshing sound. No silly jokes please, and no, I wasn't imagining it.
Nothing new, as a youngster I used to go with my plane spotting older brother and stand by the approach lights to Ringway. Whenever a BEA Vanguard passed over you got a similar effect, a rushing sound several seconds after the aircraft had passed overhead. Another spotter who was in the ATC, and had been taught about such things, explained it was the 'vortexes off the wings and props'. At the age of seven I didn't have a clue what a vortex was but I knew I liked the noise they made.
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Old 17th May 2020, 14:44
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Originally Posted by tdracer View Post
That used to be the case, but not any more.
Yes, a prop will typically burn less fuel/mile, but it's nowhere near half.
Was a simple statement yes, but I am rated on AE2100 and AE3700 powerplants. Cores are very similar. One has a propeller off the LP shaft, the other a Fan. Taking the types, both carry similar pax loads and weights. Yes one can fly 50 knts faster if it wants to and a bit higher. The jet burns a considerable higher amount of fuel that the turboprop on the same 400/500 mile sector and the prop was not much slower. Costs do add up. My last company base had turboprops. Swapped for jets, fuel costs made the base unprofitable, base closed.

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Old 17th May 2020, 19:09
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Why Turbo-props? The Lockheed Hercules comes to mind. To date, more than 2,500 C-130s have been ordered and/or delivered to 63 nations around the world. Seventy countries operate C-130s, which have been produced in more than 70 different variants.

From the highest of air strips in the Himalayas to landing on aircraft carrier runways in the middle of the ocean, the C-130 exceeds expectations. The Hercules has an ability to tackle any mission, anywhere, at any time. It is even a hurricane hunter.

I've flown on Viscounts in my youth and my teens. Although I've never flown on a Vanguard, I admired its majestic appearance, large windscreen, big port holes, (same as the Viscount's), and a cruise speed of 360 knots. In the late 1980's, a flight on a combi L-188 Electra, (freight and passenger), re-ignited my appreciation of the efficiency turbo-props.

Last edited by evansb; 17th May 2020 at 21:50.
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Old 18th May 2020, 03:05
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Originally Posted by atakacs View Post
Could be.
I guess an ATR with two of those (detuned) engines might be an interesting proposition...
if they wanted more power they could just go with PW150s like Bombardier did for the Q400. Instead they seem happy enough pottering along with their PW127s.

Saab 2000s have AE2100s now that I think about it.
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Old 18th May 2020, 08:38
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Originally Posted by Buster15 View Post
It was the nation's who defined the specification.
And we must not loose sight of the fact that the TP400 is actually a very efficient power plant indeed.
When itís not shaking itself apart
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Old 18th May 2020, 21:32
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Originally Posted by MarkD View Post
if they wanted more power they could just go with PW150s like Bombardier did for the Q400. Instead they seem happy enough pottering along with their PW127s.

Saab 2000s have AE2100s now that I think about it.
The AE2100 was originally developed by Allison (before it was taken over by RR) - and has been looked at for other commercial applications as well.
Given that the AE2100 is already 'detuned' (derated) for it's commercial applications (compared to the C130J), the TP400 would be way too powerful to be useful for a commercial turboprop installation.
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Old 21st May 2020, 15:01
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A400M - why the props
The simple answer: It replaces aircraft that have props as well - since they were made for tactical missions.

Originally Posted by VinRouge View Post
you also get a lot of lift off the prop flow meaning smaller wing area which is useful in austere areas and (may be talking garbage here) the energised flow over the leading edge of the wing means you donít need leading edge slats, which significantly cuts down on complexity of the design.
Also compare the A400M's rather modest flap system to the massive blown flaps that an airlifter with turbofans like the C-17 needs for tactical purposes.

Google "AERODYNAMIC DESIGN OF THE A400M HIGH-LIFT SYSTEM" for a paper written by an Airbus engineer (I'm not yet allowed to post links).

Originally Posted by tdracer View Post
So, props have better low speed performance (e.g. takeoff), jets have better high speed performance.
Props also have better low-altitude performance and efficiency. One of the A400M's requirements was extended low-altitude flights. Props save fuel, which leaves more weight for the cargo.

Originally Posted by atakacs View Post
But in any case, is that capability worth 10bnÄ (low ball guestimate) in R&D and many years delay in the program ? Wasn't the only issue but clearly engineering those from scratch was a very risky proposition. I don't see the reward to be commensurate, so I guess there were other matters considered...
It was the turn of the millennium. How many utopian dreams were linked to that date? There was a high tech stock bubble, everything seemed possible. France was thinking in "Grands Projets", Airbus developed the A400M AND the A380 in parallel ...
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