JSF and A400M at risk?
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I half remember asking this before but can’t remember what the answer was: doesn’t DBE rotation reinforce the formation of tip vortices on the mainplanes? Doesn’t that have a drag penalty?
Thought experiment: Consider multi-engine aircraft with all propellers rotating the same way. Why don't those aircraft have significantly unequal wing tip vortices?
Thought experiment: Consider multi-engine aircraft with all propellers rotating the same way. Why don't those aircraft have significantly unequal wing tip vortices?
Donw Between
The directions of rotation of the propellers were the result of a considerable amount of Wind Tunnel testing. In the "standard" configuration (all the same way) there were 2 contradictory problems with aerodynamics and internal noise. These meant a radical approach was needed.
This arrangement means that neither outboard engine is more critical than the other in the enigine failure case - both are more like a Herc #4 than a #1. Each wing reflecting the other then produces a symmetrical flow across the wing and, as importantly, across the rear fuselage and VTP. There being no critical failure side means a smaller VTP = weight saving. As a bonus the paratroops will also get a smoother ride. With this arrangement the troops will be steered away from the aircraft on exit. Neither side will be thrown under the aircraft to wrap themselves around their mates from the other door.
From the noise perspective - the main noise sensed inside the aircraft comes off the blade tips. The outboard noise becomes almost irrelevant whilst the inboard noise continues to follow the direction of rotation and tries to "enter" the aircraft from underneath - there is thus a far greater noise absorption (attenuation) because of the cargo bay floor.
There you have it - DBE benefits for all.
This arrangement means that neither outboard engine is more critical than the other in the enigine failure case - both are more like a Herc #4 than a #1. Each wing reflecting the other then produces a symmetrical flow across the wing and, as importantly, across the rear fuselage and VTP. There being no critical failure side means a smaller VTP = weight saving. As a bonus the paratroops will also get a smoother ride. With this arrangement the troops will be steered away from the aircraft on exit. Neither side will be thrown under the aircraft to wrap themselves around their mates from the other door.
From the noise perspective - the main noise sensed inside the aircraft comes off the blade tips. The outboard noise becomes almost irrelevant whilst the inboard noise continues to follow the direction of rotation and tries to "enter" the aircraft from underneath - there is thus a far greater noise absorption (attenuation) because of the cargo bay floor.
There you have it - DBE benefits for all.
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For Trumpet Trousers's 531 ..;
Oh, by St. Effie Neck - got me eyes crossed lookin' at the Kalendar ...
Head hung in shame.
Will be crossing fingers & all on Monday 30/11.
Back to thread ...
Head hung in shame.
Will be crossing fingers & all on Monday 30/11.
Back to thread ...
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"Handed props"
ref Green Knight's 535
de Havilland's Hornet's props rotated in different directions too - did it have the same problem as the P-38? It was said that handing the props cut out swing on take-off, which was a more frequent problem (on, for example, the "Mossie") than engine failure (said the RR brochure).
de Havilland's Hornet's props rotated in different directions too - did it have the same problem as the P-38? It was said that handing the props cut out swing on take-off, which was a more frequent problem (on, for example, the "Mossie") than engine failure (said the RR brochure).
Last edited by Jig Peter; 26th Nov 2009 at 14:22. Reason: Add ref
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Modern Elmo. I went through that exercise but it didn’t really help. The yaw from any asymmetrical vortex drag would be masked by the yaw from the fin in the prop wash.
Xercules. Thanks.
Sorry, for the incipient Thread drift.
Xercules. Thanks.
Sorry, for the incipient Thread drift.
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Here's what I think: multiple propellers opposed or not opposed does have a significant effect on p-factor, but not on wingtip vortices. This includes wingtip vortices at high angles of attack.
Take at look at photo 1566-333142 here: Crop Duster Stock Photography Images From SuperStock
Take at look at photo 1566-333142 here: Crop Duster Stock Photography Images From SuperStock
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My understanding is that Airbus carefully studied the impact that the six bladed prop on the C130J had on its operations.
The concept of having to come up with those sort of fixes on the A400 were overcome by the different rotation of the props on each wing.
There was a concern of the lack of interchange between the inboard and out board engines and props, but it was considered with the reliability of current build engines this was unlikely to be a major problem.
Does or will the A400 have a clearance to do three engine ferry trip to closest engine.
Regards
Col
The concept of having to come up with those sort of fixes on the A400 were overcome by the different rotation of the props on each wing.
There was a concern of the lack of interchange between the inboard and out board engines and props, but it was considered with the reliability of current build engines this was unlikely to be a major problem.
Does or will the A400 have a clearance to do three engine ferry trip to closest engine.
Regards
Col
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XP-38:
Each engine had a General Electric B-1 turbosupercharger. To combat torque, the propellers rotated in opposite directions, a special version of the Allison engine being produced with a left-hand rotating propeller shaft. The engines had inwardly-rotating propellers.
YP-38 & production:
The propellers were outward-rotating rather than inward-rotating as on the XP-38. This improved the aircraft's stability as a gunnery platform.
Warren M. Bodie, in his book The Lockheed P-38 Lightning: The Definitive Story Of Lockheed's P-38 Fighter, states that, "Engine rotation was changed so that the propellers rotated outboard (at the top), thereby eliminating or at least reducing the downwash onto the wing centersection/fuselage juncture. There was, by then, no doubt that the disturbed airflow, trapped between the two booms, was having an adverse effect on the horizontal stabilizer.
The likelihood of an engine failure on take-off was considered less important than increasing the aircraft's capability as a fighter.
This P-38 experience is quite opposite to the case of the P-82 (twin Mustang). The XP-82 was to be powered by two Packard-built Rolls-Royce V-1650 Merlin engines. Initially, the left engine was a V-1650-23 with a gear reduction box to allow the left propeller to turn opposite to the right propeller, which was driven by the more conventional V-1650-25. In this arrangement both propellers would turn upward as they approached the center wing, which in theory would have allowed better single-engine control.
This proved not to be the case when the aircraft refused to become airborne during its first flight attempt. After a month of work North American engineers finally discovered that rotating the propellers to meet in the center on their upward turn created sufficient drag to cancel out all lift from the center wing section, one quarter of the aircraft's total wing surface area. The engines and propellers were then exchanged, with their rotation meeting on the downward turn, and the problem was fully solved.
The experience did, however, prove the superiority of inward-rotating props for controllability & aerodynamic factors except in the P-38!
Each engine had a General Electric B-1 turbosupercharger. To combat torque, the propellers rotated in opposite directions, a special version of the Allison engine being produced with a left-hand rotating propeller shaft. The engines had inwardly-rotating propellers.
YP-38 & production:
The propellers were outward-rotating rather than inward-rotating as on the XP-38. This improved the aircraft's stability as a gunnery platform.
Warren M. Bodie, in his book The Lockheed P-38 Lightning: The Definitive Story Of Lockheed's P-38 Fighter, states that, "Engine rotation was changed so that the propellers rotated outboard (at the top), thereby eliminating or at least reducing the downwash onto the wing centersection/fuselage juncture. There was, by then, no doubt that the disturbed airflow, trapped between the two booms, was having an adverse effect on the horizontal stabilizer.
The likelihood of an engine failure on take-off was considered less important than increasing the aircraft's capability as a fighter.
This P-38 experience is quite opposite to the case of the P-82 (twin Mustang). The XP-82 was to be powered by two Packard-built Rolls-Royce V-1650 Merlin engines. Initially, the left engine was a V-1650-23 with a gear reduction box to allow the left propeller to turn opposite to the right propeller, which was driven by the more conventional V-1650-25. In this arrangement both propellers would turn upward as they approached the center wing, which in theory would have allowed better single-engine control.
This proved not to be the case when the aircraft refused to become airborne during its first flight attempt. After a month of work North American engineers finally discovered that rotating the propellers to meet in the center on their upward turn created sufficient drag to cancel out all lift from the center wing section, one quarter of the aircraft's total wing surface area. The engines and propellers were then exchanged, with their rotation meeting on the downward turn, and the problem was fully solved.
The experience did, however, prove the superiority of inward-rotating props for controllability & aerodynamic factors except in the P-38!
Last edited by GreenKnight121; 27th Nov 2009 at 00:31.
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A400M - Onwards ...
Yes, it will certainly be a great, and very welcome, event when the A400M first gets airborne. I hope that it will very soon be flying regularly, enough at the very least to clear enough of the flight envelope to be able to transit to Toulouse for the rest of the programme - followed by the other FTP aircraft of course.
While the partner countries' DefMins sort out some at least of the outstanding lumps in the porridge of the contract, there will also be a lot of internal bargaining about responsibility for the FADEC programming standards foul-up, which will be just as fierce, no doubt. This seems to have cost the programme a good 18 months of delay: if so, the FTP would have been well on the way to completion by now.
Fingers really need to be more accurately pointed, not just at "Airbus" in general, but towards what the French Senate report called the "headless" engine consortium, apart from any other difficulties in "upgrading" what was CASA's capabilities in so short a time.Strenuous efforts were already being taken to sort out the airframe side well before the FADEC problem surfaced.
I, for one, wish the aircraft and its crew a successful start to the FTP, and the whole set-up a safe emergence from all the turbulence.
Ecce Homo! Loquitur...
Britain In Talks With Boeing For Another C-17
Britain is negotiating the purchase of another Boeing C-17 airlifter to boost the Royal Air Force's ability to supply troops fighting the Taliban in southern Afghanistan. If the procurement gets the go-ahead, the Ministry of Defence here said it hopes to complete contract negotiations by the end of the year. Approval of the purchase would see the RAF's fleet of C-17s grow to seven aircraft. An MoD spokesman confirmed negotiations were underway but said no deal had yet been done to acquire the aircraft.
"The U.K. has engaged in exploratory discussions with the U.S. Air Force and Boeing regarding the feasibility of procuring a seventh C-17 aircraft for the U.K. No commitments have been made, and no decisions have been taken," he said. "If the department decides to purchase a new C-17, then we plan to be on contract with Boeing by the end of December 2009, with a view to delivery in December 2010 and an in-service date of March 2011," said the spokesman. The rapid in-service date suggests the British will be given an early delivery slot earmarked for the U.S. Air Force.
The C-17 has been the backbone of an RAF's airbridge operation, which has been severely stretched supporting Britain's growing military presence in Afghanistan. The British have been operating C-17s since 2001, when they leased four aircraft. The airlifters were eventually purchased by the RAF and the fleet has grown to the point where the British took delivery of two aircraft last year and are now poised to acquire their seventh aircraft, subject to final government approval. Analysts think the RAF has hopes to acquire at least one more aircraft before the Boeing C-17 production line closes. Funding is likely to be an issue for the cash-strapped MoD. The MoD here is estimating line closure in 2011. However, a Boeing spokesman said there was currently no cut-off point and the production line was good until at least 2012.
A Boeing spokesman in the U.S. declined to discuss the possible deal with the British beyond saying, "We continue to see strong international interest in C-17s. Our customers, however, prefer to announce their intentions on their own timetable. The question is best addressed by the U.K.'s MoD."
The British said the purchase of the additional aircraft was not directly connected with delays to the Airbus A400M airlifter program. "A400M is the replacement capability for the Hercules C-130K tactical transporter. We have looked carefully at the intra-theater operational requirement after the C130-K goes out of service in 2012. Although a C-17 can be employed in a tactical role and will help to mitigate against operational losses of C-130J, analysis suggests that the current fleet of 24 C-130J can sustain anticipated intra-theatre airlift tasking on current operations until A400M comes into service."
The first flight of the A400M is expected in the next few days. The partner nations in the program are still trying to hammer out a deal with Airbus parent EADS on the revised timing and cost of the program, which is currently three years late and hugely over cost. French media earlier this month said Britain is expected to cut the number of aircraft it will buy from 25 to 19 aircraft in order to stay within funding availability. One British industry executive said earlier this week he thought the number the RAF get could be even less.
Asked if the C-17 buy could have an impact on A400M numbers, the spokesman said, "We keep our operational requirements under constant review, and we will look hard at the implications of the acquisition of any enduring capability. We continue to work with OCCAR [the European program office] and partner nations to find a way forward on the A400M program. It would be inappropriate to comment on these discussions at this time," he said.
Britain is negotiating the purchase of another Boeing C-17 airlifter to boost the Royal Air Force's ability to supply troops fighting the Taliban in southern Afghanistan. If the procurement gets the go-ahead, the Ministry of Defence here said it hopes to complete contract negotiations by the end of the year. Approval of the purchase would see the RAF's fleet of C-17s grow to seven aircraft. An MoD spokesman confirmed negotiations were underway but said no deal had yet been done to acquire the aircraft.
"The U.K. has engaged in exploratory discussions with the U.S. Air Force and Boeing regarding the feasibility of procuring a seventh C-17 aircraft for the U.K. No commitments have been made, and no decisions have been taken," he said. "If the department decides to purchase a new C-17, then we plan to be on contract with Boeing by the end of December 2009, with a view to delivery in December 2010 and an in-service date of March 2011," said the spokesman. The rapid in-service date suggests the British will be given an early delivery slot earmarked for the U.S. Air Force.
The C-17 has been the backbone of an RAF's airbridge operation, which has been severely stretched supporting Britain's growing military presence in Afghanistan. The British have been operating C-17s since 2001, when they leased four aircraft. The airlifters were eventually purchased by the RAF and the fleet has grown to the point where the British took delivery of two aircraft last year and are now poised to acquire their seventh aircraft, subject to final government approval. Analysts think the RAF has hopes to acquire at least one more aircraft before the Boeing C-17 production line closes. Funding is likely to be an issue for the cash-strapped MoD. The MoD here is estimating line closure in 2011. However, a Boeing spokesman said there was currently no cut-off point and the production line was good until at least 2012.
A Boeing spokesman in the U.S. declined to discuss the possible deal with the British beyond saying, "We continue to see strong international interest in C-17s. Our customers, however, prefer to announce their intentions on their own timetable. The question is best addressed by the U.K.'s MoD."
The British said the purchase of the additional aircraft was not directly connected with delays to the Airbus A400M airlifter program. "A400M is the replacement capability for the Hercules C-130K tactical transporter. We have looked carefully at the intra-theater operational requirement after the C130-K goes out of service in 2012. Although a C-17 can be employed in a tactical role and will help to mitigate against operational losses of C-130J, analysis suggests that the current fleet of 24 C-130J can sustain anticipated intra-theatre airlift tasking on current operations until A400M comes into service."
The first flight of the A400M is expected in the next few days. The partner nations in the program are still trying to hammer out a deal with Airbus parent EADS on the revised timing and cost of the program, which is currently three years late and hugely over cost. French media earlier this month said Britain is expected to cut the number of aircraft it will buy from 25 to 19 aircraft in order to stay within funding availability. One British industry executive said earlier this week he thought the number the RAF get could be even less.
Asked if the C-17 buy could have an impact on A400M numbers, the spokesman said, "We keep our operational requirements under constant review, and we will look hard at the implications of the acquisition of any enduring capability. We continue to work with OCCAR [the European program office] and partner nations to find a way forward on the A400M program. It would be inappropriate to comment on these discussions at this time," he said.
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The U.K. has engaged in exploratory discussions with the U.S. Air Force and Boeing regarding the feasibility of procuring a seventh C-17 aircraft for the U.K
Well, it is a rumour network
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French media earlier this month said Britain is expected to cut the number of aircraft it will buy from 25 to 19 aircraft in order to stay within funding availability. One British industry executive said earlier this week he thought the number the RAF get could be even less.
The other option should be us walking away, cost-free, as the South Africans have done.
Airbus will recoup losses once they get wider exports, perhaps from the middle east and more sales round europe. Why should the UK taxpayer pay for future airbus profit?
Ecce Homo! Loquitur...
VR, if you read back over previous posts it would seem the Brits, the French and the Germans have different negotiating stances - perhaps jointly agreed to keep EADS off balance.
The Germans are insisting on the given fixed price,
The French are after a split buy in 2 tranches, the fixed price for tranche 1, but a higher price for tranche 2.
The Brits are willing to accept a higher unit price, but a lower number of aircraft, as long as the extra cost is taken out of long term maintenance and support costs.
Cut and splice as required.
The Germans are insisting on the given fixed price,
The French are after a split buy in 2 tranches, the fixed price for tranche 1, but a higher price for tranche 2.
The Brits are willing to accept a higher unit price, but a lower number of aircraft, as long as the extra cost is taken out of long term maintenance and support costs.
Cut and splice as required.
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The Brits are willing to accept a higher unit price, but a lower number of aircraft
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C-17's
There is no point buying more C-17s untill the people who task and load/unload the aircraft get thier game together and start using them sensilbly!!
4hr onload off loads while US C17s on the next pan take 90 mins!!
Taking big loads to the wrong destination!!
Taking pax to the wrong destination!
OHH and there is much more!!
4hr onload off loads while US C17s on the next pan take 90 mins!!
Taking big loads to the wrong destination!!
Taking pax to the wrong destination!
OHH and there is much more!!
Last edited by collbar; 28th Nov 2009 at 11:28. Reason: spaz spelling 1st time! and further rant!!
VR,
A military fixed price contract (at least a British one) is normally only fixed price until it goes wrong.
For example, I seem to remember the Nimrod MRA4 contract being re-negotiated with BAE when they said they couldn't deliver on it. A contract for 21 (wasn't it?) became a contract for 3 prototypes with a separate contract for development aircraft if my memory serves me right.
MOD hasn't got the gonads to enforce contracts, or even penalty causes in contracts, as the company (+ local MP, trade unions) usually play the loss of jobs/capability/etc card....
At least that is my opinion, looking in from the outside....
I could be wrong, but this is a rumour network after all
A military fixed price contract (at least a British one) is normally only fixed price until it goes wrong.
For example, I seem to remember the Nimrod MRA4 contract being re-negotiated with BAE when they said they couldn't deliver on it. A contract for 21 (wasn't it?) became a contract for 3 prototypes with a separate contract for development aircraft if my memory serves me right.
MOD hasn't got the gonads to enforce contracts, or even penalty causes in contracts, as the company (+ local MP, trade unions) usually play the loss of jobs/capability/etc card....
At least that is my opinion, looking in from the outside....
I could be wrong, but this is a rumour network after all
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Fixed price ???
Having seen Avweek's report of 24/11 that the JSF programme is 16 billion dollars over estimates and needs more flight test aircraft to get back on timeline, could be that it is in more real danger than the A400M ...
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Ummm... it can pull itself around ON THE GROUND with its propellers... which makes it a successful prop-driven cargo truck.
However, it is designed to be an airplane... so it has to get itself off the ground, tool around for a bit in a controllable manner, then put itself back on the ground safely before you can say "It Works"!
The first attempt to do this is scheduled for next month... we'll see then.
However, it is designed to be an airplane... so it has to get itself off the ground, tool around for a bit in a controllable manner, then put itself back on the ground safely before you can say "It Works"!
The first attempt to do this is scheduled for next month... we'll see then.
