My rant/fantasy regarding the A-10(A&B) Warthog.

Ensign Re-read wrote:The examples are not comparable.
C-130 is metal framed cargo plane (easy to re-enforce, maintain & repair).
Osprey is (largely) carbon framed troop transport (not so easy for same).
{Yes, that is an oversimplification.}
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CF fuselages are built just like Aluminum ones. The ONLY difference is that there are not thousands upon thousands of rivets. Epoxy is used instead. Sure you CAN use rivets and bolts, but there is no reason to. How do you think they do all repairs on CF planes... Rivets, bolts, screws and glue. They do not "lay-up" individual layers.

It is called standard cross section forms. Only in the wing for torsional rigidity purposes are stringers/beams laid up expressly with unique fiber orientations. A round tube? No. A barrel mandrel is used for the EXTERIOR skin thickness. Stringers are then glued on after piece is pulled from the barrel mandrel.

CF is far superior for maintenance. It does not require any at all. Ever. You do not have grounding problems for instance from corrosion. If layed up properly, far less prone to cracking than aluminum. It fatigue life is vastly superior to that of aluminum as well.

In short a CF structure should last easily 2X longer than an equivalent aluminum bird for the same weight. There is a very simple reason airliners were lining up around the block to get their hands on the 787 and only when the line was seen to be wrapped around the block twice that folks decided to venture over to airbus and check out their A350. Of course the A350 is mostly CF as well, but a lot of the very expensive hard maintenance area for checks "C" and "D" are still aluminum instead of CF which effectively negates going to CF in the first place.

I agree with Relax that CF is less maintenance intensive.

Mind you I could never understand why helicopter manufacturers made their chassis out of aluminum girders that were bolted together at corners (where they cracked), while car manufacturers that used aluminum chassis (Lotus, Audi) extruded them in one piece with computer calculated thicknesses and curves that eliminated cracking. Ok they are expensive cars, but nothing like as expensive as the aircraft.

Sorry, was going for the fun factor not a direct conparison.

Daryl wrote:I agree with Relax that CF is less maintenance intensive.

Mind you I could never understand why helicopter manufacturers made their chassis out of aluminum girders that were bolted together at corners (where they cracked), while car manufacturers that used aluminum chassis (Lotus, Audi) extruded them in one piece with computer calculated thicknesses and curves that eliminated cracking. Ok they are expensive cars, but nothing like as expensive as the aircraft.

Because I will do an assumption here that you are comparing very modern cars to old helicopters. Old cars never used extruded corners either. Cars also have far more mass in their structures for vibration damping via rigidity and extra thickness. Comparing cars to aircraft is really dumb IMO. A car outside of an F1 race car is effectively a tank in comparison to a helicopter.

Add in how it is assembled. Add in weight as a major concern. Add in cars are made by the 100,000/year while Helos are made by the several handfuls.

Crack initiation points are a major design criteria on all aircraft made from any material. So, the cracks in the corners are probably due to a resonant frequency that was not foreseen.

I was comparing modern cars with several US popular helicopters but I'll use Black Hawk helicopters as an example. New models of these are still being rolled out and in significant numbers, probably more than Lotus cars.
Colin Chapman (Lotus founder) espoused very light weight over everything in his cars. My Lotus 7 derivative (that I drove most days for 7 years) used aluminum and CF composite construction and weighed 570kgs.
All aluminum framed and clad helicopters suffer from vibration induced cracking, particularly near corners.
When we were sourcing a new fleet, Sikorsky VPs proudly told us that they were still using some jigs from Igor's early days. Eurocopter on the other hand were continually refining their CF models and there was no incidence of cracking. One burnt to a crisp but that was their test pilot's fault. Boeing saw the light and were selling replacement CF barrels for their Chinooks that were cheaper than continuing to repair the old aluminum style.

Relax wrote:

Daryl wrote:I agree with Relax that CF is less maintenance intensive.

Mind you I could never understand why helicopter manufacturers made their chassis out of aluminum girders that were bolted together at corners (where they cracked), while car manufacturers that used aluminum chassis (Lotus, Audi) extruded them in one piece with computer calculated thicknesses and curves that eliminated cracking. Ok they are expensive cars, but nothing like as expensive as the aircraft.

Because I will do an assumption here that you are comparing very modern cars to old helicopters. Old cars never used extruded corners either. Cars also have far more mass in their structures for vibration damping via rigidity and extra thickness. Comparing cars to aircraft is really dumb IMO. A car outside of an F1 race car is effectively a tank in comparison to a helicopter.

Add in how it is assembled. Add in weight as a major concern. Add in cars are made by the 100,000/year while Helos are made by the several handfuls.

Crack initiation points are a major design criteria on all aircraft made from any material. So, the cracks in the corners are probably due to a resonant frequency that was not foreseen.

Relax wrote:The gun is all of ~600lbs. Now the ammo

Fine. The GAU-8 gun system is 20 feet long and weighs over 4,000 pounds. 'Cause without its feed mechanism and ammo drum the gun is useless.

Hydraulics... as if all aircraft do not have hydraulic systems. This isn't prior to WWII aircraft here.

And you connect that high-pressure hydraulic system to a gun inside a turret how, exactly? Placing an extremely weak link in the flight control systems, I might add.

A simple, DUH! problem is, aiming.

The other massive problem? No armor/redundancy.

Now the most obvious, why the 30mm? Why not use the vulcan 20mm or simple 50cal? For every 30mm round, you can fire off 5-10 50cal or 2 20mm. Such an expensive aircraft will not be going after tanks.

Of course it is a completely hairbrained bullshit idea requiring a complete redesign of the Osprey and would have very limited forward firing in airplane mode due to propellers.

I have always considered it very bad design that the props dig 4 feet into the ground if, for some strange reason (combat damage!!), you had to land with them facing forward.
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At my house, the “things that go bump in the night” are cats.

Can anyone give an explaination as to why Turbofans (NOT jet engines) could not have been used on the V-22 Osprey?

For example: Are Turbofans just as susceptible to FOD as jets?
(I THOUGHT answer was mostly-NO.)

I do suspect that jets would have problems creating AND injesting FOD from the ground itself.

I can't begin to paraphrase what the "disc loading" and "ring vortex" issues mean, but I also thought those problems were jet related, not turbofan.





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[quote="Ensign Re-read"]Can anyone give an explaination as to why Turbofans (NOT jet engines) could not have been used on the V-22 Osprey?

For example: Are Turbofans just as susceptible to FOD as jets?
(I THOUGHT answer was mostly-NO.)

I do suspect that jets would have problems creating AND injesting FOD from the ground itself.

I can't begin to paraphrase what the "disc loading" and "ring vortex" issues mean, but I also thought those problems were jet related, not turbofan.
.[/quote]

[Down pressure is another way of saying disc loading]

A turbo fan IS a jet engine. Though it could be a piston engine as well or any other form of engine. It is called a turbo fan because the first compressor stage of a jet engine is fitted with a giant fan diameter in comparison to its compressor/turbine stage diameters. Thrust from the jet to the ratio of thrust generated by the FAN, is called turbofan bypass RATIO in simple terms. The greater the bypass ratio, the more efficient the engine is at subsonic thrust generation.

Erm, sure one could have used turbo fans instead of large diameter propellers, but, the downward velocity(pressure) on the ground would be higher than the already higher propellers. This increases FOD/brown-out problems. If you want to see this look at Tilt Wing aircraft. They are more efficient at take off lift vertically, but have a higher down velocity. They have higher speed and far greater range than a tilt rotor concept. http://en.wikipedia.org/wiki/Tiltwing Look at the graph for downpressure verses lift efficiency. Note that by theory, the Tilt rotor should be more efficient at vertical lift. In reality, the wing on aircraft like the Osprey get in the way. Also this graph was generated without the use of turbofans compared to straight propellers uses. A turbofan compared to a propeller will increase thrust by an additional 30% in most cases. In effect outside of the severe down pressure, a tiltwing with turbofans should beat the snot out of an V-22 Osprey.

Ring vortex. All vertical lift devices have this limitation. The simple explanation is recirculation. The ol' application of newtons laws of motion. For every action there is an equal and opposite reaction. Well, not always. What happens with a fluid like air, is that a circulation pattern can happen where the downward thrusting air from a floppy helo blade or a very large propeller in the Osprey's case, or a turbofan will not distribute out into the surrounding air creating the cushion. Instead a portion of this air will hit the SLOW moving air and REBOUND outward and UPWARD. The Upward velocity vector is created because the floppy helo blade or turbofan is SUCKING in massive amounts of air. The air above the turbofan is at low pressure while the air below is at high pressure. High goes to low and VIOLA circulation pattern.

A ring state vortex is formed and far less lift is generated and down down down goes the helicopter, V-22 Osprey, etc. If you think about why the Osprey is more susceptible is simple. It has a higher down pressure than a Helicopter and therefore that airpressure wants to get to a low pressure zone faster.

Why you still want to go in "up close and personal" with a cannon when there are so many other effective ways to deal with these problems from far away is beyond my comprehension. It is like arguing about the merits of a Beretta 9mm vs a Colt .45 ACP as your weapon of choice when trying to defeat a sniper.

AS far back as the late 1980's systems like "Skyguard" were demonstrating the ability to shoot bombs and guided missiles out of the air using 35mm AHEAD ammunition. Much like a Navy CIWS, this was pretty difficult, and could be overcome by "swarming" the installation with multiple targets (eventually, the guns run out of ammunition, if nothing else), with the obvious implication that if they can shoot the bombs out of the sky, then the bomb truck had better be out of range.

This explains the proliferation of long range surface to air missiles and the continuing evolution of glide bombs; better to start shooting at the target when you are many miles distant than when you are right over top of them. Just to make things even more interesting, the Fiber Optic Guided Missile (FOG-M), a technology the United States essentially abandoned in the 1980's, has proliferated throughout the world, with guided missiles uinsg this technology ranging in size from the mini-Spike anti personnel guided missile (wouldn't that suck!) with a rang of 1.2 Km to the Avibrás FOG-MPM with a range of 60km. These missiles allow a man in the loop capability so a soldier can positively ID a target as the missile closes in and make the final go/no go decision. So ground artillery (which is essentially what these guided missiles are) can also come in for precision attacks on hard targets, without the weather or "on station" issues that aircraft have.

Relax wrote:

Ensign Re-read wrote:Can anyone give an explaination as to why Turbofans (NOT jet engines) could not have been used on the V-22 Osprey?

For example: Are Turbofans just as susceptible to FOD as jets?
(I THOUGHT answer was mostly-NO.)

I do suspect that jets would have problems creating AND injesting FOD from the ground itself.

I can't begin to paraphrase what the "disc loading" and "ring vortex" issues mean, but I also thought those problems were jet related, not turbofan.

[Down pressure is another way of saying disc loading][/i]

A turbo fan IS a jet engine. Though it could be a piston engine as well or any other form of engine. It is called a turbo fan because the first compressor stage of a jet engine is fitted with a giant fan diameter in comparison to its compressor/turbine stage diameters. Thrust from the jet to the ratio of thrust generated by the FAN, is called turbofan bypass RATIO in simple terms. The greater the bypass ratio, the more efficient the engine is at subsonic thrust generation.

Erm, sure one could have used turbo fans instead of large diameter propellers, but, the downward velocity(pressure) on the ground would be higher than the already higher propellers. This increases FOD/brown-out problems. If you want to see this look at Tilt Wing aircraft. They are more efficient at take off lift vertically, but have a higher down velocity. They have higher speed and far greater range than a tilt rotor concept. http://en.wikipedia.org/wiki/Tiltwing Look at the graph for downpressure verses lift efficiency. Note that by theory, the Tilt rotor should be more efficient at vertical lift. In reality, the wing on aircraft like the Osprey get in the way. Also this graph was generated without the use of turbofans compared to straight propellers uses. A turbofan compared to a propeller will increase thrust by an additional 30% in most cases. In effect outside of the severe down pressure, a tiltwing with turbofans should beat the snot out of an V-22 Osprey.

Ring vortex. All vertical lift devices have this limitation. The simple explanation is recirculation. The ol' application of newtons laws of motion. For every action there is an equal and opposite reaction. Well, not always. What happens with a fluid like air, is that a circulation pattern can happen where the downward thrusting air from a floppy helo blade or a very large propeller in the Osprey's case, or a turbofan will not distribute out into the surrounding air creating the cushion. Instead a portion of this air will hit the SLOW moving air and REBOUND outward and UPWARD. The Upward velocity vector is created because the floppy helo blade or turbofan is SUCKING in massive amounts of air. The air above the turbofan is at low pressure while the air below is at high pressure. High goes to low and VIOLA circulation pattern.

A ring state vortex is formed and far less lift is generated and down down down goes the helicopter, V-22 Osprey, etc. If you think about why the Osprey is more susceptible is simple. It has a higher down pressure than a Helicopter and therefore that airpressure wants to get to a low pressure zone faster.

Your explanation of "Ring Vortex" does match my understanding of it, and it makes sense. As I stated however, I am not in a spot where I could have made as good of an explanation as to what it is.

What I did not notice was a clear comment about FOD re TurboFans. (I mean FOD-related damage; not the creation of FOD in the first place.)

Do you think that TurboFans are just as, more or less susceptible to FOD-related damage versus conventional Jets?

{As for my original question: Yea, it does seem that TurboFans are out for a Tilt-anything aircraft for the same "Ring Vortex" issue that conventional jets are susceptible to.}



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