1. No, not wrong. Difference of opinion. Additional blades made from ceramics and the use of optimal curves for the blades are ways you improve modern propeller-driven efficiency. And when you look at the evolution of the propeller you end up exactly the path I described, a ducted fan. Nobody wastes their time with high-tech open blade designs because these expensive changes to the basic blade don’t really add much to performance (none over a ducted fan) and they certainly do not aid survival.

Yes, wrong – very wrong.

Even propfans (which are the ultimate expression of what you are alluding to) are still speed limited by the efficiency dropping right off when the blades go supersonic.

As for no-one wasting their time with open blade designs…

Yeah, thats why the A400M, the AN-70, the Bombardier Dash8s, the Embraer EMB-120 etc etc are all being designed or built right now..

Again, I’ll repeat, at low subsonic speeds, a turbofan does not approach the efficiency of a turboprop.

2. Are you being serious? AOPA taught me all I needed to know. You are still fixated on the technical term and want to debate a canned argument. The argument was open ended and you left wiggle room for showing its not true in all cases. I merely pointed out your argument had its flaw when one engineers around the problem.

Taught you all you needed to know?!?!

Well, whatever it taught you is wrong – very wrong. Go read a book on basic aerodynamics, infact, go read one on aircraft design too – it’ll probably have graphs of propulsive efficiency versus mach number in it.

3. They designed it, tested it, it worked. History. Old water under the bridge. Get over it.

Yeah it worked – doesn’t mean it couldn’t have worked better.

COIN aircraft have traditionally used propeller driven propulsion. Their bane has been heat-seeking manpads. Why? Because they are huge infrared beacons. You have heat radiating from the cowl in almost every case simply because the engines are energy inefficient. For all-aspect seekers the propeller blades offer a tremendous target, as the propellers offer heat signatures akin to a leading edge on a high speed jet plus further enhancing the hot zone with induced airflow over the main body or wings. So from a survival standpoint, the jet is the better solution.

Thats a speed issue much more than heat related.

You stick any slow (be they jet or prop propelled) aircraft there and it will have the same problems.

You seem to be ignoring the obvious with your boundary layer wake. You’re simply talking about a compressed air layer that flows as a fluid. A ducted fan can be used to avoid the wake. Are you just arguing to argue?

No, I’m talking about a volume of flow that totally changes the local operating conditions of the propellor/fan blade. [dunno where you get the idea of a boundary layer being a compressed air layer :confused: ]

Once again – DIRECTLY behind the wing is not a good place to have an engine.

wrong, the dorsal fin is all moving surface

That does not matter worth 2 sh_ts when it comes to lateral stability.

Also doesn’t explain the micro-elevators. They are all-moving on current aircraft and are much larger.

I really wasn’t talking about how to minimize infrared signature with a jet, just that its less of a problem compared to a propellor driven aircraft. There are more effective ways to elimate infrared signatures of jet engines than one offered for engines that drive propellers. We’d of had propeller driven fighters resurge into the mainstream if it was ideal to survival.

Ahhh, no – IR signature is not the reason for moving from propellors to jets – speed is.

IR signaure is more significant on jets than props anyway – you have more friction heating from the duct etc.

I’m basically pointing out why ducted fans (think turbofans) are more ideal in the nature of airflow than an open propeller, regardless if its rear mounted or conventional. 🙂

Uhm – they aren’t.

At low subsonic speeds, nothing beats the propulsive efficiency of a propellor. At low transonic speeds, a high BPR turbofan is best, as the speed increases the optimal bypass ratio decreases.

At around Mach 2.5-3 ish, I think a RAMJET becomes the most efficient, then at Mach 4-5 a SCRAMJET is most efficient.

But anyway, in the boundary layer wake of a wing – nothing is ideal, you want your engine out of that and into clear flow – thats why fuselage mounted engine intakes have some form of boundary layer control, be it a splitter plate (like the F-4), offset mounting (like the F-15), or using fancy 3D contours to force the BL out (JSF).

A smaller nozzle and finer exhaust stream is far easier to control as far as infrared signature goes.

You mean a smaller nozzle area?

Nah, for reduced IR signature, you want to disperse the hot air as quick as possible – induce large amounts of turbulence with the ambient flow to mix it into the cool air straight away.

And last, not saying its unaffected, I am saying its controllable. A ducted fan is better than an open one when it comes to the negatives of having induced airflow over a wing or body. And you can do novel things like blade counterpitch, air vector control like an airboat, and sound baffle in the ductwork.

No, I’m definitely getting the wrong end of the stick here.

Your talking about a ducted fan/propellor directly behind the wing?

If the Iranians can find the carriers, then the Mig31 would have a good chance to get within missile range, spam supersonic AShMs and probably also be able to turn around and get back to base in one piece to come back for another go if it can. Even if they just sink a destroyer or two, the planes would have paid for themselves, and the losses may well tip the balance of US public opinion.

Absolutely correct.

Especially a carrier armed only with Hornets and “Super” Hornets.

F-14s would stand a decent chance of getting into a useful intercept position against a squadron of MiG-31s, but F/A-18s? Not a chance.

The MiGs could play with the Hornets at will, forcing them (Hornets) to try and shadow them, simply running them out of fuel.

The USN will have to get the AF to run cover with -15s to keep the MiGs at bay.

If you were designing a CAS aircraft and you ideally wanted the following:

1. Single engined
2. STOL
3. nose for mounting sensors and gun
4. turbo prop
5. Thick low aspect ratio wings
6. Armored to the class of an attack helo

what would you compromise?

Edit: forgot to add 7. rough field performance

Right now, I think the traditional CAS aircraft is obsolete, but if we rewind, say, 10-15 years.

OK, for a CAS aircraft I’d be against a single engine design from the start – any kind of small arms fire and you might be forced to lose the aircraft – pretty poor considering it may be something as small as a nicked oil line.

So it would be twin engined, with the propeller centreline above the wing. Of course, the turbine exit nozzle would be above the wing for additional lift and possibly for blown flaps.

The main gun would go in the nose and the fuselage built around it (much like the A10).

In short, it would look something like a DH Mosquito really.

My question: Is it reasonable to compare the different numbers and infer maneuverability, given that the fuselage also contributes lift?

Short answer – no.

While the lift coefficient of an aerofoil section varies quite linearly with angle of attack (AOA). The lift coefficient (variation with AOA) of a whole fighter is anything but.

LERXs dominate at AOAs above 20/25 deg

The F-22 uses cascade vortices to achieve the same (if not better).

A delta wing also induces vortices, but it is not quite as efficient as a LERX due to the area the induced vortex sweeps over.

Anyway, even given all that, the only thing you can get from the optimum lift and drag ratio is sustained turn performance at one airspeed/altitude/angle of attack… that it.

There is so much more to manouverability than that – the dynamic motions, roll, pitch, yaw and acceleration. Transonic drag rises, the efficiency of flaps and slats, the extent of the wing drag bucket etc etc