De Havilland Mosquito

[rickshaw]

Kendra, simply throwing more powerful, even draggier (if there is such a word) radial engines at a design which already has shown that because of drag it suffers less range than the original aircraft it was copied from won't overcome the inherent problems of the design.

Then you have the added problem of even higher fuel consumption (from these more powerful engines) plus the increased weight (of the more powerful engines and the required increase in fuel load to compensate for the increased fuel consumption), plus the increased drag (from these more powerful engines).   At this point, I think most others would have noticed that your on a losing wicket and rapidly sliding down that drag curve.   Basically, you cannot turn a sow's ear into a silk purse, no matter how much you try.   The Mosquito hit that "sweet spot" where all things were balanced out and it achieved it's superlative performance because the drag was kept low, the weight was kept low and the power was just right. Even the Mosquito encountered problems when people started fiddling around with the design, such as the efforts to install a power-operated turret.  It increased drag, increased weight and decreased performance so substantially that it was abandoned as a bad idea.

[KJ_Lesnick]

Kendra, simply throwing more powerful, even draggier (if there is such a word) radial engines at a design which already has shown that because of drag it suffers less range than the original aircraft it was copied from won't overcome the inherent problems of the design.

How about an airplane that has a similar function to the Mosquito but designed around radial engines?  As I recall the Japanese Zero had an unusually good range despite being a radial which owed of course to a high fuel-fraction.  Taking that concept a bit further, if you doubled the weight of the plane, kept the fuel fraction the same and put an extra engine in the design you'd have the same power-loading, and the same fuel-fraction (double the fuel, double the fuel-burn, double the thrust) it all works out.  You'd need to add some armor and self-sealing tanks to the plane, and stress it up to 8g's -- for such purposes you'd want the plane to be designed with that level of strength built in as history has shown that tends to work out better than adding strength to an existent design.  So long as the airplane's maximum weight was kept below 27,500 you'd be able to achieve a power-loading either equal to or better than the Mosquito depending on whether you used an R-2600 or R-2800 with the appropriate supercharger/turbocharger.  A fuel fraction of 33.5% or 35% would probably make up for the drag and fuel-burn provided you had a good airfoil (maybe a laminar flow design like the P-51), the right taper-ratios (or some ellipitical design) and aspect-ratios, and probably you wouldn't want a wing-loading below 40 or 45 when fully-loaded.

Sound good?

[Hobbes]

pyro-manic

Less fuel, less power, more drag? Just a guess....

I didn't know it had less fuel, less power makes sense, as for more drag is that the airframe or the engine?


Everybody

Why didn't they ever put counter-rotating props on

There's less need for them in a two-engined design since the torque of the two engines cancels each other out.
It seems it wasn't needed for power transmission either: a quick search turns up only 3- and 4-bladed props.
Spitfires with 5-bladed props had a Griffon. No Griffons on the Mosquito meant no need for more prop blades.

[Hobbes]

How about an airplane that has a similar function to the Mosquito but designed around radial engines?  As I recall the Japanese Zero had an unusually good range despite being a radial which owed of course to a high fuel-fraction. 

A high fuel fraction means less weapons load. Not a problem for a gunfighter like the Zero, but doesn't bode well for a bomber.

[perttime]

Radial engines have more frontal area than Merlins, so that means more drag.

Of course, it isn't quite that straightforward. However sleek you get the front of the aircraft (or nacelle), using a V12, you still need cooling for the V12. To get cooling, you usually need to direct air through radiators - and that definitely causes drag. Quite a lot of drag, actually.

[kitnut617]

Radial engines have more frontal area than Merlins, so that means more drag.

Of course, it isn't quite that straightforward. However sleek you get the front of the aircraft (or nacelle), using a V12, you still need cooling for the V12. To get cooling, you usually need to direct air through radiators - and that definitely causes drag. Quite a lot of drag, actually.

But, the drag can be offset by careful design of the radiator outlet to give thrust, which the Mosquito system was (as was the Spitfire's and what was proved to be an excellent design, the Mustang's system)

[sequoiaranger]

Couldn't help myself....

>No Griffons on the Mosquito meant no need for more prop blades.<

Ya mean like THIS?:



Really! With all this coulda-woulda-shoulda about engines, designs, drag, and fuel bandied about here, remember that if it was "just that easy", it REALLY would have been done! The aircraft designers of the 1940's also had a lot of imagination, were superbly competent, and had a LOT more expertise than anyone here on this board!

[perttime]

But, the drag can be offset by careful design of the radiator outlet to give thrust, which the Mosquito system was (as was the Spitfire's and what was proved to be an excellent design, the Mustang's system)

Totally agreed, and the Corsair, Bearcat, Thunderbolt and B-17 were handicapped by their radials... 
A radial is lighter than a liquid cooled engine, with all its systems, of anywhere near similar power.

Just sayin'. There's a lot of variables and I don't pretend to have an equation for picking the ideal engine.

[PR19_Kit]

There's less need for them in a two-engined design since the torque of the two engines cancels each other out.

Only if the props and engines are opposite handed and those on the Mossie weren't. The Hornet and Twin Mustang had handed props and engines but very few other twins of the WWII period did.

[Hobbes]

The torque from the left engine will try to push the fuselage down, while the right engine tries to push the fuselage up. As far as I can work out, the two cancel each other out.

[Daryl J.]

I still think the Mosquito needs fabric wings, inline 6 cylinder Half-Merlins, and a metal fuselage.   

Put a pair of Klimovs in it over in Helsinki for a Morko-Mosquito.   Low altitude American variants get Allisons. 

[PR19_Kit]

The torque from the left engine will try to push the fuselage down, while the right engine tries to push the fuselage up. As far as I can work out, the two cancel each other out.

I'm afraid not.

On aircraft with clockwise rotating props (as most do...) the whole aircraft tries to rotate anti-clockwise to port. The engine's position relative to the fuselage has no effect on this, it happens with single, twin, three or four engined aircraft. As the pilot has to counter this with opposite aileron that tends to produce adverse yaw to port and this in turn is countered with rudder trim.

See here for a detailed explanation.

http://wiki.flightgear.org/Understanding_Propeller_Torque_and_P-Factor

[Hobbes]

I did some more digging, but the info I've come across for twin-engined aircraft all refers to the 'Critical engine' problem and is silent about torque effects. http://en.wikipedia.org/wiki/Critical_engine

[famvburg]

     Trust me, unless you have counter rotating props, you have torque & it has to be corrected with rudder. Ask a multi-engined rated pilot rather than modelers. Without reading the article, critical engine has to do with prop rotation direction & which side of the a/c it's on. An a/c with counter rotating engines has no critical engine, but that's different from having torque.

I did some more digging, but the info I've come across for twin-engined aircraft all refers to the 'Critical engine' problem and is silent about torque effects. http://en.wikipedia.org/wiki/Critical_engine

[Caveman]

Not always true. Some have both engines as critical!