Douglas A-20 & Defensive Armament

[wuzak]

No. Contra-props are to eliminate torque issues, and/or to reduce overall prop diameter. They don't magically increase power.

Theoretically contra props are more efficient. But whether that efficiency gain offsets the weight gain is a different matter.

Curiously, in 1943 one of the Hawker Tornado prototypes was converted to use contra props (RR Vulture was still being used) and was found to have an adverse affect on stability!

[pyro-manic]

As for contra-props they both can eliminate torque and can be used to transmit extra power, Pyro.

Yes, but the power has to be there, untapped, to start with. Normally a single prop is of the right size to transmit all of the engine's power, so adding a contraprop will not help matters.

[KJ_Lesnick]

No. Contra-props are to eliminate torque issues, and/or to reduce overall prop diameter.

That is one result

They don't magically increase power.

The same factor that eliminates torque (neutralizing tangential flow) also results in more thrust.

Adding tailguns to the Mossie would have been enormously difficult. It would have required the entire tail section to be redesigned and re-engineered to be larger, which would have been much heavier and would have had a detrimental effect on weight, balance, drag and therefore performance.

Well I was thinking of an airplane based around the Mosquito concept but with a tail-gun in the design.  It would be a little heavier and have a bomb-load of 4,000 pounds internal (not just a cookie) instead of 2,000.  The idea would be something between a Mosquito and an XB-42 and powered by a pair of R-2800's or R-3350's with some kind of advanced cowling design like that of the Fw-190, F4U, Hawker Tempest.

Yes, but the power has to be there, untapped, to start with. Normally a single prop is of the right size to transmit all of the engine's power, so adding a contraprop will not help matters.

A propeller produces thrust which is essentially in this case lift pointing forwards instead of up and down.  The higher the L/D ratio, the more thrust for HP is produced.  See?

As Pyro suggested, Kendra.  Exactly what sort of "remote control" set up do you want?  One that moves in elevation and traverse

I was thinking of a set up that could move up and down and side-to-side.

If its the former, then you're looking at a massive weight and drag penalty for all the machinery.

How much weight and drag would be produced, and how bad would have been if a plane was built from the start with that in mind?

As for contra-props they both can eliminate torque and can be used to transmit extra power, Pyro.  It allows an aircraft to utilise smaller diameter propellers as well, which can be important in smaller aircraft.

Yup

[Go4fun]

Heck, just put a Napolic War 12 pounder back there full of grapeshot. One shot but they sure won't want to come in for seconds! 

[KJ_Lesnick]

I want to be very clear here...

I actually think the Mosquito was the right way to go -- I'm just talking about a WHIF US design which would have probably needed some defensive armament.