This is good stuff first my comments on flight Sims earlier was meant to Illustrate the point that firing cannons do slow aircraft down I would not suggest a flight sim is any where near accurate it just in my experience when trying to catch an EA where both aircraft are going flat out it firing the guns was not a good idea unless you were guaranteed a kill shot as you lost AS and fell further behind.
Whether they are perfectly accurate in the amount of speed lost is irrelevant, the fact it was factored in as best they could, therefore you would have to accept that it happens.
The calculations made above back this up and are more significant than I would have expected. The fact that these guns are very low down on the UC they would have a levering effect on the fuselage, enough I would think as I previously said to at least badly effect sighting of the Guns.

Have you ever thought of being an aircraft designer Graham?! 😀

Seriously, if noone believes me, maybe this helps:-
http://en.wikipedia.org/wiki/GAU-8_Avenger

I agree, this is very much a worst-case scenario but the total speed loss will remain the same whether it is fired in one long burst (of about 5 seconds) or multiple short bursts with time to accelerate in between.

I don’t think the power of the engine would manage to reduce the speed loss much during firing; acceleration would be poor near the top speed and firing durations are extremely short.

The whole exercise was really to demonstrate that firing these cannon wouldn’t ‘stop the Lysander dead’ but I must admit that I hadn’t realised until I just looked it up that the Lysander was quite so slow with a maximum speed of only 212mph.

dont forget recoil springs….I am just so pleased that there are others with time on their hands 🙂

Interesting.

I’m not saying that the cannons would necessarily have affected the pitch of the Lysander to the point that it was unacceptable during firing…

…just that logically it would be better to have them closer to the centre-of-mass surely?

The problems of fitting them anywhere else (in the time available) would probably have outweighed any disadvantage (at that time) and there were advantages, such as being close to the position of the original guns and at a point stressed for bombs.

Goes to show that compromise is the number one law of aviation design.
In an ideal world you would put them where they would cause the least effect on weight, balance, handling….putting them on the centre line (horizontal datum) would be good then you would need interrupter mechanism…they are big, take up loads of room and are heavy….ergo longitudinal CG probs….on the spats/ undercarriage it is strong as you have noticed and also approx below the longitudinal CG so ok thatwise…..
if I have time I will see if we have any reports at work on this fit.