Modelling the effects of gun-recoil

[Thunderbolt56]

Just to clarify, in the book I've read this information in, the author didn't really write it. It is interviews and memoirs of different aces (yes, all are aces) and while one pilot in particular quoted the number "400 hp" it was just his statement and gave the impression it was just a number he might have pulled out of his arse.

I didn't think too much about it until I read in at least 3 other exerpts where each pilot was concerned about firing all his guns at a particular angle of attack or at a particular low speed for fear of wing departure. It may have been a thought bordering on pilot's superstition (kinda like gremlins in bomber squads), but it was mentioned enough to actually get my attention...that's all.

I'll try to go back through and mark the individual sentences and post them here. They may clarify a bit.

[choctaw111]

Anthony G Williams & Emmanuel Gustin have some great books on Combat aircraft. I have two books. One from the first world war and another from the second.
I was going to do the math on this once I saw how this thread was turning out, but I was beaten to it. I may try some other math and see what I come up with.

[IceFire]

Originally Posted by Thunderbolt56

Just to clarify, in the book I've read this information in, the author didn't really write it. It is interviews and memoirs of different aces (yes, all are aces) and while one pilot in particular quoted the number "400 hp" it was just his statement and gave the impression it was just a number he might have pulled out of his arse.

I didn't think too much about it until I read in at least 3 other exerpts where each pilot was concerned about firing all his guns at a particular angle of attack or at a particular low speed for fear of wing departure. It may have been a thought bordering on pilot's superstition (kinda like gremlins in bomber squads), but it was mentioned enough to actually get my attention...that's all.

I'll try to go back through and mark the individual sentences and post them here. They may clarify a bit.

It should surprise nobody that even WWII veterans are likely to tell a good tale now and again and use a fair bit of exaggeration. I'm sure firing the guns felt like a kick in the pants but I doubt the actual impact to the plane was that significant.

In another Mustang pilot story the Mustang pilot was locked in a battle with a 109...and at the end of the fight the Mustang pilot ended up behind the 109 at low altitude. In the process 3 out of 4 guns (was a B model) were jammed. I believe the interview references the need to counter the additional yaw from firing a single .50cal but that it was easily countered with the rudder. That never sounded to me like it was reducing the planes power by 400hp or 100hp or anything like that.

I think its just a bit of a tall tale.

[II./JG1_Krupinski]

Originally Posted by Thunderbolt56

Just to clarify, in the book I've read this information in, the author didn't really write it. It is interviews and memoirs of different aces (yes, all are aces) and while one pilot in particular quoted the number "400 hp" it was just his statement and gave the impression it was just a number he might have pulled out of his arse.

I didn't think too much about it until I read in at least 3 other exerpts where each pilot was concerned about firing all his guns at a particular angle of attack or at a particular low speed for fear of wing departure. It may have been a thought bordering on pilot's superstition (kinda like gremlins in bomber squads), but it was mentioned enough to actually get my attention...that's all.

I'll try to go back through and mark the individual sentences and post them here. They may clarify a bit.

Makes sense, since it seems like these are some old flyboy's sitting around the campfire sharing stories; love those types of books.

From your PoV, do you think the guns are modeled well in the game? (regardless of the accuracy)

Me, I've thought that some planes were too unsteady. The spit seems as steady as I have imagined it. I'm not too familiar with the in game 51s/47s so I couldn't say there.

In the end, I think recoil is model fairly decently. But could use some attention. You can actually use your guns to help slow you down on your landing roll out, which I think is too much.

I bet the next versions will be similar in value, but possibly modeled/implemented differently. I bet they'd apply the forces to the velocity vector in some published value and tweak for playability.

[_RAAF_Stupot]

This should be an easy problem for anybody with high school physics to solve.

Remember, momentum is always conserved! Ignore air resistance!

Momentum = Mass x Velocity

What is the Mass of a 20mm (Hispano) round?
What is the Muzzle Velocity of a 20mm Cal round?

What is the Mass of a (say half-loaded) Spit MkV?
Assume the Spit is doing 200 kts.

That is all the info you need to determine by how much the Spit slows down after a single cannon round is fired.




Now, as far as the force and power of the recoil is concerned - this depends on how long the recoil is applied to the aircraft. That in turn depends on the length of the barrel of the cannon (assume that the round travels at 0.5 x muzzle velocity right through the barrel). Once the round has exited the muzzle, the recoil is effectively absent. (Ignore mass of propellant gases).


The force of the recoil = Mass of Round x Acceleration of Round

Acceleration of Round = Muzzle Velocity / Time through barrel



Power of recoil = Change of Kinetic Energy / Time through barrel

Kinetic Energy = 0.5 x Mass of Round x (Muzzle Velocity)^2


To make all these sums work, use consistent units....

Mass (Kg) Kilograms
Velocity (m/s) Metres per second
Time (s) Seconds
Force (N) Newtons
Energy (J) Joules
Power (W) Watts

Assume 1 knot = 1.8 km/h

I'm too tired to actually do these sums now, but this is a good problem for anybody doing High School physics that has exams coming up.