Author Topic: 190D9 20mm guns, left deviation (Read 669 times)

Urchin · « **Reply #15 on:** January 26, 2002, 08:21:21 PM »

Very interesting. If the dispersion isnt the same for the two planes, there is definately something that isnt right about the Doras guns after all. Good work Mandoble.

J_A_B · « **Reply #16 on:** January 26, 2002, 09:26:55 PM »

Mandoble, what I see in the image up there is the bullets are mostly striking slightly to the left of the gunsight's center dot.

This could indeed mean there is something wrong with the D-9's guns/dispersion.

However, it might also mean that the gunsight is in the wrong place. With the new gunsights, the sight is now fixed in relation to your viewpoint; if the Dora's sight is fixed in the wrong place (slightly to the right of where it should be), it would have the same effect of making the bullets fall left of the gunsight.

In my own trials the machine gun rounds fall to the left of the gunsight, just as the cannons do. Therefore, if there IS a problem with the D-9's guns, it's not just limited to the cannons.

J_A_B

MANDOBLE · « **Reply #17 on:** January 26, 2002, 10:30:35 PM »

J_A_B there are two different problems:

1 - bullets go to the left of the GS center. That could be due a GS problem.
2 - If you take a look to the hits, left hits have markably different dispersion than right ones. That could be due bad aligment of each gun relative to the other one.

And you are right, MGs have same problem as guns.

MANDOBLE · « **Reply #18 on:** January 26, 2002, 10:34:00 PM »

Quote

Originally posted by Urchin
Very interesting. If the dispersion isnt the same for the two planes, there is definately something that isnt right about the Doras guns after all. Good work Mandoble.

Urchin, if the had same disperion for the two planes, then we had a common problem for both.

GRUNHERZ · « **Reply #19 on:** January 26, 2002, 10:41:12 PM »

Draw an imaginary line down the center of the black hit dot circle in lephturns picture.

Notice how much tighter the dots are in the left half of the cicle both verically and horizontally.

There is much tighter dispersion on left than on right. Gunsite issues or not.

MANDOBLE · « **Reply #20 on:** January 26, 2002, 10:49:43 PM »

GRUNHERZ, that is just what I mean. IMO, guns have some kind of problem, perhaps, also the GS.

Tyro48 · « **Reply #21 on:** January 27, 2002, 12:41:30 AM »

Positioned a D9 in the hanger, hit the " H " button then F3 and zero to get a head on look at it, tapped the " B " button to fire, seemed like the right wing gun fired far left a whole lot more than the left wing gun fired far right, this was done backed of as far a way as the braket keys would send me, not bench test data but take a look and see if a few more of ya see the same thing ! The " B " button was tapped slowly to get a good look at each tracer shot.

Tac · « **Reply #22 on:** January 27, 2002, 02:57:02 PM »

maybe a lame solution, but adjusting your gunsights a bit to the left would neutralize this effect?

I remember when the dispersion for the guns used to give a "+" pattern, was hilarious.

MANDOBLE · « **Reply #23 on:** January 27, 2002, 06:01:47 PM »

190D9

190F8

As you can see, F8 suffers a bit of left deviation, but not as noticeable as with 190D9.

Conv 600, target 600 yards.

Test done shot by shot, not spraying, only 20mm.

Kweassa · « **Reply #24 on:** January 28, 2002, 12:41:48 AM »

I'll be sure to aim a little more to the right of the bogey, next time I fly a D-9

I do hope there is a proper explanation for this.

Or if there ain't, we may declare the thing 'broken'

and plead to the HTC to fix it

mrsid2 · « **Reply #25 on:** January 28, 2002, 01:32:49 AM »

Quote

Originally posted by Kweassa
I'll be sure to aim a little more to the right of the bogey, next time I fly a D-9

I do hope there is a proper explanation for this.

Or if there ain't, we may declare the thing 'broken' and plead to the HTC to fix it

This might explain some of the weakness many experience in dora guns.

hazed- · « **Reply #26 on:** January 28, 2002, 10:56:07 AM »

could this be a trim/engine torque issue?

could someone do similar tests but with the typhoon to see if its bullets drift to the right?

Regurge · « **Reply #27 on:** January 28, 2002, 10:57:50 AM »

Last night I tried this and noticed that even in auto-level the plane (p47) slowy yawed right. Firing over several seconds, I got a pattern similar to mandoble's.

I'm not sure whether the plane was yawing right or the target was moving left, but either way something is screwy, and not neccessarily the guns.

If youre seeing a left-biased pattern put up a target and zoom in and just watch it. It also may depend on plane type as the p38 does it very very slowly, taking several minutes to notice any change at all.

MANDOBLE · « **Reply #28 on:** January 28, 2002, 12:11:13 PM »

Regurge, each shot implies a "vibration" that cause a little yaw to the left or to the right depending on the firing gun. I've noticed that if you fire a single shot and wait, the plane will yaw a bit to one side and, inmediately, it will compensate to the other side, keeping your nose pointing to the original course. If you keep spraying, you may have a real (minimal) course change.
Cause that, my test was done shot by shot. That is, shot, wait til vibration is compensated (your GS center aims again at the original point), shot again, and so on. Doing these tests at a constant 250 mph speed you ensures that torque effect does not affect the aiming. Supposing it was due a minimal yaw caused by torque, it should displace your GS center to the left, and you'll see the hits displaced to the right in the target (190D9).

If in your P47 test you noticed a yaw to the left, then you'll have just opposite results to mine. Your GS will move to the left and you'll see the hits displaced to the right in the target.

Tyro48 · « **Reply #29 on:** January 28, 2002, 01:16:53 PM »

You can sit on the ground and do a .target 100 and get the target close enough to see, eng off, brakes on, fire away, there you can see what your guns are doin in relation to you sight without the worry of side to side movement, you can also set your convergence to 150 yards to get a real good idea, the p47 sits pretty high so you may have to fiddle a bit with the settings but you can pretty well extrapolate whats going on as to whether the sight needs to go up and left or whatever !