P-51b Convergence

[bustr]

Mtnman,

Could you reccomend an autolevel speed for this audience to fly their P51B/D at offline so they can see there trajectory across target ranges from 100-1000? They just need to remember the nose will push down 5Mil when they pull the trigger. The armeors instructions from the inside of the gun hatch on the P51D states the airspeed at 301 IA. I'm not sure how that corrisponds to the AH programatical environment.

From the Gun Hatch:

90% indicated airspeed at low blower
Critical altitiude 301 m.p.h.: Set airplane level<------Factory speed setting. Handbook has chart of other speeds.
Lugs 0' 35' nose up.

Once everyone does this and is on the same footing from a common experience, maybe they will understand better your presentation. If the convergence function is raising and lowering the gun barrels to achive the convergence range set IP at reticle center, then you may never see the round pattern above the reticle centerline.(other than in response to the 5Mil nose down during firing) This would suggest the convergence function also raises and lowers the gunsight centerline programaticly in responce to the change in the manner an armorer would in the cockpit during bore sighting.

If you look at the convergence chart for the P47, at 500 yards the average hight of rounds above the reticle centerline @500 is 9 inches and 200 -11 inches. 9 inches above or 11 inches below from 200-1000 yards looks like it's on the plate it's so small. So effectively you will get the optical illusion from the gunsight FOV that your rounds shoot almost flat to 1000 yards. The P51 will be a variation on 9 and 11 due to the guns being closer on the horizontal plain to the reticle centerline.

This is the reason for my comment about setting the 50cal vertical IP to 200 yards. It would require setting the reticle centerline lower because making the bullet stream pass up through the graticle CL closer to the gunsight than 300-350 would require increasing the gun barrel's loft. I wonder if the armeror was actualy asked to make the horizontal component cross at 200 while the N9 was set to it's low graticle CL line to pass through the center of the dispersion cloud at 200? The K14 had a fixed 100Mil ring with 10Mil cross to allow adjustment of the unit during borsighting.

[Babalonian]

Because, it's not nearly as cool unless you've seen it yourself:

[mtnman]

Mtnman,

Could you reccomend an autolevel speed for this audience to fly their P51B/D at offline so they can see there trajectory across target ranges from 100-1000? They just need to remember the nose will push down 5Mil when they pull the trigger. The armeors instructions from the inside of the gun hatch on the P51D states the airspeed at 301 IA. I'm not sure how that corrisponds to the AH programatical environment.

From the Gun Hatch:

90% indicated airspeed at low blower
Critical altitiude 301 m.p.h.: Set airplane level<------Factory speed setting. Handbook has chart of other speeds.
Lugs 0' 35' nose up.

Once everyone does this and is on the same footing from a common experience, maybe they will understand better your presentation. If the convergence function is raising and lowering the gun barrels to achive the convergence range set IP at reticle center, then you may never see the round pattern above the reticle centerline.(other than in response to the 5Mil nose down during firing) This would suggest the convergence function also raises and lowers the gunsight centerline programaticly in responce to the change in the manner an armorer would in the cockpit during bore sighting.

If you look at the convergence chart for the P47, at 500 yards the average hight of rounds above the reticle centerline @500 is 9 inches and 200 -11 inches. 9 inches above or 11 inches below from 200-1000 yards looks like it's on the plate it's so small. So effectively you will get the optical illusion from the gunsight FOV that your rounds shoot almost flat to 1000 yards. The P51 will be a variation on 9 and 11 due to the guns being closer on the horizontal plain to the reticle centerline.

This is the reason for my comment about setting the 50cal vertical IP to 200 yards. It would require setting the reticle centerline lower because making the bullet stream pass up through the graticle CL closer to the gunsight than 300-350 would require increasing the gun barrel's loft. I wonder if the armeror was actualy asked to make the horizontal component cross at 200 while the N9 was set to it's low graticle CL line to pass through the center of the dispersion cloud at 200? The K14 had a fixed 100Mil ring with 10Mil cross to allow adjustment of the unit during borsighting.

It'll take me a little while, but sure, I'll write something more detailed up and toss in some visual aids as well.  I'll need to stretch it out over a few days since I don't have time to do it in one shot, and because I'll need to prepare some visuals.

I'll probably start another thread to do this though, because it'll derail this one and because there's no point in hiding the discussion in here; it'll probably get kind of lengthy.

For starters  we're not really comparing apples to apples on the bore sighting thing.  That's because that's all that P51 diagram is...  It's a recommended method for bore sighting.  

We don't bore sight in AH, and we don't "sight in" in AH.  We don't need to, and I'm unaware of any real method to simulate either one in-game (or offline).

Bore sighting is not "sighting in".   They're not the same thing, and they're not necessarily dependent on each other.



I need you to restructure this first sentence though, because I'm not sure what you're really asking.

Mtnman,

Could you reccomend an autolevel speed for this audience to fly their P51B/D at offline so they can see there trajectory across target ranges from 100-1000?

This question is too open-ended.  They can fly at any speed they want to in auto-level to see their trajectory across target ranges from 100-1000 (yds). 

They'll see different things/results though, depending upon what speed they choose and of course on how much variation they allow to contaminate their testing.  Speed will definitely have an effect on things, so it would depend to a large extent on exactly what they wanted to test/see in order to pick a particular speed.  Altitude will effect things too, so that would potentially have to be factored in as well.

I'll begin a new thread, but will place it in the Help and Training section.  I'm going to begin it with the basic "How's and Why's", and plan to take it into the differences between shoulder-fired weapons and wing-mounted guns.  If you have other topics to discuss, feel free, but I'm going to avoid too much detail on nose-mounted guns and cannons for now.

[bustr]

I wish Hitech would be done with it and lock the "Hollow Airscrew" mounted autocannons at the engine 0 line.

They could not be tilted for bore sighting. The gunsight was adjusted from the cockpit like the Revi16B's negative 14 degrees, or lower stadia markings were included below the center dot for the ballistic drop. The N3 in the P39 comes to mind with the lower stadia mark bombing ladder. The Yak's ShVAK 20mm and NS-37 both fired almost flat compaired to the MG151/20 or MK108/30 so the PBP or PAK gunsights didn't need much adjustment. The Yak's had a centering mark on the backside of the prop.

I know shooting at the offline target is not bore sighting. But, somehow a common terminology has to be agreed on to carry the discussion forward that players can grasp and communicate the subject to each other and back to the Trainers when asking questions. Offline Target = Shot/Dispersion Patterning. Still you can graph your ballistic trajectory with it, or coarsly using angular mil math the bore pattern. There is nothing wrong with technical granularity for those who are inclined. Different people learn differently ie, visulising of concepts at times.

[drgondog]

I know shooting at the offline target is not bore sighting. But, somehow a common terminology has to be agreed on to carry the discussion forward that players can grasp and communicate the subject to each other and back to the Trainers when asking questions. Offline Target = Shot/Dispersion Patterning. Still you can graph your ballistic trajectory with it, or coarsly using angular mil math the bore pattern. There is nothing wrong with technical granularity for those who are inclined. Different people learn differently ie, visulising of concepts at times.

Bore Sighting is literally positioning the target in the center of the bore.  Basic purpose is to align the axis of the machine gun (or rifle) prior to Sighting In.. in order to ensure that the barrel was pointin at the target, more or less.

Sighting in is aligning the SIGHT to the theoretical point of impact of the Bore Sighted axis. 

For a sporting or target rifle, bore sighting is a useful way of adjusting a scope to the bulls eye at a reasonable distance - say 100 yards - so that when starting the Sight In process of making fine adjustments, the barrel and scope are in pretty close alignment to the target before one round is expended.

For this discussion, precision requirements for fixed guns mounted in an aircraft are neither as high as a sporting/target rifle with sights nor could such precision be expected for a gun/sight system mounted to what amounts to a 'flexible' platform when used in actual conditions.

In the case of an operational Mustang, pre-equipped with say an N-9 sight and four .50 caliber M3's, the a/c would be jacked up until the target was acquired and centered by the N-9 sight. Then each of the Guns would be boresighted and adjusted to center on the target point.  If you wished to be anal for sighting in to 300 yards, the armorer would adjust the elevation once more for each of the weapons so that the boresight axis would be, say, 8 inches above the target aiming point to account for ballistic properties over that range.  I have zero idea regarding the practice of attempting such ballistic precision. 

When new sights were installed at the factory, or K-14s were provided in field mod kits, IIRC there was a factory kit supplied which mounted on the cowl forward of the windscreen.  It was used to Boresight the gunsight during installation, by adjusting the gunsight/mount to the target, then boresight and adjust the machuine guns. The Sighting In was then performed after the kit was removed, by making fine adjustments to the sight.

When bullet drop compensation computing was integrated into sights, no such adjustments were necessary when sighting in to the boresighted targets

Boresighting is essentially a laser line of sight with no ballistics built in. 

[SectorNine50]

I was always curious about this:

Did they actually have a 400+ yard range that they would align the guns and sights to, or did they basically just do the math to know where the guns should aim on a target that might be something like 100 yards away?

[drgondog]

I was always curious about this:

Did they actually have a 400+ yard range that they would align the guns and sights to, or did they basically just do the math to know where the guns should aim on a target that might be something like 100 yards away?

The 355th FG had a 250 yard target/embankment combo - can't speak for rest of the groups.

[bustr]

Do you think the 355 retained the the static angle of attack for the 301mph referenced speed while adjusting their patterning and reticle center at 250yd? I've looked at about 3 different static sighting setup pictures with P51D around the internet and all have the P51 with a slight down nose atitiude. Against the offline target 285 true was the speed at which the centerline of the engine stayed level with the centerline of the target. At 300 it was below or a nose down atitiude.

I compiled a list of true airspeeds offline for all of our fighters to keep the engine centerline, or on twins, fuselage centerline level with the offline target centerline. Wish I had a list of the factory speeds/nose atitiudes for those aircraft. It helped my sight picture quite alot at different ranges performing the testing to get all of those speeds against the offline target. Interesting the things you see during long drawn out testing you don't think about in the "seconds to react" sound and fury of the MA combat.

Or that could have been a wasted day out of my life........

[drgondog]

Do you think the 355 retained the the static angle of attack for the 301mph referenced speed while adjusting their patterning and reticle center at 250yd? I've looked at about 3 different static sighting setup pictures with P51D around the internet and all have the P51 with a slight down nose atitiude. Against the offline target 285 true was the speed at which the centerline of the engine stayed level with the centerline of the target. At 300 it was below or a nose down atitiude.

I compiled a list of true airspeeds offline for all of our fighters to keep the engine centerline, or on twins, fuselage centerline level with the offline target centerline. Wish I had a list of the factory speeds/nose atitiudes for those aircraft. It helped my sight picture quite alot at different ranges performing the testing to get all of those speeds against the offline target. Interesting the things you see during long drawn out testing you don't think about in the "seconds to react" sound and fury of the MA combat.

Or that could have been a wasted day out of my life........

I simply didn't know enough then to ask all the right questions but a couple of armorers are still alive in the 355th and i'll ask.

There isn't much of AoA for 301 mph TAS on the deck.

[bustr]

Wonder how much nose down tilt was perceivable in the real cockpit suring the war while firing?

[mtnman]

Wonder how much nose down tilt was perceivable in the real cockpit suring the war while firing?

I wouldn't think any.  For starters, they could just build the cockpit to have the seat and controls alignment "comfortable" at normal to high speeds.  We're only talking about a very few degrees of difference over a 200mph range.  I wouldn't think it'd be much more noticeable than driving a car up or down a very slight incline.  Maybe even less noticeable, since apparent gravity in the plane wouldn't be as constant as it is in a car.

Also, the engine isn't necessarily mounted "level" with the plane.  It would likely be tilted up or down a few degrees, and maybe even pointed a few degrees to one side or the other.

From what I saw in my P51 testing of a few days ago, 300mph or so is where the nose more-or-less stops dropping, regardless of how much faster than that you go.  If that's modeled somewhat close to a full-scale P51, I think I see why they chose 301mph (indicated) as the "critical" speed.  I'm not positive, but it looked pretty convincing in the TA...

What I found was that at speeds lower than 300 the nose was somewhat (or even quite a bit) elevated in level flight, but lowered as speed built and was "pretty dang level" at 300mph and up (indicated).  I wonder if the extra 1mph they list is just a way of saying >300mph?  Got me...

Also, 301mph indicated is right around top speed for the pony at 20k.

I tested both the P51B and the P51D with practically identical results, and I did it at 1K, 10K, and 20K alts.

It makes sense really, since the airspeed is measured by the air pressure against the pitot, and the air pressure is also what's dictating the AoA and speed required to maintain level flight at a given speed.  Of course at alt I was flying faster than 301mph (400+mph), but I was still doing 301 indicated.  The nose cannot just keep dropping as speed increases because it would eventually go into a negative AoA.  If it actually maintained level flight with a negative AoA there'd be something quite odd about the design.  Maybe with a flat-bottomed airfoil, high speed, and lots of down elevator trim or an incorrect wing incidence?  Even then I'd be surprised.

Also, I suspect that it would be fairly "odd" to do too much firing at the top-end speeds (much above 301 indicated).  It took full throttle and some time to achieve those speeds, and as soon as maneuvering begins you begin losing speed.

[mtnman]

I was always curious about this:

Did they actually have a 400+ yard range that they would align the guns and sights to, or did they basically just do the math to know where the guns should aim on a target that might be something like 100 yards away?

They could do it either way, and they did it both ways.

The guns could be bore sighted using the dimensions given in the diagram bustr posted. 

That was basically a target used to align the sight and gun bores at a target 1000 inches away.  That target may have actually pointed the bores at a mathematical point, or it could have had the trajectory mathematically factored in to those points, or it could have even been made up after live-fire sighting a planes guns in (by placing a blank target in front of the plane, sighting through the bores, and marking the target in order to more accurately bore sight future planes).  Regardless, to truly get the guns firing accurately they'd have needed some live firing and adjustment following bore sighting; bullets don't actually fly to the point the bore points.  They'll drop with gravity of course, but will also drift to one side (depending on which direction the rifling is cut).  Add in the other factors that effect bullet flight and it gets pretty easy to miss a 4' x8' sheet of plywood at 300yds with bore sighted guns.

[mtnman]

P51 in auto-level flight at 150mph indicated.  1K, 10K, 20K alt.  Note the high AoA due to the low speed.







@301mph indicated at 1K, 10K, 20K alt.  Note this is 411mph true at 20k.

[mtnman]

And at @350mph indicated...  Note that the nose doesn't drop much with this increase in speed.  Also note that although the aim-point doesn't a APPEAR to be much different, the center ring of the target is 20ft in diameter, so there's more difference than it appears at first glance.  Really just a tiny change in AoA though.

[bustr]

Would that mean the 5Mil+- nose down in response to firing the P51D guns when you test against the offline taget is not realistic? So then it isn't a factor in your aim while in MA combat ergo then was not a factor in the real WW2?

Remember when I tested all of the fighters in the game some time back with my Miltest gunsight on full zoom for dispersion patterning? Wing guns cause the nose to lower. Lavochkins raise up. Center nose mounted stay level. I beleive the 262 raises a bit due to the 4 MK108. You didn't give the range you set the target to. I'll have to duplicate it being equal to the width of the K14's reflector plate. I bet on full zoom the anglular mil math at 301 will show the K14 center to be near the manuals 32 inches above the fuslage reference line.

Looks like you use a 20Mil+- dot for your gunsight by eyeball guesstimation.