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#44015 - 01/21/00 01:27 AM Guns Tutorial - Andy?  

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Hey Andy,

Firstly thanks for doing such a firsty rate tutorial.

Now the question i have is related to what you said about guns depression. Judging from Jane's F-15 (which i am currently flying) the gun cross is high (pure departure line), while the water mark sits lower, and the velocity vector below this.

I am a little confused by the sight line concept. Understandably there is a focal point, for the convergence of this and the gun line, but from the Jane's configuration the gun must be set to point high (as a function of lead); so why do this?
If the lines were parallel, what would be the short coming? (capability of predictor?)

Thanks

Zed

Inline advert (2nd and 3rd post)

#44016 - 01/21/00 01:48 AM Re: Guns Tutorial - Andy?  

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Err..i think i figured it; got to do with the pipper falling off the bottom of the gunsight.

Zed

#44017 - 01/21/00 02:42 AM Re: Guns Tutorial - Andy?  
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Zed

The F-15 (and the F-18) are unique examples. Their gun lines are actually above the longitudinal axis of the aircraft...about 2 degrees or so. This results in the gun line being above the flight path marker (velocity vector) in nearly all cases. Your analysis of the HUD symbology is correct.

This was done as an aid to A2A gunnery. The idea was that the F-15 would be able to achieve a tracking shot without having to get the nose out in front of the target so far...in effect, this gun installation allows a 'lag' type position and still have the pipper on the target.

This works OK for A2A, but for A2G, it is a nightmare. Now the situation is reversed. In order to get the gun pointed at the ground target, the F-15 must have its nose pointed below the target..in other words, the F-15 has to steepen its dive angle to get the pipper on the target. For low altitude strafing situations, this is pretty uncomfortable for the pilot!!

Glad you liked the article. Part Two is in draft and should be done by the end of the month.

Andy

#44018 - 01/21/00 03:11 AM Re: Guns Tutorial - Andy?  

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"This works OK for A2A, but for A2G, it is a nightmare"

...tell me about it! [Linked Image]

OK, thanks for that (piper won't drop off bottom of gunsight). About lateral harmonisation, there will be point at which the gun line will cross the longitudial axis of the a/c, so shouldn't this mean that the piper drifts from left to right as range closes? What distance is it currently harmonised to?

Thanks

Zed

...so thats why in F-15 when i put the pipper in the target and fire it doesn't hit! [Linked Image]

#44019 - 01/21/00 05:21 AM Re: Guns Tutorial - Andy?  
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>>so shouldn't this mean that the piper drifts from left to right as range closes? What distance is it currently harmonised to?<<

I see what you are getting at, but the sight is not designed to move sideways as a function of the gun line position (it will move sideways if the aircraft is yawed.).

The sight reticle always stays centered on the centerline if there are no forces to move it off. If we have a gun mounted on the right wing, and it is harmonized for 500', then we can expect the gun line to cross from right to left of the centerline at the 500' point. The pipper will also be at the 500' point. For ranges inside of 500' or past 500', the pilot must expect a slight sight error...but the error is small. Project that gun line out to 1000'. At that point, the gun line will be the same distance laterally from the centerline that it is at the wing of the aircraft. When you consider the dispersion of the gun, these distances are pretty small.

Andy


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