Bomb aiming calculations

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46th_Terror
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Joined: 17 May 2004, 18:22
Location: North Carolina

Bomb aiming calculations

Post by 46th_Terror »

Is there a formula or a chart somewhere that tells you how to do the math for a bomb site adjustments. Eg at X speed and Y alt you set the lead angle to Z degrees? This would be for a munual site and not a computerised or assisted one.

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JJB17463rdBombGroup
Senior Master Sergeant
Posts: 2042
Joined: 24 May 2004, 22:28

Post by JJB17463rdBombGroup »

Here is what I wrote in Wikipedia on the article for the B17 Flying Fortress.
I wrote it just because someone didn't have it in the article.

"the B-17 and other bombers were able to accurately bomb from high altitudes by the use of the then-secret Norden Bombsight, which was an optical electro-mechanical gyro-stabilized computer. During daylight bombing missions and sorties, the device was able to determine, from variables input by the bombardier, the point in space at which the bomber's ordnance type should be released to hit the target. The bombardier essentially took over flight control of the aircraft during the bomb run, maintaining a level attitude during the final moments"

Check the links out of this article.
http://en.wikipedia.org/wiki/Norden_Bombsight
Be sure to check this link out.
http://www.aafcollection.info/

A/C or AC gave me this video on DVD which I have and which demonstrates its operation (Shows the computed drop angle to target).You might want this for your research.
http://www.shoestringprod.org/

The bombsight was an ANALOG computer which computed the calculations through gears which solved the ballistics differential equations.
Over 25 years ago I wrote in B.A.S.I.C. and later compiled for machine language a Amateur Rocket Ballistic Missile Trajectory program which uses the ballistics formulas but which is far more sophisticated as it also computes the variation in thrust parameters for various Rocket Motor(s),tilt,variations in drag,multistaging,change in gravitation,separate atmospheric models etc.
Basically I computed the trajectory at an interval of .02 seconds of time through millions of calculations or more.I would later use multi precision for this on another version of the program as to not introduce large errors.It could be interpolated at other units of time to obtain interpolation of results to far greater precision too.
It's very similar to the program in the Handbook of model rocketry but a lot more complicated(They left out some of the DARK SIDE purposes and formulae).That handbook would be VERY USEFULL for you for some of the physics.
If you want my program I could send it to you but I'd have to print it out again on an antique computer which I still have.I think I could print out an early version of it which I still have.
I do have some books on that matter too which demonstrate these formulas.If you would like them I'll reference their ISBN numbers and Title so you could perhaps find them in a library.I'm sorry but it has been over 23 years since I messed with this stuff and my programming skills are totally obsolete too.I did like programming a long time ago.

The missile or bombs ballistics drag of course varies at different velocities.
I've found the drag variations of the Mk82 body type online.
This variation is computed by wind tunnel studies.
I don't think the Norden or Sperry had this incorperated though.It probably used a simplified drag figure as in the Lord Rayleigh equation which would be iterated through an atmospheric model and the results transferred to analog gear form.It would be best to have the REAL engineering books on the Norden or Sperry.I don't know if these could be found.

You could start here and check out the links
http://en.wikipedia.org/wiki/Aerodynamic_drag
http://en.wikipedia.org/wiki/External_ballistics

Through programming you could emulate a ballistics computer though multiple iterations of those equations and add Norden input features.
Ideally it would be better to completely model the Norden or Sperry even with their faults.

I think the Norden transposed on gears emulating the Lord Rayleigh drag equation with Altitude,Speed functions with a simplified atmospheric model ( I see a couple of them in a Supersonic Aerodynamics and Rocket Propulsion book by Robert F. Lee from the ancient era of 1963) and a simple drag constant rather than a complicated variable drag body variation to compute the drop angle.Well this is my hypothesis on part of its working.

Only the Germans had a supersonic wind tunnel (simulated) for their A-4
(V-2) ballistic missile program during the war.The Germans always had great research on ballistic physics.
Son of a U.S.A.A.F. 15th Air Force 463rd bomb group 772nd squadron B17 pilot.
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Maenniskopesten
Airman First Class
Posts: 54
Joined: 21 Jan 2005, 05:19
Location: Germany
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Post by Maenniskopesten »

There's a programm on the german community website called: www.sturmovik.de
I've just downloaded a programm call "bombenrechner" (bombcalculator) you can put in speed and altituted and the bombenrechner will calculate the bombsight angle:

http://www.sturmovik.de/module/downtrac ... echner.rar

Höhe in Metern = Hight in meters
Geschwindigkeit in KmH = Speed in Kilometers p H
Bombervisier-Winkel = Bombsightangle

and then click "Berechnen" = Calculate

Hope it helps

Cheers
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JJB17463rdBombGroup
Senior Master Sergeant
Posts: 2042
Joined: 24 May 2004, 22:28

Post by JJB17463rdBombGroup »

Good job Maenniskopesten.That is a decent calculator.It would be best if it could be directly incorporated into the sights function graphically in the simulation.
Son of a U.S.A.A.F. 15th Air Force 463rd bomb group 772nd squadron B17 pilot.
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ROB - A2A
A2A Colonel
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Joined: 02 Mar 2004, 02:56

Post by ROB - A2A »

It would be more usefull to know the math behind...

BTW Does the calculator need IAS or TAS for the speed?

regards
ROB
A2A Simulations Inc.

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JJB17463rdBombGroup
Senior Master Sergeant
Posts: 2042
Joined: 24 May 2004, 22:28

Post by JJB17463rdBombGroup »

If you need the math(physics) a good tutor to start out on would be this book.
I don't know if its sold anymore though.It has algorithm flowcharts so you could use it to program in whatever language you want.
If you need anything guys I'd be happy to donate for the cause.
If you need the book or books just ask and I'll send it to you by mail.

Countdown: Skydiver,Rocket and Satellite Motion on Programmable Calculators by Robert Eisberg & Wendell Hyde
dilithium press,1979
ISBN: 0-918398-26-6
Library of Congress catalog card number : 78-24836

The Handbook of Model Rocketry is another good book for formulae for beginners at least the old one in 1980 was.
Once you delve into these algorithms you can add extra formulae in there to make them as complex as you want.

Here is another one I think.

http://www.automediabm.cz/pacific_fight ... able_2.zip

Here is a decent math links about falling bombs.The first book I mentioned is good though for beginners.

http://www.saltspring.com/brochmann/mat ... -1.00.html

Here are USAAF bomb types it doesn't go into extensive detail though.

http://www.303rdbg.com/bombs.html
Son of a U.S.A.A.F. 15th Air Force 463rd bomb group 772nd squadron B17 pilot.
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Maenniskopesten
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Posts: 54
Joined: 21 Jan 2005, 05:19
Location: Germany
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Post by Maenniskopesten »

As it works for Sturmovik I guess that it's TAS. About the Math's part behind it I can't help but I'll do a little researche over the weekend
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