Bomb Fuses (research and issues)

[Avimimus]

Hello everyone,

 

It came to my attention that the 20lb Cooper bombs are taking too long to arm - so I made a mod:

 

It is a broader issue though - as the developers appear to be applying the default 'flight times to arm' for WWII bombs to WWI bombs... which means releasing very small bombs from relatively high altitudes where they are likely to be ineffective. Perhaps we could get official fixes if we can get enough reference information to submit!

 

So if anyone has data on WWI bomb arming mechanisms and flight times - it would be appreciated - both for the mod and for submission to the Flying Circus team.

[JG1_Vonrd]

I found this:

http://www.theaerodrome.com/forum/showthread.php?t=34737

 

I have no idea how much time since release it would take 25 revolutions to happen though.

[JG1_Vonrd]

Some color pictures here which show the spinning vanes (props). They look like pretty coarse pitch which means lower RPM:

 

http://www.wwi-models.org/Photos/Various/Bombs-brit/

 

Here's an old discussion from the ROF forum:

https://riseofflight.com/forum/topic/24335-bombs-ah-bombs/

 

I think the general consensus would be 50 ft or above in order to make the Coopers go boom.

[czech693]

I found that changing the Live Time reduced the arming time for the default (not contact) bomb fuse setting.  I got down to using fractions of a second.

 

 

[Avimimus]

54 minutes ago, JG1_Vonrd said:

Some color pictures here which show the spinning vanes (props). They look like pretty coarse pitch which means lower RPM:

 

Thanks! This is good work.

 

Usually a powered prop has coarser pitch at low speeds and finer/lower pitch at cruise speeds... but this is a very short diametre prop designed to pinwheel passively at relatively low airspeeds so the analogy might not work. Judging from the pictures the spinner has a radius of about 6.18 cm (assuming my measurements & maths is correct)... so we're talking aerodynamics closer to model aircraft.

 

Tom-Cundall cites a number of accounts of Camels seeking to release the bombs at 100 feet from the target, which works out to about 0.5 seconds of flight time. This would imply these props were able to pinwheel in excess of 1500 rpm (and if his reports of arming at over 50 feet are accurate then a value closer to 3000 rpm is likely).

 

This does get me thinking that - if we had the number of rotations for the French bombs arming mechanism - we might be able to do some aerodynamic analyses to infer the arming distance (if we can't find out the flight time or arming distance from historical sources). Also, if anyone happens to have an antique copy of one of these bombs/fuses on hand - do speak up! 

 

44 minutes ago, czech693 said:

I found that changing the Live Time reduced the arming time for the default (not contact) bomb fuse setting.  I got down to using fractions of a second.

 

Interesting! I believe that this value is actually used to determine how many second a weapon exists in the simulation after it has travelled 1000 metres from its point of release. If you had that working then it probably means that bombs always detonate prior to being 'culled' from the calculations. Essentially you'd be telling the simulation to remove the bomb early, and it would detonate the bomb first (thus overriding the minimum fusing distance). That is my initial theory at least... we'd have to test it.

 

The current mod (see link in the original post) modifies "FuseArmDelay"... which appears to be the minimum number of seconds of flight time for a contact fuse to arm (and might also apply to time delayed fuses which are less than five seconds - although this last inference is based only on experiences in the game and hasn't been tested rigorously to my knowledge).

[czech693]

I believe you are correct.  I never thought to look in ballistics.  So, I was working on the 112lb bomb.  Using your mod as a guide I looked at the 112lb bomb ballistics.  Its FuseArmDelay=-1.  What the heck does that mean time wise?

 

On further review I see that the original Cooper bomb had FuseArmDelay=-1.  I'm going to try 1.0 on the 112lb bomb and see if it arms quicker and can be dropped lower.

 

Okay, that worked.  You can drop them from 200 ft and they explode.  Below that they're duds.

Edited January 19, 2023 by czech693
New Info

[Avimimus]

56 minutes ago, czech693 said:

I believe you are correct.  I never thought to look in ballistics.  So, I was working on the 112lb bomb.  Using your mod as a guide I looked at the 112lb bomb ballistics.  Its FuseArmDelay=-1.  What the heck does that mean time wise?

 

Entering a negative value (or zero) causes the behaviour to revert to the default time-to-arm. A positive value overrides the default behaviour with the new value.

 

P.S. The text after the two forward slashes is a programmer's comment in Russian.

[czech693]

What do you think this HitDefaultDelay=2 might be doing?  Could that  be the default detonation fuse delay?

 

When I get a chance I'm going to try setting FuseArmDelay=1 and HitDefaultDelay=1 and see what happens.

Edited January 21, 2023 by czech693

[Avimimus]

3 hours ago, czech693 said:

What do you think this HitDefaultDelay=2 might be doing?  Could that  be the default detonation fuse delay?

 

When I get a chance I'm going to try setting FuseArmDelay=1 and HitDefaultDelay=1 and see what happens.

 

Sounds like it:

Задержка до взрыва после попадания бомбы = Delay before explosion after bomb hit

 

This could possibly allow a realistic 90 second delay for the special P.u.W. 50kg low level fuse.