GBU-38/31 Flight dynamics

[Flagrum]

I am not sure where people in this thread are getting the idea it needs a high end-game velocity, and at the same time glides better... after all, gliding is going to slow it down vs free-fall. Aren't range and speed pretty much mutually exclusive for a gliding weapon?

 

With sufficient starting altitude and nosing over into freefall before hitting the target, it might be able to hit terminal velocity before impact, but a gliding weapon isn't going to hit terminal velocity *while it is gliding*

 

I am sure there are problems with range, probably due to the simplified guidance and afm, but the low terminal speed doesn't mean anything.

Huh? The more energy the weapon initially has, the farther it can glide, right? Less forward speed, less range (i.e. 0 forward speed = 0 range)

 

And the goal is not to reach terminal velocity, but maximum range ... so I don't understand what you are saying there.

 

Also, while a JDAM proably does not exactly follow a ballistic path when steering towards the target, it also does not really glide. At least that is probably not the main design goal of those tiny fins.

[fltsimbuff]

Huh? The more energy the weapon initially has, the farther it can glide, right? Less forward speed, less range (i.e. 0 forward speed = 0 range)

 

And the goal is not to reach terminal velocity, but maximum range ... so I don't understand what you are saying there.

 

Also, while a JDAM proably does not exactly follow a ballistic path when steering towards the target, it also does not really glide. At least that is probably not the main design goal of those tiny fins.

 

 

That's pretty much what I was saying. I see complaints a little earlier in this thread about how slow it is moving when it hits the target... It makes sense that it would be moving more slowly at impact than a bomb in free-fall that doesn't try to convert downward momentum to more horizontal travel.

[Flagrum]

That's pretty much what I was saying. I see complaints a little earlier in this thread about how slow it is moving when it hits the target... It makes sense that it would be moving more slowly at impact than a bomb in free-fall that doesn't try to convert downward momentum to more horizontal travel.

Ah, now I got it. There were threads merged - the first one about the speed, the second about the range. I didn't realize this at first and had only the range aspect in mind.

 

But for the speed argument, well, given an appropriate release altitude, the terminal velocity should not really differ much between a JDAM and an Iron Bomb, I think. I don't think that a JDAM trades anything for range - it does not really glide as the JDAM kit does not really generate significant lift. At least not in DCS where the trajectory does not really differ between both types. I rather believe that the terminal velocity predominantly depends on the drag - which should be comparable between a dumb bomb and a dumb bomb with a JDAM kit

[PFunk1606688187]

It makes sense that it would be moving more slowly at impact than a bomb in free-fall that doesn't try to convert downward momentum to more horizontal travel.

Not to the degree that its slower. How can a JDAM that uses a more efficient guidance system than the inefficient bang bang concept of the GBU-12 take longer to get to the same target than a GBU-12 pickled after it? Simple - by having a highly unrealistic flight model.

 

The JDAM we have doesn't even have good range to justify that reasoning.

[howie87]

Hi guys... Been a while since I commented on here but my original point was that the difference between the flight models of an iron bomb and that same bomb with a JDAM kit are completely enormous at the moment in DCS.

 

I appreciate the points about Max range being achieved by dropping from faster aircraft and I don't really have an issue with that.

 

The terminal velocity however is important as it heavily influences the time to impact and I don't believe the current differences in flight time we're seeing between JDAM bombs and iron bombs are in any way realistic.

 

In my opinion, simply increasing the terminal velocity of JDAMs would be a satisfactory solution and the best option short of rewriting the entire flight model.

Edited August 4, 2015 by howie87

[Aginor]

I'd like to come back to this topic and just ask the question whether ED is planning to change this behaviour in the next few months?

 

This problem will only become more severe with more weapons becoming available, for example with the F/A-18C module, like the GBU-32.

 

So I'd like to ask for at least changing the SFM parameters of the weapon to allow for a more realistic behaviour, but of course an AFM would be better.

 

 

...and now that I typed this I realize I haven't tested JDAMs in the last few versions. Was it changed already and I am making me look like the fool I may really be right now?

EDIT: Ok, checked in 1.5.3, still the same.

Edited March 4, 2016 by Aginor

[razo+r]

after 3 years, this flight model is still present in dcs...

 

can we hope for a fix?