GBU-38/31 Flight dynamics

OK, I get what you're saying but just don't believe it would be 'that' difficult for ED. It's beyond my abilities but then again, I failed physics at college. Someone like Yoyo or Olgerd would surely be able to figure it out though?

Is a coasting missile not just steering towards its ballistic solution (whilst also gliding, and constantly calculating lead on a moving target)?

I'm not saying they aren't able to. I'm just saying that it is going to be a big project and they probably think that other things are more important right now.

Else we'd have it in our hands already. If i had to guess, i'm going to say that they are probably going to wait with financing such a feature until a fast mover comes along that can give a JDAM some real legs. The lobbing distance on the A-10 is just a joke, comparatively.

It's the same for missile guidance, basically. Those are really crude compared to real ones. The update has to happen at some point, the question is when do they see such a gain from implementing such a labour intensive feature that they will actually budget it inside a project?

Else we'd have it in our hands already. If i had to guess, i'm going to say that they are probably going to wait with financing such a feature until a fast mover comes along that can give a JDAM *some* legs. The lobbing distance on the A-10 is just a joke, comparatively.

That's my main issue with it at the moment, from what I've read the GBU-38 should have much more range than a GBU-12 or Mk82 because of the strakes that increase its lift and glide range and the ballistic guidance.

I understand the cost/benefit argument and realise there has to be a cut off point somewhere but man... I really want half decent JDAM's.

The JDAMs range comes from its efficient guidance (namely it doesn't expend energy for unneccessary maneuvers, it always tries to fly the energetically "optimal" path), but it needs speed. Note that the control surfaces on the LGBs are actually quite large (when summed up).

I just re-tested at 20,000ft with ballistic trajectory set for the GBU-12 and a maximum range shot with the GBU-38.

Here's a nice graph that demonstrates the difference in the flight model.

The GBU-38 did actually travel further but its terminal velocity seems waaaaaaay off.

I've also attached a Mk-82 vs GBU-38 Mach vs Time graph.

They were both dropped at 30,000ft.

The GBU-38's time of fall is more than double the Mk-82's and it impacts at Mach 0.3 vs Mach 1.1 for the '82.

Nice!

Only tells us something we already know, but still nice to see it. :)

Yeah, nice to see I'm not just going crazy thinking about how off the GBU 38s are.

The most startling difference to me is that after 30 seconds of freefall, the Mk-82 breaks the sound barrier and the GBU-38 has slowed down to Mach 0.5!

Where does terminal velocity appear?

Where does terminal velocity appear?

A Mk-84 dropped at Mach 0.78 from 45,000ft will fly 10nm and top out just under Mach 1.3 (in DCS anyway)

I can't test any higher/faster than that with the A-10!

Edit: Added Mk-82 for comparison - looks exactly the same

how did you managed .80 at 45000' with the A-10 ?!

how did you managed .80 at 45000' with the A-10 ?!

It's called the mission editor ;)

The engines cut out before I even dropped the bomb!

Even tuning the terminal velocity of the gbu-31/38 to a higher number would be enough at the moment and shouldn't be hard to do? :huh:

Couple of seconds can matter in the battlefield :smilewink:

Why DCS Downgradet the GBU ?

It make not sense that the GBU is downgradet in Range around 80% ?

a good test pilot is always in training

Thomas

It make not sense that the GBU is downgradet in Range around 80% ?

 

a good test pilot is always in training

Thomas

:huh:

Explain please.

Which GBU? What do you mean with "range"? And what was it before and what is it now? And why does that make no sense?

Then try release the JDAM at 25.000 feet 7 and 40.000 at 14 NM from targent and tell me if it work.

a good test pilot is always in training

Thomas

http://forums.eagle.ru/showthread.php?t=120924&highlight=gbu-38

http://forums.eagle.ru/showpost.php?p=2063567&postcount=13

Regards

Thanks, that say all what I think and found on my research flight.

a good test pilot is always in training

Thomas

Allright, GBU as in JDAM ... but "downgraded" in relation to what? There was no recent change afaik. Or do you mean downgraded in relation to the real weapon? Then yes, there are several aspects of JDAMs that do work differently than in reality.

Anyhow, I've set up a test flight starting at 40K ... and could not keep that altitude. How did you manage to test that?

But I was able to keep the A-10 at about 35K and got a good solution (GBU38) at around 5nm distance on the ground (at 300 kts over ground / 160 IAS). Where do your expectations for 14 nm come from btw?

Probably stuff like: http://en.wikipedia.org/wiki/Joint_Direct_Attack_Munition

Claims 15nm with an ER version being worked on with 80km range, triple that.

Probably stuff like: http://en.wikipedia.org/wiki/Joint_Direct_Attack_Munition

 

Claims 15nm with an ER version being worked on with 80km range, triple that.

But delivered from which aircraft? Probably not an A-10 ...?

I agree. With the higher speed and altitude delivery greater range can likely be achieved.

I don't know if the F-14B (if we should get a bombcat) or F/A-18C can drop bombs while supersonic, but even if not that's still a fair bit more speed than you can drop a bomb at in the A-10C and so it will be interesting how much additional range that brings.

Its a football that can alter its glide path dynamically, but can only go as far as the arm can throw it. Supersonic jets are much bigger arms.

Although faster a AV-8B can drop a GBU-12 around 10K feet at about 7-8NM. Im not saying thats max distance either.

With that said in my opinion the GBU-38 should have no problem doing the same. Also, programmable are impact angles. I.E. close to 90 degrees to mitigate collateral damage and desired tgt effects.

63

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.