May not be that mysterious after all.
readers will remember a couple of days ago when I put up my first post speculating about features seen on representations of a, I assume, proposed Lockheed Martin initiative: the 'CUDA' missile. I showed a 'rough estimate' of it's proportions and component locations IF the missile were truly "SDB-size".
It didn't take much research to come up with what I think is a highly-probable explanation for those 'mysterious' spots. I assume someone else has probably already figured out a likely explanation somewhere as well, and since I work long hours, they probably have already spilled the beans, but here comes my analysis anyway, with some weight and performance analysis thrown in to boot :
Kudos to Scott Lowther Who Was, at the Very Least, MOSTLY Right...
In his original post at the Unwanted Blog, Scott Lowther had speculated:"My guess would be that this might be a large number of small solid rocket divert motors designed to help pitch the missile hard over in order to nail incoming jinking missiles head-on".While I wouldn't rule out the capability to pitch the missile hard over to get 'incoming', I'm convinced the 'divert motors' idea is 'spot on' for the missile concept as shown. I believe that if the details are ever revealed, in retrospect, this feature is easy to explain.
Ockham's Razor
The spots are almost certainly Attitude Control Motors (ACMs). The design and placement are most suggestive of Lockheed Martin's PAC 3 Missile design:
I couldn't find a technical description of the PAC 3's ACMs, but did find a paper (source) that discussed the ERINT-1 missile's (from which the PAC 3 evolved) ACM installation:
I did manage to find a closeup of the PAC 3 ACM module being manufactured in a Lockheed Martin PAC-3 product brochure. It appears to be just as the one described in the ERINT-1 paper. :The ACS contains 180 solid propellant Attitude Control Motors (ACMs) that thrust perpendicular to the centerline of the missile to provide pitch and yaw control during the homing phase. The ACMs are spaced evenly around the centerline of the missile in rings containing 18 motors. There are 10 rings in the ACS in the longitudinal direction for a total of 180 motors. The ACMs are commanded by the Motor Fire Circuit (MFC).
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| I submit that the ACMs are what puts the 'Hit' in "Hit to Kill" for the CUDA design. |
Estimating CUDA Component Weights and Performance
[And remember, we're basing all this 'estimating' on a convention display model, vague comments, and a computer graphic!]The discovery of what the magic spots were all about greatly simplified some assumptions that needed to be made as to CUDA missile weights, which in turn can give us clues in estimating performance.
Rather than 'absolute' performance, I will be discussing the possible CUDA numbers in terms of relevance to AMRAAM performance. I'm doing this for a couple of reasons. First, there is an EXCELLENT discussion of air-launched missile performance in general and likely AMRAAM performance available as 'backgrounder' on a thread here. Second, the AMRAAM makes an excellent 'baseline' for comparative analysis.
Sizing the CUDA
If the CUDA is as it appears to be, it is just under half the length of the AMRAAM.
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| AMRAAM Profile Layed Over CUDA Graphic to Estimated Scale. (AMRAAM is white space INSIDE border shown) |
But the relative fractional composition of the CUDA and the AMRAAM are significantly different. The following shows the CUDA's estimated relative proportion to the AMRAAM.(Notes: 1. Length is in Inches, 2. Rocket Motor (RM) Length is without blast tubes that run through the rear control section. 3. RM% comparison indicates that percentage of length of the CUDA that is RM is 26% greater a proportion of overall length than the AMRAAMs % and 4. Estimated total volume is not including radome which is assumed to be mostly 'empty'.)
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| The CUDA estimate indicates a larger rocket Motor as a Percentage of total Length and Volume than the AMRAAM |
If we refer to the 'Delta V' formula at the thread I linked to above, and assume the CUDA uses the same rocket propellant mix that the AMRAAM does, we will find that the CUDA can weigh as much as 181 lbs, providing ~71.15 of the CUDA's 83.7 lb RM is propellant, to have an EQUAL top speed potential of the AMRAAM. As the discussion thread also notes, the AMRAAM isn't advertised to go as fast as the RM could carry it, because a percentage of propellant is reserved for a reduced 'sustainer boost'. This could also be true for the CUDA.
Depending upon how fast the CUDA decelerates due to drag after the RM burns out will determine what the actual range of the CUDA would be compared to the AMRAAM. Again, from the thread linked to above, we find:
Drag force (Newtons) = 0.5 x P x V^2 x Cd x AWe've reduced the variables for our comparison to Cd and A
P = Density of Air (kg/m^3)
V = Velocity (m/s)
Cd = Co-efficient of Drag ; ~ 0.6 to 0.95 for rockets depending mostly on finnage,
nose and tail profile
A = Sectional Area (m^2)
Since,
1. we've already established the fineness ratio for the CUDA concept shown is closer to the optimum '14' than the AMRAAM is in my earlier post, and
2. it appears the finnage and tail profile may be slightly higher drag features than the AMRAAM's (hard to tell, perhaps insignificantly so, or little better or worse either way), in all likelihood the Cd of the CUDA is approximately equal to the AMRAAM.
3. In any case, the 'A' of the CUDA is about 27% lower than the AMRAAM's which is definitely an advantage to the CUDA
We can reasonably conclude that the CUDA is a Medium Range Missile design, and approximate to the AMRAAM in range.
I like the idea of an F-35 carrying 8-12 of these suckers and I'd like to see this kind of missile come to fruition.
I'm MOST certain that if I missed anything on this late night exercise, SOMEONE will let me know. Did I mention we're basing all this 'estimating' on a convention display model, vague comments, and a computer graphic?
11 comments:
Just FYI LOSAT and CKEM also used a similar pattern of thrusters so LM definitely has a handle on the technology.
I am not sure of the physics involved for determining fin drag, but it seems to me that the fins on the CUDA are proportionally smaller than on the AMRAAM. This would also mean that they must work harder to control the direction of the CUDA.
IMHO this is the reason for the ACM. It was a tradeoff; less drag in flight thereby better range but still maintaining terminal HTK capabilities.
ACM is also going to be more effective than diverters on the CG as NCADE uses. Having the diverters up front means you can take advantage of atmospheric lift because you're change your AOA. The diverters on things like NCADE and KKVs simply "scoot" the vehicle side to side meaning they aren't going to have as much divert capability.
@SpudmanWP if they fins are proportionally smaller, why would they have to work any harder?
If they are smaller then it would take longer for a corrective action to take place. Think of a boat with a small tiller vs one with a large tiller.
On the NCADE thrusters: Couldn't they move the thrusters to a position just behind the seeker. Maybe mid-body is better for ABM work?
Hi Guys,
RE: Drag
I think wing and fin drag (or any drag for that matter) aren't truly understandable unless you do the CFD modeling and wind tunnel work first. I would say the CUDA concept has bigger wings proportionally than the AMRAAM, but 'eyeball engineering' the aft steerable fins, I can't really tell the difference there. I think the CUDA concept wings are optimized for LO and compact carriage, and low aspect wings on missiles have been known to be beneficial at high speeds since at least the 60s, so perhaps there's a 'speed' reason for the wings as well. The big unknown in estimating drag is how the concept is to be controlled. How the surfaces are used (and 'shaping'of the flyout) will determine how much total drag will limit range. Is it a Skid-to-turn, bank-to-turn, or 'rolling airframe' missile? I'd guess it is a more efficient, less reactive bank-to-turn design, and makes up the end-game disadvantage with that method with using the ACMs.
RE: LMs experience with ACMs. Their total experience struck me as impressive as well -particularly the use of ACMs on ever-smaller missiles.
A question on the warhead: could a gimbaled explosively formed projectile be a viable design for an A2A warhead? You would need a very HOB seeker and very quick gimbal actuators but it would let you get away with a much lighter warhead.
RE: EFP Warhead.
I don't know about viable, but it would be doable. The Navy took out a patent late 60s-early 70s where they had a warhead surrounded by detonators. Depending on wherethe target was in relation to the missile when it went by, the detonators would supposedly sequence to direct the blast in the right direction. I would doubt you'd want an EFP for air-to-air, as EFPs were conceived for cracking hard targets. EFP effectiveness is also very dependent on distance to target. Some anti-tank weapons use top-down attack with a WH that shoots downward over the target where the armor is ostensibly thinner among othrer things. I think your logic is sound concerning fractional explosive/shrapnel weight possibilities if you could direct damage where you wanted to, but the benefit may be eaten up by the structural, mechanical, and control system complexity added to steer and command the warhead. On an air-to-ground system, you could just fly the missile so it was a certain side up and send blast fragments and heat in the desired direction.
Focus-able warheads is something they are working on and have demonstrated already.
Thanks for the insights guys. The focus-able warhead that SpudmanWP links to strikes me as a variable direction shaped charge that relies on a cone of fragments rather than a condensed jet of plasma (or copper penetrator) to do the damage.
Do you guys have any links/insights on the seeker requirements for using focus-able warheads? Would laser proximity fusing be sufficient or would you need IIR or imaging radar?
I have no idea which fuzing would work best. I haven't thought much about it, but I suspect the really good info on that is classified or held-close proprietary
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