Finally had a chance to do some testing on the illumination flares. I have to admit I really geeked out on this one but in the end, I think we'll have some new stuff to add to our TTPs with respect to illumination rockets.
SUU-25 Flare Dispenser:
- Holds 8 x LUU-2 Illumination Flares
- Dropped via manual release. Flare dispenses immediately and activates.
- DSMS / Inventory settings of FF Dist and Height Over Target (HOT) have no affect on operation
M257 Illumination Rocket:
- Each rocket pod holds 7 x M257 rockets
- When rocket is fired, it flies for 17 seconds then releases a LUU-2 Flare which activates immediately
- Like the SUU-25, DSMS settings have no impact
- During the 17 sec TOF, the rocket travels 4.6 NM. Altitude, airpseed, or pitch (0 to 20 degrees up) have little to no impact on the distance flown prior to activation
- Winds have little marginal impact on the rocket but significant impact on the flare once deployed
LUU-2 Flares: *Note, this applies to both the SUU-25 and the M257*
- Flare has a rate of fall (ROF) of 11.5 ft/sec. Altitude has little to no impact on ROF.
- Flares burn for 300 seconds, or 5 minutes
- Given the above numbers, this equates to 3450 feet of drop while the flare is providing illumination
- At 4000 feet AGL, there is minimal illumination by the flare
- At 3500 feet AGL, there is good illumination by the flare
- At 3000 feet AGL and below, there is exceptional illumination by the flare
- Given the above illumination characteristics, 3500' AGL is the optimal activation altitude. Combined with the burn time/ROF information, flares deployed above 3500' AGL will burn out prior reaching the ground so there is no benefit to using them higher.
- Flare drift is significantly impact by winds as the flare travels with the same direction and velocity as the wind. (See table below)
Tactics, Techniques, Procedures Discussion (The so what of it all)
The goal is to ensure we provide illumination over the target. To do this we have to solve a lateral location and a vertical location where we want the flare to activate.
Vertical Placement of Flares:
Optimal flare activation is at 3500 feet AGL as determined above. For SUU-25 dispensing, simply "pickle" at 3600 feet AGL (100 above to account for initial stabilization under the chute). For M257, its a bit more complicated as we are launching a rocket that will follow a ballistic path for 17 seconds before activating the flare. In table 1, I've developed a rule of thumb (ROT) that uses your TVV vs altitude gained or lost. For example, if you are LOWAT at 200 AGL when launching, you will want to pitch up to about 12 degrees nose up to have the flare activate at 3500' AGL. In another example, if you were at 10,000' AGL (High Altitude), you would want to pitch down to -10 degrees TVV.
Table 1
Lateral Placement of Flares:
Given that the LUU-2 flare drifts with the wind, we need to place the flare upwind of the target so that as it drifts down, it illuminates the target as long as possible. If we can place the flare where its directly overhead the target after half its burn time has expired, we can maximize its usefulness. Table 2 shows how much a LUU-2 will drift for a given wind speed. So given a 20 knot wind, the LUU-2 will drift 10.3 meters every second, 618 meters every minute, 3090 meters over its 5 min burn. At the halfway point, it will have drifted 1545 meters or 0.83 NM. So all we need to do is have the flare activate 0.83 NM upwind of the target. Again, SUU-25 is relatively easy, simply fly to an offset 0.83 up wind and dispense.
For the M257, we have to apply some math and Kentucky windage. For headwind simply adjust by the 2.5 min drift distance (yellow column in Table 2) closer to the target. For example, given our 20 knot wind, I would fly into the wind at the target and release the rocket at 3.8 nm from the target (4.6 nm rocket - 0.83 nm drift). If it were a tailwind, I'd do the opposite and release 5.4 nm from the target (4.6 nm rocket + 0.83 nm drift). If only we always had head or tail winds...We don't so we have to have a way to deal with crosswinds.
I'll spare y'all the math but using the good old 60-to-1 rule, we can determine how many degrees left or right I need to compensate for a given windspeed. Using our trusty old 20 knot wind again, this time a direct cross, we can see from table 2 that we need to turn into the wind 11 degrees to get our flare on the upwind side. But I'll be damned if Pythagoras didn't make it so we also have to adjust our range to target when we launch otherwise we'll come up short. So again in table 2, we can see that not only do we turn 11 degrees into the wind but we launch at 4.5 nm from the target.
Table 2
Figure 1
But, what if we have wind that isn't a head/tail wind or a direct cross....
Well, you've got to improvise. If its 45 degrees off, take about half the range correction and half the turn correction. Or just wing it. All you really need to know is this:
The TL, DR
- For M257, figure out what altitude your launching from (relative to target elevation) and determine what pitch you need to put the flare at 3500' AGL (table 1).
- The M257 rocket flies 4.6 NM before dispensing the LUU-2.
- The flare will drift about 0.8 NM per 10 knots of wind during its fall. Use half that distance to put it upwind.
Reply With Quote
