Forum: F-35 Lightning II

AIM-9 sidweinder has burn time of 4-5 seconds from the avaiable videos on the internet. A HUMRAAM burns for 7-8s (also avaiable on the net, AIM--120B's I think), considering latest variants it might reach 10 seconds, after that its a supersonic glider.

Pilotasso...

(2) What kind of Sidewinder is that described in the document? Early sidewinders have ranges of under 5km. Also, the thrust graph shows what is clearly a boost only motor, not a dual thrust boost-sustain motor.

(3) Another missile we have declassified info on is the AIM-54C Phoenix. This has an all boost motor with a 22 second burn.

(4) In any case, the point is that rocket propulsion is definitely -- without question -- capable of pushing a missile to Mach 4 in an air combat launch and keeping the missile above at high supersonic speeds for ranges far in excess of 20~30km as you had suggested. They do so by producing a lot less thrust during the sustainer burn compared to during the boost burn. Also, medium and long range AAMs tend to accelerate more slowly compared to short range ones.

(5) The way rockets work is that if I remove 1 second worth of thrust production at say 3000 lbs, I can produce 300 lbs of thrust for 10 seconds. How much is that? That is about a 1:1 thrust to weight ratio for a MRAAM.

(6) As far as the plume issue is concerned, what I was saying is that you may be seeing the boost grain's giant plume for 10 seconds and thinking that the motor has gone out when it switches to sustain burn. The motor may be producing 1/10th the initial thrust on sustain and the exhaust plume can be much much less pronounced and hard to spot -- especially with contemporary reduced smoke propellants.

5)Do you have any real figures to confirm this? AFAIK your just assuming this directly from your logic and kneepad assumptions. I highly doubt Sustained burn has so low thrust. It wouldnt do squat at low altitude resulting in a missile that falls short everytime, no mater how long sustained burn is. 1:1 T/W is just too litle you would better off to balance perfomance VS altitude with a pure boost mottor.
Boost is typicaly 2-4 seconds depending on the missile, the rest of the time is taken by sustained thrust, but never lasts more than the AIM-54, even if its pure boost.

6)All the time the plume should be visible, for the simple fact solid rocket motors fuels are nealry explosive and produce light wavelengths in the visible spectrum, even if the missiles are nearly smokeless (one doesnt imply the other though).

France wont change Raffale for F35.... ...would you change F35 for Raffale?

While, France may not want or need the Carrier Based F-35C. It could use the STOVL F-35B for Amphibious Ships............

While, France may not want or need the Carrier Based F-35C. It could use the STOVL F-35B for Amphibious Ships............

No, it could not : the top decks of our actual amphibious ships were not designed to sustain the effects of a VTOL aircraft engine (in order to save money, I guess). That is a frequently asked question on French forums, and the answer is a definite no.

Question: How much sustainer thrust is needed in an AAM like the AMRAAM?

Drag force (Newtons) = 0.5 x P x V^2 x Cd x A

P = Density of Air (kg/m^3) ; ~1.29 kg/m^3 @ sea level; ~0.232 kg/m^3 @ 12,000 m
V = Velocity (m/s) ; Mach 1 = 340 m/s @ sea level; ~295 m/s @ 12,000 m
Cd = Co-efficient of Drag ; ~ 0.6 to 0.95 for rockets depending mostly on finnage, nose and tail profile. For model rockets we typically use 0.75 Cd as a rough rule of thumb.
A = Sectional Area (m^2) ; ~ 0.025 m^2 for a 7" diameter missile.

Therefor, for an AMRAAM like AAM going at high altitudes (40,000 ft)

Drag Force @ Mach 4 = 0.5 x 0.232 x (295x4)^2 x 0.70 x 0.025 = 2827 Newtons = 636 lbs
Drag Force @ Mach 3 = 0.5 x 0.232 x (295x3)^2 x 0.70 x 0.025 = 1590 Newtons = 357 lbs
Drag Force @ Mach 2 = 0.5 x 0.232 x (295x2)^2 x 0.70 x 0.025 = 707 Newtons = 159 lbs
Drag Force @ Mach 1 = 0.5 x 0.232 x 295^2 x 0.70 x 0.025 = 177 Newtons = 39.8 lbs

It'll take approximately 500 lbs of thrust to sustain a velocity of Mach 3.5+ at high altitudes.

For a 335 lbs missile with a 40% fuel fraction and a 245 second specific impulse (about right for missile grade HTPB solid propellant). It can for instance use about 2/3 of its fuel on a 5 second boost @ ~4400 lbs of thrust 1/3 of that fuel for sustain burn @ 500 lbs thrust, it'll be able to sustain the requisite level of thrust for ~22 seconds. Using the classic Delta V equation:-

Delta V = 9.8 x IpSec x LN (Initial Mass / Final Mass) = 9.8 x 245 x LN (335/(335-90)) = 751 m/s = Mach 2.55

We'll correct it by a factor of ~0.9 to counter the fact that at Mach 4 about 16% of the thrust is simply to overcome drag, whereas at Mach 3 only 8% of the thrust is to over come drag and it falls to rather insignificant levels below that.

Mach 2.55 x 0.9 = Mach 2.3

Hence, the missile will attain about Mach 2.3 over launch speed or approximately Mach 4.1 on a Mach 1.8 dash release. It will then cruise at that speed for about 22 additional seconds on the sustainer before burning out. At 27 seconds after launch it'll become a gliding dart. At this point it'll be going about Mach 3.6 and about 30 km from the launch point. It'll be decelerating at a rate of about Mach 0.085 per second at Mach 3.6. This will decrease to a rate of Mach 0.059 per second as it crosses Mach 3 and further to Mach 0.026 per second as it passes through Mach 2. It'll take more than 40 seconds more to slow to Mach 2. At this point the missile is about 60~65km from the launch point.

Well, that explains why the Spanish BPE design won in Australia! No, offense but the lack of operating STOVL types has to be considered a shortcoming...................at least if France hopes to export the type?