Acceleration rates

[Supreme_Warlord]

Hi,
I am doing some original fiction and need some help with figures. Does anybody know the rough ratio of the acceleration of fighters compared to air-to-air missiles? Any examples would be appreciated.

Thanks.

[Supreme_Warlord]

Apologies if this is in the wrong forum.

[Ted C]

Actually, since the SLAM forum is appropriate for discussing matters of real science, such as the acceleration of real-world aircraft and missiles.

One problem you'll run into, though, is that the faster a plane or missle goes, the more drag it experiences. Drag exerts force that opposes the thrust created by the plane's engines, and since all planes and missiles have a limit on thrust, their maximum acceleration will decline as their speed increases.

You can find thrust and weight specifications for many modern aircraft on line. An example follows:

http://www.af.mil/factsheets.asp

[Wicked Pilot]

Perhaps a better comparison would be a simple thrust to weight ratio for the plane and missile. This would not be dependent on airspeed. Getting the thrust to weight ratio for fighters would be very easy, but getting it for a missile may be a difficult find.

[Warspite]

There is also the problem that most AAM's, if not all, accelerate imediately after launch for a few seconds, and then coast towards their target on the impulse provided by that initial burst of aceleration. Either you'll have to use the specific impulse at launch, or the burn time, (both a function of the weigth of the propellant).

[Supreme_Warlord]

Thanks Wicked Pilot - wonders why I didn't thnk of that

Doing some research, I managed to dig up the following figures:

F-15 (C/D)
Maximum t/o weight: 68,000 pounds
Thrust: 46,900 (af.mil) / 50,000 (fas.org) - don't know which one is correct
Thrust-to-weight ratio: 0.69 / 0.74

AIM-120
Weight at launch: 335 pounds
Thrust: n/a
Thrust-to-weight ratio: n/a

Su-37
Maximum t/o weight: 74,956 pounds
Thrust: 61,710 pounds
Thrust-to-weight ratio: 0.82

AA-12
Weight at launch: 385.8 pounds
Thrust: n/a
Thrust-to-weight ratio: n/a

Does anyone have any figures for the thrust output of the air-to-air missiles?

Thanks.

[Ted C]

Does anyone have any figures for the thrust output of the air-to-air missiles?

Thrust values were listed as "classified" at the Air Force website.

[Wicked Pilot]

Does anyone have any figures for the thrust output of the air-to-air missiles?

I've looked, but have not found anything other than approximations for max speeds. It is possible that the info is classified.

[phongn]

A lot of the information on missile performance is classified.

[Supreme_Warlord]

A lot of the information on missile performance is classified.

In that case, anyone care to offer an informed guess on what the thrust-to-weight ratio of a standard medium range AAM (i.e. AIM-120/AA-12) should be?

Thanks.

[Supreme_Warlord]

Hi,
Been doing some more research and came across the following:

The multi-channel mobile S-300PMU (SA-10B 'Grumble') was designed by the Grushin and Rospletin OKB and entered service in 1985. The S-300 serves for covering cities and industrial installations from enemy air raids, defending stationary control posts located in tactical depth. The system has a short reaction time, high degree of automation, and high firing capabilities (3 seconds per launch). It can simultaneously track 9 targets and independently fire at 6 targets, one or two SAMs to each. The S-300PMU can hit targets flying at speeds of up to 10000 km/h at altitudes from 25 to 30000 meters and has a guaranteed effective range of 90 km.

The system consists of the 6AN6E 'Big Bird' phased array surveillance radar, the 36N6E 'Flop-Lid' phased array multi-function engagement radar capable of tracking stealth targets. The control post can manage up to 12 self-propelled launchers each carrying 4 SAMs. The 'Flap-Lid' radar rests on a single four-axle chassis with high off-road capabilities. The S-300 launches SAMs in the upright position, which enables it to fire at targets approaching from any direction. This gives the system big advantages in conditions of intensive maneuvering combat as this eliminates the necessity of turning the launchers beforehand to cover all directions.

The system employs the 48N6E SAM. It is a single-stage solid-propellant missile effective against any airborne targets (aircraft, helicopters, tactical and cruise missiles) at medium ranges in wide altitude limits. The 48N6E is fitted with a 143-kg blast-fragmentation warhead. The SAM blasts off upright from the launching container with a catapult to an altitude of 20-25 meters, then the rocket motor ignites. Blastoff acceleration may be as high as 100 Gs allowing the SAM to quickly pick up speed, which can reach 7500 km/h. In flight the 48N6E is controlled by exhaust deflector vanes and ailerons.

The S-300PMU employs inertial guidance in mid-course with commands from the 36N6E engagement radar and in the terminal phase semiactive track-via-missile mode. The 36N6E radar illuminates the target and the missile's onboard passive radar seeker receives a reflected signal. The SAM then relays this signal through an ECM-resistant data link to the control post computer. The control post then transmits control commands to the SAM. Such a method allows one to fit the 48N6E SAM with light and relatively cheap equipment and at the same time to use highperformance signal processing ground facilities.

Site reference

The S-300PMU2 Favorit variant is a new missile with larger warhead and better guidance with a range of 200 km, versus the 150 km of previous versions. Unveiled at the MAKS'97 exhibition in August 1997, it represents a thorough modification of the S-300PMU1. The first tests were performed on 10 August 1995 at the Kapustin Yar firing range. One new element is the entirely new 96L6E autonomous mobile radar, which works in conjunction with the 83M6E2 control post and S-300MPU2 launchers. The new 48N6E2 missile, developed by MKB Fakel, weighs 1,800 kg, and is 7.5 m long and 0.5 m in diameter. After a cold start in the upright position with help of a catapult, the 48N6E2 accelerates up to 1,900 m/s in 12 sec time, and then approaches the target from above. The 48N6E2 differs from the older 48N6E in having a new warhead specially designed for destroying ballistic missiles, with a warhead weight of 145 kg versus 70-100 kg.

Site reference

Assuming these figure are correct, can someone more mathematically able than me please derive a rough figure for the thrust of the rocket motor (in pounds)?

48N6 S-300PMU1 (SA-10)
Weight at launch: 3,968.3 pounds
Thrust: n/a
Thrust-to-weight ratio: n/a

Thanks.

[Darth Wong]

Blastoff acceleration may be as high as 100 Gs

This means that its thrust is roughly 100 times its mass. If its mass is (for example) 3000 lbs, then its thrust in open air must be 300,000 lbs (since Imperial units uses lbs for both force and mass; it's fucked up, I know). But blastoff acceleration is not open-air thrust; its thrust will be confined in the launcher and will have an extra propulsive effect due to pressure that does not apply once the missile is in open air.

The new 48N6E2 missile, developed by MKB Fakel, weighs 1,800 kg, and is 7.5 m long and 0.5 m in diameter. After a cold start in the upright position with help of a catapult, the 48N6E2 accelerates up to 1,900 m/s in 12 sec time, and then approaches the target from above.

In order to reach 1900 m/s in 12 s, you need a minimum acceleration of 1900/12 = 158 m/s^2 (obviously). That's roughly 16 G's, which (given the 1800kg mass) implies roughly 285 kN of thrust (around 63,000 lbs). It's probably higher because the acceleration curve won't be flat, and will be severely retarded by atmospheric drag at high speeds.

[Ted C]

Assuming these figure are correct, can someone more mathematically able than me please derive a rough figure for the thrust of the rocket motor (in pounds)?

48N6 S-300PMU1 (SA-10)
Weight at launch: 3,968.3 pounds
Thrust: n/a
Thrust-to-weight ratio: n/a

Lessee, accelerating to from 0 to 1900 km/s in 12 seconds yields nearly 160m/s^2 acceleration.

The rocket weighs almost 4000 lbs, which is 2500 kg, so the acceleration requires 396,000 N of force.

One pound is about 6.125 N, so the thrust is about 65,000 lbs.

That makes the thrust-to-weight ratio about 16-to-1.

The thrust-to-weight ratio of an F-15 is around 0.7-to-1.

[Supreme_Warlord]

This means that its thrust is roughly 100 times its mass. If its mass is (for example) 3000 lbs, then its thrust in open air must be 300,000 lbs ...

In order to reach 1900 m/s in 12 s, you need a minimum acceleration of 1900/12 = 158 m/s^2 (obviously). That's roughly 16 G's, which (given the 1800kg mass) implies roughly 285 kN of thrust (around 63,000 lbs). ...

I bow to the number crunching abilities of the Dark Lord. Seriously, now that you have explained it, it seems trivially simple, although when I first looked at the problem, it seemed indecipherable to me (like it was in another language). I have yet to deduce why I am so bad at maths.

Lessee, accelerating to from 0 to 1900 km/s in 12 seconds yields nearly 160m/s^2 acceleration.

The rocket weighs almost 4000 lbs, which is 2500 kg, so the acceleration requires 396,000 N of force.

One pound is about 6.125 N, so the thrust is about 65,000 lbs.

That makes the thrust-to-weight ratio about 16-to-1.

And a thank you to you as well for your kind help.

Thanks.

[Queeb Salaron]

In order to reach 1900 m/s in 12 s, you need a minimum acceleration of 1900/12 = 158 m/s^2 (obviously). That's roughly 16 G's, which (given the 1800kg mass) implies roughly 285 kN of thrust (around 63,000 lbs). It's probably higher because the acceleration curve won't be flat, and will be severely retarded by atmospheric drag at high speeds.

I should think that, because the missile is launched vertically, you'd also have to take into account that the thrust is probably much higher than can be emperically shown because the first half of the flight path fights gravity. Were this missile used as an air-to-air missile, for example, we might find that it had a higher thrust, even after taking into account air resistance and atmospheric pressure.

...Or I could be wrong...

[NapoleonGH]

Blastoff acceleration may be as high as 100 Gs

(since Imperial units uses lbs for both force and mass; it's fucked up, I know). [.

Im pretty sure by 100gs he meant 100 times the acceleration of gravity, so 100 * 10meters per second^2, aka 1000m/s^2

also i was not aware imperial units were different from the english (or standard) units (the ones used in the states) where mass is measured in slugs

[Darth Yoshi]

Slugs are the "proper" unit of mass in the Imperial system. However, practically noone except engineers even know what it is, so laypeople end up using lbs. for mass.