Rocket recoil

[Suchacz]

Maybe dumb question, but...

 

What causes the rocket recoil force on the Huey? Is the rocket held for some time in the rack while it's motor is already burning? :huh:

[Irregular programming]

Physics :)

[Suchacz]

Physics :)

...oh come on. There are few things I know about how things behave in our world, aka Physics :smilewink:

 

What I wrote is the only explanation I can imagine.

 

If the rocket is at first unlocked and after that the rocket motor is ignited, there won't be any (or minimal) recoil, caused only maybe by the rail friction when leaving it.

 

...but if it is locked on the rail for some split of the second during motor ignition until it gains full power and after that it is unlocked and leaving the rack, then there can be some reacting force on the airframe. Edit: but this reacting force should cause some pendulum effect, which should push the COG of airframe forward.

 

That's what I'm asking about, is it as I wrote, or is there some other explanation of the rocket recoil?

Edited May 28, 2013 by Suchacz

[Sundowner.pl]

There is no locking mechanism per say - only friction. There should be no recoil, but a vibration caused by the imperfection of engine nozzle (the thrust vector is offset slightly from the rocket axis). There is also slight change of center of gravity height.

 

Nothing else, it is also strange to me that those rockets rock the airframe around like that. But on the other hand you can't physically fit Mk.66 rocket motor to a tube of M158 or M159 launcher either (not to expect it to reliably firing), so I treat the FFARs as pure fantasy item on the DCS: Huey.

 

http://youtu.be/qyBPsl3mxNA?t=1m6s

Edited May 28, 2013 by Sundowner.pl

[leobasil]

The exhaustion gasses hiting against the frame of the launcher

[Sundowner.pl]

Are negligible, its dispersed, slow, and low in mass. Plus most of the propellant is burned while the rocket is in the tube.

 

Edited May 28, 2013 by Sundowner.pl

[Griffin]

Does this happen in Black Shark too and other modules?

[Suchacz]

Does this happen in Black Shark too and other modules?

I didn't notice that, but even if the reaction force caused by rocket recoil is correct in its size and direction, it would be imho highly reduced due to BS's higher weight.

There is no locking mechanism per say - only friction.

If you are correct, the rocket motor should push the plane a little, until the forward force overcomes the initial friction between the rocket and the tube. The launcher tube is open on both sides, so there shouldn't exist any other force except the friction. Now the recoil feels like shooting big caliber gun.

 

I can compare it to the RPG-7, I shot it personaly during my army service. It has very little recoil. It's based on the same principle > 2:25

[Sundowner.pl]

The funny thing is, since the whole thing is from the "la-la-land" it's hard to apply real life knowledge to this.

 

Because we have Mk66 rocket motor, that was made to work with LWL launchers like the M260 and M261 (and LAU-68, etc.). Now, the Mk66 have a retainer groove, and the LWL launchers have a retainer that is overridden by the rocket kick at ignition - the retainer releases the rocket after a force is applied from 170-600 lbs.

 

Now the problem is, that we don't have the LWL launchers, we have the M158 and M159 - those don't have such retainers, and the rocket is pretty "loose" inside of the tube. Not only that, but the rocket could stick quite a bit out, because the Mk66 rocket motor is 2.4 inches longer than the Mk40, and the visual model on DCS huey is of M158/M159 launchers loaded with rockets with those shorter Mk40 motors.

 

You see the whole thing doesn't add up.

[Focha]

The funny thing is, since the whole thing is from the "la-la-land" it's hard to apply real life knowledge to this.

 

Because we have Mk66 rocket motor, that was made to work with LWL launchers like the M260 and M261 (and LAU-68, etc.). Now, the Mk66 have a retainer groove, and the LWL launchers have a retainer that is overridden by the rocket kick at ignition - the retainer releases the rocket after a force is applied from 170-600 lbs.

 

Now the problem is, that we don't have the LWL launchers, we have the M158 and M159 - those don't have such retainers, and the rocket is pretty "loose" inside of the tube. Not only that, but the rocket could stick quite a bit out, because the Mk66 rocket motor is 2.4 inches longer than the Mk40, and the visual model on DCS huey is of M158/M159 launchers loaded with rockets with those shorter Mk40 motors.

 

You see the whole thing doesn't add up.

 

Is it the final version of the DCS: Huey?

[Suchacz]

Is it the final version of the DCS: Huey?

It's irrelevant if it's final or not. We're discussing the current state.

[Sundowner.pl]

As far as armament goes ? Nobody said we'll get anything more than what we already have. maybe the XM60E1 pilot sight, maybe M130 countermeasures, maybe M23 pintle mounts for Slick, maybe the radio altimeter... and that's it, nobody said anything about properly modeling the FFARs.

 

And there is a lot to do to get them accurate - so far those are hand-me-downs from the A-10C with same bizarre choices in warheads: the Mk5 which was pretty unique (only Navy had them), already outdated, and not fielded during Vietnam conflict, and no M247, which replaced it and was widely spread throughout late 70's and 80's, and still in US Army and National Guard inventory.

Edited May 28, 2013 by Sundowner.pl

[Fuzzy_bear]

On a personal observation...When firing the rockets or guns the apparent "recoil effect" is more a result of "stick twitch" for me than actual recoil effect. I find that I sometimes(ok always) get a bit over excited on a rocket strafe run and yank the trigger instead of squeezing... usually also makes for very lousy accuracy.

[159th_Falcon]

Its quite easy, rocket recoill is a bug, and should be resolved / changed.

 

I simply refuse to believe that a pair of rockets can initiate a several degree pitch change by firing them.

 

Don't forget there trying to move a helicopter that weights multiple tons.

 

Then there is the fact that the rocket pods are open on both sides, so the propellant from the rocket is not hitting any significant surface that would then create a force on the helicopters airframe.

 

The only thing transmitting any kind of force from the rocket motor to the airframe would be whatever device is holding the rocket in place during flight.

 

This device would obviously be designed to fail/move out of the way when the motor ignites.

So, what's causing this sudden and violent change in pitch?

 

And what's the reason we don't see it on the blackshark? which can fire far bigger rockets.

 

Would be nice if someone from belsimtek could jump in and explain a thing or two.

[Suchacz]

The only thing transmitting any kind of force from the rocket motor to the airframe would be whatever device is holding the rocket in place during flight.

If it fails to release the rocket and if the whole propellant burnt inside the rack, then the nose should be forced to go UP, not down!

Edited May 28, 2013 by Suchacz

[ericoh]

It "recoils" because the nozzle pressure hits the rocket pod when leaving it.

[Suchacz]

It "recoils" because the nozzle pressure hits the rocket pod when leaving it.

...see post #5 and #6

[Sundowner.pl]

Ericoh, we're talking about M158A1 rocket pod... its 7 2mm thick tubes, with two clamps in the middle... there is simply nothing to push against ! The frontal area of that rocket pod where exhaust gases are pushing is 3,16e^-3 m^2... that's less than a shoe polish can. Those are gases, low in mass, dispersed, and deccelerating rapidly after leaving the nozzle.

 

Anyway:

 

Kiowa:

UH-1N:

Apache:

http://youtu.be/uz4yxYJ1gvk?t=54s

Tiger:

Bell 407AH:

 

Now Mk40s.

UH-1B:

Edited May 28, 2013 by Sundowner.pl

[Weta43]

The frontal area of that rocket pod where exhaust gases are pushing is 3,16e^-3 m^2... that's less than a shoe polish can.

 

True when you fire the last rocket.

Not true when you fire the first.

 

When you fire the first, all the tubes but one are blanked off, and so there's a relatively large area for any exhaust gasses to act on.

 

 

Not commenting on the recoil question, just your estimate of the frontal area being 31cm^2

[Sundowner.pl]

Would be relevant if we would see any difference between first fired rocket, and the last - but we don't. Now I took the Mk66 rocket motor data, and did some worst case scenario numbers crunching on it, giving its specific impulse, acceleration, amount of propellant - the highest number you could achieve of the gases transmitting all of their kinetic energy on the launcher is 5,7N... in real world it's way less - as the propellant is not transferred in 100% to gas in the specified burn time, the exhaust gases disperse more than in the nozzle cone angle, etc. etc. So I'm estimating that number is at least 4 times greater than achievable in reality.

 

And still 5,7N is 2550 times less than that of both minigun firing.

 

So no, those exhaust gases can't react with a force enough to change that helicopter's pitch.

Edited May 28, 2013 by Sundowner.pl

[AlphaOneSix]

Firing rockets from a helicopter is, for all intents and purposes, recoilless. Certainly not enough to affect the airframe in any noticeable manner.

 

A better Apache rocket demo, imo:

 

Kiowa: http://youtu.be/dY34ZIBKybM

Edited May 28, 2013 by AlphaOneSix

[Suchacz]

Seems to me, that guys from BST added rocket recoil for some purpose, it's even mentioned in training mission. :huh:

[159th_Falcon]

In that case i am VERY curious on there thinking behind it.

And if there gonna fix it for the final release, which they should. IMHO

 

***EDIT***

From manual page 132;

 

When firing the M134 miniguns in STOW mode or 2.75 rockets while
continuing to manually fly the helicopter, a slight recoil force (70 kg) will
produce a pitching down tendency. For long bursts, anticipate the recoil by
aiming 0,5..1 pipper widths ABOVE the target.

So the same recoil force affects both the miniguns and the rocket pods.

Though in the simulation the recoil of the miniguns is not or barely noticeable.

 

And that's all mentioned about it in the manual.

 

Anyone from Belsimtek can clarify things? Please...

Edited May 28, 2013 by 159th_Falcon

[PilotMi8]

Bell 407AH:

guys! Maybe we can calculate not very accurately, however:

1) When you shoot one or two rockets really not visible recoil

2) Also, when you look from the side - not visible recoil

3) But, if you look closely at the video

after 1.50 to 1.59, which shows the pilots in the cockpit, it is clearly seen that even while firing two rockets helicopter shakes.

Finally, when I have employ rockets with a MI-8 in salvo 32 (8 from each launcher), the 11 tonn Mi-8 had reduced speed at 200 km / h to 180 ... 185 km / h, the direction of flight changed by about 10 degrees, and the pitch helicopter (nose) had gone up to about 5 degrees.

Maybe launch a 70-mm rockets from the XM158 or XM159 associated with less recoil, maybe...And it can be configured easily, but need information from practice. This information must be much more accurate than the video shown here (ie in numbers).

PS more, pay attention, how to construct the rear side of the launcher (see att.)

[SimFreak]

Mi8 answered here in russian...

 

http://forums.eagle.ru/showpost.php?p=1770243&postcount=1692

 

edit. sniped!