HVAR recoil

I was wondering why the HVAR recoil behaves the way it does, pushing back on the wing fired from an down on the nose. This is the sort of behavior a cannon would exhibit. The rocket exhaust gasses don't push against the plane, only the air. Firing a free-hanging rocket should produce almost no recoil. Of anything, it would pull the wing forward slightly until the retention force of the rack was overcome.

I still think their would be some recoil as the rockets are fixed to the rails so they dont just slide off, so the initial thrust of the rocket motor would need to overcome the rocket holding mechanism, thus producing some sort of recoil.

How much recoil I couldnt say, but their must be some as the rockets are fixed/held in place so they dont slide off on takeoffs/landings and whilst in flight, so my guess is that the recoil is coming from the rocket retaining mechanism which would need to be A, broken by the thrust of the rocket motor and break at a given pressure or B, the rocket holding mechanism holds the rocket in place and a certain amount of thrust from the rocket motor is needed to make the rocket slide off the rail.

I think thats where the recoil would come from, but I am just thinking out aloud.

Just to add, huey pilots in vietnam said that if they fired all their rockets or a good few of them at once it felt like the helo went backwards 20 feet and stood still in the air for a few seconds.

So recoil is coming from somewhere, even today it still happens with aircraft.

Its cause the rockets dont exactly fire fast.unlike a Hellfire missle pod where they just insta poof. WW2 rockets burned slowly and had a excessive blast behind it,so the intial part of comming off the rail starts to pull the plane forwords(slightly) then when the blast wave of the rocket comming offf the rail hits the wing it pushes the plane back.

I still think their would be some recoil as the rockets are fixed to the rails so they dont just slide off, so the initial thrust of the rocket motor would need to overcome the rocket holding mechanism, thus producing some sort of recoil.

 

How much recoil I couldnt say, but their must be some as the rockets are fixed/held in place so they dont slide off on takeoffs/landings and whilst in flight, so my guess is that the recoil is coming from the rocket retaining mechanism which would need to be A, broken by the thrust of the rocket motor and break at a given pressure or B, the rocket holding mechanism holds the rocket in place and a certain amount of thrust from the rocket motor is needed to make the rocket slide off the rail.

 

I think thats where the recoil would come from, but I am just thinking out aloud.

 

Just to add, huey pilots in vietnam said that if they fired all their rockets or a good few of them at once it felt like the helo went backwards 20 feet and stood still in the air for a few seconds.

 

So recoil is coming from somewhere, even today it still happens with aircraft.

The thing is, the retaining mechanism holds the rocket fixed to the plane while it produces forward thrust. So whatever really happens, this at least can only "pull" the aircraft forward, but not produce recoil.

The DCS Huey showed in the beginning some quite pronounced "recoil" effect when firing rockets - up to the point where firing salvos was totally pointless as they would go all over the area due to the attitude change of the helo. There is a very length thread somewhere burried in the Huey sub-forum discussing this, including that story of the "felt 20ft displacement".

If there was 1 rocket on each wing and they both fired at the same time, would there be any recoil or just an extra speed boost?

If there was 1 rocket on each wing and they both fired at the same time, would there be any recoil or just an extra speed boost?

Who are you adressing with this question?

If it was me, then I don't really know - I know too less about the physics that might or might not play a role in here. But if we only look at the retaining mechanism, probably a very tiny speed boost would happen. But I doubt that it would be really noticable.

But an other thing worth considering perhaps: weight change and change of CoG. When the rocket comes off, the weight of the aircraft decreases and leads probably to more lift. Depending on a possible change of the center of gravity, an attitude change (which may or may not amplify the increased lift) may also happen. How much of this is applicable to the OPs question concerning the Mustang and HVARs .. I can't say, though.

Who are you adressing with this question?

 

If it was me, then I don't really know - I know too less about the physics that might or might not play a role in here. But if we only look at the retaining mechanism, probably a very tiny speed boost would happen. But I doubt that it would be really noticable.

 

But an other thing worth considering perhaps: weight change and change of CoG. When the rocket comes off, the weight of the aircraft decreases and leads probably to more lift. Depending on a possible change of the center of gravity, an attitude change (which may or may not amplify the increased lift) may also happen. How much of this is applicable to the OPs question concerning the Mustang and HVARs .. I can't say, though.

I wasn't really asking anyone just whoever felt like answering.) Thanks for the reply it's interesting to me, to know this things.)

But an other thing worth considering perhaps: weight change and change of CoG. When the rocket comes off, the weight of the aircraft decreases and leads probably to more lift. Depending on a possible change of the center of gravity, an attitude change (which may or may not amplify the increased lift) may also happen. How much of this is applicable to the OPs question concerning the Mustang and HVARs .. I can't say, though.

I've been musing over the OP's question and I came to the same thought as you: Fire off rockets -> less weight and shifting CG -> pitch change.

One would need to have a close look at the retaining mechanism to evaluate which pull/push forces apply during launch.

What is out of question, depending on their weight, you will loose some momentum due to less weight of the overall AC and thus decelerate a little bit while having a nose down attitude. This may not be noticeable at all as it is a rather slow working process compared to the launch of the HVAR. One would either also need to put the P-51 upside down on a cradle and check the CG before and after mounting/dismounting the HVAR(s) or have drawings for both that show CG and mount points so you can calculate yourself what will happen. Usually, if not always, the load is mounted so that it adds to the CG or forward of it, never ever after the CG if you can avoid it.

Assuming it's added right on the CG or slightly in front of it, you will get a more agile AC after launching/dropping the rockets. Usually, a plane becomes more tail heavy during flight with it's peak at touch down. All fuel cells are tailored to consume in such a way that your CG stays within limits but with the max CG aft in mind, you will add it forward in first place and such make it considerably nose heavy for lift off, way out of the dogfight range etc.. In flight, as you burn fuel and drop loads you get to the snappy point of the CG where the plane becomes responsive.

Always expect a shift to a more agile AC whenever you drop or burn anything as a general rule of thumb. The most snappy version of your AC is empty load out and 10% fuel, that would be very very close to the max aft CG that is human controllable. Now loose 2 cowlings in front and there you have your REAL snappy and AGILE AC, touch elevator and you look 90° up, thatÄs when it is called TAIL HEAVY.

I have flown a few models tail heavy, error by design and builder ( ME ) and I tell you, you only look at the stick with your eyes and it snap rolls. The only way to bring that thing down is by gentle throttle and a hopefully somewhat stable attitude of the AC wíthout any input other than throttle. Any modest aileron other than super soft will also result in a nice "UP WE GO".

The good thing about models is that we can experience things a RL pilot would not do willingly

or never talk about if done by purpose through misjudgment.

Bit

I still think their would be some recoil as the rockets are fixed to the rails so they dont just slide off, so the initial thrust of the rocket motor would need to overcome the rocket holding mechanism, thus producing some sort of recoil.

which would tug the wing forwards and up, not backwards and down.

Its cause the rockets dont exactly fire fast.unlike a Hellfire missle pod where they just insta poof. WW2 rockets burned slowly and had a excessive blast behind it,so the intial part of comming off the rail starts to pull the plane forwords(slightly) then when the blast wave of the rocket comming offf the rail hits the wing it pushes the plane back.

In addition to this, the rocket nozzle never points directly at the wing, and even if it did, the only portion of the wing directly exposed to the exhaust from the rocket would be the underside, which would kick the wing up, not down.

But an other thing worth considering perhaps: weight change and change of CoG. When the rocket comes off, the weight of the aircraft decreases and leads probably to more lift. Depending on a possible change of the center of gravity, an attitude change (which may or may not amplify the increased lift) may also happen. How much of this is applicable to the OPs question concerning the Mustang and HVARs .. I can't say, though.

The CG change is something that matters, and it would result in slightly more climb. But one rocket weighs very little, certainly less than a 1000-lb bomb, the release of which only produces a list of 5-10 degrees (if left uncorrected by the pilot.) The only effect firing an HVAR should have is a CG change which is less pronounced that the bomb release.

The excuse I tried to find to justify this "quite-not-reasonable-at-first-thought" behavior (that wasn't present in earlier versions), is that the exhaust gas from the rocket "pushes" on the leading edge of the wing and thus generating some backwards force.

EDIT: Only now I read the last posts on this thread.

From videos I saw I don't remember seeing any change of aircraft axis direction when launching rockets.

Yo-Yo, If it was that simple, there would be no recoilless rifles, RPGs or any handheld rocket launchers invented, because soldiers using them would not be able to fire without being thrown the other way :D.

Which brings me to conclusion that I wouldn't compare cardboard & dryer combo (negligible cardboard weight to dryer "thrust" ratio) to a 4-ton plane & a single HVAR combo (the other way around). I understand effect You're describing, but I doubt the scale of it is powerful enough to cause such a pronounced yaw of an airplane. At least you can't see it on old guncams with US and Brit planes launching different types of rockets.

Newton's third law FTW.

Thanks Yo-Yo, very interesting!

^ http://en.wikipedia.org/wiki/Recoilless_rifle

As far as RPG's...they do kick. It kicks like a 12 guage as does the M203 mounted to an M16. The LAW did not kick so much. The RPG kicks from the energy it takes to dislodge it from it's mount. The LAW pretty much just sat in a tube and was held in by snugly mounting into the tube, so the only energy taken by the person firing was the energy it took the rocket to dislodge from the tube. Needless to say, it wasn't much.

I imagine in my mind that this is how much recoil the pilot of a P-51 might feel from the cockpit. But it's not important to me, I don't mind the way DCS has it set up at all.

 

If you watched the guy from middle east shooting a RPG he did clean with a too short stick, from both ends. ( plugging it), you would know what the differense of recoilless means. The recoil you talk about is the pressure differense from exhaust leaving the tube, thats all.

The term 'recoiless' rifle, means it's not too hard recoil. Compared to the energy it produce.

Newton's third law FTW.

Yes, the rocket fuel burns into a hot gas, which is shaped by the rocket body into a rearward moving stream. The reaction to this is that the rocket is propelled forwards. At no point in this equation does the rocket push backward on the wing of the plane.

Not that I'm being argumentative and that I think this whole argument is really going anywhere but......I have never fired a recoiless rifle in my life, and I have fired a lot -o- weapons. The term recoiless does not mean there is no recoil, like the term silencer does not mean silence. The buffer spring absorbs the energy from the gasses moving and reduces the kick but it is anything but recoiless.

If you think that buffer springs and recoilless rifles belong in the same sentence, you need to do some more research before talking theory on this.

rockets overcame some (if not all) of the recoil problems associated with heavy calibre machine guns

Typhoons, 4 rockets seem to come out simultaneously from one wing (and I can't see if there are other 4 from the opposite wing). Absolute no recoil observed.

Symmetrical releases, flight path looks smooth.

Perhaps this is the reason why the were fired in pairs?