Bullets from a Jet Fighter Mach 3.2

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In summary, the conversation discusses the relative speed of different projectiles and how it is affected by the speed of the aircraft they are fired from. The topic of friction and pressure on bullets at high speeds is also brought up, along with some stories and speculations about firing guns at Mach 3+.
  • #1
OSHP295
:confused: A gentlemen on another site, not related to physics stated the following:

[moderator removed personal information of third: indeed something that is inappropriate without consent]

Bullet speed is relative. A .22 long rifle compared to the .22-250 is a great example. The SR-71 Blackbird aircraft was surreptitiously as the YF-12A fighter airplane until they realized that, at speed, the YF-12A was flying faster than the machine gun bullets it fired and that they would actually explode inside the gun magazine if fired.

This particular rocket, accelerated after it passes the hold of Earth's gravity can attain and maintain a speed of 47,000 miles per hour, yet light travels at a speed of 186,000 miles PER SECOND. Doesn't seem very fast when compared to the grand scheme of things, does it.

My theory, using my very limited knowledge of physics is: If an aircraft is flying at Mach 3, the weapons in the aircraft, are also moving at Mach 3 until they are fired. When they are fired, the speed of the bullets or projectiles would be Mach 3 plus the speed of the bullet upon firing.

Thanks in advance, Bill
 
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  • #2
First of all, please remove personal information from your thread, especially if it's not your own information.

Velocities add up at such low speeds << speed of light. The bullet out of the airplane would have been ejected at the speed of the aircraft in addition to the normal ejection speed of the bullet. What I SUSPECT is that a bullet fired at such a speed (Mach 3.2 + probably a few thousand FPS) directly into the atmosphere would create tremendous friction and possibly destroy the barrel as it is going down it. If you'll notice the space shuttle's re-entry into the atmosphere, you'll see the enermous frictional energy being created when that baby hits the atmosphere. The friction might have caused some sort of barrel deformation once it was fired and on its way down the barrel.
 
  • #3
There would be higher pressure in front of the bullet, but it would be negligible compared to the pressure behind it. For all intents and purposes, such a bullet would be unaffected by the speed of the aircraft until after it was fired.
 
  • #4
I have never heard of a gun being tried on a YF-12. The only armament that I knew of tested on that airframe was a missile. The Falcon IIRC. The story reeks of folklore to me. Why anyone would think of trying to fire a cannon at M3+ is beyond me.
 
  • #5
OSHP295 said:
My theory, using my very limited knowledge of physics is: If an aircraft is flying at Mach 3, the weapons in the aircraft, are also moving at Mach 3 until they are fired. When they are fired, the speed of the bullets or projectiles would be Mach 3 plus the speed of the bullet upon firing.

Yes, that's correct. Since the bullet, and the air in the barrel of the gun already has the speed of the gun, how fast the airplane is flying has nothing to do with the bullet moving through the barrel of the gun. (And it certainly won't "explode inside the gun magazine"! A bullet can't even be fired while it still inside the magazine!)

I have, long ago, heard stories about a jet fighter firing a bullet, speeding up, and getting hit by its own bullet but that might be also be "urban legend".
 
  • #6
Nerp --- early '50s, gunnery exercise shooting in a climb at a drone, or towed sleeve, nose down, throttle open, and the poor sap flew right into his own 20mm as they dropped on the far side of the parabola.

He made it, the plane didn't.
 
  • #7
HallsofIvy said:
I have, long ago, heard stories about a jet fighter firing a bullet, speeding up, and getting hit by its own bullet but that might be also be "urban legend".
I recall the F-86 Sabres (the first planes to unofficially encounter the sound barrier) had this problem. They'd go into a dive, aiming their guns at ground targets, manage to outrun their own bullets in the dive, and then when they pulled out, get hit.

I confess, I have no credible source, and to be honest can't be sure I am not subject to urban legend myself.
 
  • #8
FredGarvin said:
The story reeks of folklore to me. Why anyone would think of trying to fire a cannon at M3+ is beyond me.
Aw, c'mon Fred. Mach3 dogfights are pretty common these days. They have to use full flaps to turn at 9g, of course, but going to guns at M3 has been a Top Gun tactic for a while now. :uhh:
 
  • #9
FredGarvin said:
I have never heard of a gun being tried on a YF-12. The only armament that I knew of tested on that airframe was a missile. The Falcon IIRC. The story reeks of folklore to me. Why anyone would think of trying to fire a cannon at M3+ is beyond me.
I was going to let that part go - [for OSHP295:] the YF-12 wasn't going to be a fighter, it was going to be an interceptor. Interceptors fire missiles and take out targets at long range while fighters fire missiles or guns and engage in dogfights at shorter range. With a turning radius on the order of 100 miles at mach 3.2, the F-12 would have had somewhat limited dogfighting capability... :uhh:

Regardless, if you did want to fire a gun from it, it wouldn't be a big deal.
 
  • #10
berkeman said:
Aw, c'mon Fred. Mach3 dogfights are pretty common these days. They have to use full flaps to turn at 9g, of course, but going to guns at M3 has been a Top Gun tactic for a while now. :uhh:
You're right. If Tom Cruise could do it...
 
  • #11
FredGarvin said:
You're right. If Tom Cruise could do it...

The Navy's F-14 Tomcat is listed as a Mach 2 aircraft, not Mach 3. The same applies to the Air Force F-15 Eagle. The old P-58 Hustler and XB-70 Valkyrie were Mach 3. But because of it's fixed intake geometry, the F-22 Raptor has a top speed of about Mach 2.4. I don't know of any currently commissioned or planned aircraft capable of Mach 3 flight. At least, not any that they'd let me hear about.

I have two questions about cannon fire at such high speeds. In the case of the SR-71 Blackbird (same airframe as the YF-12), managing the shock waves was an important consideration. Would cannon fire generate additional shock waves that would give the aircraft problems to fly through? Secondly, would the unpowered bullets be subject to drastic reduction in velocity due to friction, so that the plane would fly (straight line) into them, basically overtaking them and possibly sucking then into the engines. I sould see somethig like that happenig and spoiling the pilot's day.
 
  • #12
Overtaking and getting hit by your own bullets is equivalent to the poodle in the microwave tale. Bar talk. You would need to go into a ballistic (zero g) trajectory to accomplish that, since the bullets drop down in relation to your own flight path (or above you, should you happen to push negative g, very very hypothetically)) However getting into your own ricochets is a rather high risk in air to ground strafing. So remember guys, pull nose up 4-5 g, maintain g and always break away when level.

Ah I can still do it
 
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  • #13
Andre said:
Overtaking and getting hit by your own bullets is equivalent to the poodle in the microwave tale. You would need to go into a ballistic (zero g) trajectory to accomplish that
Not if the bullets are caught up to so quickly due to drag than they only fall a short distance. Also bullets do "glide", a bit, decreasing the rate of fall, once they start falling, there's an angle of attack, because the spin rate is enough to reduce the downwards pitch reaction of the bullet as it falls. (This also answers the question about which falls faster, a dropped or fired bullet, the dropped bullet hits the ground first unless the bullet was fired in a vacuum on a flat earth).

Regarding high-g maneuvers, I don't think there's any human driven aircraft that can pull high-g turns while going supersonic. Either they use their missles (which is most of the time), or they go sub-sonic for dog-fighting manevers.

The only 9-g aircraft so far is the F-16, which tilts it's seat backwards about 30 degrees to allow the pilot to do this without passing out. I'm pretty sure flaps aren't used to do this as it would add too much drag. I've personally seen high g turns in F-16's and F-18's from directly below during air shows,and the angle of attack to do this is huge, and requires full after-burners just to maintain speed to overcome the drag. (Note, it's also very loud, bring earplugs).

Missles have no problem pulling very high g's though. The most awesome missles were/are the anti-ballistic missles that launched at very high g's in order to intercept an incoming missle as quick as possible.
 
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  • #14
Highest g's of a land based vehicle during launch is a rocket sled, over 150 g's during the last stage of this one, the stop was even quicker (it ran into a solid barrier at 6000+mph). Took about 6 seconds to go from 0 to over 6000mph, a small fraction of a second to go back to 0mph.

Info and video on this web page (this website is hard to find):

Click on the picture, to see the video. Note how long and narrow the rocket flame gets near the end of the run.

http://www.46tg.af.mil/world_record.htm [Broken]

Cool pic of a smaller rocket sled at 4800ft/sec.

http://www.meggaflash.com/rocket%20photographed%20using%20PF310%20flashbulbs.htm [Broken]

One of many articles:

http://www.rdecom.army.mil/rdemagazine/200401/itl_amrdec_roadrunner.html [Broken]
 
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  • #15
The only 9-g aircraft so far is the F-16, which tilts it's seat backwards about 30 degrees to allow the pilot to do this without passing out.

No the seat is tilted for design, to allow it to be fit in a smaller cockpit. the g part is a selling story. Actually you're not inclined to sit back at all during flying. Probably psychologic, you seem to loose eagerness and agility when leaning back. Moreover you cannot reach several controls on the front panel and you have to adjust the seat pretty high to look through the head up display.

I'm pretty sure flaps aren't used to do this as it would add too much drag.

Wrong again. The flapperons and leading edge flaps are essential in getting the lift required to attin the g. There is no flap control in the cockpit though. All automatic - fly by wire computer work.
 
  • #16
I could use some better figures, but if the shell was made out of lead, was 6 inches long, and was fired at 3x the speed of sound at sea level, it could de-accelerate at around 25 g's as soon as it left the barrel.

Unfortunately I think the actual cannon shells are HE so they probably aren't as dense as lead, and planes generally don't fly at sea level, and I really don't know how long the cannon shells are.

Here are the formulas I used

[tex]
\mathrm{Drag}=.5 \rho_{air} A v^2 C_d
[/tex]
[tex]
\mathrm{Mass of bullet}= \rho_{bullet} A L
[/tex]
[tex]
a = \frac{\mathrm{Drag}}{\mathrm{mass}} = .5 C_d \left( \frac{v^2}{L} \right) \left( \frac{\rho_{air}}{\rho_{bullet}} \right)
[/tex]

The [itex]\rho[/itex] are the densities of the air and bullet, [itex]C_d[/itex] is the drag coefficient and should be about .7 or so for a hypersonic blunt cone, A is the cross section of the bullet and L is its length. The mass of the bullet is slightly overestimated by area*length because it's not a cylinder.
 
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  • #17
Bob3141592 said:
The Navy's F-14 Tomcat is listed as a Mach 2 aircraft, not Mach 3. The same applies to the Air Force F-15 Eagle. The old P-58 Hustler and XB-70 Valkyrie were Mach 3. But because of it's fixed intake geometry, the F-22 Raptor has a top speed of about Mach 2.4. I don't know of any currently commissioned or planned aircraft capable of Mach 3 flight. At least, not any that they'd let me hear about.
I have two questions about cannon fire at such high speeds. In the case of the SR-71 Blackbird (same airframe as the YF-12), managing the shock waves was an important consideration. Would cannon fire generate additional shock waves that would give the aircraft problems to fly through? Secondly, would the unpowered bullets be subject to drastic reduction in velocity due to friction, so that the plane would fly (straight line) into them, basically overtaking them and possibly sucking then into the engines. I sould see somethig like that happenig and spoiling the pilot's day.
It is a B-58 Hustler. And yes I know about the other aircraft. We were joking around about top gun stuff. The point being that even if you could get the physics around firing a cannon at that high of speed to work out, it's not practical because of the close proximity that one has to be to use it. At M=3 you are not going to do much of any kind of turning and you would have absolutely no time since the rate of closure on a target would be huge.

The cannon won't effect the aircraft in terms of shockwaves like that. The main thing that we have no idea on is the aerodynamics of the shells at that speed. The speed at the time of firing is relative, so at that point in time it doesn't matter if the aircraft is moving or going that fast. The point of interest is when that shell hits the free stream and loses any effects of being in the barrel. My take would be that the shell had better be supersonic itself (relative to the barrel) or the ram pressure alone would kill off any energy it had. The whole point is kind of moot considering the pilot wouldn't have enough time to squeeze the trigger, let alone realize that he should shoot.

The only instance I know of where a cannon has any effect on the aircraft is the A-10. Because the size of the shell and the momentum imparted to the airframe when it fires, there are burst limits when firing the cannon. Theoretically, it can bring the aircraft to a complete stop.
 
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  • #18
seat tilt 30 degrees in F16
No the seat is tilted for design, to allow it to be fit in a smaller cockpit. the g part is a selling story. Actually you're not inclined to sit back at all during flying.
Well these are the people that make the seats, and they seem to differ. In most fighters, the limit is around 7gs, the F-16 seems to be in a class by itself at 9gs. The F-22 with seat tilt at 22 degrees may be close.

http://www.ejectionsite.com/f16seat.htm

F-16 cockpit layout
Probably psychologic, you seem to loose eagerness and agility when leaning back. Moreover you cannot reach several controls on the front panel and you have to adjust the seat pretty high to look through the head up display.
The stock seat height is high, visiblity is good, but you're pretty exposed as most of your body is above the base of the canopy. I have a view of the old El Toro Jet base in California, (a townhome with a nice view), and a few pilots haved lived in our complex, and from what they've told me and what I've seen from actual cockpit videos, they pretty much don't move much at all during dog-fight or air show maneuvers. More info on the F16:

http://www.voodoo.cz/falcon/info.html

F-16's don't use flaps
Wrong again. The flapperons and leading edge flaps are essential in getting the lift required to attain the g. There is no flap control in the cockpit though. All automatic - fly by wire computer work.
Big difference between flaps and flaperons, which are just ailerons that can move in the same as well as in opposite directions. The leading edge flaps just rotate up and down and don't extend forward like the ones used on commercial airliners. The wind is a semi-delta wing, the front leading edge is angled backwards quite a bit, allowing for a high AOA while still producing a lot of lift (this is because vortices flowing across the leading edge help provide lift that you don't get with non-delta wing designs).

I have flaperons on a few of my radio control gliders, in addition to actual center flaps, with the ability to move the entire trailing edge as a single surface, mostly to adjust the camber to work well through a range of speeds, and sometimes just opposing elevator for aerobatics (less down elevator requried for inverted flight), the F16 uses it's leading edge flaps and trailing flaperons for both purposes as well, camber adjustment for air speed, and increased response to elevator input.
In the case of gliders, both full scale and models, dropping the flaps fully (almost 90 degrees in most rc gliders) is mainly use used to act as an air brake.

Sameple video using flaps for hand catch landings, common when you don't want to scuff up an expensive model:

http://jeffareid.net/rc/jrartms.wmv

Since rc gliders don't have pilots they can pull some fierce g forces. Some F3J models like the one in that video have snapped 200 lb test fishing line during a tow launch (two big guys and a pulley), and these are models that weigh around 4.5 to 5.5 lbs. The strongest models are the ones used for dynamic soaring, the last time they had a good santa ana wind blowing over a local ridge here in so cal, a new 301mph record (radar gun) was set. Videos of this and other dynamic soaring stuff at the link below. All of the contest gliders use hollow molded fiberglass / carbon fiber / kevlar fiber contruction, strength depending on thickness and choice of materials (all carbon / kevlar fiber is strongest). Along with the videos, is a good picture of an 8 inch hole in hard packed dirt made by a rc glider crashing into the ground at 180mph.

http://www.slopeaddiction.com/thekids.html [Broken]
 
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  • #19
Quite a response on this thread!

First of all, I would like to apologize about posting the personal information. It was late, I was tired, but no excuse. I am a pilot, CFI, single and multi-engine, instrument. I also have to many hobbies and too little time. I performed a lot of crash reconstruction in my 27 years as a State Trooper and yes, I received help from some of the local math gurus.

Believe it or not, this thread started because of a comment on a taxidermy website. I like to hunt, fish and do my own taxidermy and I always drop in on the taxidermy forums to see the topic of the day. In this case, it involved the bullets blowing up in the magazine of YF-12A due to its speed. Well, it got into a peeing contest and so I searched and found this site or should I say your site. Now on the taxidermy website there is no registering or log in. The one old timer likes to use phrases such as, it's too bad birth control isn't retroactive or you are an idiot, dumba.., etc. So I had to jump in on this one and was quickly "shot down" with a "crash and burn."

If you go to this website http://www.taxidermy.net/forums/ and click on the green currents events bar, just scroll down to "You think a bullets fast" (01-19-06) it makes for some enjoyable reading on a site that only the moderators friends can break the rules.

Thanks again, The Red Baron:cool:
 
  • #20
Just one thing, Jeff - the g-forces that pilots can withstand is all about duratinon. F-4 and A-4 pilots in 'Nam pulled up to 12 for short periods (less than a second) to evade missiles, and 9 is the typical limit for several seconds. The F-16's seat was reclined more than usual to improve g-tolerance, but it helps only a little-bit. Still, Mercury astronauts were able to withstand 12 g's for relatively long periods of time (a minute or so, I think) in a fully-reclined position.
 
  • #21
Note, that he F16 seat tilt was an afterthought, the original prototypes didn't have the seats tilted back that far. If you can believe the air show announcers and air force media, some F16 pilots can sustain a 9 g turn for 360 degrees or more, which takes quite a few seconds.

As mentioned before, there have been a few times where I've been directly under an F-16 pulling one of these high g-turns about 300 feet (or less) overhead, the AOA is incredible (looked like 15 to 20 degrees), and the sound is incredibly loud, not just from the engine, but because it's accelerating so much air in order to pull the high g-turn. When they had the local airshow, there was a train station parking lot directly beyond the south end of the north south runway, and a person could observe a lot of very close fly-by's from this location. It's was also a cool place to go to at night to watch after-burner takeoffs.

In terms of takeoff's the most impressive jets where the F-15's departing after a show weekend. With no weapons and probably light on fuel, they'd hit the afterburners and be wheels up in just a few seconds, but staying withing 50 feet of the runway until they reached the other end, before pulling into vertical. Just to show off, I remember one of them just yawing into knife edge flight after going vertical for a few thousand feet, and dissappearing into the distance while staying in knife edge flight. Probably a case of the Air Force guys wanting to show the Navy what a "real man's" jet can do.

I'm probably one of the few in my area that wishes they never shut down El Toro. For most of the year they only flew during daytime hours on weekdays, with just a few weeks of practicing night carrier landings on a lit up portion of one the runways. My townhome was essentialy under one end of the loop they flew while 6 or so jets would be in a holding pattern practicing touch and go's in prepration for the night carrier landings. Plus having a yearly local 4 day air show that you can watch from my home overlooking the base from about 2 miles from the south end of the runway was nice, as well as the arrivals and departures of the static display aircraft (I would take vacation days to watch the whole event).
 
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  • #22
Aircraft historians, ground-based observers, and R/C pilots all have different insights about flight in general, but would you guys please keep in mind that Andre actually flies the real thing. I'm more inclined to follow his responses.
 
  • #23
Well, actually that's history. But I logged a few hundred hours on that bugger, the early A-B versions, block 10's 12,5's 15's, with OCU and Z2 modifications and of course F100-200 or F-100-220 enigine with big essential differences. it was always a surprise where to find the FCNP switch. That would tell you which version you just strapped yourself onto. So switchology in the F-16 was the worst. But other than that, the most ultimate flying experience. A pilots dream, to be able to do anything you'd liked but never were able to do in the older generation jets. Picture yourself at 100 feet doing 600 knots straight through http://www.donner-minerals.com/images/photos/Harp_Lake.JPG [Broken] in Labrador Canada. Nothing in the world can beat that.

Did not make it to the MLU version, medical thinghies. Too bad. The block15 MLU combines modern block 60 types electronics with the light weight of the early versions (before block 25 AKA F-16CD) making it the most agile fighter in the world.

And the only times I'd leaned back comfortably in the tilted seat were on the long boring ferry flights. Other than that, flying fighters requires "rubber necking", "checking 6" every other second and that simply doesn't work leaning back.
 
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  • #24
OSHP295 said:
First of all, I would like to apologize about posting the personal information. It was late, I was tired, but no excuse. I am a pilot, CFI, single and multi-engine, instrument. I also have to many hobbies and too little time. I performed a lot of crash reconstruction in my 27 years as a State Trooper and yes, I received help from some of the local math gurus.
Believe it or not, this thread started because of a comment on a taxidermy website. I like to hunt, fish and do my own taxidermy and I always drop in on the taxidermy forums to see the topic of the day. In this case, it involved the bullets blowing up in the magazine of YF-12A due to its speed. Well, it got into a peeing contest and so I searched and found this site or should I say your site. Now on the taxidermy website there is no registering or log in. The one old timer likes to use phrases such as, it's too bad birth control isn't retroactive or you are an idiot, dumba.., etc. So I had to jump in on this one and was quickly "shot down" with a "crash and burn."
If you go to this website http://www.taxidermy.net/forums/ and click on the green currents events bar, just scroll down to "You think a bullets fast" (01-19-06) it makes for some enjoyable reading on a site that only the moderators friends can break the rules.
Thanks again, The Red Baron:cool:
Just out of curiosity, what actually started the whole thing? Just an off handed comment or something innocent like that?

BTW...bravo Danger.
 
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  • #25
Andre said:
Well, actually that's history. But I logged a few hundred hours on that bugger ... And the only times I'd leaned back comfortably in the tilted seat were on the long boring ferry flights.
Cool picture, hopefully you know where all the sharp turns are before doing a canyon run?

What I meant in my post, and what I've been told and seen from cockpit videos, was that during a 9 g full afterburner turn (is 450 knots about the right speed for one of these?) the pilot would lean back and grunt. Other than high-g turns, I would expect the pilot would just sit in a position so he/she could do a lot of rubber-necking as you mentioned.

Sorry if my post implied otherwise, I didn't mean to imply that a pilot would be locked into position like a F1 racing car driver. Even their helmets rely on a snug fit between two pads above the seat so that up to 4 g's of lateral force, while racing for 2 hours or so, don't wear out the driver's neck.
 
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  • #26
Overtaking and getting hit by your own bullets is equivalent to the poodle in the microwave tale.
True in a real world situation, except in the dive case as you mentioned, but the original post was about firing bullets at mach 3+, a pretty unrealistic situation.

Getting back to the hypothetical firing of bullets at mach 3, flying into your own bullets isn't a good thing. In a real world situation, the fact that you have some time before you could catch up to your own bullets, combined with the fact that a rational pilot isn't going to induce zero lift flight while firing his guns, eliminates this problem. If a gun / cannon were to operate at mach 3, it would have to ensure that projectile speed was high enough that there would be sufficent time for the aircrafts path to deviate from the bullets path, or it could simply angle the guns slightly downwards.

A real world potential issue is that during high g, high AOA flight, your guns AOA is also increased, but the bullets speed is so much higher than the aircraft that that this doesn't become a real issue, as long as the pilot doesn't do something really stupid like firing bullets nearly vertically upwards, followed by going into near zero lift vertical flight to intercept his own bullets.

If an aircraft was designed for strafing ground targets, aiming the guns a bit downwards so that level flight could be maintained while firing at ground targets would be a smart thing. I wonder if A-10's are setup this way. The other solution is to aim the guns sideways, and bank the aircraft in order to aim the guns (C-130).

Getting back off topic again, I'm not aware of any onboard human controlled aircraft that can sustain supersonic speed and a high g, high AOA flight. If I remember correctly, terminal velocity of a F16 pulling a 9 g turn with full afterburners while maintaining altitude is around 450 knots. If the initial speed is faster, the F-16 will slow to 450 knots, and if the initial speed is slower, the F-16 will speed up to 450 knots. There's also a minimum airspeed that a F-16 can generate 9 g's worth of lift. At supersonic speeds, I don't know how much g force / AOA the airframe can take, but my guess is at high supersonic speeds, the limitation is the airframe and not the pilot.
 
  • #27
Danger said:
Aircraft historians, ground-based observers, and R/C pilots all have different insights about flight in general, but would you guys please keep in mind that Andre actually flies the real thing. I'm more inclined to follow his responses.
True, but remember, the original topic is about firing bullets at Mach 3, which is a bit unrealisic.

Regarding knowledge of aerodynamics, excluding military trained pilots, I find that glider pilots, both real full scale and rc models, are more likely to be knowledgeable than powered aircraft piliots, since they don't have motors to ovecome pilot mis-judgements.

For example, there's a simple rule both full scale and model glidier pilots learn, when asking is my aircraft going to clear that object in front of me? One way to figure this out is to aim for the top of the object, if you're airspeed increases, you're going to clear the object, if you're aircraft slows down, you need an alternate plan.

Edit update: another glider rule, if a glider becomes unresponsive, the first control input is down elevator. Most of the time this is kind of obvious, because excessive AOA is due to trying to fly too slow. However when "hi-starting" a model glider, which bascially applies tension to a tow hook just in a bit in front of the center lift, the trim setup, or an updraft may create excessive AOA at high speed, causing a snap roll situation, where the model may "kite" right into the ground, and with very high tension to weight ratios, like 40g's for an F3J contest launches, time from launch release to impact is pretty quick (I witnessed one where launch to impact was less than 2 seconds, speed at impact about 90mph). Seeing the model rolling and/or yawing, the untrained instinctive response is to use ailerons and/or rudder, which are bascially useless. You pretty much have to anticipate using down elevator, and use it if you hint of getting of the model getting out of shape. Normally this is only an issue when trimming a new model, but if the launch setup is aggressive with a high AOA, thn launching through a thermal can push AOA beyond crictical. The main point here, is that contest rc pilots are well aware that stalling / snap rolls have nothing to do with speed and only to do with AOA. My own personal experience was with another
person's small slope glider, that had a large amount of elevator throw (unknown to me). While at a high and safe
alititude, I dove the model and then fed in a lot of up elevator, but there was no pitch response, just a roll response,
which was kind of cool once it was no longer a surprise, it was my first true snap roll with a model.

This leads to another rc model rule: a models altitude should be 2 or 3 mistakes high, especially when trying out
new stunts and/or with a new to you model.

Getting back to the normal glider pilot stuff, high end models allow camber adjustments that the pilot manually controls depending on the situation. Minimum sink mode while thermalling, best glide ratio while searching for thermals, and for the rc pilot bringing his model back from a downwind thermal, best glide ratio for high speed flight; for some model glider higher camber airfoils, as much as 3 degrees of reflex (entire trailing edge surfaces raised) is used. For models, the range of camber adjustment is pre-programmed via transmitter.

One of my pet peaves is how many web sites and books use "hump" theory to explain lift: "the hump on top of a wing makes the air travel further to catch up to the air below and faster moving air has less pressure". For example, older versions of Microsoft Encarta used "hump" theory, until the 2002 and later versions. You can still find a lot of web sites that still refer to "hump" theory.

I work with a group of programmers / engineers and I remember a co-worker with an instrument rating that believed in hump theory, as well as other co-workers, and it took a bit of convincing to get them to change their beliefs.

It's a two step process.
Step 1, explain how pressure differential is how air exerts it's weight inside a container. For example, putting 80 cubic feet of air into a scuba tank increases weight by 6 pounds, and it's the pressure difference versus alititude within the container that causes the net downwards force exactly equal to the weight of the air inside the container.

Step 2. Replace 1 pound of air with 1 pound model aircraft. It's a closed system, so as long as the center of mass isn't accelerating vertically, the total weight of the system never changes, regardless of what the model is doing, as long as the center of mass of the model has no vertical component of acceleration. If the model is flying within the container, then it has to increase the pressure differential by just enough to create a net downwards force within the container equal to the models weight. Therefore the model lifting surfaces are air pumps creating a downwards flow of air that results in the net increase in pressure differential within the container.

There's a third step for explaining lighter than air baloons within a container

Step 3. If the model is a helium baloon, then as the balloon is inflated within the container, it increases the pressure within the container, which increases the pressure differential. If the balloon is hovering,then the net increase equals the weight. IF the ballloon rests on the bottom, the net increase is less or zero. If the balloon is pushing against the top, the net increase in downforce due to pressure equals the weight of the model balloon plus the upwards force the balloon exerts on the top of the container.
 
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  • #28
Please let's not bring up the whole lift generation bit AGAIN...that horse is long since dead.
 
  • #29
glider pilots more knowledgeable than powered pilots

Another glider rule, if a glider becomes unresponsive, the first control input is down elevator. Most of the time this is kind of obvious, because excessive AOA is due to trying to fly too slow. However when "hi-starting" a model glider, which bascially applies tension to a tow hook just in a bit in front of the center lift, the trim setup, or an updraft may create excessive AOA at high speed, causing a snap roll situation, where the model may "kite" right into the ground, and with very high tension to weight ratios, like 40g's for an F3J contest launches, time from launch release to impact is pretty quick (I witnessed one where launch to impact was less than 2 seconds, speed at impact about 90mph). Seeing the model rolling and/or yawing, the untrained instinctive response is to use ailerons and/or rudder, which are bascially useless. You pretty much have to anticipate using down elevator, and use it if you hint of getting of the model getting out of shape. Normally this is only an issue when trimming a new model, but if the launch setup is aggressive with a high AOA, then launching through a thermal can push AOA beyond crictical. The main point here, is that contest rc pilots are well aware that stalling / snap rolls have nothing to do with speed and only to do with AOA. My own personal experience was with another person's small slope glider, that had a large amount of elevator throw (unknown to me). While at a high and safe alititude, I dove the model and then fed in a lot of up elevator, but there was no pitch response, just a roll response, which was kind of cool once it was no longer a surprise, as this was the first model I flew with an extreme snap roll response (you didn't need a lot of air speed as you would with a more typical model to get a snap roll response).

The reason for the aggressive F3J launches is in the rules. You're penalized for the amount of time it takes to launch the model, and you're trying to get high altitude from the launch, espeically in a light lift situation (few or no thermals) The power souce is two large humans (think football players), each holding a handle on a harness attached to a pulley. A fixed lenth (by rules) 200+ lb test monofilament fishing line is triple staked (for safety), run to the pulley and back to the model, so the human supplied tension is cut in half, but the speed is doubled. The models typically glide at 20mph, so it takes a 30 to 40 fold increase in downforce to get them to climb at 100 to 120 mph. To increase speed before release,the pilot increases tension with a bit of up elevator, then pitches the model down a bit to convert the tension into speed, then goes vertical, which released the line off the tow hook (the line has a ring that slips on the tow hook), called a zoom launch. During this time the model pretty much stops the humans forward motion. If the pilot gets too aggressive, the 200+ lb fishing line will break. These are 4.25 to 5 pound models, so over 40g's. Contest model construction consists of hollow molded components made up of fiberglass, carbon fiber and kevlar composites, with a carbon fiber weave pattern over high stress areas, and a wing joiner made up of all carbon fiber, which is why a 4.25 to 5 lb model with about a 3 meter wingspan model handle 40 to 50 g's.

This leads to another rc model rule: a models altitude should be 2 or 3 mistakes high, especially when trying out new stunts and/or with a new to you model.
 
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  • #30
FredGarvin said:
Please let's not bring up the whole lift generation bit AGAIN...that horse is long since dead.
Sorry, I started a separate thread, as mentioned, it's just a pet peave of mine, and while looking for info on the F-16, I saw a reference to hump theory again on an otherwise informative web site, which ticked me off, and this unfortunately led me to include it in this thread.

By the way, I wonder how many people in this forum know that Fred Garvin was a character from Saturday Night Live? For those that don't, do a web search for Fred Garvin. I wonder how many Fred Garvins and Richard Craniums (shouldn't need a web search for this one) there are out there in forum land?
 
  • #31
The F-86 fired 50 cal. guns in flight but only flew at about 550 mph. Keep in mind that to push the shock wave cones on the engines of an SR-71 it takes 14-16 tons of pressure. Also, at Mach 3+, forward surface temps will be as high as 450 degrees. The SR-71 was never designed to fire a gun at speed as the mind set at the time was missles only.
 
  • #32
I was just wondering what happens at the exact moment the bullet exits the gun barrel and hits air that is moving Mach3 faster than the air inside the barrel? Could this be like hitting a wall, causing the bullet to just disintegrate a few inches out of the muzzle?

Also, regarding the impossibility of hitting one's own ammo; when a bullet leaves the barrel at a muzzle velocity of about Mach1.5, and then encounters a headwind of Mach3+, couldn't it be shoved back into the gun? That might be where the concern about "exploding inside the magazine" originated.
 
  • #33
No, it certainly wouldn't be like hitting a wall, it's not even like splashing into a pool. There is no surface interface and the transition is relatively smooth. Nor could the bullet be shoved back into the gun. Remember, whatever pressure the bullet is going to feel in front of it, it feels vastly more behind it, so there is no chance of it disintegrating and deceleration is much smaller than the acceleration was. Even if the bullet decelerated at 10 g's (which would be an awful lot), it would still take more than 10 seconds for it to get back down to the speed of the plane.
 
  • #34
russ_watters said:
No, it certainly wouldn't be like hitting a wall, it's not even like splashing into a pool. There is no surface interface and the transition is relatively smooth. Nor could the bullet be shoved back into the gun. Remember, whatever pressure the bullet is going to feel in front of it, it feels vastly more behind it,
Not true. Once out of the barrel, the bullet feels no pressure behind it. It is coasting, and only feels the pressure in front of it.
...and deceleration is much smaller than the acceleration was. Even if the bullet decelerated at 10 g's (which would be an awful lot), it would still take more than 10 seconds for it to get back down to the speed of the plane.
Yeah, now you say it, that's a sure thing. I don't know what typicall accelerarion is for a bullet, but even 1,000g for 1/10th of a second would make your numbers accurate, and the chance of "blow-back" essentially zero.

But I also wonder; wha would be the aerodynamic effects of putting a hoolow metal tube (a gun barrel) on the front of an aircraft going Mach3+ with the open end facing forward? Any effect, or would the turbulent buffer zone form an envelope that prevetns direct interaction between the tube and the on-rushing headwind? Probably the latter, yes? BTW; did the Blackbird use Petot tubes?
 
  • #35
LURCH said:
But I also wonder; wha would be the aerodynamic effects of putting a hoolow metal tube (a gun barrel) on the front of an aircraft going Mach3+ with the open end facing forward? Any effect, or would the turbulent buffer zone form an envelope that prevetns direct interaction between the tube and the on-rushing headwind? Probably the latter, yes? BTW; did the Blackbird use Petot tubes?

It would melt.

The pitot tube is on the nose.


pitot%20tube.jpg



In fact, the tires were made with aluminum powder and filled with nitrogen or they would heat up and explode inside the wheel wells in supersonic flight.

right%20mains%20again.jpg
 
<h2>1. How fast do bullets from a jet fighter Mach 3.2 travel?</h2><p>Bullets from a jet fighter Mach 3.2 can travel at speeds of up to 2,400 miles per hour, which is approximately three times the speed of sound.</p><h2>2. What type of ammunition is used for bullets from a jet fighter Mach 3.2?</h2><p>Bullets from a jet fighter Mach 3.2 typically use specialized ammunition such as armor-piercing rounds or high-explosive incendiary rounds, designed to penetrate and destroy targets at high speeds.</p><h2>3. How accurate are bullets from a jet fighter Mach 3.2?</h2><p>Bullets from a jet fighter Mach 3.2 are highly accurate due to the advanced targeting systems and precision-guided technology used in modern jet fighters. However, factors such as wind and distance can still affect accuracy.</p><h2>4. What is the range of bullets from a jet fighter Mach 3.2?</h2><p>The range of bullets from a jet fighter Mach 3.2 can vary depending on the specific aircraft and ammunition used. Generally, they have a range of several miles and can hit targets from long distances.</p><h2>5. Can bullets from a jet fighter Mach 3.2 be used for air-to-air combat?</h2><p>Yes, bullets from a jet fighter Mach 3.2 can be used for air-to-air combat. They are designed to be versatile and can be used for both air-to-air and air-to-ground missions, depending on the situation and mission objectives.</p>

1. How fast do bullets from a jet fighter Mach 3.2 travel?

Bullets from a jet fighter Mach 3.2 can travel at speeds of up to 2,400 miles per hour, which is approximately three times the speed of sound.

2. What type of ammunition is used for bullets from a jet fighter Mach 3.2?

Bullets from a jet fighter Mach 3.2 typically use specialized ammunition such as armor-piercing rounds or high-explosive incendiary rounds, designed to penetrate and destroy targets at high speeds.

3. How accurate are bullets from a jet fighter Mach 3.2?

Bullets from a jet fighter Mach 3.2 are highly accurate due to the advanced targeting systems and precision-guided technology used in modern jet fighters. However, factors such as wind and distance can still affect accuracy.

4. What is the range of bullets from a jet fighter Mach 3.2?

The range of bullets from a jet fighter Mach 3.2 can vary depending on the specific aircraft and ammunition used. Generally, they have a range of several miles and can hit targets from long distances.

5. Can bullets from a jet fighter Mach 3.2 be used for air-to-air combat?

Yes, bullets from a jet fighter Mach 3.2 can be used for air-to-air combat. They are designed to be versatile and can be used for both air-to-air and air-to-ground missions, depending on the situation and mission objectives.

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