Guns

[davparlr]

Another quote from wikipedia but a sourced one:

"The recoil force of the GAU-8/A[14] is 10,000 pounds-force (45 kN),[3] which is slightly more than the output of one of the A-10's TF-34 two engines (9,065 lbf / 40.3 kN each).[15] While this recoil force is significant, in practice cannon fire only slows the aircraft a few miles per hour.[13]

13. ^ a b Jenkins, Dennis R (1998). Fairchild-Republic A/OA-10 Warthog. North Branch, Minnesota: Specialty Press. ISBN 1-58007-013-2."

That's because the pilot doesn't hold the trigger in very long.

I saw on the History Channel, I don't think it was "Dogfights", a video with two aces talking about the first flight of one while the other was the lead. They were chasing a Mig and slowly catching all the while lead was telling the anxious newbie to hold fire, hold fire, and the newbie fired at max range then realized firing the gun affected airspeed, I think, he said 10-20 mph, allowing the Mig to pull away. Both commented on this phenomena. Of course the Sabre was not overpowered and at max velocity it would not take much of a drag or negative thrust to slow the plane.

 

[renrich]

The recoil of the 50 BMG is much greater than that of a 3006.
From"80 knots to Mach 2" by Ralph Linnekin, page 99, the chapter on the F8F, which he had much experience with: " In operation there was one phenomenon that I experienced in no other airplane. These were small, short-coupled airplanes with a modestly sized vertical tail. If, in the middle of a firing run, the gun(s) on one side jammed or stopped, you could suddenly find yourself trying to fly sideways. This was noticeable when firing only a pair of fifties; when four 20-millimeter cannon were firing and you lost two on one side, the phenomenon was dramatic."
Judging from that paragraph the gun's recoil must have had a noticeable impact on the airplane.

 

[Shortround6]

How much force does it take to slew or turn an airplane as opposed to checking it's speed by a fair amount?

as in how much effort would you have to put into using the rudder vs deploying an airbrake?

 

[renrich]

SR, all I can do is quote from Linnekin's book, which incidently, is a gem. He was a career Navy pilot, grad of Annapolis, aeronautical engineer, test pilot, surface navy WW2 and flew combat in Korea. Stearmans to Phantoms. If you want to know how they really flew, partial list, SNJ, Hellcat, Corsair, Bearcat, Panther, Banshee, Cougar, Crusader, Phantom II., Get his book.

 

[renrich]

The gun on the A10 is mounted off center but I believe the barrel that fires is aligned along the center line.

 

[mikewint]

renrich, check post #9, the firing barrel is at the 9 o'clock position.
wing mounted MGs or cannon would have their force multiplied by the length of the wing which would act as a lever arm and i believe cannon are for that reason generally mounted within the airframe. with only one side firing the unbalanced forces would push the nose in that direction just as moving the rudder alters the frictional forces on that side and the force is multiplied by the length of the fuselage, turning the nose of the aircraft.
the origin of this thread was the slowing of an aircraft by 50 - 60mph by the balanced forces generated by several machineguns
as to the M2HB recoil, i have fired this weapon several times and its recoil is easily controlled with a tight grip on the two handles and one thumb on the trigger. Of course the gun is always mounted in some way as it would be impossible to hold and fire. the HB weighs close to 90lbs and about 50lbs for the tripod so generally speaking it is a three man operation.
a good portion of the recoil is used to work the action and there is also a muzzle brake to help with the rise and the cyclic rate for the ground version is about 400rpm to help preserve the barrel which was a pain to change

 

[davparlr]

According to Wikipedia

The fuselage of the aircraft is built around the gun.[54] The gun's firing barrel is placed at the 9 o'clock position so it is aligned on the aircraft's centerline.

Which makes sense to me even if it is wikipedia.

 

[renrich]

According to "The Great Book of Modern Warplanes" page 42, "The 9000 pound (40kN) recoil thrust of the GAU-8/A cannon demanded a centerline location and the forward fuselage was designed around the gun and it's ammunition." This is from the section on the A10. It further states that the recoil thrust is equal to the thrust of one of the engines of the A10. It appears from the photos that the gun is mounted off center(on the port side) but the firing barrel is on the centerline.

 

[bobbysocks]

in my research i did find this...its from bud anderson's book. now this quote is when he was in a P51B with 4 50cals....

"I close to within 250 yards of the nearest Messerschmitt--dead astern, 6 o'clock, no maneuvering, no nothing--and squeeze the trigger on the control stick between my knees gently. Bambambambambam! The sound is loud in the cockpit in spite of the wind shriek and engine roar. And the vibration of the Mustang's four. 50-caliber machine guns, two in each wing, weighing 60-odd pounds apiece, is pronounced. In fact, you had to be careful in dogfights when you were turning hard, flying on the brink of a stall, because the buck of the guns was enough to peel off a few critical miles per hour and make the Mustang simply stop flying. That could prove downright embarrassing."

so it can slow you down...just enough in the right situation in the right ac to stall.

 

[mikewint]

A question for pilots. if an aircraft's stall speed is, let's say, 120mph, does it fly OK at 120.1mph and stall at 199.9mph? What kind of leeway do you have? In such a turn as described wouldn't the engine be on full throttle? wouldn't the aircraft recover speed pretty quickly?
and another question: WWI aircraft had the ability to "hang by the prop" (if i have the phrase correct). was that possible for a WWII fighter. I have seen stunt aircraft do that on a climb until they nose down and dive to recover speed
anderson's book states what has been said before "a few miles per hour" not the 50 - 60mph stated in the first post.

 

[davparlr]

A question for pilots. if an aircraft's stall speed is, let's say, 120mph, does it fly OK at 120.1mph and stall at 199.9mph? What kind of leeway do you have? In such a turn as described wouldn't the engine be on full throttle? wouldn't the aircraft recover speed pretty quickly?
and another question: WWI aircraft had the ability to "hang by the prop" (if i have the phrase correct). was that possible for a WWII fighter. I have seen stunt aircraft do that on a climb until they nose down and dive to recover speed
anderson's book states what has been said before "a few miles per hour" not the 50 - 60mph stated in the first post.

I'll take a stab but I am sure others can provide a better response. Aircraft stall occurs when the airflow separates from the wing and the wing loses lift. This occurs at a specific angle of attack, or, angle in which the air strikes the wing, which is not associated to a specific airspeed. Several factors affect the stall speed of a wing, one is the weight of the aircraft another is the load put on the wing by the pilot inputs to the elevator. At a non loaded angle of attack, that is, the pilot is not pulling "gs", an aircraft typically becomes sluggish or mushy in response to control inputs at angle of attack, thus airspeed, approaches a stall. In a high speed maneuvering situation, control can be sensitive up until the time the stall occurs. Recovery for a non-loaded stall typically is to reduce angle of attack by lowering nose and adding power. For a loaded, or high speed stall, recovery can be exciting depending on the characteristics of the aircraft. I remember my instructor telling me that a stall cannot occur if there in no input to controls. One day, I entered a loop at a barrel roll speed which is slower, on reaching the top of the loop, upside down, I notice the controls being very sloppy, looking at my airspeed indicator, I saw that it was below 50 knots, basically zero, not wanting to stall upside down in an aircraft that would spin, the words of my instructor came to me, no control input, no stall. I did nothing and aircraft lazily fell nose down through the loop and no stall recovery was required.

I think your reference to hanging on a prop has to do with climbing at a steep angle. The better the power to weight value an aircraft has, the longer it can climb at a given steep attitude before it slows down and has to recover from a stall. If the thrust generated is greater than the weight, it will never slow down. Many modern fighters can do this. Some special props can do this. No WW1 or 2 props could do this. The SPAD XIII, a powerful WWI aircraft, had a power to weight ratio of .13 hp/lb, the WWII P-51 had .18 hp/lb. The P-51 could maintain a climb attitude longer than a SPAD. This is simplistic since thrust vectors all come into play.

 

[mikewint]

davparlr, thank you. all of you please excuse any ignorance on my part, i am not a pilot strictly a passenger and mostly helos.
lets go back to the high speed stall, an aircraft making a high speed turn as bobby described, would lift even be a question?
the aircraft would have banked so the wings are essentially vertical and you would be pulling back on the stick to "raise" the nose into the tun. airflow over the control surfaces should be pretty constant???
in your example you had slowed down until air flow over the control surfaces was insufficient to continue to direct the plane. inertia and the eventual dive restored air flow and the control surfaces once again became effective
i have seen WWI and models go into a steep climb until airspeed is zero. the down thrust of the prop balances the force of gravity. i was told this was "hanging on the prop"

 

[fly boy]

i could see that working on biplane

 

[bobbysocks]

that is hanging on a prop and some of the acrobatic prop jobs and modern jet fighters can do that. but even the high performance ac of ww2 would sooner or later stall. that same story of bud anderson's that i got that quote from talks about his scariest dog fight with a 109...and they both reached for the sky. noses pointed up, engines straining....the one who stalls first ( most of the time ) loses. and that is what happened...his 51 had just a little more balls to keep it afloat. to the subject of high speed turns....its about the same thing as if you have been on a boat. and if you ever tried to dock one...you will know when you turn...you skid. in a high speed turn you bank and yank but the inertia of the plane makes it want to go in the direction previous to the turn....so you are mushing around a corner...you have a lot of forces fighting here...mike this stuff is all you for calculating. but centrifical force is pushing the belly of the plane out ( decreasing air flow over top of the wing ) ...gravity is pulling towards the earth, engine torgue twisting you( works with you or against you depending ),.... air density, temp, humidity...will factor the lift. to not stall you have to keep these in ballance shall i say. its easier to stall a plane in a steep turn than one might imagine...hense why it is part of pilot training. WW2 jocks knew their planes and would "ride the crest" ( the shuttering of controls ) of a stall in a tight turn...either to get a kill or keep from getting killed. despariate acts which some survived....and some didnt.

 

[renrich]

I actually saw an airplane stall in a 90 degree banked turn. It was a three quarter scale Mustang, I think and he was only perhaps 1000 feet AGL although at about 10000 feet above sea level ( it was at Crested Butte, CO) and the air plane stalled and went straight into the ground only about 500 yards from where I and some others stood on a golf course. Both people in the plane died of course.

 

[bobbysocks]

a lot of stalls occur during landing or take off and because there is no buffer to recover...usually dont end plesantly. when i was 10 or 12, my dad and i went out for a usual sunday afternoon fly. we landed at another local airport and had an ice cream as we watched planes land and take off. as i am eating this ice cream sandwich a piper took off and got about 2-300 feet off the ground and the engine quit. i heard my dad mutter "S#!T" and bolt for the airport office as the guy tried to do a quick 180 back to the runway. without engine power planes arent going to make that sharp of a turn without losing a hell of a lot or air. trying to keep his altitude he lost airspeed and stalled. but i dont think the pilot had too many options tho at that time because there was a huge housing project off the end of the runway. he augering into someones back yard. he, like us, was going up with his daughter for a pleasure ride. they got a little banged up but both luckily survived.

here's a video of an acrobatic ac hanging by it prop...


View: https://www.youtube.com/watch?v=TsEYryZ6xoc

 

[mikewint]

Bobby, you hit the nail on the head, for me it is indeed all intellectual and i really appreciate all of you taking so much time with this old ground-pounder. it's like my post on inertial coupling. i know the terms and what they mean but putting it all together is very difficult, i.e. reading about playing the piano does not make one a piano player.
with the old WWI planes lift was very important because engine power was marginal as hp goes up lift is not a factor. with enough hp you can fly a barn door. so i'm not always sure to what you are refering to when you use the term "lift".
planes like the f-104 certainly derive no lift from those stubs. they're airflow directors. so where does lift come into play?

 

[bobbysocks]

i loved the f-104... and all the old jets i used to play with as a kid. starfighters and the like. the f-104 was basically a guided missle...guided from inside the missle byt the pilot. you are correct in that the "wings" did very little to nothing as far as lift was concerned.
"It used an exceptionally small wing span of only 21 feet, and provided low speed lift through air bled from the engine and vented over the wing."
all they did was aim the rocket. but the f 104 was not a dogfighting ac in the sense that it was not going to win in a turning battle but the era of air to air missles was erasing that concept of dogfighting ( a mistake they would learn later in viet nam ).
"The speed of the F-104 came with the sacrifice of handling and maneuverability. It was not meant for dogfighting. The best pilots found that the aircraft needed their constant attention. Novice pilots could find the aircraft outpacing their control inputs. The results were numerous fatalities."
but the F104 design was the exception and not the norm....most ac were built with longer broader wings to provide the lift and better manuervability. the slower the speed the more you need lift.

 

[mikewint]

thanks bobby, There were plenty of f-104 in VN. we turned a lot of them over to ARVN since they were relatively easy to maintain as jets go and they did indeed have a terrible time at low speed. i remember the big leather covers placed over the leading edge when they were on the ground. asked an old AF mech why he said, "boy, run your hand over them" (i was dumber then). i still have the scar. The 104 had a bad time in VN as either a interceptor or fighter bomber and something like 15 were shot down with a zero MIG kill
anyway, back to the p-51, wings vertical, stick back "lifting" nose toward the inside of the circle while inertia slides the entire plane to the outside of the circle. (i picture a big old american, front-end heavy car under-steering through a curve). to balance gravitational force it would seem to me that the engine would have to provide some down thrust since wing-lift would be toward the center of the turn, so tail down through the turn? with no up-force, except what is provided by the engine and decreased air-flow over the control surfaces it is difficult to end the bank and bring the wings to horizontal. the aircraft starts to fall out of the curve??
am i making any sense to you?

 

[bobbysocks]

yeah you make sense but think you have reached beyond my ability to adequately explain it....but will take a stab. in the turn there is still air passing over the top of the wing but it has diminished somewhat. the harder you yank the stick...the lower the tail goes and the more you pancake into the turn...and the less air travels over the top of the wing. engine power is fighting centrifical force for forward progress...but depending on the speed underwhich the turn commenced..it may not be able to overcome. the more the plane pancakes the more the decrease in forward airspeed and if the stall "zone" is reached without correction....gravity will take over and the plane will drop out oof the sky. at any time you can make a correction....the severity of the manuever will provide resistance in flight controls but you can still wrestle it easily enough. was reading one of the combat pilots stories and his trainer told him..."no control manipulation..no stall" and that is pretty much ( not always ) true. just relax the controls and you can avoid a stall...your attitude may still need to be adjusted... hope this helps. anybody feel free to correct me or explain in real tech terms.