Aces High Bulletin Board
General Forums => Aircraft and Vehicles => Topic started by: niklas on August 11, 2001, 12:48:00 PM
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ok on the runway the 262 has poor acceleration, but once airborn only few aircrafts can catch it in a climb.
It climbs with ~4000ft/min at sealevel with full internal fuel tanks, only few propeller driven aircrafts were better. And the Me262 could climb with 4000ft/min @340mph, which is for most propeller driven aircrafts close to topspeed (or higher). That means it could easily outclimb near sealevel an enemy at this speed.
Of course climbrate drops fast with altitude, but acceleration near sealevel was not so bad!
niklas
P.S
Will we get this armment option?
(http://people.freenet.de/luftwaffeln/me_bk5.jpg)
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ALL the WWII jet engines revved up very slowly. The Meteor, ME-262, P-80 could only accelerate well if you put several sticks of TNT up thier pipe :)
Don't confuse acceleration with cruise speed, maximum speed, dive or climb rates. Once these planes were up to speed THEN yes, not much could touch them at all. It just took quite a long distance to do that.
Westy
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Don't confuse acceleration with cruise speed, maximum speed, dive or climb rates.
Of course i can compare acceleration with climb rates. They´re close together. A plane that outclimbs an other plane at a certain speed will outaccelerate it at this speeed in a horizontal flight
niklas
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From a standing start every fighter in AH can get to 300 mph faster than the Me-262, and every fighter can get to 10K faster than the 262. Once the 262 gets to 300 mph or to 10K, everything changes.
ra
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262 did climb nicely after its turbines got enough rpm.
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But how well does it climb/accelerate at speeds under say, 300mph? That's when the prop fighters will murder it - but in high speed acceleration the Me 262 will be far superior.
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Originally posted by Staga:
262 did climb nicely after its turbines got enough rpm.
But later, in a flight, the rpm was almost constant. There was an automatic regulator to keep rpm constant.Thrust was regulated by the "jet-needle" at the end of the turbine (it changes the area for the massflow: less area faster speed of the exhaust gases = more thrust).
Of course the pilot could choose lower rpm settings, but even for economic flight, rpm setting was 8000 compared to 8700 (maximum).
The major problem was to get the engine from 0 to 8000+ for takeoff
btw ra, altitude is not good for a jet like the me262. The 262 performs best near sealevel compared to prop driven fighter, where the engines produce the most thrust.
niklas
[ 08-11-2001: Message edited by: niklas ]
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Spool time.
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The poor climb and acceleration at low speeds is partly caused by the engine taking time to spin up, but also due to the low thrust from the engines, even when at full rpm. Jets will produce more thrust as speed increase, though not by much. Props produce far more thrust at low speed than at high speed. At lower speeds a typical WW2 fighter will have better thrust/weight ratio than the 262.
[ 08-11-2001: Message edited by: Nashwan ]
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niklas,
Altitude reduces the maximum thrust of the engines but gives the pilot the ability to dive away from any attacker. I was trying to point out that only when a 262 reaches about 10K does it's performance make it nearly invulnerable to attack. A low 262 even at maximum level speed can still be caught by a diving fighter.
ra
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Niklas figure out thrust to weight ratio at sea level and 150 mph for Me 262 and Me 109. Then you will see what people are talking about. :)
It's got nothing to do with spool time or altitude. It's got everything to do with the fact that props have maximum thrust at low airspeeds, while jets have roughly constant thrust regardless of airspeed.
Acceleration of the 262 at high speeds was unmatched by prop planes. But at low speeds it was a dog.
[ 08-11-2001: Message edited by: funkedup ]
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what funky said
the jet produces relatively similar thrust across a range of airspeeds
the prop, while having lower efficiency at low airspeeds has much much higher thrust
for example, at stall speed a 109 g10 is producing a helluva lotta thrust :) it can just from 100 to 200 mph real quick like
the me262 has comparaticvely low thrust in this case
plus the me262s wing's sweepback is a big disadvantage from a turning standpoint. swept back wings have inherently lower lift curve slopes and lower clmaxs until u get into the range of leading edge extentions and severe delta effects
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Yeah, funk?
You ever have a student flare high and whip the throttles to idle in a turbojet KC-135R?
14 seconds idle to max.
Did I mention 14 seconds can be a lifetime? :)
Spool time.
... in some cases. ;)
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But the 135 R model doesn't have turbojets, it has turbofans :D
<G,D,R>
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Chunder, my son.. back in the mists of time there was a KC-135R. In those olden times, the "R" stood for Reconnaissance.
<EDIT>
http://www.aerospaceweb.org/aircraft/transport-m/c135/index.shtml (http://www.aerospaceweb.org/aircraft/transport-m/c135/index.shtml)
Here ya go, ya young pup. Check out this webpage:
"KC-135R Originally designation for KC-135A airframes modified for special reconnaissance duties; 4 converted
There was just one left of the four when I got to the squadron. We used it on the Cuban missions because the "package" was less capable than the RC-135C/M/V/U which had TF-33's. Cuba did not require the latest technology.
We also used it for the "pilot trainer" because the equipment wasn't so sensitive to the bump and thump of touch and goes.
I know I have the ship number in my logbook somewhere.
You are correct about the Johnny-come-lately KC-135R's though. Usurpers of a proud name, they are 'fans.
I'm going back to the rocking chair now. :)
(mumble, mumble "young pups") ;)
[ 08-12-2001: Message edited by: Toad ]
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Originally posted by Zigrat:
swept back wings have inherently lower lift curve slopes and lower clmaxs until u get into the range of leading edge extentions and severe delta effects
Now guess why the 262 had leading edge slats over the full wingspan ;)
niklas
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Was not aware of that... alas, my touchy-feely experience is limited to formerly fixing B-52H's and now working this hydraulic sprinkler they call the B-1B.
PS, thanks for the young pup, most of the guys I work with call me an old fart. ;)
[ 08-12-2001: Message edited by: chunder ]
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Originally posted by niklas:
Of course i can compare acceleration with climb rates. They´re close together. A plane that outclimbs an other plane at a certain speed will outaccelerate it at this speeed in a horizontal flight
HAHAHAHA!
Guess again.
[ 08-12-2001: Message edited by: AKHog ]
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Originally posted by niklas:
P.S
Will we get this armment option?
(http://people.freenet.de/luftwaffeln/me_bk5.jpg)
wtf is that!!! :eek: Is it a 40mm cannon or something?? :confused:
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BK-5 50mm
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i dont know why you laugh at his statement akhog, it is correct.
tho his statement that the me262 accelerates "well" has holes, since it accelerates like a dog at low speeds, it does indeed accelerate well, compared to propeller driven aircraft, at high speeds.
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I was not laughing at his statement about the 262, i know very little about it. but where he says accel and climb rate are basicaly directly related made me laugh.
Given that in AH we see the best climbing planes also have good accel the 2 actualy have nothing to do with eachother.
One is a function of thrust vs wiegh and the Co of lift at a speed, the other is a result of total mass and has a lot to do with areodynamics, rather then just pure power.
If your intrested look up the actual equations, you'll see they have very little to do with eachother.
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OK thinking about it more.
I guess if you look at this in the most basic way then accel can relate to climb rate. but this is looking at it and disregarding areodynamics. like a model rocket, if you make if heavier or take away power you can hurt its accel AND climb performance. Without going to deep into things just look at the areo equations for climb and accel and i think you'll know what i'm talking about.
I'll try to find em and post a link to em here.
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I wonder if we're going to get those wonderful flame outs and fire warnings this time around? Kinda dumb to include yet another Jumo powered plane without it's most historically significant feature.
Heck, there's not even an exhaust nozzle temp gauge to contstantly eyeball in the 234.
Well come to think of it, the pony starter engine in the intake cone was probably the most significant, then the the fire related stuff :)
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AKHog Climb rate and accelertaion are almost the exact same mesurment. But both have to include an (at what speed term). The only areodynamic part that makes them different is the decrease in lift needed (hence less drag) in a climb VS 1'g of lift needed in level flight where Accel is messured.
Basicly both are a direct computation of excess power (total thrust - total drag) * speed. That excess in power can either be used to climb or accelerate, both climb and accel are function purly of the mass and excess power.
I think the reputation of the 262 for crapy acceleration comes mostly from is take off performance. In the slow speed realm props generate much more thrust than the jets.
HiTech
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HiTech,
I disagree about climb/Acceleration being so closely linked. I know that they are both a measure of excess power however there are many other variables.
1. The wing ultimately determines the climing ability of an A/C. A high lift wing (Aspect ratio) will give an A/C excellent climb with relatively low power and yet poor acceleration.
2. An A/C such as the GeeBee racer with an extremely low Aspect ratio and very good power to weight would have excellent acceleration and (relatively) poor sustained climbing ability.
I know that WW2 fighters where somewhere in between these two design concepts but the basic idea for good acceleration is the same, power/weight + low drag, from the GeeBee to the F-15. Not to mention other variables such as cowl flaps being open for cooling during climb which would slow climb rate but not affect an A/C in level acceleration.
All in all I have never accepted the climb/acceleration relationship in AH.
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Some trivial figures:
Jumo 004B thrust: 1,980 lbs
Me-262-a1
Twin Jumo 004B engines
Total thrust: 3,960 lbs
Typical weight: 14,101 lbs
Thrust to weight ratio: 0.28:1
Ar-234B
Twin Jumo 004B engines
Total thrust: 3,960 lbs
Typical weight: 18,540 lbs
Thrust to weight ratio: 0.213:1
F-16 :D
Single P&W turbofan
Total thrust: 29,100 lbs
Typical weight: 28,000 lbs
Thrust to weight ratio: 1.04:1
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Flakbait [Delta6]
Delta Six's Flight School (http://www.worldaccessnet.com/~delta6)
Put the P-61B in Aces High
"For yay did the sky darken, and split open and spew forth fire, and
through the smoke rode the Four Wurgers of the Apocalypse.
And on their canopies was tattooed the number of the Beast, and the
number was 190." Jedi, Verse Five, Capter Two, The Book of Dweeb
(http://www.worldaccessnet.com/~delta6/sig/life_modem.gif)
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Wells and HT are absolutely 100% correct guys.
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Thanks HiTech. I looked at some areo eng books last night that an old friend let me borrow. Although I couldnt find the exact equations, they do seem pretty closely related from what I did find. The exact opposite from what I remeber. I stand corrected, admit to my mistake, please dont ban me :D.
F4UDOA: I think they are talking more about accel at a given speed vs climb rate at that same speed. You point is good and valid but if you speed the geebee up to it's max climb speed it'll have relatively equal accel from or around that speed compared to other planes.
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Flakbait: Can you find T/W on a 109 g-10??
That would be intresting. Assuming all the numbers posted by people here are close to true, and seeing how the 262's T/W is .28/1, I would guess the 109 is much closer to .5/1 if not higher, yet the 262 would have a better climb rate of 4000ft/min at ~320 ish kph.
I wonder what the 262's accel from around 300 to 350 kph is. If they [accel and climb rate] ARE closely related then the 262's 300-350 performance should be better then the 109 g-10's 150-200 accel rate.
Just a thought ;).
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All drag that a wing produces is already included in the power you need to do a horizontal flight with same constant airspeed! (With climb angles less than 30° we can neglect that influence on the induced drag, what Hitech already mentioned (sin 30° is still 0,86))
That means if you do a horizontal flight at a constant speed, all further power will directly increase your climbrate, and you don´t have to care about drag. The problem is to know how much power you need for the horizontal flight.
Of course reality is not so easy. In a full power climb you need other ailleron deflections compared to a horizontal flight at 160mph. Maybe your cooling flaps will open widly (full power at low airspeed). This can cause different drag conditions.
The steeper you climb, the less important becomes a wing, or lift generally. In a vertical tailstand you don´t need any lift at all (like a rocket), because the lift vector is pointing now vertical to the gravity vector. Lift simply can´t help you anymore to overcome gravity. The steeper the climb becomes, the better perform planes with high wingloding (read: small wing, small surface area, ...)
btw, the thrust of a jumo engine is not constant over the speed range. At 330mph it drops to 1650lb near sealevel, compared to 1980lb for 0mph.
niklas