Aces High Bulletin Board
General Forums => Aircraft and Vehicles => Topic started by: LLv34_Snefens on August 09, 2002, 08:41:51 AM
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The following was taken from this (http://www.flightjournal.com/articles/me163/me163_1.asp) article:
"We’d take off and try to keep the plane low, say 15 feet up, and then start to trim it for speed and then very gradually climb as we accelerated to the best climbing speed, which was about 420 miles per hour. The airplane was very short-coupled, so you didn’t want to over-control it in pitch as you took off. When we reached the best climbing speed, we’d pull back and climb at approximately 70 degrees."
I did a little math and those figures seem way off, at least if one assume that it could hold 420 mph in that climb, something that also seems impossible when looking at its thrust/weight ratio.
Actually as far as I could calculate it, ideally, could only climb at about 23 degree when loaded, rising to about 63 degree when empty.
If it DID hold the 420 mph it only needed to be in about a climb at about 17 degree to make it to the 40000ft in 3:35.
What's wrong here?
Someone made a typo/error when writing down the interview?
I don't know whether it was made in english or german, but in both languages 17 and 70 is fairly equal sounding.
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Ltn. Snefens
Lentolaivue 34 (http://www.muodos.fi/LLv34)
My AH homepage (http://home14.inet.tele.dk/snefens/index2.htm)
(http://home14.inet.tele.dk/snefens/209.gif)
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this plane was basicaly a rocket.. very light very areodynamic..
once it reached speed it went stright up..wings only came into it once it reach alt and was gliding..:D
ive seen a film on the net i wll try and find it..:)
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Video clip of Komet getting shot.
http://dazzle.mightyeyes.com/content/contentViewer.asp?cID=7DAE9EFC-EB66-464E-B63D-87625A77CDB9&authID=39D73E21%2D43EF%2D4378%2DA400%2DBB3560E80030
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Originally posted by LLv34_Snefens
What's wrong here?
Someone made a typo/error when writing down the interview?
Yep, that appears to be the most likely explanation because your calculations aren't too far off. The best angle of climb is determined by the ratio of excess thrust to weight, and even if you ignore the drag the best angle of climb doesn't reach the quoted value.
Badboy
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Selector, thats the problem. I didn't calculate in any drag or lift from wings when figuring out that it couldn't climb at that angle, much less vertical, from it's Thrust/Weight-ratio. If I did (read: could), the angles would be even lower.
Just so we are on same page. These are the figures I used:
Thrust = 3.748 lb at alt., 3.300 at SL (To keep it simple I just used the max thrust)
Weight empty = 4,206 lb
Weight max loaded = 9,502 lb
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Maybe the guy said "17 degrees" and the interviewer marked down "70 degrees".
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Me 163b climb
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time to alt. Note chart includes time of takeoff run.
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Btw. It seems that red line (enchanged afterwards) takes in account weight loss from fuel consumption.
So with full tank (which never runs empty) climb to 10km would take 2min 10sec. (calculations were usually done for full load.)
But in real conditions climbrate would go up to 200m/s because of decreasing weight of airframe.
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Thanks Illo. cool graphs
I think however the last graph DO take weight loss into account?
When looking at the top graph a plane that weighs 4 ton will have a climb of 42m/s at SL, rising to 70m/s at 10km. Dividing the climb into 2000m sections, with a climb of 45, 53, 60, 65, 69 m/s respectivly (climb at 1000m, 3000m, etc), it would take 2min 51 sec to reach 10km. Fully loaded this would even be a bit slower.
If we do the same with the red line (where weight loss IS taken into account) we get 2min and 11 sec, matching the last graph nicely.
What also can be seen is that the much qouted 3:35 (3:30) to 12km includes take-off time, and speed build-up. I am not so much into test-procedures, but is this normally included?
__________________
Ltn. Snefens
Lentolaivue 34 (http://www.muodos.fi/LLv34)
My AH homepage (http://home14.inet.tele.dk/snefens/index2.htm)
(http://home14.inet.tele.dk/snefens/209.gif)
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Ohh, and since I in the calculations in my first post, didn't know these were included, the approx climb angle to make it to 12km with climb speed of 210 m/s (472 mph) is instead around 22.4 degree.
Really it wouldn't hold this angle off course, but instead steadily increase the angle.
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Just a word for anyone who may be more familiar with propeller driven aircraft, where the climb rate drops with altitude. The type of thrust producing engine on the Me163 results in a climb rate that increases with altitude, the high fuel consumption, enhances the effect. The red line on the diagram suggests a climb angle ranging between about 13° at sea level, increasing to about 33° at an altitude of 12km.
Badboy
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Terve Snefens.
This is first time I see climb to altitude graph with takeoff included. I think its because of special role of point defence interceptor.
I have 1 question to others.
Are these all full loaded weights as you would see in normal tests? (calculated performances with 100% fuel?) or is fuel loss taken in account (wouldnt be suprised since takeoff run is there also)
There is this complete test somewhere over net...I just forgot where.
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"When we reached the best climbing speed, we’d pull back and climb at approximately 70 degree"
He doesn't say that 420mph was sustained in 70degree climb.
He says he pulled up to 70degree climb AFTER 420mph WAS REACHED.
Maybe this is the point youre looking for.
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all i know is ive seen a grainy old film of a komet taking off shakily then with a billowing cloud of white looking smoke it rises straight up much like one of your toy rockets you buy in modelling shops!
it was WAY over 45 degrees but i guess it could have been the way it was filmed?.
are you sure you are adding the thrust correctly?
if i remember correctly there were 4 rocket nozzels sticking out the tail at the aircraft museum i saw a real komet in.Are you sure the poundage is for all motors?
i have a book 'wings of the luftwaffe' by captain eric brown cbe,dsc,afc,rn
its the book of the after war tests of many of the captured LW aircraft including me163 me262, 109s, 190s, arado 234's, do 335, fw189 bf110, he 111, he 219 among many others.
it quotes this for performance in me163B-1a
powerplant: one walter HWK 509A-1 or -2 bi-fuel rocket motor with maximum thrust rating of 3,748lb
max speed: 516mph at sea level, 593mph between 9,850ft and 29,500ft
time to 29,000ft: 2.6 minutes
time to 39,370ft: 3.35 minutes
max powered endurance 7.5 mins
powered endurance after 29,500ft at 497mph: 2.5 minutes
initial climbrate 15,950 ft/min
normal radius of action 22 miles at 497mph
take off distance to clear 15ft: 700 yards (640m)
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Originally posted by illo
Btw. It seems that red line (enchanged afterwards) takes in account weight loss from fuel consumption.
correct
So with full tank (which never runs empty) climb to 10km would take 2min 10sec. (calculations were usually done for full load.)
210 seconds aren´t 2min 10seconds. As long as we go with a non-decimal time system ;)
niklas
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Originally posted by LLv34_Snefens
Thanks Illo. cool graphs
I think however the last graph DO take weight loss into account?
Probably.
We can get an average climbrate for a given alitude band easily out of the last graph, because speed is dx/dt.
with dx = 2km
alt. --- t_end --- dt ----- v_climb(2km average)
-0km : 60s
-2km : 97s ------ 37s --- 54m/s
-4km : 126s ---- 29s --- 69m/s
-6km : 151s ---- 25s --- 80m/s
-8km : 173s ---- 22s --- 91m/s
-10km: 191s --- 18s --- 111m/s
-12km: 208s --- 17s --- 117m/s
It goes along with the red line.
Those data is project data btw, calculated, like most german stuff available in the net.
niklas
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Illo, that might be, but I can't believe that such an angle would be very efficient to use. I haven't done any calculations on it, but my intuition tells me (dangerous I know :)) that the kinetic energy would be used up long before even getting close to 40K ft. (or even 30), despite the engine running on full power.
Hazed, even our propplanes can go vertical for a while after take-off. The Komet would be even better at this, so maybe it was just a "show-off"?
Off course I am not 100% about the thrust, that was one of the reasons I started this. I found a picture of a museum Komet that clearly shows the exhaustion, where only a single chamber can be seen.
Like the description says it's maybe just a dummy, but even so they would probably make it authentic looking anyway:
http://www.sml.lr.tudelft.nl/~home/rob/me163/berli004.htm
http://www.walter-rockets.i12.com/design/comb.htm
A better view of the combustion chamber. I can see where you get the 4 holes from now. I don't know enough about such engines to know how they calculate thrust, but it seems unlikely that they would give out thrust for each fuel outlet
Nikas. the 2m and 10 sec Illo is refeering to comes from when retracting the 60 secs it uses before starting climb from the 190 secs it uses from start to 10km. that's 130 sec = 2min and 10 sec :)
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The rocket motor for the 163 had just 1 combustion chamber and exhaust.
Here is a site with info on the motors used.
http://www.walter-rockets.i12.com/walter/me163b.htm
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hey Niklas - you never gave the answer to this
(http://www.hitechcreations.com/forums/attachment.php?s=&postid=483887)
guess the A/C you posted a while back
you stumped us all - will you now divulge the secret ID of the aircraft?
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Originally posted by niklas
210 seconds aren´t 2min 10seconds. As long as we go with a non-decimal time system ;)
niklas
err thanks :)
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sry i assumed you refer to total time. But after that K4 chart there seem to be some misunderstanding about minutes and total seconds....
whgates, i replied already in the thread that i don´t know the exact designition myself, search for the thread (or my user name) to read it. Probably someone who can understand russish language can ask in russish forums (airwar.ru?) whether they know this aircraft.
niklas
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ROCKET powered, not prop, turbojet, ramjet, turbo prop, ROCKET powered.
How come the Saturn V was launched at a 90degree angle and not 30?
Masher
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How come the Saturn V was launched at a 90degree angle and not 30?
Because unlike the Me163, the Saturn V had a Thrust/Weight > 1 (7.5 million pounds of thrust / 6.2 million pounds in weight = 1.21) that ALLOWED it to climb at 90 degree :)
Just because something is rocket powered does not guarentee a vertical climb.