Me163 climb - this can't be right

[LLv34_Snefens]

The following was taken from this 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.
__________________
Ltn. Snefens
Lentolaivue 34
My AH homepage

[SELECTOR]

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..
ive seen a film on the net i wll try and find it..

[AAvenger]

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

[Badboy]

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

[LLv34_Snefens]

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

[Karnak]

Maybe the guy said "17 degrees" and the interviewer marked down "70 degrees".

[illo]

Me 163b climb

[illo]

time to alt. Note chart includes time of takeoff run.

[illo]

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.

[LLv34_Snefens]

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
My AH homepage

[LLv34_Snefens]

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.

[Badboy]

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

[illo]

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.

[illo]

"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.

[hazed-]

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)