The 50k Speedbump

[Bullethead]

I was trying to see just how high I could get the 163 before it ran outta go-juice.  So I set the autoclimb to 200 knots and it went almost straight up.  As it got higher, it's TAS naturally got way more than the 200 IAS, and as I rocketed through 45k, my TAS was up over 400, nearly totally vertical, so the altimeter needles were spinning like mad.  I figured I'd reach about 100k no problem.

Then I hit the 50k Speedbump.  

Right at 50k, the plane jerked like it really had run over something.  Instantly, the TAS needle snapped down to match the IAS needle at 200 knots.  ROC naturally fell off to reflect the new TAS, even though the plane remained nearly vertical.  And the TAS remained identical with the IAS from there on, as long as I remained over 50k.  As a result of the 50k Speedbump, I was only able to reach about 62.5k before fuel exhaustion.

I tried this several more times to be sure.  It happened every time.  At 50k and above, the difference between IAS and TAS disappears.

[Innominate]

The atmosphere technicallly stops at 50k alt.

Above that it's like flying at sea level(sort of)

[hazed-]

I thought the whole point of a rocket engine is that it carries its own fuel and in that fuel is all the combustable gases it needs?

shouldnt a rocket perform exactly the same even in a vacume?

I didnt think the height would matter to the rocket engine.

[MANDOBLE]

I didnt think the height would matter to the rocket engine. [/B]

You are 100% correct about the engine, but the fluid where the plane travels matters a lot. At that height you would need a enormous speed to make the surface controls effective.

[Sox62]

Originally posted by MANDOBLE
You are 100% correct about the engine, but the fluid where the plane travels matters a lot. At that height you would need a enormous speed to make the surface controls effective.

 Yes...he needs to grab a real high-alt plane....

  THE C-47!!!  

[Skuzzy]

Try the C-47 Sox,...  Go ahead,..I dare ya.

[Wilbus]

Ta152 had cealing at 52k.

[Chairboy]

You're not entirely correct about rockets and altitude.

As you go higher, the air pressure drops.  As it drops, the plume from your rocket expands.  All conventional rockets are designed to have a sweet spot where their nozzles are most effective at directing the exhaust for maximum acceleration.  For the space shuttle, for example, the main engines on the shuttle reach a maximum ISP of 453.5 in vacuum even though they only have an ISP of 368 at sea level.

Of course, the SSME is designed for a broad flight profile from sea level to orbit, so the difference isn't as big between the sl isp and the vacuum isp as with many other engines.  (for those interested in why, the SSME uses extremely high chamber pressure to keep high isp through the burn.  This is why SSMEs, while very high performance, are a maintenance nightmare and cost so much).

[Bullethead]

All this discussion about rockets in vacuums misses the point, which is:

WE NOW HAVE AN AIRCRAFT QUITE CAPABLE OF EXCEEDING THE ALTITUDE ABOVE WHICH THE AH FM BREAKS DOWN.  

I was just trying to draw attention to this fact, in hopes that somebody from HTC would realize they now have to tweak the FM so it works above 50k.  I mean, the MA is not real life.  Folks will be taking 163s as high as possible, so they can glide (at 400+ IAS) for many, many miles, and thus be able to use them in areas far from the few fields at which they are available.  While this isn't historical, it's possible so it will be done.  And this will expose this limitation of the FM, which won't look good.  Either that, or the 163 as modeled by HTC has way more alt potential than it really had, which doesn't look good, either.  So something's gotta be fixed IMHO.

Now, as to the erroneous statement of the {edit} atmosphere "ending" at 50k...  Last I heard, we had air-breathing jet aircraft routinely flying well in excess of that alt, so there must still be air up there