question on DG2 re-entry

[canadave]

OK, this may sound silly, but for the most part I've just enjoyed flying the DG2 around and about in
space.  Wheeeee, fun  Now I'm FINALLY getting to the point where I'm seriously paying
attention to re-entry scenarios for Earth with it.  And I'm having some problems.

Here's what's going on.  I de-orbit no problem.  I generally find myself pretty close to the Cape,
around 45k altitude, about 2.xxx k speed.  From there, it seems that either I drop really quickly
without losing speed, or I lose speed quickly without dropping altitude.  I never seem to get a
smooth constant-sloped re-entry.

The next problem is that the Delta Glider 2 doesn't seem to live up to the Glider part of its name
very well.  One would think that 150k from the Cape, at 40k altitude and high speed, I could glide
in from there.  But it seems that once the speed drops below 1.0 k, forget it.  Speed drops VERY
quickly after that, and I can't hold any kind of gentle glideslope.  It feels like I'm flying a brick.

Is anyone else seeing this?  Does this thing have any lift, or is it all the overweight passengers I
have on there?  I find myself looking for sandbags to toss overboard.  This shouldn't be!

Cheers,
Dave

[DanSteph]

Hello Dave,

I would say at first that there is not enough lift at 45k due to the low pressure
so you are not really gliding here (you can only fall at "low" speed)
Also when you come lower as the pressure increase your speed should
drop dramatically due to the drag force.... this is normal also....
(at high pressure high speed generate an hugh amount of drag)

Did you follow the tutorial ? I didn't flyed it recently but it seem to me that
the first part 45k->20k is more a falling part if you are at low speed (<2k)
and the gliding part come more when your below 20k alt.

(150km seem to far to me if your speed is below 2k, even if your alt is
40k while most part of this alt isn't usefull to glide-in)

Try to brake less until your closer from the cape then take a gliding angle of 45°
until you come at acceptable altitude for gliding (20k?)

When you glide from high altitude as you do, the things to do is to maintain
your speed at first with your gliding angle... if your speed increase
lower your angle, if it decrease , increase your angle... you will see that you
will need less angle as your altitude drop... (pressure increase)
(I mean "normal" AOA angle and not one where you are stalling)

Anyway things seem normal to me, the pressure increase isn't linear
and the speed VS pressure drop seem normal also.

Watch also your AOA so you are not at a stalling regime when you
try to glide.

Hope this help ?


Dan

[canadave]

Dan,

Thanks, it does help, lots.  It tells me that what I'm seeing is normal behavior for the ship.  

Is this how gliding spacecraft like the Space Shuttle behave in real life?  I would've thought that at
40k altitude, you would still have enough atmosphere to provide a decent bit of lift.  Or is this just
a matter of Orbiter not quite being realistic as far as modeling real-life Earth atmosphere?

Also, I find that even around 15-20k, in "thick" atmosphere, I can hardly glide at all.  To maintain a
near-constant speed in the glide, I have to be at a steep angle of descent and AOA...around 30-
40 degrees.  I would've thought a ship with "Glider" in the name would have more lift than that!

Maybe it's just that I'm not flying it right.  I'll keep trying....it's probably just because Dave "Stone
Hands" Klein is at the controls.....

Thanks,
Dave

[DanSteph]

canadave wrote:
> near-constant speed in the glide, I have to be at a steep angle
> of descent and AOA...around 30-
> 40 degrees.  I would've thought a ship with "Glider" in the
> name would have more lift than that!

Well, the wings are ridiculous for a glider
(maybe I should rename it DeltaStoneII ??

This angle seem normal and yes the shuttle maintain an high angle
of descent also (another "stone" glider ?) at high altitude
it's more a "controlled falling" then a glide.

At 20k the pressure isn't also dramatically high  (try to open the windows
and see if there is enough air to breath    (badly not linear at all as I said)

if you continue to manage your speed with the angle you will see how
your angle will decrease smoothly as you alt drop... if you do this and record
your descent path you will see that your curve will fit the pressure curve


Dan

[DanSteph]

And here a graph about pressure vs altitude....

As you see there is a fraction of pressure at 40k and not so much also at 10k
vs sea level....



Dan

[canadave]

whoa....great graph!!  Interesting....

I see your point about the glider and the Shuttle.  I guess I always had this picture in my head of
the Shuttle cruising in like a 747, but I suppose that comes from watching too many sci-fi shows  
I'm going to go try it again with this new info and this graph, and this time I swear to you I'm
going to NAIL the landing

Dave "Silk Hands" Klein (I hope)

[Orbiter Fan]

Canadave, remember: The DG is an powered ship. So running low on speed just start your main
engines, just like in an normal airplane. I guess we have flown the shuttle a little bit too long.

[canadave]

Yeah, I know....I think that's part of why I haven't brought this issue up before now--I always just
used the engines at the end to get me the last bit to the Cape.  But I figured, since I'm flying
a "GLIDER", I should be able to...ahem....GLIDE........lol!  

I still think I just gotta get it right and I'll be able to glide in noiselessly like a ninja spacecraft....

Dave

[DanSteph]

following the Tutorial (very well written btw I wonder who... ??
I usually land without touching the engine at all.... I find managing
the remaining energy during the descent intteresting, and taken
the size of the dgII this would be more realistic as a ship like this
should not have much fuel remaining when it come back.

(to make things more challenging you can dump fuel overboard
before reentry, it will glide even better)

Dan "nervous bee" Polli

[canadave]

Dan, you read my mind....first thing I did was dump the fuel  If there were any farm animals,
science experiments, free weights for lifting to keep in shape in orbit, I would've dumped them
too.  Anything to lighten the load!!

By the way, I am an idiot....I was hallucinating that "20k" in the HUD meant 20,000 FEET, not 20
kilometers!!  That would explain a lot....sheesh.  I sometimes wonder how I make it out of bed in
the morning without a tutorial.

Well, armed with the knowledge that k means kilometers, and with a fuel trail a mile long in orbit,
and with Dan's able and patient help, I've managed to crash more gently  Actually, I made it
pretty much on target...one more try and I think I'll have it down pat.  Thanks guys....I RTFM'd, but
I didn't RTFMC...C for Carefully :0

Cheers from the Great White North (can you believe it's SNOWING AGAIN here??? Geeez...),
Dave

[DanSteph]

canadave wrote:i]
>  If there were any farm animals,
> science experiments, free weights for lifting to keep in shape
> in orbit, I would've dumped them
> too.  Anything to lighten the load!! [/i]

ROTFL

This remind me an aventure like that writted by a flying doctor
Benoit Wangermez who write in the "french flyer list" he is a very good
writter (and pilot) and have always some hallucinating story to write....
(in africa flying rules are ... less strict and the plane are often composed
of material that have a far link with original plane's part)
This guy for sure don't go at desk at 8 and come back at 17.

The story:

Things happenned in kenya,  A DHC6 Buffalo bring each week food
and supply to some far base. This week they decided to make a
combined plane with some Army-men that needed some training.
In brief in the middle of the flight they will jump outside of plane with
a chute and come back acrosse the jungle back to base.

As we are in africa no one saw a problem if they took also some
alive sheep in the plane that must be given to the destination.

In the middle of the flight the pilot looked his map for the point where the
men should jump and gave his "go" with the micro to the back cabin....
But as soon as they oppened the door, instead of the army-men it was the
sheep and: hop ! hop ! hop !  without chute....

(I can imagine the head of the guy in the plane harf harf harf)


Don't know if I translated well but I always rolled on the floor when
I read it..... Benoit is an excellent writter and his modesty is also great.
I absolutely love his story, in africa flying mean that adventure isn't far.  
Wangermez's story can be read here:
http://www.pilotlist.org/bestof/resultats.php3?auteur=wangermez
(for french reader only, too bad)

> I was hallucinating that "20k" in
> the HUD meant 20,000 FEET, not 20

I had those sort of problem with the speed until I converted them in km/h
to see that "no" my gentle final at 150k wasn't gentle at all...

> (can you believe it's SNOWING
> AGAIN here??? Geeez...),

Oh great I love the snow we don't have too much here in the winter...
but now the nature around is full of flower smell and the temperature are already
hoooooot.....  not bad also (I had a small sleep this afternoon on the grass
yaaaawn

> Cheers from the Great White North


Cheers from the great heuu hem ... midle ?

Dan



Post Edited (05-07-03 20:51)

[canadave]

LOL that Wangermez story is too funny!!!!  Too bad he's not in English...

For what it's worth, one of my favourite writers is Louis-Ferdinand Celine...but I read him in the
translated English, not the original French

You're sleeping on the grass, eh?  Lucky guy.  What a life!  Nothing to do but lie around, dreaming
of little Delta Gliders 2's flying around your house...."oooh, look, one's coming to pick me up, I
wonder if I'm going to the ISS or the Moon today!?"

I envy you....

Cheers,
Dave

[DanSteph]

canadave wrote:
> You're sleeping on the grass, eh?  Lucky guy.  What a life!
> Nothing to do but lie around, dreaming...

...And I woke up covered by ants just to see that I must
digg another 200m2 of terrain with only a small shovel.

Lucky me (nhaa for sure I can't return live in town, lets touch some wood)

I had read Celine but it's not my favorite I usually read to escape
those kind of thinking    in this kind I preffer Steinbeck, Camus
and Emile Zola  (dark also but not so... crude)

But my all day's book are more light so I'm currently reading
again my whole Jule Verne collection (I'm now in "turn around the
world in 80 days" )

1am , no sleep ? let's see where is phileas fog.

Dan

[canadave]

heh...I hear you about Celine being dark.  I grew up in the type of urban nightmare he describes,
so I guess that's why I like him so much.

Funny you mention about "80 Days"--I just watched one of the episodes of the Michael Palin
documentary "Around the World in 80 Days" on TV a couple of days ago.  Great stuff..and of
course the book is awesome!

Have fun digging

Dave