DG-III Flight Test Data (post bugfix)

[Savanik]

With the new, bug-fixed release, the thing is a lot more survivable on re-entry. Here's some flight data.

Level flight safe speeds are now limited by temperature on the forward hull/cockpit. The yellow warning indicator will
sound off at 1300 degrees. The following speeds are the maximum rated speeds before the indicator sounds off.

Altitude - Safe Speed -- Mach
10 km ------- N/A ------- N/A
15 km ------ 0.961 ------ 3.3
20 km ------ 1.080 ------ 3.7
25 km ------ 1.303 ------ 4.4
30 km ------ 1.676 ------ 5.5
35 km ------ 2.121 ------ 6.7
40 km ------ 2.640 ------ 8.2
45 km ------ 3.250 ------ 9.8
50 km ------ 3.956 ----- 11.7
55 km ------ 4.843 ----- 14.6
60 km ------ 6.003 ----- 18.8
65 km ------ 7.561 ----- 24.8
70 km ------ 9.799 ----- 33.8


At 10 km in level flight, the DG-III's top speed with turbopump engaged is 701.2 m/s. This only brings the cockpit
surface temperature up to 788 degrees celcius, well within safety margins. We estimate that top safe speed is
somewhere between 800 and 900 m/s at this altitude.

It should be noted that the maximum safe speed at 70 km is well above orbital velocity. To obtain these
measurements, the pilots had to fly in an inverted position, with hover engines used to keep them from gaining
altitude.

The following stall speeds were determined using the ailerons, which are capable of taking the DG-III to a maximum
steady AOA of 12 degrees, which is where the following measurements were obtained.

For the unenlightened, the 'stall speed' is the slowest speed at which level flight can be maintained. If you're going
slower than this speed, you will start to lose altitude. These speeds are not, in fact, indicitive of a true 'stall' - vertical
damping is maintained throughout. However, at these speeds, the amount of lift produced at the maximum AOA (12
degrees) is not sufficient to sustain level flight.

Stall speeds:
Altitude Stall Speed
100 m ------ 90 m/s
1 km ------- 95 m/s
5 km ------ 121 m/s
10 km ----- 154 m/s
15 km ----- 215 m/s
20 km ----- 317 m/s
25 km ----- 482 m/s
30 km ----- 700 m/s

Stall speeds for flying with the RCS system are not available because it highly depends on the vehicles current weight. As the vehicle lightens, higher AOAs are possible, which increase the stall speed significantly.

Also, the DG-III doesn't seem to exhibit ground effect (virtual increase of lift near the ground), and does not show a marked increase in parasitic drag as it is not truly 'stalling'.

Savanik



Post Edited ( 05-05-04 21:19 )

[DanSteph]

Savanik once I will start to rewrote the reentry stuff I would be glad to have you
as a beta tester. Just let me know if your intterested.

The reentry is hard to do because each small variation may need 5-10mn test
(because the reentry isn't a process you can test in 10secondes as many others stuff)
So good testing of the whole reentry and some advice may be a real help here.

Dan

[freespace2dotcom]

DanSteph wrote:
The reentry is hard to do because each small variation may need 5-10mn test
(because the reentry isn't a process you can test in 10secondes as many others stuff)
So good testing of the whole reentry and some advice may be a real help here.
Dan

!!!!!


Dan!! I'm interested in being one!!!
I realize that I'm not as... thorough...  nor were you talking to me....  but....

if there's a thing or two or thirty you want checked, I am *so* there! just tell me what you want to have checked and
how you want the report!  SIR!

*stands at attention*

[DanSteph]

The beta (well alpha) are in general public, I just asked savanik
specially because he seem to study very closely the number
and this is very valuable for the reentry coding wich need
many adjustements.

So anyone can be *beta* tester in fact (and you welcome as well).
Somes report only bug wich is usefull but in the case of reentry I
need more.

Dan



Post Edited ( 05-06-04 01:56 )

[Savanik]

I'd love to. Where do I sign?

Sav

[freespace2dotcom]

Just tell me what you want to know, And I'll do my darndest to test it out!

[DocHoliday]

Hehe, seems we could organise a pretty nice outfit around here. Squaaad.. teeeeen HUUUT!!

Hey Dan, what about that project we were discussing with (cana)Dave about the manual/tutorial text, the english
translation part of it. Still on, or did you think up another solution?

Cheers,

[DanSteph]

DocHoliday wrote:
Hehe, seems we could organise a pretty nice outfit around here. Squaaad.. teeeeen HUUUT!!
Hey Dan, what about that project we were discussing with (cana)Dave about the manual/tutorial text, the english
translation part of it. Still on, or did you think up another solution?
Cheers,

Still on, no problem. I didn't hear from canadave lately but as I'm not near doing
any docs yet, well. We'll ask in the meaning time

Dan

[DocHoliday]

Still on, no problem. I didn't hear from canadave lately but as I'm not near doing
any docs yet, well. We'll ask in the meaning time

Heh, is that entirely true. I read on the french forum, that you are making progress on your dg3 manual and the
thumbnails looked nice!

And Savanik and Freespace's "scientific" approach and data tested will also add great quality and value to the
manual.

Looking forward to it! I am too low on time to test myself. Haven't ran Orbiter in almost two weeks now Playing
around with php, webdesign and english translating.

[freespace2dotcom]

Just lead me in the right direction, what do you want done.. I'll do my best..

PS. two weeks w/o orbiter? you poor thing. I try for every weekend at the very least.

[DocHoliday]

I'm working on getting the ropes with php, so I can set up a tutorial site, I once promised. Basically an extended
version of Dan's Links page, with multiple categories. A sort of a Google type directory, where Orbinauts may post
links to their tutorials and even upload their tutorials in case they cannot or will not have their own site.

But before all that, I need to know enough php and mysql to tackle the task. Since I'm quite new at this.

Right now, you can help Savanik with the "NASA" test pilot operations, and do collect any link you find that may be
useful to people into Orbiter. Be it how to install addons, how to fly and also general topics on astronomy and future
tech that can be applied to Orbiter. When time comes, your effort will bear fruits and you will join the other people in
the golden annals of the Orbiter community!

Ah, the Prophet has spoken. Sorry.. been reading Alamut again.

[freespace2dotcom]

Yeah, I've naturally been abusing the dg3. It's just that I find the weirdest things to do to it. one time I came to a
near complete stop from orbit by doing one very long retro burn, and although I had to use the hover engines to stop
from crashing into the surface, I do recall that although the crew lost conscienceness, I intentionally tried to keep the
ship from burning up and succeeded, but for some odd reason, I don't think the crew was seriously hurt by all the g's.

all the lift for the dg was used as a brake because of the angle, so they experienced that extreme, plus I had the
hover engines on, not quite on full power, but more than 80%, very powerful g force they experienced indeed, but I
don't remember what that was... I'll test it out later again. but it would seem as though the crew is almost
invulnerable to g forces considering that the hull temperatures seem to burn out before the crew can experience
death, but by then they're already "dead" like I said, I don't remember, I never wrote anything down, but that'll be
my project over the weekend.

[DocHoliday]

Interesting. I actually tried that on the Moon, but it's a whole different ball game there. I just stopped and lowered
the DG3 down with the hover autopilot.

I'm not sure I got that about the lift being used as a brake because of the angle? The way I see it, you were hanging
at like 100km and controlling your rate of descent with hover only, trying to keep the horizotnal speed around 0..?

Of course, if I know you, you just let it drop down like a rock and then engaging full thrust at 10km or so, which'd
explain the high Gs

I don't know how Dan takes Gs into account, but the human body can endure extreme G (like 40), but only for a few
miliseconds or so. That's why we often survive car crashes against logical odds Sustained G is another matter.

[DanSteph]

DocHoliday wrote:
I don't know how Dan takes Gs into account, but the human body can endure extreme G (like 40), but only for a few
miliseconds or so. That's why we often survive car crashes against logical odds Sustained G is another matter.

Accurate way: (I'm proud of that)

Duration and number of G taken in account, you can take high G as you said for a short time
but you may experience G-LOC if you have for exemple 4G for several second.
It's also accumulative. Also the heart start to increase it's beat if you take G.

Look on the DGII's doc there is two graph that show effect of G/duration
and an complete explaination.

The only effect that is not modelled is the direction of the G.

Dan

[freespace2dotcom]

DocHoliday wrote:
I'm not sure I got that about the lift being used as a brake because of the angle? The way I see it, you were hanging
at like 100km and controlling your rate of descent with hover only, trying to keep the horizotnal speed around 0..?

Of course, if I know you, you just let it drop down like a rock and then engaging full thrust at 10km or so, which'd
explain the high Gs

Ok, I *was* dropping like a rock, but I actually started the thrusters at around 50km or so, I wouldn't survive the
heat otherwise. During a normal re-entry, you're supposed to raise your nose so that some of the lift that the DG
produces adds to the braking, (right, dan?) the deal is, that I was using a rediculously steep slope ( >65 degrees)
and since almost all of my intertia was making me go straight down, just keeping the ship level with the horizon
would be like having the nose at a 75 degree angle during a normal reentry. as a result of this braking AND the hover
thrusters on, (all at an altitude of *about* 35-45 km) you experience quite a bit. I'm at school right now, so I can't
test it, but I have fridays off, I'll give a more detailed report then. The only thing I want to comment is that even
though the crew experienced all that, they *did* survive the g's. Granted they were unconsious for awhile. It almost
seems that while you pilot the dg3, you have no danger of dying of g's, because the force required to get the crew to
die from such a thing would burn the hull out long before. that's what I'm trying to get at. but like I said, I'll get back
to you guys on this.

[DocHoliday]

Hm.. I guess I'll try it too. I'm curious now.

During a normal re-entry, you're supposed to raise your nose so that some of the lift that the DG
produces adds to the braking,

Yes, if you're coming in at several thousand m/s, otherwise no. You have four forces at play and the idea is to get the
resultant to a desirable direction and magnitude. You get pulled down by gravity, your velocity/kinetic energy gives
you the forward component, while atmospheric drag induces a backward component, slowing you down. Now in case
of an aerodynamic body like the DG3, when the atmosphere is dense enough, you can pitch up and augment the
drag, by adding an upward velocity to decrease the gravity's effect and additionally indreasing the backward
component, lowering your forward momentum.

Now with a zero horizontal velocity drop, all you have to deal with is the gravity's pull and small forward momentum
as the DG3's wings "try" to produce drag and slowly increase your forward velocity. So ideally if you can keep your
nose level and of course have a rediculously high angle of attack (near 90 deg), you can just go down with the hover
engines (assuming you burned a lot AND had enough fuel, which I'm pretty sure after that retro burn you don't -
unless you cheat and edit the .scn - but you're heavier than)...

It almost seems that while you pilot the dg3, you have no danger of dying of g's, because the force required
to get the crew to die from such a thing would burn the hull out long before.

In this case, yes. With normal reentry, no. Since your whole bottom surface of the DG3 is doing ALL the braking, while
falling like a rock at a level attitude, the body has to absorb all the drag and converts it to heat. At the same time,
since it's a big surface, you get a considerable drag, which in turn means good braking, which in turn means, high G
So at some point or another, you have to pitch the DG down, to get forward velocity, and reduce the wing stress. Of
course your downward velocity will also start to increase, which means that when you eventually want to pull out of
the dive, the G force will be extreme Also your nose might not take the temp increase either. Am I making any
sense?

Oh, and, you do know Dan designed the pilot of the DG3 to be more resistant to GLOC, being a trained individual,
whereas the crew are just regular people. So you can easily have your crew dead, and your pilot just a little
nausea Don't remember the exact numbers, but the crew can sustain like 3-4 Gs, while the pilot up to 7-8. I will
have a look at that diagram, Dan. Now with the corrected temp bug, DG should be a LOT easier to deorbit. Most of
the times I was unsucessful precisely because of excessive temp. If I tried to lower it, I ended up with the crew dead
of GLOC

[freespace2dotcom]

hmmm.. I DO have to test it, but so you know, I WAS going blazingly fast. I started dropping from 350 km. gravity
continued to pull at me making me go at some serious speeds. It wasn't nearly as much as a regular de-orbit mind
you, but it was enough that I feel the same rules apply. I did read the DG2 manual, so don't think you're such a hot
shot for mentioning the pilot's training..

but yeah, I need to take all that in and think about it before I make a really stupid response... who knows. I think it'd
be cool to see each other's flying technique, everybody has they're own style, maybe mine has a natural way of
avoiding g's by some coincidence. (can you tell I want orbiter to have multiplayer.. hehe) But seriously. This is gonna
be second on my to-do list when I get home. the first being sleep.



Post Edited ( 05-06-04 14:52 )

[DocHoliday]

hehe, okay. It makes more sense to me as well now. I had assumed you started your "ride" at something like 100km
not 350.

If I were a hot shot, I'd stuff this post with all the number, formulae, statistical comparissons I would of course pull
right out of my sleeve, plus I'd send you a movie of how *I* routinely do it with stereo anime music... with
cranberries... with sugar on top... and uh... with HONORS!! ... *whew* that exhausted me.

But I'm not. I'm just an Ace pilot, heh.

[DocHoliday]

Ah, CORRECTION.. JUST A STUDENT ASTRONAUT!!!!

[freespace2dotcom]

yeah, but I'll be a "real" astronaut before you.



Post Edited ( 05-06-04 15:14 )

[DocHoliday]

Considering you live in the US, quite possibly

[freespace2dotcom]

Actually, I was referring to the amount of posts I have compared to you. I know "official astronaut" has to be in the
ranks somewhere...

[DocHoliday]

Yup, you'll be official at about 328 posts.

I'm getting my champagne ready!

[freespace2dotcom]

wow! That's cool! And just think, while I'm making posts here, I could be doing real work at school.. oh well...

[freespace2dotcom]

All right, I'm home and made my tests. I'm fully aware that one simple test flight means nothing, so I will make more
in the future.. *ahem*

first off, I started off docked to the iss, from the built in DG3 scenario at about 362km.

After I made a perfect no-eccentricity orbit. (I only tolerate 0.00) I did my retro burn, although I gradually titled the
nose higher up to compensate for the lack of speed to avoid "dropping in" prematurely. after that, I dumped fuel until
the main tank had 2953 kg, and the rcs had 208.8. kg, the I turned on the autopilot "level horizon" and made sure I
was facing prograde (to my horizontal speed, anyways.) my re-entry slope was 81.84 (!)

At 80Km my vertical speed was 2272m/s and airspeed was at 2296. At this time I was experiencing 0.959 Gs, which
got me curious because technically I was still in a freefall just like an orbit and there wasn't any atmosphere to
generate *that* much force. it gradually decreased until the next step.

next, (a few seconds later) at 41.3km, The autopilot couldn't keep up with the pressure and the ship temporarily tilted
to one side, my temperature read this at this time.

Nose. 595
Left Wing 401
Right wing 230
cockpit -7
hull -9

I also had a nice and easy 0.6 G's! but after that...

literally a split second later, at 33.8 km, the ship sagged and the nose pointed very straight down. dooming the crew.
(my fault, but still funny) the temperature at this point was

nose 1635
cockpit 493
hull 382
left wing 1279
right wing 1290

I will note that here, all my downward inertia was stopped, and I started to go *UP* The g's at this point were 3.9
very uncomfortable, but livable, especially since it hasn't been very long.

Another split second later, the ship burned up due to the nose being too hot. (a first for me, but yeah, I was coming
in that fast) The g's did in fact reach about 5.5, maybe even higher, but it decreased so fact I wasn't able to record it.
according to that action logger that you have, the ship burned up before the dangerous g's were reached. but a split
second after that, all of the ships heated up way past the red danger level and the g's went down to like .2

hope this helps. after some sleep, which I still haven't had, I'll run some more tests and average them out.