Based on this photo from STS-82(the last mission that only flew with the airlock), I can say that there's no A6L or A7L: http://spaceflight.nasa.gov/gallery/images/shuttle/sts-82/hires/s82e5644.jpg
Space Shuttle Ultra development thread
- Thread starter DaveS
- Start date
Aren't the APAS currently used and APAS-75 very similar, both in appearance and functionality?
And the new mesh is just about done.
SiameseCat
Addon Developer
Does anyone know how to calculate the force exerted by the drag chute?
tblaxland
O-F Administrator
Like this:
http://en.wikipedia.org/wiki/Drag_equation
A domed parachute has a Cd of about 1.5:
http://www.basd.net/technology/STEEP/Technology/3.6/Para Design is.htm
New External Airlock only mesh checked in. Sill finalizing the new separate ODS mesh but I should have that one ready pretty soon too.
-----Posted Added-----
The ODS have now been finalized and checked in! Have fun coding it!
-----Posted Added-----
The ODS have now been finalized and checked in! Have fun coding it!
Urwumpe
Not funny anymore
- Joined
- Feb 6, 2008
- Messages
- 38,965
- Reaction score
- 3,937
- Points
- 203
- Location
- Wolfsburg
- Preferred Pronouns
- Sire
Do you use a variable drag element? In that case, the constant you throw into the function is Area * Cd = 1.5 * Area.
The reference point is where the rope of the parachute attach to the shuttle.
SiameseCat
Addon Developer
Do you know the axis along which the variable drag force acts? I've been wondering whether to use CreateVariableDragElement or AddForce to simulate the drag force.
SiameseCat
Addon Developer
What units should the cross-sectional area be in? In m^2, the area is 78.53 (radius of parachute is 5m), which gives an overall drag coefficient of 118. This seems a bit high.
Well, remember the orbiter is a big and heavy object.
Design specifications for the drag-chute was for it to stop a TAL Orbiter(248,000 lbs) in 8,000 ft with a 10 kt tail-wind on a hot(103°F) day and maximum braking at 140 kts or one half runway remaining.
Edit:
Oh and the radius of the chute should 6 m as it is 12 m in diameter.
tblaxland
O-F Administrator
@SiameseCat, use CreateVariableDragElement since it will have the same effect as AddForce but it will save you having to do the drag calculation yourself. Your method for calculating the drag factor is correct but should be adjusted to 169.6 per DaveS' comment. The attack vector should be the point of attachment of the drag chute to the shuttle.
My calculations, under the conditions DaveS nominated, with a landing air speed of 205 kts, a relative air density of 90% (hot humid day, nominal sea level pressure) and not including chute transient conditions:
Initial decelaration: 9.25 m/s
Time to slow from 215 kts to 140 kts GS: 6.6s
How do those numbers look to you guys? Decelaration seems a bit high to me, maybe some reduction of the chute area to allow for the bleed hole would be in order.
My calculations, under the conditions DaveS nominated, with a landing air speed of 205 kts, a relative air density of 90% (hot humid day, nominal sea level pressure) and not including chute transient conditions:
Initial decelaration: 9.25 m/s
Time to slow from 215 kts to 140 kts GS: 6.6s
How do those numbers look to you guys? Decelaration seems a bit high to me, maybe some reduction of the chute area to allow for the bleed hole would be in order.
Last edited:
I'll do a few timings off landing videos.
-----Posted Added-----
Checked off STS-115 and time between chute deploy(185 kts) and reaching 140 kts was 10.5 seconds.
SiameseCat
Addon Developer
Using a drag coefficient of 118, the shuttle slows from 180 kts to 140 kts in 4 seconds with the drag chute reefed. For reference, the speedbrake has a drag coefficient of 15 (in SSU).
tblaxland
O-F Administrator
The only thing I can see to account for the difference is that the chute is less efficient than predicted because it is in the wash/wake of the shuttle so it is not receiving the full free stream dynamic pressure. I think all you can do is derate the chute to match real world performance. Some rough calcs indicate that a coefficient of about 60 will do the trick (not knowing the exact parameters of the STS-115 landing - wind speed/direction, air temp, humidity, air pressure all play a role).
EDIT: You will need to subtract the speedbrake from that too. So a coefficient of about 45 for the chute.
SiameseCat
Addon Developer
I' ve put the drag chute stuff on sourceforge. Note that the chute disappears when jettisoned; I'm working on fixing this.
