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g_boxwood
Anmeldungsdatum: 08.06.2006 Beiträge: 172
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Verfasst am: Sa 16 Mai 2009, 10:35 Titel: |
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... and smoothed out with a belt sander (80 and 120 grit)!
You got it: the absorber thing on flying objects isn't a big deal at all!
The BPC tip inside the airframe is useless...
... and it was removed:
At this point the booster skirt can be glued in place to lead to the (almost) completed booster section:
_________________ Giacomo 'g_boxwood' Bosso
TRA#9986 L2 |
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g_boxwood
Anmeldungsdatum: 08.06.2006 Beiträge: 172
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Verfasst am: Sa 16 Mai 2009, 10:36 Titel: |
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The last hassle deals with both the booster section and the capsule: we need to route the launch rods inside the capsule via some pretty long launch lugs (aluminum tubing).
I transferred the rod openings both to the capsule tip and heatshield:
It is better to glue the lugs to the heatshield first: join the booster section to the capsule, slide the lugs in place with the rods inside and turn everything upside-down:
I used blobs of epoxy to secure the lugs as the openings I drilled were larger:
It is really important to work with the entire assembly together and the rods in place to grant for the alignment between each length of the lug! _________________ Giacomo 'g_boxwood' Bosso
TRA#9986 L2 |
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g_boxwood
Anmeldungsdatum: 08.06.2006 Beiträge: 172
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Verfasst am: Sa 16 Mai 2009, 10:36 Titel: |
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Now, the lug-tubes won't stay where they belongs until you glue their top ends as well: use plenty of epoxy again...
... but mask the exposed area...
... so it won't stick to the BPC! Why? because you need to re-assemble everything together and let it cure upside-down with the rod inserted!
Now it is a simple matter of tirmming and sanding the lug-tubes flush with the skin:
_________________ Giacomo 'g_boxwood' Bosso
TRA#9986 L2 |
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g_boxwood
Anmeldungsdatum: 08.06.2006 Beiträge: 172
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Verfasst am: Sa 16 Mai 2009, 10:36 Titel: |
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Views of the capsule during these finishing days:
The other sections are being dressed up as well:
_________________ Giacomo 'g_boxwood' Bosso
TRA#9986 L2 |
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g_boxwood
Anmeldungsdatum: 08.06.2006 Beiträge: 172
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Verfasst am: Sa 16 Mai 2009, 10:37 Titel: |
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As I'm pretty close to completing the first phase of the program... ehm... project I end up this update with 2 pictures I tailor-made for the topic:
"The anatomy of the vehicle"
The simplified flight-profile of the first mission
_________________ Giacomo 'g_boxwood' Bosso
TRA#9986 L2 |
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Louis
Anmeldungsdatum: 19.02.2007 Beiträge: 765 Wohnort: Zeven
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Verfasst am: Mo 18 Mai 2009, 10:28 Titel: |
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Very impressive work! I look forward to see it on ALRS.
Louis _________________ Always keep the pointy side up!
TRA #11409 L3 TAP |
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Juerg Site Admin
Anmeldungsdatum: 27.02.2005 Beiträge: 4545 Wohnort: Oberengstringen
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g_boxwood
Anmeldungsdatum: 08.06.2006 Beiträge: 172
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Verfasst am: Do 21 Mai 2009, 15:19 Titel: |
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CM Recovery System
I worked hard onto the finsh and I sprayed a huge amount of white paint... Now, while the paint dries for at least a week I'm working onto the final designing challenge of the project: the capsule recovery system (for the next generation of flying capsules).
This is going to be a tough task as I'll show you. I started with a classic Apollo recovery picture: it helped me scale both the canopy diameter and the distance between the canopies and the CM attachment point.
It turned out that:
. the diameter of each chute is 122" = 310 cm
. the distance is 615 cm
The following pictures models 3 120" fruity chutes (16 gores) at the scale distance from the CM: not bad if we consider that each 120" is rated for a 50 pounds load while the CM weights 4 to 6 pounds!!!
Please stop laughing!
Second and alternate design involves 3 60" fruity again (12 gores) at the same scale distance from the CM:
There's little I can do with it. I read the Apogee Newsletter # 187 dealing with parachute clusters in the hope of getting some knowledge and find some sort of inspiration.
I hope you don't mind if I sum things up a bit:
Parachute clusters
1. all the chutes in the cluster must be identical (obvious but worth saying)
2. not all the identical chutes inflate at the same time:
. the first one inflating "bear the worst of the opening shock" and blanks out the other chutes
. there's no way to know whichever chute will inflate first (so they all need to be strong enough to inflate first)
3. inflated chutes "fly tipped over at some angle of attack instead of flying directly over a payload like a single chute does"
. they do interfere with each other leading to a certain degree of drag loss (God only knows how much) plus they're less efficient at such high angle of attack
. angles are higher as the payload weight gets lower
4. some geometrical features need to be checked to make sure the systme will perform fine.
Let's get into details.
4. some geometrical features need to be checked
The Effective Rigging Length (ERL) is "the distance between the payload attachment point and the skirts of the chutes in the cluster when the recovery system is stretched out flat".
The ERL is a minimum value and it helps reducing "the amount of interference between the chutes in a cluster".
ERL = square.root(n)*D
where n is the number of chutes in the cluster and D is their inflated diameter. Quite simple, let's check it using the project as an example:
Let's consider the 120" 3 chutes cluster configuration:
ERL_120 = 1.73*(120*2.54) = 528 cm = ERL_120 , the yellow line.
Those 528 cm do include the projected shroud line length (red line) equals to 315 cm: the required shock cord length to get the minimal ERL is then given by
528 - 315 = 213 cm (blue line)
The more shock cord you add the better behaviour you get in terms of
Forebody Wake Effect (FWE): "basically the air flowing past the payload (forebody) produces a wake which can interfere with the chutes, dropping their drag by as much as 25%".
Now
. the ERL accounts for chute-to-chute interference and consequent drag loss
. the FWE accounts for payload-to-chute cluster interference and drag loss
It seems to me that FWE is more critical for the 60" canopy config than it is for the 120" version: the bigger canopy catches more air than that the CM actually shields!
IOW, the smaller the canopies the bigger the CM will be (with respect to the canopies themsleves), the more the shadowing effect, the longer the lines to avoid FWE.
That is automatically achieved by leaving the same CM to canopy distance (which is a scale length) regardless of canopy diameter!
Moreover, I think that some kind of math law should be needed to compute the required anti-FWE length in terms of the parameter payload dia-to-chute dia ratio: the lower the ratio the higher the length, that would make sense!
i.e.
CM is 24", each canopy is 60" thus param = 60/24 = 2.5 == more critical
CM is 24", each canopy is 120" thus param = 120/24 = 5 == less critical _________________ Giacomo 'g_boxwood' Bosso
TRA#9986 L2
Zuletzt bearbeitet von g_boxwood am Do 21 Mai 2009, 18:44, insgesamt 2-mal bearbeitet |
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g_boxwood
Anmeldungsdatum: 08.06.2006 Beiträge: 172
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Verfasst am: Do 21 Mai 2009, 15:34 Titel: |
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Now let me introduce the CM internals!
That's a 4" airframe tubing housing
. the recovery electronics
. the tower release device
. the black powder can that fires the tip and the pilot chute
Around the 4" tube I designed 3 main compartment sectors that offers the largest volume available for the chutes themselves.
2. not all the identical chutes inflate at the same time
Let's try to figure out what could happen:
1. the CM releases from the tower and reaches the apogee, the BP charge fires and eject the tip and the pilot:
2. the pilot inflates and starts to pull the mains out of the CM:
. each main is bagged inside its own deployment bag
. the mains deploy one after the other instead of all at the same time: this way the system favours what usually happens instead of fighting it!
3. all the bags out of the CM, chute #1 out of its bag and starting to inflate:
4. all chutes inflated, CM tip and bags hanging from the pilot on their path to the ground:
_________________ Giacomo 'g_boxwood' Bosso
TRA#9986 L2 |
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g_boxwood
Anmeldungsdatum: 08.06.2006 Beiträge: 172
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Verfasst am: Do 21 Mai 2009, 18:43 Titel: |
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3. inflated chutes "fly tipped over at some angle of attack [...]"
. angles are higher as the payload weight gets lower
This is what may give the impression that larger-than-required chutes could be employed. As the payload weight decreases the chutes automatically tip over to a greater angle of attack thus reducing their Cd: this leads toward a new equilibrium in the ultimate attempt to allow the entire system to... descent!!!
Is it feasible? We can expect that the system would fail if the chute dia grows beyond a certain point: the new equilibrium state may be found by the system itself in a 'different' configuration in the form of
. non inflated chutes whose drag is enough to recover the payload for a given (low) weight
. collapsed chute(s)
. tangled system
What to do?
My original idea was to artificially lower the chutes' Cd by
. enlarging the spill hole (again, beyond certain boundaries)
. replace rip-stop nylon with meshed material that filters the air rather than catching it
but still, packing the 120" low-Cd chutes could pose some problems.
At the time being I'll see what's the biggest standard chute that can be packed in the sector, then I'll model it and see if it simply lloks fine: mods will then be considered to lower the Cd even more and flight testing will determine if the less-efficient-behaviour helps with the rest...
Stay tuned! _________________ Giacomo 'g_boxwood' Bosso
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g_boxwood
Anmeldungsdatum: 08.06.2006 Beiträge: 172
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Verfasst am: Fr 22 Mai 2009, 8:57 Titel: |
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g_boxwood hat folgendes geschrieben: |
. replace rip-stop nylon with meshed material that filters the air rather than catching it |
Here it is what I mean:
that's a base jumping pilot chute, they replace the shroud lines with meshed fabric to avoid tangling: now, that meshed fabric could be used for the canopy and I think it would decrease the Cd dramatically. _________________ Giacomo 'g_boxwood' Bosso
TRA#9986 L2 |
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Juerg Site Admin
Anmeldungsdatum: 27.02.2005 Beiträge: 4545 Wohnort: Oberengstringen
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MikeHB
Anmeldungsdatum: 16.07.2005 Beiträge: 157 Wohnort: Bremen
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Verfasst am: Fr 22 Mai 2009, 22:34 Titel: |
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Every time I read this postings, my mouth is getting more and more open! Amazing! Whats next, a Little Joe in the same scale?
I hope that somebody will do a video on this flight!
Keep on walking, Giacomo!
Ciao,
Michael _________________ Sagt Abraham zu Bebraham: Kann ich mal Dein Cebra ham? |
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g_boxwood
Anmeldungsdatum: 08.06.2006 Beiträge: 172
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Verfasst am: Mi 27 Mai 2009, 16:47 Titel: |
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Mike, thank you!
I'm working hard on it and I already got the 4 CTI I170 reloads... flight test #1 is getting closer and panic arises...
Everytime I test fit the vehicle together I tell myself "Maybe this time I'm asking too much!". I wonder if I'm right.
Enough with me being anxious. _________________ Giacomo 'g_boxwood' Bosso
TRA#9986 L2 |
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Felix
Anmeldungsdatum: 13.04.2005 Beiträge: 168 Wohnort: Leimen
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Verfasst am: Mi 27 Mai 2009, 19:18 Titel: |
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Really astonishing work Giacomo!
You´re a great inspiration to go back to the hobby room and actually build some new rockets =)
Thanks for sharing the build and all the great ideas with us.
I wish you the best for the first flight!
best regards,
Felix _________________ Sky´s not the Limit! |
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