d21 machbuster

[Tedman]

Has anybody brooken mach with a d21 if so how light would an md have to be to break mach.

 

[cjl]

As light as possible. Rocksim says that a .76" diameter (MD) rocket would break mach if it was less than 1oz and not too long (longer=more drag).

 

[outasight13]

I think I'm gonna try this with my Hi-Flier. Its never flown before so this should be a good maiden flight
Are D21 motors available yet?
My rocket only weighs .6 ounces.

 

[Countdown Hobbies]

Yes they are available, in 4 and 7 second delays.

 

[shinbone]

Available where?
I'm not seeing them on the Countdown site.
Am I missing something?

 

[thejohnchapman]

Given the big fins on the Hi-flyer, you'd better think of a lightweight way to reinforce the roots of the fins. Remember, if the fins strip off, you have an unguided D 21 moving around VERY quickly.

 

[Initiator001]

Originally posted by tedman
Has anybody brooken mach with a d21 if so how light would an md have to be to break mach.

Yes.

Back around 1990, Scott Pearce made a batch of White Lightning D21 (Tested out as D16) motors.

I built a rocket out of BT-20, the longest BT-20 plastic nose cone (I bought a bunch of Zinger kits) & G10 fins.

I tower launched it around midnight out at El Dorado Dry Lake outside of Las Vegas.

We had quite a crowd for the 'Speed Trials' with several folks showing up to fly rockets.

This was back before all these nifty onboard electronic payloads so velocity was determined using cameras and a slotted wheel spinning in front of the lens at a known rate of revolution.

We had to wait for the pictures to be developed before we could check the results. Scott crunched a lot of numbers and told me that my D21(D16) rocket had flown just barely over Mach 1.
Too bad my E45 and F55 models didn't show up very well in the pictures. My FSI Mach 1 kit did not ignite the second stage so I never found out if the kit would actually break Mach. The first stage did reach over 400 MPH.

The top speed at the event? Scott Pearce flying an AeroTech G300 with fins and nose cone glued to the motor casing. Tower launched, it reached a velocity of Mach 2.19.

 

[shinbone]

Available where?
I'm not seeing them on the Countdown site.
Am I missing something?

 

[cls]

consider using (18mm) D24 RMS instead of D21s.

 

[Countdown Hobbies]

Originally posted by shinbone
Available where?
I'm not seeing them on the Countdown site.
Am I missing something?

They are there under Aerotech Single use, you can also search for " D21 " and they will both show up.

 

[shinbone]

Dummy me.
I searched under Ddash21.
Doh. Thirty plus years of rocketry and still can't remember the dash comes before the delay time.
Thanks!

 

[r1dermon]

i launched an estes star dart with epoxy fillets and CA soaked balsa fins on a D21, launched off one of the low power estes pads at a local park...never found it, but it didnt shred, as i saw the ejection puff WAAAAAY up there. it simms out to 700mph supposedly, so thats good enough for me. lol.

 

[cls]

..never found it

I guess that's a good recommendation - against using an RMS!! don't want to lose a $20 motor in a $5 rocket

 

[Parrothead]

Well, I just tried this last Friday at SpringFest shortly after joining TripoliVegas .

D21-7 in a High Flyer - rocket on pad, rocket gone ! Ejection puff way up and out there, but no sign of the rocket - go figure!

Thankfully, someone found it for me on Saturday and the only damage to the rocket was a bit of paint missing around the top of the fins. I guess the ejection charge must've cooked the tube just a bit .

Now I'm designing a minimum diameter rocket for the new Ellis Mtn. single use 24mm G37 - OH YEAH !!!

 

[Tedman]

i have all the parts and they weigh .6 oz. without luanch lug. Ill try to have it completed sonn for a built weight. the fins area little big so if its too heavy ill make them a little smaller.

 

[r1dermon]

i might attempt another star dart D21 vanishing act at the first CMASS launch. we'll see.