H128 Question

[eggplant]

I am almost ready for my L1! My rocket weighs 2 pounds 12 ounces with nearly everything in it (recovery, retention, etc). It is 4"x4' and is a basic 3FNC design. OpenRocket says that it will fly to about 1500' on an H128. I already have an H128-M. Will this be the correct delay? I have no idea what delay time an M equates to, so I can't plug it into OR. Thanks!

[Aksrockets]

I am almost ready for my L1! My rocket weighs 2 pounds 12 ounces with nearly everything in it (recovery, retention, etc). It is 4"x4' and is a basic 3FNC design. OpenRocket says that it will fly to about 1500' on an H128. I already have an H128-M. Will this be the correct delay? I have no idea what delay time an M equates to, so I can't plug it into OR. Thanks!

I think it's a 10 second delay. 1500 is an awkward spot between an "S" and a "M".

EDIT: GOOD LUCK WITH YOUR CERT!!!

Alex

[eggplant]

I think it's a 10 second delay. 1500 is an awkward spot between an "S" and a "M".

EDIT: GOOD LUCK WITH YOUR CERT!!!

Alex

Thanks! I was worried about that. Hmmm... I may see if I can drill it out a bit. I can't wait for my cert flight. It will likely be within this next month! Then I will (hopefully) join an elite group of teenagers... Those who are Jr L1 certified! After all, who can wait until they are 18?

[DAllen]

You can buy a delay drilling tool from Aerotech for that very reason.

[CarVac]

Or just use slide calipers and a drill bit: that way you can drill any amount that you want. (1/32 is a second)

As long as I simmed my rocket before flight and hand-drilled out the appropriate amount, I never had an early or late ejection.

[Sgt Blowfly]

Or you can swap out the delay grain, if drilling isn't your thing

Bob
TRA6797

[bobkrech]

S = 6 seconds, M = 10 seconds, L=14 seconds. What is your calculated turn over time?

My quick sim says you have the proper delay.

Do not try to drill out the delay unless you have an Aerotech delay drilling tool, or one made according to their instruction sheet. The allowable delay variability for a 10 second delay is +/- 2 seconds. It is difficult to remove less than 3 seconds from a delay column since it is rubber and it moves. The minimum delay change with the Pro38 tool is - 3 seconds, probably for these reasons.

Bob

[CarVac]

You don't need a special tool; where do the instructions tell you how to make one other than by just hand-twirling a 1/4" bit?

The flexibility of the rubber binder isn't a significant issue in drilling out small delays, and if anything it gets more annoying the more you drill out, in my experience.

[Stewart]

When ive encounted a delay that the delay drilling tool would'nt cut clean a 1 or 2 second variation ive used a No11 hooby knife blade to cut a countersink /cone to the required depth - its not difficult

[JonSivier]

I am almost ready for my L1! My rocket weighs 2 pounds 12 ounces with nearly everything in it (recovery, retention, etc). It is 4"x4' and is a basic 3FNC design. OpenRocket says that it will fly to about 1500' on an H128. I already have an H128-M. Will this be the correct delay? I have no idea what delay time an M equates to, so I can't plug it into OR. Thanks!

What does OpenRocket say is the optimum delay time? Knowing the predicted altitude doesn't really tell you anything about how long it took to get there. My guess is that the M (10 second) delay will be acceptable, but you should be able to check that with the sim program.

Jonathan
-----
Jonathan Sivier
jsivier AT illinois DOT edu
NAR #56437 | Tripoli #1906
Home Page: http://www.sivier.me/

[eggplant]

It said about 8 seconds, which is half way between a short and a medium. What I wanted to know is which one to go with.

[Peter Olivola]

Go with a drilled medium.

[Stewart]

Two more things re drilling delays , the drill depth is measured in the centre of the hole/depression, so a 2 second or 1/16" drilling wont look like much, second the drilled side of the delay must face towards the fuel grains

[o1d_dude]

...so a 2 second or 1/16" drilling wont look like much...

This!

Every time I drill out a delay I am surprised at how small the dimple is.

[Pantherjon]

It said about 8 seconds, which is half way between a short and a medium. What I wanted to know is which one to go with.

Go with the Medium delay..Don't bother drilling or adjusting the delay, don't complicate things on your certification flight...Yeah, a 10 second delay may be a bit on the long side, just make your shock cord a couple feet longer, if possible..I am sure it will do fine.