AT G64W delays discrepancy

[Dane Ronnow]

I'm trying to run a flight sim in OR with the AT G64W, but when I create a new motor configuration, the delays listed for that motor are 4, 8 and 10 secs. The thrustcurve file for the motor shows the delays as 4, 7 and 10. I tried adding the thrustcurve profile in my motor database as both .eng and .rse files, but neither one shows up when I reopen OR. Any help would be appreciated.

 

[cerving]

Just override the delay in the motor selection. It will let you set anything. It doesn't really matter all that much, AT delays are notoriously inaccurate, they tend to be on the short side.

 

[Dane Ronnow]

Just override the delay in the motor selection.

Thank you! (I learn something new every time I come on these boards.)

 

[Dane Ronnow]

AT delays are notoriously inaccurate, they tend to be on the short side.

I'm just getting my feet wet with RMS hardware and reloads. The delay that comes in a kit can be shortened, correct? So if I need a 9-second delay, I order a G64-10W and shorten the delay by a second. Am I understanding this correctly?

 

[Neutronium95]

I'm just getting my feet wet with RMS hardware and reloads. The delay that comes in a kit can be shortened, correct? So if I need a 9-second delay, I order a G64-10W and shorten the delay by a second. Am I understanding this correctly?

The Aerotech delay tool shortens them in increments of 2 seconds. If a 9 second delay is optimal, then I would just leave it at 10 seconds.

 

[dhbarr]

Note that the g64 specifically used to come as monograin but is now two half grains. AFAICT this accounts for the two different sim values.

dhbarr's hdk research : final

 

[KenC]

Most gift cards and credit card blanks are about 1/32" thick. If you really want to deal with it, you can use either a spent or out of date card with a holed drilled through the card to provide 1 second increments... Flat non-embossed hotel keys and gift cards are perfect.

 

[Dane Ronnow]

Most gift cards and credit card blanks are about 1/32" thick

That's actually what I was thinking—what can I use that's half the thickness of the washer that comes with the drill.

If a 9 second delay is optimal, then I would just leave it at 10 seconds.

I would if the extra second didn't up my deployment velocity from 15 mph to 30 mph. That's on the descent side of apogee.

 

[Steve Shannon]

While it’s possible to tweak a delay grain by some slight amount in hopes of getting closer by a second, the actual burn time of delay grains frequently are one to two seconds different from what is listed on the package. They are simply not precise. Alan Whitmore wrote an excellent article about that topic a couple years ago that was published in the Tripoli Report.
If you truly want to hit apogee consistently, you’ll have to use electronics.

 

[Dane Ronnow]

the actual burn time of delay grains frequently are one to two seconds different from what is listed on the package.

That figures.

 

[Steve Shannon]

That figures.

It’s really not something that can be blamed on the manufacturers. Composite rocket motors are almost never end burning motors and so the delay grain is ignited at the same time the motor is lit. The delay grain burns at a different rate depending on the internal pressure of the motors. While the motor is burning that portion of the delay that burns does so at a rate of nearly five times as fast as it burns once the motor burns out.
Also, greater ambient pressure causes the delay to burn faster. Alan and I tested some full length delays by dividing them in half lengthwise and burning half at his elevation (near sea level) and half at my elevation (a mile high). At my elevation they consistently burned 8% longer.

 

[Dane Ronnow]

It’s really not something that can be blamed on the manufacturers.

When I said, "That figures," I didn't mean to imply this was the fault of the manufacturers. What I meant was that each time I decide to go in a different direction with the design of this rocket, I hit every obstacle imaginable. It's Murphy's Law.

I appreciate your post. It explains very clearly why delays vary. Thank you.