Launch report - Nov 22, 2008
 

I made it out for some flying at the DARS launch today. Lots of broken fins, but still had a great time. Doug.

Report and pics here: http://home.flash.net/~samily/stuff/nov-22-2008.html



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Doug,
I was out at the launch today, flying with my daughter.

This was the first time we have flown in the cold weather.
We sent up three rockets we have previously flown on that field, with motor selections that have been perfect for the rocket / field size.

On two of the flights, the altitude was significantly lower, and the ejection delays seemed longer.
Third flight was an E9 that got about the same altitude as previous flights, but it's delay was noticably longer than previous flights with the same motor selection (same package!)
No broken fins, but a small zipper from the late deployment.

Also witnessed two CATOs, which I have heard can be caused by temp cycles.
Seemed like a lot of flights had late deployments.

Is this possibly a reaction the BP motors have to colder weather?
Slower burn times in the delay possibly?
Or maybe just due to denser air?

Had a lot of fun flying today, but left the field wondering about the performance drop of the motors.

Big thanks to DARS for putting on these launches!

JW

Lots of broken fins.....must have been windy down there. I've never had a problem with broken fins except when I flew in Huntsville with the HARA guys at the old airport (now soccer fields) or with Don in Memphis. Traveling that far, I flew rockets in winds that I'd never fly in here at home.

LOL...and I think the only broken fin came when I stepped on my rocket.... :o

I think the Serval launch was the most demonstrative of the wind. With the tubed fins, it didn't weather cock. Nice vertical ascent that had a cross slide of close to 30 feet I'd guess downwind.... :chuckle:

It was tricky windy. It didn't seem that strong at the pads. But the landings were rough. That's why I concluded it was a combination of the wind and the hard ground. Either that, or I'm in denial about how much chute I shoulda been using :)

Doug

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Keep in mind, that while it was cold to us, it was Texas cold. Many of our Yankee brethren would consider our 60° outing beach weather :D

Flying a motor cold shouldn't make it more cato prone unless it was already damaged. Repeated temperature cycling, at pretty good extremes, say between freezing to over 100°, is required to make motors pop. So the two E9's we saw let go yesterday were either defective from the factory or had been improperly stored. That is, a lot more than just our cold day was involved.

As for the burn times and delays, I know temperature slighthy affects APCP, but not sure about BP.

With the cold, dry conditions, the air is denser and thus the drag will be increased and affect altitudes, but I imagine that's only a small factor. Instead, what happens in the wind is that you get some binding on the rod, and crabbing in flight. At liftoff, some impulse gets expended overcoming the increased friction of the launch lug due to binding. I even saw one rocket, when launched, move up a bit, then hesitate, then take off.

When the rockets weathercock, they crab some, and that dramatically increases drag substantially reducing altitude. So the wind effects were much more likely factors than air density.

Glad you came out to the launch. We need to bug Don now about having another one next weekend :) I still got some rockets with fins that aren't broken :)

Doug

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Thanks for the reply Doug.
I had not thought of the binding on the rod, that would explain a lot.
Our E9 flight was in a upscale Rouge, which does weathercock severly. I noticed some rod whip as it left the pad.

The winds on Saturday were tricky.
I noticed at one point some low flying clouds that were moving much faster than the ground level wind speed.

Still a fun launch, good turn out and a lot of flights.

I'm ready for another one!

JW

I had an E9-4 blow a nozzle a week ago. Is that what happened to the E9's you speak of? Maybe there's a bad batch.

Yes. I saw the casing from one and the nozzle was completely gone. We even searched for it. And I'm pretty sure the other one was, too, but I don't have as distinct a memory of it.

I believe one motor was an E9-4 and the other an E9-6. I've heard stories before, not long after these motors were introduced, of some nozzle failures, but I've never had one fail, knock wood.

Doug

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Yeah I've heard of E9's popping nozzles before. First time it's happened to me though.