Early Deployment With A Redline

[bguffer]

Put up my Aerotech Mirage up with a Memorex 7-in-1 camcorder again. This is the fourth time i've used that rocket camcorder combination. Deployment came way too soon.

Rocksim stated 4.8 second delay would be optimal. I used a G71R-4. Deployment seemed to occur between 2.0 and 2.5 seconds.

I don't think it was due to drag seperation. Never drag seperated before. I've put the rocket up with the same tape on the coupler in colder weather than launch conditions, and i have to work hard to shake the booster from the payload in 70 degree temperatures.

Noticed some powder marks on the chute which was nearest the motor.

When i got the redline i seperated the prepellant from the delay element, and stored the redline seperate from all my other motor grains and delay element grains. The redline propellant delay grain problem was supposed to be fixed a long time ago, but i took no chances. I did build the motor 12 hours prior to the launch.

Normal speed:
https://www.youtube.com/watch?v=-Bqaj6iZrjk&feature=channel_page

Fourth speed (repeating frames):
https://www.youtube.com/watch?v=3LLgoWbPoo8&feature=channel_page

What do you think? Drag seperation? Fast burning delay grain? If fast burning delay grain, should i bother contacting Aerotech?

 

[DAllen]

I've seen and personally experienced some early ejects on AT loads. One was on an F40 and the other on a friends H128. In both cases the liner around the delay grain leaked a little and was enough to set off the ejection charge. I could see a little black line that followed up one of the seams up to the top. With the F40 - that was my fault. I pealed some of the thin layers off the delay sleeve to get it to fit in the closure. The H128 - I am not sure what happened since it wasn't mine.

-Dave

 

[MarkM]

1) Difficult to tell IMO from the video. Although it doesn't look like drag separation. To really know, you need video looking at the rocket from the field, not from a rocket-cam.

2) Keep in mind. Aerotech delays can be as much as + or - 20%. For a 4s delay, that's almost a full second in either direction. Happens ALL the time. It's the nature of the delay grains and unfortunately this error is perfectly acceptable.

3) You could try contacting AT, but I doubt they'll do much. AT is very good at replacing motors that completely malfunction. A shorter than expected delay may not be one of those, however. Was there any damage to the rocket? It never hurts to try to contact AT, but I wouldn't be expecting anything especially if a rocket or hardware wasn't damaged.

4) Assembly 12 hrs prior to launch probably didn't have any affect. I assembled redlines the night before a launch when AT was still having issues with the chemical interaction of the propellant with the delay and never noticed a significant difference in the delay time beyond the normal + / - 20%. I don't think that was the problem.

You probably just got a shorter burning delay that still conforms to manufacturer error specs. You might not like it, nor does anyone else, but that's the way it goes sometimes...."luck of the draw" - or unlucky in this case.

 

[jj94]

I had a similar problem during our TARC qualification flight. Very nice boost with the G71, but then about a second after burnout, there was deployment. I'm inclined to believe that the deployment was caused by an inaccurate and fast burning delay grain. That's because I didn't see a puff of smoke that signals the ejection charge after deployment. I contacted Aerotech and got in touch with Mark Hayes (I think that's his name; his username he used to use here was Metalwizard). They sent out a replacement motor in no time, though shipping did take a while for some reason. I posted about that on the old TRF, and someone brought up a good point about pressure differences. Since the G71 gets a typical rocket up high fairly fast, there might not be enough time for the pressure inside the body tube to equalize with the exterior pressure. That means that the interior pressure could be great enough to cause deployment. Not sure if it's a plausible idea, but it sounds reasonable to me. So I also went ahead and drilled a single 1/8" hole in the body tube to help with pressure for when it flies on high thrust motors.

 

[Boosterdude]

That's really strange because I had the exact same thing happen this weekend using the same load, G71-4r. I was flying my G-Force and it separated very early. I thought it might be drag separation, but I've flown it many times without issue. Plus I never heard the ejection charge go of after it separated which I thought was strange. I recovered with no damage, so I was happy about that.

 

[Pantherjon]

Kind of what happened to me last year! But with a G76G-7..I put it in my NSL Thor to fly it single deploy, and that 7 second delay was more like a 1 second delay! Ripped the forward bulkhead thru the coupler and bent the all thread! That and put about a 1/2" 'gouge'(not really a zipper cause the BT was glassed) in the lower tube...

 

[billspad]

1)
2) Keep in mind. Aerotech delays can be as much as + or - 20%. For a 4s delay, that's almost a full second in either direction. Happens ALL the time. It's the nature of the delay grains and unfortunately this error is perfectly acceptable.

It's 20% or 1.5 seconds, whichever is greater (but less than 3 seconds).

 

[jadebox]

Sometimes the way the motor ignites can affect the delay. The delay might start burning before the motor comes up to pressure which can subtract a second or two from the delay period. Usually, though, the problem is the other way. The delay takes a little while longer to ignite than the propellant so you get a "bonus delay."

-- Roger

 

[UhClem]

I have seen a few G64 delays that had voids in the propellant exposed on one end. These will obviously cause a shorter than nominal delay. If a void is buried inside where it is invisible (which is more likely than having it appear on either end) it would have the same effect.

Solutions for this are vacuum degassing (if that isn't already done) and/or better process controls. The expensive cure would be some sort of X-ray or sonic inspection of the cast delay grains.


As a workaround with one delay that had a very minor void in one end I carefully packed a little grease into the void. I was very careful to get grease only into the void and not on the surrounding area as that would be bad. I then assembled the reload with this end towards the propellant. The goal was to slow down the ignition of the delay grain within the void. That particular flight went well.

 

[bguffer]

I have seen a few G64 delays that had voids in the propellant exposed on one end. These will obviously cause a shorter than nominal delay. If a void is buried inside where it is invisible (which is more likely than having it appear on either end) it would have the same effect.

Solutions for this are vacuum degassing (if that isn't already done) and/or better process controls. The expensive cure would be some sort of X-ray or sonic inspection of the cast delay grains.


As a workaround with one delay that had a very minor void in one end I carefully packed a little grease into the void. I was very careful to get grease only into the void and not on the surrounding area as that would be bad. I then assembled the reload with this end towards the propellant. The goal was to slow down the ignition of the delay grain within the void. That particular flight went well.

I built 4 motors. I do remember see a small void in one of the delay grains, but forget which one. I suspect it was a G64W-7 or the G71R-4 in question. It was tear shaped, about 3/64" deep by 4/64" long. Maybe there were other voids as well. Not sure... I'll definitely look start looking for voids, and keep that grease tip in mind. If i find a void, i think that motor will go into a rocket without a camcorder payload.

 

[bguffer]

Sometimes the way the motor ignites can affect the delay. The delay might start burning before the motor comes up to pressure which can subtract a second or two from the delay period. Usually, though, the problem is the other way. The delay takes a little while longer to ignite than the propellant so you get a "bonus delay."

-- Roger

I thought about that delay starting burn prior to motor burn. But ground video and on board video confirms that was not a problem. Did not know that some of the bonus delays were caused by propellant grains igniting prior to the delay grains. Learn something new everyday.

 

[Graham Orr]

Drag separation. What is the ballistic coefficient of your payload section? How about booster? If you divide the former by ladder and is > 1 then you have a problem.

 

[cjl]

Drag separation. What is the ballistic coefficient of your payload section? How about booster? If you divide the former by ladder and is > 1 then you have a problem.

On most rockets, that will be >1. It still isn't a problem unless the fit is really loose.