Aerotech F44 "Econo-Max" 24mm x 70mm ???

[dshmel]

The only thing that's different is ... a few thousand feet of altitude.

I was commenting to my wife that is seemed like quite a few motors were slow to get up to pressure. I wonder if the higher altitude does have an impact on motor ignition (?)

 

[billspad]

I was commenting to my wife that is seemed like quite a few motors were slow to get up to pressure. I wonder if the higher altitude does have an impact on motor ignition (?)

It might but the elevation where those motors are made is 1200 ft. high than Pueblo.

 

[dpower]

Saw one blow the forward end off under thrust last Saturday, wasn't pretty. Maybe Paul will chime in with more details. His old Arapahoe was still smoldering ten minutes after the flight.

Yep, first one I've flown. Ignited promptly with the included First Fire Jr. Flames coming out the front & side of my Thrustline Arapahoe-E 50' in the air. I've contacted AT, and submitted a MESS.

After the flight, I noticed the package says "Put a Bolt of Lightning in your rocket!". Boy, they weren't kidding!

 

[Donaldsrockets]

Sorry to hear about these issues. I really wanted to try some of these.

It appears these motors are either at or very close to the limit of what the casings/bulkheads are capable of withstanding.

I guess I'll be holding off for now.

 

[TopRamen]

Sorry to hear about these issues. I really wanted to try some of these.

It appears these motors are either at or very close to the limit of what the casings/bulkheads are capable of withstanding.

I guess I'll be holding off for now.

Me too.

 

[Winston]

It appears these motors are either at or very close to the limit of what the casings/bulkheads are capable of withstanding.

From the Aerotech press release. I've italicized what I think may be the possible contributing factors:

So how did AeroTech squeeze nearly 83 N-sec out of case size that previously was limited to around 53 N-sec (a 56% increase)? According to AeroTech President Gary Rosenfield, after 41 years of designing composite rocket motors, a number of new design ideas all came together:

• “High-solids” propellant with higher specific impulse (Isp), high density and higher burn rate to minimize throat erosion and delay grain length.

• Volumetrically efficient “finocyl” propellant grain design.

• No separate case liner, so larger diameter propellant grain.

• Longer propellant grain due to shorter delay and bulkhead.

• Slightly higher motor peak operating pressure.

• Relatively flat thrust curve to increase average pressure.

 

[dpower]

From the Aerotech press release. I've italicized what I think may be the possible contributing factors:

So how did AeroTech squeeze nearly 83 N-sec out of case size that previously was limited to around 53 N-sec (a 56% increase)? According to AeroTech President Gary Rosenfield, after 41 years of designing composite rocket motors, a number of new design ideas all came together:

• “High-solids” propellant with higher specific impulse (Isp), high density and higher burn rate to minimize throat erosion and delay grain length.

• Volumetrically efficient “finocyl” propellant grain design.

• No separate case liner, so larger diameter propellant grain.

• Longer propellant grain due to shorter delay and bulkhead.

• Slightly higher motor peak operating pressure.

• Relatively flat thrust curve to increase average pressure.

Well, this text would seem to refer to the G74, but perhaps similar tricks were used on the F44. My cato was a not a case failure, it was a failure somewhere in the foreword end, perhaps the seal between the propellant and delay, or seal between the delay and yellow bulkhead. The yellow bulkhead was still securely epoxied in place. It would be interesting to disassemble the remaining motor to see how they're constructed.

 

[bill_s]

I had similar problems with the F30FJ, 2 of 2 early ejection with varying damage, and I'm not the only one. Those motors are lower performance than the same size F32T which is reliable, although pressure could still be high due to a smaller nozzle. Seal issues, no doubt. One didn't even make it off the pad. But is this a design or assembly problem?

 

[marcusSRG]

I also had an F30FJ fail on the forward end. Yellow bulkhead was still in place but burnt through the middle. Delay was totally bypassed and burnt out--possibly ejected, can't remember. Propellant burnt from both ends after the bulkhead failed.

Not happy to hear of some of these results, but it sounds as if some of the failures are common to this 24mm design, not necessarily the uprated motors, although it very well could be.

I'm most concerned about these ignition issues I'm hearing about since I plan to cluster these. I hope the long ignition times were altitude related. Like the optimized WL they use in the E20W (same propellant I'm pretty sure, just in a smaller grain w/a liner), I would expect it to light up fast, as E20Ws seem to do. That is, with a good igniter like the FirstFire Minis provided with these EconoMax motors. A lot of E20W's went out with Q2G2's which definitely won't work.

I'm still very intrigued by these and look forward to trying some. I want to cluster these using the FirstFire mini igniters...er starters. They seem as if they would be up to the task as regular FF's and FF Jr.s work well in a cluster. Ground start with a 12V system of course!

 

[dpower]

Marcus, that F30FJ failure sounds similar to my F44 failure.

In the interest of science, the remaining F44 was carefully disassembled. Kids, don't try this at home.

After removing the ejection charge, a hacksaw was used to (very) slowly cut around the case, right where the delay insulator would be expected. Bingo.

Photo 1 shows the two halves
Photo 2 shows propellant grain removed
Photo 3 another angle, highlighting the interesting forward geometry of the grain
Photo 4 shows the delay grain, insulating sleeve, O-Ring, and aft bulkhead, which threads into the case, and is epoxied
- also note cuts in the delay sleeve from this procedure
Photo 5 shows most pieces removed, the delay is still in its sleeve
Photo 6 another angle, from which the grain core can be seen
Photo 7 the delay has been removed from its sleeve
Photo 8 shows the delay, sleeve, and O-Ring re-inserted, to illustrate a roughly 1/32" gap when pressed in tightly



That's all folks. Aerotech is sending me a new pack of motors.

 

[dpower]

I also had an F30FJ fail on the forward end. Yellow bulkhead was still in place but burnt through the middle. Delay was totally bypassed and burnt out--possibly ejected, can't remember. Propellant burnt from both ends after the bulkhead failed.

Not happy to hear of some of these results, but it sounds as if some of the failures are common to this 24mm design, not necessarily the uprated motors, although it very well could be.

I'm most concerned about these ignition issues I'm hearing about since I plan to cluster these. I hope the long ignition times were altitude related. Like the optimized WL they use in the E20W (same propellant I'm pretty sure, just in a smaller grain w/a liner), I would expect it to light up fast, as E20Ws seem to do. That is, with a good igniter like the FirstFire Minis provided with these EconoMax motors. A lot of E20W's went out with Q2G2's which definitely won't work.

I'm still very intrigued by these and look forward to trying some. I want to cluster these using the FirstFire mini igniters...er starters. They seem as if they would be up to the task as regular FF's and FF Jr.s work well in a cluster. Ground start with a 12V system of course!

Yep, I'd like to cluster some 24mm AP too, I have a bird that takes 7x D12, but needs more power. I'm going to give these some time first, though. The igniters included in these are very nice, and they do light faster than a typical small WL motor (for example, the E18 or F24). I'm disappointed to hear of your F30 failure, the F32 has been reliable for me. The case was fine on my cato, clearly some sort of forward seal failure.

 

[dpower]

I had similar problems with the F30FJ, 2 of 2 early ejection with varying damage, and I'm not the only one. Those motors are lower performance than the same size F32T which is reliable, although pressure could still be high due to a smaller nozzle. Seal issues, no doubt. One didn't even make it off the pad. But is this a design or assembly problem?

Good question. The yellow forward closure threads in, and is epoxied. The disassembled one was clearly at the end of the threads (i.e. it couldn't have been any tighter). Perhaps the O-Ring didn't have quite enough pressure? Or maybe the compression of the grain allows the seal to be less effective than with a liner (which wouldn't explain an F30 cato)? That's all speculation of course, but I'm hopeful that early feedback like this to AT will help their failure analysis and tweaking of the design or assembly if necessary.

 

[CarVac]

Marcus, that F30FJ failure sounds similar to my F44 failure.

In the interest of science, the remaining F44 was carefully disassembled. Kids, don't try this at home.

After removing the ejection charge, a hacksaw was used to (very) slowly cut around the case, right where the delay insulator would be expected. Bingo.

Photo 1 shows the two halves
Photo 2 shows propellant grain removed
Photo 3 another angle, highlighting the interesting forward geometry of the grain
Photo 4 shows the delay grain, insulating sleeve, O-Ring, and aft bulkhead, which threads into the case, and is epoxied
- also note cuts in the delay sleeve from this procedure
Photo 5 shows most pieces removed, the delay is still in its sleeve
Photo 6 another angle, from which the grain core can be seen
Photo 7 the delay has been removed from its sleeve
Photo 8 shows the delay, sleeve, and O-Ring re-inserted, to illustrate a roughly 1/32" gap when pressed in tightly
View attachment 181041View attachment 181042View attachment 181043View attachment 181044
View attachment 181045View attachment 181046View attachment 181047View attachment 181048

That's all folks. Aerotech is sending me a new pack of motors.

Dang, that's a short smoke grain. They did mention that it was shorter than usual, but it's still 8 seconds??

Also, what does the grain look like from the bottom? Circular core?

And lastly, those pictures are too darned small on my new monitor. But than you anyway for posting them! Very cool.

 

[rcktnut]

Dang, that's a short smoke grain. They did mention that it was shorter than usual, but it's still 8 seconds??

Also, what does the grain look like from the bottom? Circular core?

And lastly, those pictures are too darned small on my new monitor. But than you anyway for posting them! Very cool.

Bottom of grain is visible in pic. 6.

 

[Donaldsrockets]

Dang, that's a short smoke grain.

Maybe that's the problem - the delay element looks too thin to effectively hold back the pressure.

If this is the case, I would imagine the problem would be worse with the 4 second delay.

I wonder if any problems have been reported with the F44-4W's yet.

 

[dpower]

Here's a zoomed in pic of the grain, aft end.

 

[RochonRockets]

Dang, that's a short smoke grain. They did mention that it was shorter than usual, but it's still 8 seconds??

Also, what does the grain look like from the bottom? Circular core?

And lastly, those pictures are too darned small on my new monitor. But than you anyway for posting them! Very cool.

If you hold the control button and tap the "+" on the number pad you will zoom in [CTRL] + "-" Zooms out.

I often have to Zoom in on Pictures to get the details.

 

[CarVac]

If you hold the control button and tap the "+" on the number pad you will zoom in [CTRL] + "-" Zooms out.

I often have to Zoom in on Pictures to get the details.

Not size, pixel count. I leave scaling off so I can fit the maximum content on screen, but when you have eight million pixels to fill, ant sized pictures are pretty fuzzy when you zoom in.

 

[CarVac]

Maybe that's the problem - the delay element looks too thin to effectively hold back the pressure.

If this is the case, I would imagine the problem would be worse with the 4 second delay.

I wonder if any problems have been reported with the F44-4W's yet.

I don't think the delay grain itself is not able to support the pressure. I was just remarking that it was quite squat and that is how they fit more impulse in the same form factor.

 

[bobkrech]

From the Aerotech press release. I've italicized what I think may be the possible contributing factors:

So how did AeroTech squeeze nearly 83 N-sec out of case size that previously was limited to around 53 N-sec (a 56% increase)? According to AeroTech President Gary Rosenfield, after 41 years of designing composite rocket motors, a number of new design ideas all came together:

• “High-solids” propellant with higher specific impulse (Isp), high density and higher burn rate to minimize throat erosion and delay grain length.

• Volumetrically efficient “finocyl” propellant grain design.

• No separate case liner, so larger diameter propellant grain.

• Longer propellant grain due to shorter delay and bulkhead.

• Slightly higher motor peak operating pressure.

• Relatively flat thrust curve to increase average pressure.

AT has a new 29/80 casing https://www.rocketmotorparts.com/2980_EMK__Single-Use_Experimental_Motor_Kit/p1577809_7833141.aspx for the G74 single use motor as well as a new 29/60 casing. https://www.rocketmotorparts.com/2960_EMK__Single-Use_Experimental_Motor_Kit/p1577809_7833130.aspx

The F44W has a total impulse is 41.45 Ns which fits in a 24mm x 70 mm casing. https://www.nar.org/SandT/pdf/Aerotech/F44W.pdf

Bob

PS Thanks to CarVac and ShredVector for pointing my error out. I should have remembered that since I was on the certification team.....

 

[CarVac]

AFAIK AT has a totally new 29/80 casing https://www.rocketmotorparts.com/2980_EMK__Single-Use_Experimental_Motor_Kit/p1577809_7833141.aspx

as well as a 29/60 one. https://www.rocketmotorparts.com/2960_EMK__Single-Use_Experimental_Motor_Kit/p1577809_7833130.aspx

But here is the certification paperwork for the F44W https://www.nar.org/SandT/pdf/Aerotech/F44W.pdf The total impulse is 41.45 Ns so it's barely an F....which is easy to fit in a 29mm x 70 mm casing.

Bob

The F44 is 24x70, not 29x70.

 

[TopRamen]

The F44 is 24x70, not 29x70.

Right! His Post confused me too.

 

[shreadvector]

I sent him an IM, he corrected it, but the correction note has an error (22mm). The main message is now correct.

If therre is a bubble inside the delay grain, it will probably fail and burn through the top. if flames came out the top and center of the delay ejection housing, then the dealy either failed straight through (bubble/void) or the seal at the forward end of the delay did not seal properly inside the delay housing.

It sounds like there were no failures of the epoxy holding the housing into the casing, so that is a good thing.

Report any failures with as much detailed info as possible to Aerotech and they will certainly look to see if there is possibility that some delay elements had voids or if the sealing is an issue. I'm sure they do things to eliminate voids (like curing with a vacuum?) and they can look at improving this or doing a post-cure NDI (ultrasonic or X-ray? I'm sure that will cost more than just increasing the vacuum and covering the hopefully very few ramaning failures per warranty). If it is the seal, then a teeny change to an o-ring or a teeny bit more grease might do the trick.

FWIW, I've seen dozens and dozens of the F32 motors launch and only one failure, which was just like these. I would estimate that the F32 failure rate was lower than the D12 failure rate based on the many launches I've observed.

I've still got a large motor supply from my last big orders, but when i order again, I will order some of these F44 motors. And if they show up at a LHS, then I will buy a pack or two.

BUT I really want an F44-6. The -4 and -8 are not optimum for my biggest use which is right in the middle and includes TARC. An F44-6 would be PERFECT for this year's TARC.

I've done one test flight for this year's TARC using an Estes E16-6 and I got an altitude of 802 feet. I build light and that model was built to play around with last year's TARC has flown 6 or 7 times already with no damage other than the original shock cord (1/4" elastic and very long) was no match for the F15-6 ejection charge. It has been replaced with a Kevlar anchor cord mounted along a fin root and tied to a new 1/4" elastic shock cord.

OK, I'm done rambling now.....

The F44 is 24x70, not 29x70.

 

[Winston]

Well, this text would seem to refer to the G74, but perhaps similar tricks were used on the F44. My cato was a not a case failure, it was a failure somewhere in the foreword end, perhaps the seal between the propellant and delay, or seal between the delay and yellow bulkhead. The yellow bulkhead was still securely epoxied in place. It would be interesting to disassemble the remaining motor to see how they're constructed.

I suspect the same tricks would be used. “High-solids” propellant + no separate case liner possibly equals a less rubbery propellant not adequately bonding to the linerless casing and/or the shorter delay and bulkhead at higher peak operating pressure leading to blow-by around that.

 

[swatkat]

I see the lot numbers on the side for the unit above. Can someone verify if all the failures were from the same lot? I've launched three F44-8s to date without issue. I don't have any F44-4's, but I do have thee more 8's. I'll grab the lot numbers here today. All of mine have taken a few seconds to ignite at only 250 feet above sea level in dry conditions. This is with a 12v 2A ignition system, so should be PLENTY of power.

 

[swatkat]

102544 are on all mine, including the spent ones. Another guy in our launch group has six more, purchased about 3 weeks before mine. He has yet to launch them, but we will here early next month in a 13" 24mm carbon fiber dart.

 

[Winston]

FWIW, I've seen dozens and dozens of the F32 motors launch and only one failure, which was just like these. I would estimate that the F32 failure rate was lower than the D12 failure rate based on the many launches I've observed.

I've never had a CATO with the F32, but in a recent flight with one using an altimeter (AltimeterTwo) for the first time, the 8 second delay was actually 11. The 8 second delay was already chosen to be a bit long to avoid pre-apogee deployment, so it was one of those "come on... any time now would be good" flights.

 

[PhlAsh]

One of our guys had one of these Cato on him last weekend - AeroTech said there was an issue with the o-rings in earlier batches and provided him a refund. Check your batch number with AeroTech before launching.

 

[bob jablonski]

I fired a half a dozen F's and watched a few more with no issues. Must be a later batch.
Mr. Bob
Countyline Hobbies
Grovertown, IN.
574-540-1123
[email protected]
www.countylinehobbies.com

 

[billspad]

One of our guys had one of these Cato on him last weekend - AeroTech said there was an issue with the o-rings in earlier batches and provided him a refund. Check your batch number with AeroTech before launching.

Are you talking about F44's or F32's? Do you have the batch number of the bad motors?