Warp 9 reload issues

[timothyterpsalot]

I am using the G69N reload.
The instructions say to grease the front end of the propellant and the aft end of the smoke grain. Staying faithful to the directions that aerotech put down for me. I was a bit confused and worried that the tracking grain wouldn't ignite. It didn't. Should I stray from the directions and not grease the end of the grains? Thanks
-Timothy

 

[cjl]

It's not supposed to light. It's really only there to take up space so there isn't a void.

 

[Handeman]

What cjl said. You don't have to grease the delay grain, but because of the nature of the Warp9 propellant, it usually "blows out" the delay grain when the burn ends and the case pressure drops. That is why none of the Warp9 loads have motor ejection.

 

[cls]

definitely put some grease on the end of the grain!!

without it, the case will overpressure when the end of the grain lights.

I don't have the pictures handy right now so I can't post them, but the results ain't pretty.

good for you, reading the instructions!

 

[Handeman]

definitely put some grease on the end of the grain!!

without it, the case will overpressure when the end of the grain lights.

I don't have the pictures handy right now so I can't post them, but the results ain't pretty.

good for you, reading the instructions!

Why would lighting the delay grain cause the casing to over pressurize? The delay doesn't burn fast enough to add any pressure to the casing. If you had a casing blow an endcap, I'm sure it wasn't from the delay grain burning.

 

[jj94]

Why would lighting the delay grain cause the casing to over pressurize? The delay doesn't burn fast enough to add any pressure to the casing. If you had a casing blow an endcap, I'm sure it wasn't from the delay grain burning.

I was always confused about that too, but I think Gary also said something like that.

 

[JDcluster]

For one thing; the G 69 is an end burning Warp 9 load. I built mine according to the direction & worked out fine. I did use the electronic forward closure for deployment. I flew it in a 4" x 3lb rocket with a 5 sec programmed into the timer.
it only went maybe 500ft or so.

JD

 

[clreynolds]

Why would lighting the delay grain cause the casing to over pressurize? The delay doesn't burn fast enough to add any pressure to the casing.

I think we are mixing two separate but related subjects.

1) Grease the propellant grain to reduce the burning surface and keep the overall pressure in range.

2) Grease the delay grain so it doesn't burn and reduce it's thickness.

The delay grain acts as a forward pressure seal. Since pressure is already high, if the delay is buring, it will quickly become thin enough to blow thru, drastically reducing the pressure prematurely, and freaking up the works.

Just my :2:, I could be wrong about this just like most other mysteries of life, like women.:confused2:

 

[Rocketjunkie]

You do not need to grease the smoke grain in a BATES grain Warp9 motor. It's plenty thick to withstand the pressure.
You *DO* need to grease the forward end of the end burning Warp9 grains like the G69 or I49. If you don't, the forward end is likely to light doubling the burning area - *bad news*.

 

[jj94]

I think we are mixing two separate but related subjects.

1) Grease the propellant grain to reduce the burning surface and keep the overall pressure in range.

2) Grease the delay grain so it doesn't burn and reduce it's thickness.

The delay grain acts as a forward pressure seal. Since pressure is already high, if the delay is buring, it will quickly become thin enough to blow thru, drastically reducing the pressure prematurely, and freaking up the works.

Just my :2:, I could be wrong about this just like most other mysteries of life, like women.:confused2:

I don't think that can happen because the Warp 9 load's we're talking about are all end burning, so then the delay wouldn't be burning with the propellant. Once the propellant reaches the forward end (by the time the motor is done burning), then the delay should catch...or so I would think. I've never flown one of these so I wouldn't know exactly either.

You do not need to grease the smoke grain in a BATES grain Warp9 motor. It's plenty thick to withstand the pressure.
You *DO* need to grease the forward end of the end burning Warp9 grains like the G69 or I49. If you don't, the forward end is likely to light doubling the burning area - *bad news*.

That makes more sense to me, but still, how would the front end catch a burn if it's an end burning grain? Does the grain have a physical burn profile that isn't flat? I don't know if what I'm saying makes sense to anyone, I'm kind of making some words up as I go...I don't know the exact terminology. So, with an end burner, I would typically expect to burn from end to end flatly, so that all the propellant burns at the same rate. The only way I could imagine the front end of the grain catching would be if it burned with maybe a conical profile. So that the middle of the grain, when looking from the side, was ahead in the burn than the sides. So that by the time the burn got to the forward end, the front would burn through the end first, and then make the rest of the forward end flare up causing a pressure spike.

 

[troj]

You *DO* need to grease the forward end of the end burning Warp9 grains like the G69 or I49. If you don't, the forward end is likely to light doubling the burning area - *bad news*.

Okay, that just doesn't make sense...

On an end burning grain, if you light the aft end, the only way the flame front gets to the forward end is if it burns through the grain.

Either that, or you've got a seal problem, and gasses are getting around to the front of the grain, which is indicative of other problems.

-Kevin

 

[shreadvector]

End burning motors virtually NEVER have a completely flat face to the burning surface. They form a dome. It may be a shallow dome or a deep dome. Either way, when the tip top of the dome reaches the end of the grain, it will rupture through and ignite the entire exposed forward face. This will then be burning along with the already burning exposed dome and the combined surface area will blow the motor apart.

This even happened on the old black powder AVI "Gold Series" uber-fat E and F motors. They were giant booster motors with a delay grain and ejection charge inside a 24mm motor tube that was epoxied into the top. They routinely blew out the side of the main motor tube when the motor burn reached the top. They solved this by painting the top of the propellant with paint.

 

[Shade]

End burning motors virtually NEVER have a completely flat face to the burning surface. They form a dome. It may be a shallow dome or a deep dome. Either way, when the tip top of the dome reaches the end of the grain, it will rupture through and ignite the entire exposed forward face. This will then be burning along with the already burning exposed dome and the combined surface area will blow the motor apart.

This even happened on the old black powder AVI "Gold Series" uber-fat E and F motors. They were giant booster motors with a delay grain and ejection charge inside a 24mm motor tube that was epoxied into the top. They routinely blew out the side of the main motor tube when the motor burn reached the top. They solved this by painting the top of the propellant with paint.

Interesting, but the delay grain still can add that much to the pressure of the burning fuel? As the dome ruptures and the opening gets larger you burning surface area drops off fast and the delay grain is much slower burning. Or is the combination of the chemistries the issue. What do the Warp-9 engines use to get their higher performance/burning rates?

Most of Aerotechs trust profiles show that the thrust drops off in the last 20% or so the the burn time, so I would assume case pressure also drops off.

 

[shreadvector]

Interesting, but the delay grain still can add that much to the pressure of the burning fuel? As the dome ruptures and the opening gets larger you burning surface area drops off fast and the delay grain is much slower burning. Or is the combination of the chemistries the issue. What do the Warp-9 engines use to get their higher performance/burning rates?

Most of Aerotechs trust profiles show that the thrust drops off in the last 20% or so the the burn time, so I would assume case pressure also drops off.

I do not think the burning of the delay in THIS reload would contribute to pressure in any meaningful way. The grease is simply to prevent it from burning. As to why, you should e-mail Gary and ask him. We are simply guessing. We do know it MUST be there to provide a good seal of the top of the motor. If it were to burn thin, it would fail under pressure through the delay material itself, but we all seen to wonder how it could possibly burn that much since the 'flame front' will not hit it until the motor is virtually burned out (teeny fraction of a second).

The other Aerotech thrust profiles have nothing to do with this load. They have larger bits of propellant remnanats/slivers remaining as their burn completes.

https://www.nar.org/SandT/pdf/Aerotech/G69.pdf

The flat burn slightly increases over time, most probably a combination of 2 things: dome gets larger as the burn along the liner will lag behind the burn at the top of the dome and slight mass consumption from the consumed liner as the burn progresses. The remanat at the end which forms the tiny 'tail' is the clearly the bit left over at the top and it is clearly inhibited on the top surface (if not, the curve would jump off the scale - and I know this because I ran thrust curves on the AVI gold motors at MIT to help confirm myb theory of why they were blowing out).

 

[Rocketjunkie]

Okay, that just doesn't make sense...

On an end burning grain, if you light the aft end, the only way the flame front gets to the forward end is if it burns through the grain.

Either that, or you've got a seal problem, and gasses are getting around to the front of the grain, which is indicative of other problems.

-Kevin

There are enough gaps between the grain and liner and liner to case that hot gases can go around the grain to the front end. It's just momentary as the motor comes up to pressure but it is enough sometimes to light the front surface unless it's inhibited. You've probably seen soot on the outside of the liner on some RMS motors when you clean them.

 

[shreadvector]

There are enough gaps between the grain and liner and liner to case that hot gases can go around the grain to the front end. It's just momentary as the motor comes up to pressure but it is enough sometimes to light the front surface unless it's inhibited. You've probably seen soot on the outside of the liner on some RMS motors when you clean them.

And that is another excellent point that I did not mention. Thanks!

 

[falingtrea]

My guess is that the delay does not ignite consistantly, so the recommendation for greasing the delay or using a plugged forward enclosure. And the delay element is included in the kit so you can use the standard enclosure.

Greasing the motor grain is probably to keep the forward end from igniting and causing an overpressure when the burn front breaks through. If you look at the thrust curve, the thrust increases slightly as the burn time increases, until the abrupt drop when I assume the burn front breaks through. I would bet that is you did not grease the forward end of the grain, the thrust curve would show a spike at the end.

 

[C.O.B.H.C.]

Yes grease both the delay grain and fuel grian because if you flight the motor ungreased it will CATO the motor. I know a friend of mine flew the G69 and forgot to grease the both the delay grain and fuel grain and the motor CATO'd.

 

[Binder Design]

Okay, that just doesn't make sense...

On an end burning grain, if you light the aft end, the only way the flame front gets to the forward end is if it burns through the grain.

Either that, or you've got a seal problem, and gasses are getting around to the front of the grain, which is indicative of other problems.

-Kevin

Kevin,

If you don't inhibit the front of the grain the flame will propagate around the liner and ignite the grain causing burning from both ends. This would be especially likely with warp 9 which is magnitudes more sensitive than AT's other formulas. Remember, the liner is not a pressure vessel, it is only there to insulate the casing and is designed for a loose seal so that the gasses do not pressurize the liner causing it to crack.

Mike Fisher

 

[jcsalem]

I flew an ungreased G69. While I avoided a CATO at launch, the end of the grain did eventually burn through the top of the liner tube. This caused a "mini-CATO" towards the very end of the burn. You could hear a loud "pop" from the ground and, examining the motor afterwards, you could see that motor lost pressure as the liner tube collapsed.

Sounds like it could have been worse! A great motor but don't skip the grease,

Jim

 

[georgegassaway]

I flew an ungreased G69. While I avoided a CATO at launch, the end of the grain did eventually burn through the top of the liner tube. This caused a "mini-CATO" towards the very end of the burn. You could hear a loud "pop" from the ground and, examining the motor afterwards, you could see that motor lost pressure as the liner tube collapsed.

This is as Fred described earlier.

While the grain is an end-burner, the burning surface is not flat. It is dome-shaped as it burns. When it reaches the end of the propellant grain, the top of the dome breaches the front end of the grain, igniting the entire front face of the grain, effectively doubling the burning surface area. Also, it could potentially even cause the remainder of the top of the grain to fragment into loose pieces that would be VERY bad if they were not totally consumed before they got to the nozzle (i.e. blocking the nozzle throat).

So, grease the front end of the fuel grain, and the delay train as indicated.

The effect of an endburner is something that I have dealt with many many times with the "R/C" reloads like the 24mm D7/E6, and 32mm F13/G12. If the front ends are not greased, there will be a big spike in thrust at burnout. With the grease, the burnout is smooth. Actually, since I was told of this before I did my first one, I do not even think I have flown one without the front end greased, I only know of a few people who have not done it because either they did not know, or forgot. And those have been with Blue Thunder propellant. I understand the Warp-9 is a much faster burn propellant, and I suspect it would be even more pressure sensitive in burn rate than Blue Thunder (more pressure causing faster burn, causing more pressure, and even faster burn, a very vicious cycle that ramps up VERY fast). So I can see how a Warp-9 propellant endburner may be a whole lot stronger when it comes to NOT greasing the front end compared to the "R/C" Blue Thunder reloads.

- George Gassaway