Backing up the apogee “drogue” event at lower alt. to mitigate separation fail in high alt. flights

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If I may, I would like to help here. There are many attempts to get BP to burn at high altitudes (Read: "In a vacuum") some work, others are rather spectacular and heartbreaking when they fail. I watched a VERY experienced flyer's rocket come in rather hot from 30K ft when the BP charge did not burn enough to eject the nosecone. I first designed The Peregrine CO2 ejection system (followed by the RAPTOR CO2 ejection system) for this reason. It should be noted that I tested these devices in a vac chamber and pulled 28.5"Hg (Simulating about 80K ft) to make sure they can deploy at high altitudes.
I have tested other gas generation devices in a this vac chamber with a 1/2" plexiglass top so that I can see and video test results. All I can tell you is that it is absolutely FASCINATING to watch the vacuum "suck the burn right out" of some of these devices! Scientifically and intuitively we know what will happen but to watch it is another thing all together! So my advice, if you decide to try and get BP to work at high altitudes is to find someone near you with a vac chamber to test it before you fly it!

If you are interested in CO2 ejection devices that have been tested in such a vac chamber you may wish to consider either the Peregrine or The RAPTOR from Tinder Rocketry!
https://www.tinderrocketry.com/rocketry-co2-ejection-system

23&35gm RAPTORS.jpg 45-60-75gm RAPTORS.jpg
 
richP said:
Wouldn't the deployment of the main handle that risk? Of course you'd have a shredded chute and damaged rocket, but it would still be separated, not-aerodynamic and possibly similar to drogueless profile.
Click to expand...

No question it mitigates the risk, in part that's the genesis of this idea, but if you can get that airframe separated at a higher altitude (w/o ripping the rocket apart) what's the difference between a drouguless event failing from 30K and one from say 10K both will have a terminal velocity that the main should survive when it deploys at say 1K.
 
Reinhard said:
The amount of gas that needs to be generated is the same at sea level and at high altitude. The important part is the pressure differential to ambient, not the absolute pressure. That's why parachute compartments on high altitude birds should be vented, so the rocket wont separate prematurely just from the near sea level pressure inside.

The problem with black powder on high altitude is that the ambient gas plays a role in the heat transfer between the grains. Black powder will not burn well at low pressures. Therefore at least partial containment is necessary for high altitude charges until the charge has burnt completely. If the containment fails before that, combustion will likely not continue completely. Tony Alcocer and Jim Jarvis have documented ways to achieve this.
A while ago, I had a chat with a professional in the area, who mentioned that ambient oxygen also plays a role in the combustion of BP. Apparently it has a negative oxygen balance. Don't quote me on that though, I might miss-remember that part, and the context was a different one, namely industrial safety and not high altitude deployment.

Reinhard
Click to expand...

Generally, that's what I understand as well, but I would expect that the amount of gas generated needs to be more because of the reduced pressure at altitude. It not only about generating more gas it is also about expanding the gas (atmosphere) that is there through heat. Actually I expect that is the most of it. While there will be less pressure outside the rocket the force required to shear the pins and overcome any friction will be the same.

Also, containment can be an issue at any altitude. I have had ground tests that fail when the same amount of BP is used in a typical cup style holder that are more than adequate when using a Pratt or Pratt style cartridge. Inspection revealed unburt grains of BP that I never see using the pratt style containers.
 
Tinder Rocketry said:
If I may, I would like to help here. There are many attempts to get BP to burn at high altitudes (Read: "In a vacuum") some work, others are rather spectacular and heartbreaking when they fail. I watched a VERY experienced flyer's rocket come in rather hot from 30K ft when the BP charge did not burn enough to eject the nosecone. I first designed The Peregrine CO2 ejection system (followed by the RAPTOR CO2 ejection system) for this reason. It should be noted that I tested these devices in a vac chamber and pulled 28.5"Hg (Simulating about 80K ft) to make sure they can deploy at high altitudes.
I have tested other gas generation devices in a this vac chamber with a 1/2" plexiglass top so that I can see and video test results. All I can tell you is that it is absolutely FASCINATING to watch the vacuum "suck the burn right out" of some of these devices! Scientifically and intuitively we know what will happen but to watch it is another thing all together! So my advice, if you decide to try and get BP to work at high altitudes is to find someone near you with a vac chamber to test it before you fly it!

If you are interested in CO2 ejection devices that have been tested in such a vac chamber you may wish to consider either the Peregrine or The RAPTOR from Tinder Rocketry!
https://www.tinderrocketry.com/rocketry-co2-ejection-system

View attachment 399425 View attachment 399426
Click to expand...

I'm probably as familiar as one can be with these without actually owning one, but it has been my understanding they are hard to get. Have I been told incorrectly?
 
jahall4 said:
I'm probably as familiar as one can be with these without actually owning one, but it has been my understanding they are hard to get. Have I been told incorrectly?
Click to expand...
I mostly ship next business day, sometimes same day if the order comes in early, so with respect, you have heard incorrect information!
 
jahall4 said:
Why? Are you suggesting that the resulting pressure from ignition somehow would be the same at any altitude using the same size charge?
Click to expand...

The pressure differential between inside the body tube and outside the rocket will be the same or even higher if the drogue bay vent is small.

The pressure increase from the charge will be the same at any altitude as long as you achieve full combustion.
 
Steve Shannon said:
The pressure increase from the charge will be the same at any altitude as long as you achieve full combustion.
Click to expand...

That's what I'm going to need some proof of. For that to be the case ALL of the pressure increase would have to be the result of the generation of gasses that previously did not exist. So while most of the increase may be the result of the gas, some of it would also have to be the heating of the air already present.
 
jahall4 said:
That's what I'm going to need some proof of. For that to be the case ALL of the pressure increase would have to be the result of the generation of gasses that previously did not exist. So while most of the increase may be the result of the gas, some of it would also have to be the heating of the air already present.
Click to expand...

My belief is that the heating of the trapped air at lower altitudes is done at the expense of cooling of the combustion gases. The amount of heat energy released is a constant.

Of course it’s always important to ensure that the chamber you have to pressurize is no larger than necessary. A piston could be a lot more effective than a high speed deployment.
 
Steve Shannon said:
The amount of heat energy released is a constant.
Click to expand...

Yes, no question assuming the same amount of BP is burned.

I'm thinking about the difference between heating air present inside the airframe at sea level vs a near vacuum where there is practically no air at all. I got a query into someone that's probably already run the number for 30K we'll see.
 
jahall4 said:
I'm thinking about the difference between heating air present inside the airframe at sea level vs a near vacuum where there is practically no air at all. I got a query into someone that's probably already run the number for 30K we'll see.
Click to expand...

As Steve pointed out, this effect is counteracted by the air cooling the combustion gases, which reduces the partial pressure by the combustion gases itself.
If one wants to really nitpick: The combustion gases of BP contain the triatomic CO2 with a higher heat capacity than the other biatomic gases involved (N2, O2, CO). Therefore, one would expect a slight gain in total pressure by exchanging heat from the combustion gases to the ambient N2 and O2. But this effect appears to be negligible from a quick look at the numbers. There are also liquid and solid particles. The burn holes in unprotected parachutes imply that at least not all of them have the time to cool down and transfer significant heat to ambient gas before ejection happens.

Reinhard
 
Some time back, I looked at the calculations for combusting BP and the pressure produced. I found out that the BP calculators assume that the temperature of the gas is the combustion temperature (somewhere in the range of 2500F as I recall, but it's been a while). I always thought this was an odd assumption because the average temperature in the recovery bay would be reduced by whatever amount of air is present. Further, the mass of air would be on the same order as the mass of the BP combustion products. So, there would be a significant reduction in the average temperature if air is present. I suspect that the consequence of this would be that a given charge would be somewhat less effective at low altitude compared to high altitude, assuming that all of the BP burns and that the same combustion products are formed.

Back when I did my L3, I was using a piston that had a pretty good seal with the air frame. I did my ground test, and the chute came out fine, but when I looked in the tube, it appeared that the piston hadn't moved. Hmm. So, I tried it again and got the same result. That's when I did the calculation of the volume of gas produced by the BP, which in my 4" L3 rocket, would have been enough to move the piston an inch or so at ambient temperature. So, I suspect the piston was moving quite a bit when the charge fired, and then it got sucked back to near its starting position as the gas cooled.

Jim
 
JimJarvis50 said:
Some time back, I looked at the calculations for combusting BP and the pressure produced. I found out that the BP calculators assume that the temperature of the gas is the combustion temperature (somewhere in the range of 2500F as I recall, but it's been a while). I always thought this was an odd assumption because the average temperature in the recovery bay would be reduced by whatever amount of air is present. Further, the mass of air would be on the same order as the mass of the BP combustion products. So, there would be a significant reduction in the average temperature if air is present. I suspect that the consequence of this would be that a given charge would be somewhat less effective at low altitude compared to high altitude, assuming that all of the BP burns and that the same combustion products are formed.

Back when I did my L3, I was using a piston that had a pretty good seal with the air frame. I did my ground test, and the chute came out fine, but when I looked in the tube, it appeared that the piston hadn't moved. Hmm. So, I tried it again and got the same result. That's when I did the calculation of the volume of gas produced by the BP, which in my 4" L3 rocket, would have been enough to move the piston an inch or so at ambient temperature. So, I suspect the piston was moving quite a bit when the charge fired, and then it got sucked back to near its starting position as the gas cooled.

Jim
Click to expand...

Jim, Thanks for taking the time to comment. I just spent about an hour talking to my "numbers guy" about this idea. He generally thought there was merit in the idea of a low altitude "safety" charge, but ONLY because you would be assured of containment via the ambient air pressure (of course this assumes the airframe is adequately vented). The presence of a ambient pressure for other reasons was of minimal or negligible.

Question if you don't mind... I'm just starting to read Mark Canepa's LDRS book, does it discuss your techniques for high altitude deployments?
 
jahall4 said:
Question if you don't mind... I'm just starting to read Mark Canepa's LDRS book, does it discuss your techniques for high altitude deployments?
Click to expand...
No, he did not discuss that. I made him aware of it, but it's on the cutting room floor.

Jim
 

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