Possibility of using spring to boost Estes rocket on launch

[SolarYellow]

...................or

Paging @lakeroadster
Your next spool design is here.

 

[Stefan2k4]

As for "augmenting" a piston by adding something to it, why not add a non-combustible but volatile liquid, like water? It would seem that this would address the safety concerns and also the issue of "unfairness". I'm thinking this would add to the thrust created by the piston by converting wasted heat into thrust. In essence is that not what a piston does anyway? The way I see it, the hot exhaust has energy left in it when it leaves the nozzle, but without a piston that energy is simply lost. The piston uses that to create additional thrust. Adding a liquid like water would help achieve that by further cooling the exhaust and transforming that energy into thrust as it underwent phase change into gas which would help drive the piston. Obviously this would be safer that adding black powder or any other combustible. And one could view it as being more "fair" since you aren't adding any energetic material but are simply adding something that will better utilize the energetic materials already present in the motor and more efficeintly extract the energy that's already there.

 

[shockie]

If it weren't for the competition rules, I think a bit of black, golden or crimson powder where the motor exhaust could hit it would make sense with a piston. Or make something like a potato cannon. The piston could be a much looser fit. If I was doing this, I might wrap any PVC components with Kevlar or heavy nylon and/or I might pressure test to make sure they'd withstand as much pressure as a stoichiometric mix would generate. With water inside to prevent much of an explosion, or else in a hole in the ground, with ignition provided from a long way off.
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A catapult system that was fast enough to make the rocket stable from the moment it left the rail, and was initiated before ignition was confirmed, might lob an unlit rocket to a very consistent location where one could put a mattress, lots of hay, or a tarp set up a few feet above the ground. ;-) Might be good to test with an equivalent weight, though. Partial, insufficient ignition would be another story.

The problem with BP, Crimson & Golden powder mixes are they act. As an explosive in small confined spaces. After all, all 3 are used as ejection charges.

Black Powder is probably the worst possible additive to use in a piston because it only produces about 40% gas and 60% solids residue.


This requires cleaning after each use.

Plus ALL 3 of the above will create a power pulse whereas NC releases it's gas more gradually which is what you want in a piston


I quit using BP over 15 years ago and started using single base powders which are at least 80% nitrocellulose.

NC will produce approximately 4 to 6 times more gas than BP, and it produces almost no residue.

I have been using Hodgens Powder Accurate 4064.

 

[SolarYellow]

Wait, smokeless for piston supplementation? I like it.

I’ve thought about it for other stuff and concluded a fast pistol powder like AA2 or HP38 would make the best ball of fire at low pressure.

 

[Spacedog49Krell]

I prefer 4227.

 

[lr64]

I'm sure there are tweaks which would make crimson powder, or most fuels, burn more slowly. Specifics not to be discussed here.

 

[Alan15578]

As for "augmenting" a piston by adding something to it, why not add a non-combustible but volatile liquid, like water? It would seem that this would address the safety concerns and also the issue of "unfairness". I'm thinking this would add to the thrust created by the piston by converting wasted heat into thrust. In essence is that not what a piston does anyway? The way I see it, the hot exhaust has energy left in it when it leaves the nozzle, but without a piston that energy is simply lost. The piston uses that to create additional thrust. Adding a liquid like water would help achieve that by further cooling the exhaust and transforming that energy into thrust as it underwent phase change into gas which would help drive the piston. Obviously this would be safer that adding black powder or any other combustible. And one could view it as being more "fair" since you aren't adding any energetic material but are simply adding something that will better utilize the energetic materials already present in the motor and more efficeintly extract the energy that's already there.

You are going to have to show your thermodynamics math on that one.

 

[shockie]

I was using self turned Teflon piston heads since the late 70's.

I'll take your word on it. This shows that great minds think alike.

In 1974 Howard Kuhns puston used some Teflon tape around the piston head.

I didn't know this until decades later but that's where I got my idea from.

 

[lr64]

You are going to have to show your thermodynamics math on that one.

I should think the water would have to be sprayed as a mist in order for it to heat up fast enough. Or else a tiny, thin bag of it could be inserted behind the igniter. I'm no thermodynamicist, but it's not clear to me that it would help much. Aren't internal combustion engines generally comparable or better in efficiency than steam ones? Unless, maybe, you're talking about a gigantic, stationary steam turbine as used in electric power plants. Someone who uses pistons should try this. At least if the apparatus is robust. Since I'm not a thermodynamicist, I don't know if there's some fluid that would work better.

Hmmm... the water bag might be hard to catch. Especially if the bag was made out of something that was a propellant in itself. I've heard of something called Primasheet.

 

[Alan15578]

I should think the water would have to be sprayed as a mist in order for it to heat up fast enough. Or else a tiny, thin bag of it could be inserted behind the igniter. I'm no thermodynamicist, but it's not clear to me that it would help much. Aren't internal combustion engines generally comparable or better in efficiency than steam ones? Unless, maybe, you're talking about a gigantic, stationary steam turbine as used in electric power plants. Someone who uses pistons should try this. At least if the apparatus is robust. Since I'm not a thermodynamicist, I don't know if there's some fluid that would work better.

Hmmm... the water bag might be hard to catch. Especially if the bag was made out of something that was a propellant in itself. I've heard of something called Primasheet.

You would have to ask Stefan what he was talking about. My thermo class what taught by an Indian, and I couldn't really distinguish his pronunciation of entropy and enthalpy. I don't really trust my thermodyamics, but I still have my old book of steam tables.

FWIW, the Navy uses steam to launch it's aviators off the deck, but they do not take steam or energy from the A/C jet engines.

 

[MidOH]

Ok, heck. If a booster is just too darn easy and efficient.....

Need gas? Don't want to carry a scuba tank?

Make the rocket out of nonflammable materials, carbon fiber could work, and put a rocket motor in the bottom of the tube, or easier yet, some kind of black powder. Launch it out with a cannon.

 

[shockie]

Ok, heck. If a booster is just too darn easy and efficient.....

Need gas? Don't want to carry a scuba tank?

Make the rocket out of nonflammable materials, carbon fiber could work, and put a rocket motor in the bottom of the tube, or easier yet, some kind of black powder. Launch it out with a cannon.

I don't think you're allowed to launch rockets from bazooka type tubes or cannons unless they are within a 60 degree cone.

Closed breech launchers are allowed.

Holding a CBL pointed vertical is not.

 

[Gus]

Most contest piston tubes are made from paper body tubes, Those tubes are too elastic and can balloon enough to allow leakage past the head. I covered mine with a layer of thin fiberglass. On the other hand, allowing blow by may be keeping peak pressure low enough to keep your tube from bursting.

Using piston primer may make sense, but it is not sportsman like. I think the FAI had it right when they banned piston launchers for altitude events. They and the NAR should take it a step further and ban them from all performance events. Sure it is fun to play around with, but after that, it is just one more piece of kit to haul around and futz with. The only thing it was really good for was R&D, and most of that was flawed.

The idea that paper piston tubes are elastic and "balloon" is not supported by any evidence, research or practice, that I have seen.

Wrapping a paper tube with fiberglass just adds weight, which is one of the major ways to reduce piston tube performance. Lighter is better.

I've seen well over 1000 piston tube launches over the last 17 years I've been competing both NAR and FAI. I have never seen a piston tube explode from internal pressure, even when a piston head jams part way up/down the tube.

I HAVE seen a number of piston tubes rip their bottoms off due to extreme force hitting the piston head. Way more common with fixed head pistons as indicated in my video. But I ripped the bottom open on a floating head piston, 13mm x 34", just last week setting a new B-Payload record. Ripping the bottom off a floating head piston tube which sails 20 feet in the air is a pretty good indication of a piston performing optimally.

FAI banned floating head pistons after the U.S. won several events in 2014. We were the only team using floating head pistons. But in all honesty, it was not unreasonable to ban floating heads because competitors launch very close to each other in lanes at FAI events. We were routinely dropping piston tubes on our fellow competitors as they were prepping their rockets.

FAI did not ban fixed head piston launchers for most events, though, because most non-US fliers do not use towers to launch. Requiring towers would have been a big change requiring lots of new equipment for almost all the teams.

As for banning pistons in NAR events, that was suggested a few years ago but rejected by the membership. Pistons are useful, fun, and just another option to demonstrate expertise.

 

[Spacedog49Krell]

The idea that paper piston tubes are elastic and "balloon" is not supported by any evidence, research or practice, that I have seen.

In the realm of micrometers and milliseconds, paper tubes are elastic. Not like a balloon, but the internal pressure from the exhaust gases does cause a measurable change in the piston tube diameter when measured in milliseconds. This deformation is desirable. It reduces the gas loss around the piston head as the tube moves over the piston head.

 

[Gus]

In the realm of micrometers and milliseconds, paper tubes are elastic. Not like a balloon, but the internal pressure from the exhaust gases does cause a measurable change in the piston tube diameter when measured in milliseconds. This deformation is desirable. It reduces the gas loss around the piston head as the tube moves over the piston head.

I am not familiar with any of this data. If you have a link, I would love to read the studies, both about the extent of tube deformability and gas loss around piston heads. Thanks.

 

[lr64]

I am not familiar with any of this data. If you have a link, I would love to read the studies, both about the extent of tube deformability and gas loss around piston heads. Thanks.

There are no perfectly rigid materials. In the case of paper, you might find some with an elastic modulus of 300 kpsi. If you have a 3 inch diameter cylinder with a .050" wall, then the material will be stressed at around 3kpsi circumferentially, and will stretch by about 1 percent, increasing the diameter to 3.03". This number is approximate, of course, because we don't know the exact properties of our cylinder. It might have an elastic modulus of 150 kpsi or 600. And I'm just guessing about the pressure.

I'm probably not visualizing the device properly. Does the cylinder move, or the piston?

 

[Gus]

…

 

[SolarYellow]

Revolvers work quite well even with a cylinder gap.

 

[lr64]

I wasn't saying how much the loss was, just that a paper tube WILL deform a measurable amount with any significant pressure. I think that flexible seals are possible, though.

 

[SolarYellow]

You could also make a piston with the skirt facing upward. It should tend to be expanded outward by the pressure and follow any expansion of the "cylinder" tube.

 

[Alan15578]

You could also make a piston with the skirt facing upward. It should tend to be expanded outward by the pressure and follow any expansion of the "cylinder" tube.

Those are called wiper seals and are commonly used on bicycle pumps etc., and should be used in piston launchers, although I like to keep things simple.

 

[Alan15578]

In the realm of micrometers and milliseconds, paper tubes are elastic. Not like a balloon, but the internal pressure from the exhaust gases does cause a measurable change in the piston tube diameter when measured in milliseconds. This deformation is desirable. It reduces the gas loss around the piston head as the tube moves over the piston head.

True, but what is another one word descriptor for expanding radially under internal pressure?

 

[Spacedog49Krell]

True, but what is another one word descriptor for expanding radially under internal pressure?

The one parameter I find missing in the scientific analysis is the internal cylinder pressure? I've been running a number of performance calculations of hoop stress, pressure losses, and friction losses of piston launch systems. The acceleration data indicates that frictional losses between the cylinder and piston is a primary concern. Teflon and Teflon coated piston heads outperform other materials. To better understand pressure loss issues, I need cylinder pressure values.

Gus, do you have or can you direct me to cylinder pressure values?

 

[lr64]

If friction is really significant, maybe a bellows arrangement would be better than a piston and cylinder. It might weigh more, though. Half of one, six dozen of the other, I guess.

 

[Gus]

Gus, do you have or can you direct me to cylinder pressure values?

That data does not exist.
Neither does any data exist for expansion of model rocket piston tubes from internal pressure.
There is no data for gas loss around the piston head in model rocket piston tubes.
No data either for any benefit from teflon piston heads.
No data for relative effectiveness of piston head shapes or weights.

The NAR R&D archives contain 40 reports on piston launchers (https://www.nar.org/members/rd-reports-in-chronological-order/). Lots of altitude data, lots of thrust-time curves. Lots of data on effect of piston tube length, piston tube diameter, zero-volume vs. buffered starting condition, fixed vs. floating heads, oscillatory effects in thrust-time curves, etc.

But absolutely nothing on any of the items so confidently asserted in the posts above.

If there is another repository of scientific investigation of model rocket piston launchers other than the NAR R&D reports I am unaware of it.

So those of you posting so authoritatively please point me to where I can learn what you "know." I actually use this information in the real world and am always looking to get better.

Thanks

 

[BEC]

I just did a one hour presentation on pistons for the Juniors hoping to make the next U.S. Spacemodeling team.

It covers both fixed and floating head pistons.

You can see the presentation here:

Thanks for this. Avis and I will be changing some details of how we approach piston use for NARAM thanks to your insights (and Chris Flanigan's recent report as well). They both show a couple of areas where I can improve how to make/use them without over-complicating things.

 

[Spacedog49Krell]

That data does not exist.
Neither does any data exist for expansion of model rocket piston tubes from internal pressure.
There is no data for gas loss around the piston head in model rocket piston tubes.
No data either for any benefit from teflon piston heads.
No data for relative effectiveness of piston head shapes or weights.

The NAR R&D archives contain 40 reports on piston launchers (https://www.nar.org/members/rd-reports-in-chronological-order/). Lots of altitude data, lots of thrust-time curves. Lots of data on effect of piston tube length, piston tube diameter, zero-volume vs. buffered starting condition, fixed vs. floating heads, oscillatory effects in thrust-time curves, etc.

But absolutely nothing on any of the items so confidently asserted in the posts above.

If there is another repository of scientific investigation of model rocket piston launchers other than the NAR R&D reports I am unaware of it.

So those of you posting so authoritatively please point me to where I can learn what you "know." I actually use this information in the real world and am always looking to get better.

Thanks

The pressure is in the accelerometer values. Using Chris Flanigan's equation (3) in his paper, Fp = pi*r^2(Pp-Patm) we solve for Pp. We have the mass of the rocket, 130.2 grams, and its acceleration measured by the Raven. The id of the piston cylinder tube is 18mm. Keep all the area values in meters and the pressure is in Pascals. I was hoping that someone would have verified the pressure values with either direct measurement or duplicating the acceleration with compressed gas launches.

I haven't calculated the expansion of a piston tube, but I have for a thin wall BT-60. It expands 0.01" in diameter per psid. This expansion stress is short lived as the trapped gases quickly permeate through the thin wall.

The NAR piston archives can now be updated with cylinder pressure values.

Where do you start on a 70 year journey of questions? We are each a unique product of personal experiences and relationships with people we meet along the way. Most of the people who had a profound influence on me, have passed away. Most of the books they wrote are no longer found on library shelves. If you find my information useful, then validate it and use it. If you find I'm wrong, well nobody is perfect.

 

[SolarYellow]

You need to account for the mass of the piston tube, as well as subtract off any frictional force (there may be multiple points of contact, depending on the design.