Possibility of using spring to boost Estes rocket on launch

[Gus]

It's my understanding that the Russians Regularly used "a pinch of something" in their pistons, for a while , until it became obvious.

It's my understanding that the Russians Regularly used "a pinch of something" in their pistons, for a while , until it became obvious.

Terry,

Less nefarious than one might suppose. Not just the Russians, almost all of the Europeans flying 10 mm Euro motors use a pinch of black powder.

First, almost all the 10 mm motors are "quasi-composites" using modified black powder propellant. Nozzles are really tiny and very shallow. So contact area for ignition and flammability of exposed propellant are much less than for something like an Estes motor.

Almost all Euro motors are flown off pistons where the igniter is a very short V-shaped piece of wire which is plugged in to the top of the piston head. Unlike Estes igniters these little wires have no accelerant applied to them. The Euro motors just sit down onto the igniter wire, very similar to how micromax motors sit on the little uncoated igniters.

Because of this, most Europeans press a small pinch of loose black powder in the motor nozzle before setting it down on the igniter wire. Honestly, the amount of black powder involved isn't substantially more than the black accelerant that used to be on the old Estes Solar Igniters.

Are there some who might use more black powder than really necessary? I'm sure it happens. And there are those apocryphal stories of motors failing to ignite and the rockets still sailing 20 feet off the piston. So that's why FAI outlawed pistons for the altitude events. Do those fliers still put a pinch of black powder in the motor nozzles before putting them down on the igniters? Almost assuredly. They need to to ignite the motors. Is it possible some still use too much to get a little extra kick, possibly.

But the bottom line is that most of our competitors are completely honest and when we get beat, which happens often, it's simply because there are so many truly world-class competitors out there.

Steve

 

[troj]

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:

I saw this thread and immediately thought of your presentation!

-Kevin

 

[Spacedog49Krell]

Thanks for your piston report. It might be worth revisiting piston launch systems with the technology available today. I've bench tested a system at 1000Hz and it probably can be faster. The more significant characteristic today would be reduced mass. The Raven 3 was 1 oz and required a BT-60 tube. My bench prototypes fly in BT-20 rockets. I believe the mass can be reduced to ~5 grams.

 

[lr64]

I still think compressed air would be fun, for someone motivated enough. Much of the required tech is already well developed by HAM guys wanting to loft a weighted tennis ball with a string over a tree branch to pull up an antenna, which I gather they do pretty often. Only problem is that they do it with PVC pipe. Or they did the last time I checked. Lofting a string would also be good for shaking the branches of tall trees for retrieval purposes. Dual use. Appropriate safety precautions might be necessary, depending on just how powerful the system was.

Come to think of it, the easy way is probably to use some of that 1010 rail with a light sled with ball bearing rollers. Surgical tubing instead of a spring. Set the rocket on the sled, free to come off the top. Sled to have own chute if necessary. Some clever device to pull the trigger the instant heat or exhaust was detected.

If what I think was the original idea of a compression spring was used, it could be protected by sacrificial fabric, soda can aluminum, etc.

 

[Art Upton]

^We have used Tethered Tennis Ball launchers to get rockets out of the trees at our club in the past. Probably the best rocketry use for them. Get the cord in a position to pull on the shock cord or parachute.

 

[Alex (Boyce Aerospace)]

I can't remember where, but I read a research paper about using very long launch rails with a sled that was propelled by a thin cable around a pully at the top of the rail and a drop weight. The paper fully described the construction and testing of the launcher along with a study of the use of different amounts of weight and at what point to ignite the rocket's motor on the sled (or after leaving the sled) to achieve the highest altitude. I believe in his tests he insured that the rockets would be stable as they left the rail even if no ignition occurred making the use of the device similar to a second stage flight event. I found the project very interesting.

Alex

 

[SolarYellow]

A drop weight can't accelerate at more than 1g. You'd need a pulley system to provide mechanical advantage to multiply that into a level of accel significantly useful to launch a model rocket.

 

[BABAR]

. I believe in his tests he insured that the rockets would be stable as they left the rail even if no ignition occurred making the use of the device similar to a second stage flight event. I found the project very interesting.

Alex

this initially sounds good, but on consideration may be a problem.

In the absence of an electronics initiated EJECTION event (I.e. Jolly Logic Chute Release doesn’t help if no deployment), a standard single deploy rocket that leaves the rail stable without motor ignition is most likely to imitate the St Louis Arch and return ballistic.

This is generally considered poor form. Definitely want to aim at least 5 degrees AWAY from the flight line.

I theeenk there was an article in Peak of Flight where a young rocketeer teamed with a senior rocketeer and created a tower catapult which accelerated the rocket before ignition, but I searched Apogee site and couldn’t find it.

I DO think the idea of a band or a spring PULLING the rocket forward might be more easily implemented than a PUSHER system, and easily implemented with a burn string to insure rocket ignition.

In fact, I believe such a system is used for RC gliders.

 

[Art Upton]

In fact, I believe such a system is used for RC gliders.

The Surgical Tube Glider Launchers are stretched out along the full length of the runway at the R/C club to get them in the air. I have not seen it used at our club since Electric Motor powered gliders became lightweight [ >2 decades ago]

Edit: probably used in some competitions where they don't allow motor power on the glider. But we don't do competitions in my club anymore.

 

[lr64]

Winches and hi starts have been used much more recently than that and are still used in some competitions. If you strapped a rocket to one of the carbon fiber competition models and zoom launched the model with a good winch, you could separate from the model during the zoom, with hundreds of feet of altitude and maybe 100 mph velocity up. Maybe not so very practical, of course. Plus, the pilot would probably be upset if you ignited early and burned the tail off.

I haven't seen the rocket and burn string thing, but I have seen a small RC rocket glider get an extravagantly high launch from what may have been only a D motor.

 

[bad_idea]

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:

Great presentation, Steve. Thank you for making and posting it.

 

[MidOH]

Booster still makes more sense.

 

[lr64]

Booster still makes more sense.

More sense than a winch launched sailplane? I agree. OTOH, launching from an aircraft, RC or not, at 10 or 20,000 feet might make sense. But that's not line of sight any more and requires licenses, etc. I suppose a free flight aircraft could get to a height like that, but it would likely never be seen again, unless on the ocean or the great lakes, with a radar equipped chase boat or something. A booster is more practical.

 

[shockie]

Terry,

Less nefarious than one might suppose. Not just the Russians, almost all of the Europeans flying 10 mm Euro motors use a pinch of black powder.

First, almost all the 10 mm motors are "quasi-composites" using modified black powder propellant. Nozzles are really tiny and very shallow. So contact area for ignition and flammability of exposed propellant are much less than for something like an Estes motor.

Almost all Euro motors are flown off pistons where the igniter is a very short V-shaped piece of wire which is plugged in to the top of the piston head. Unlike Estes igniters these little wires have no accelerant applied to them. The Euro motors just sit down onto the igniter wire, very similar to how micromax motors sit on the little uncoated igniters.

Because of this, most Europeans press a small pinch of loose black powder in the motor nozzle before setting it down on the igniter wire. Honestly, the amount of black powder involved isn't substantially more than the black accelerant that used to be on the old Estes Solar Igniters.

Are there some who might use more black powder than really necessary? I'm sure it happens. And there are those apocryphal stories of motors failing to ignite and the rockets still sailing 20 feet off the piston. So that's why FAI outlawed pistons for the altitude events. Do those fliers still put a pinch of black powder in the motor nozzles before putting them down on the igniters? Almost assuredly. They need to to ignite the motors. Is it possible some still use too much to get a little extra kick, possibly.

But the bottom line is that most of our competitors are completely honest and when we get beat, which happens often, it's simply because there are so many truly world-class competitors out there.

Steve

"... it appears that little scientific data has been accumulated to determine what works best for piston launchers."
Actually, there has been a very large amount of research done over many years. The problem is that piston function is just extremely complex and multi factorial. The net effect of a particular piston depends on a large variety of factors such as particular motor, rocket weight, piston tube length, piston tube weight, fixed vs. floating head, piston head shape, piston head length, piston head weight, piston head surface friction, tube internal surface friction, internal vs. external igniter leads, piston tube deceleration, forcefulness of motor fit in piston tube, etc. etc.

One of the most interesting studies done several years ago showed that for a particular motor type and rocket weight, best tube length is not a straight linear function but actually looks more like a sin wave, improving up to a certain length, then declining to a nadir then improving again with more length. Just incredibly complex.

As I have often said about another ridiculously complex competition rocketry item, streamers, until the U.S. military comes up with a serious need for this item we will never really know the answer, LOL. But that's what makes it so much fun. And pistons, they are just fun. If you've never launched one, watch the video and build a simple floating head piston with the rod stuck in the ground and launch it.

Steve

Steve:

Just how tiny are the nozzle dimensions?

I actually participated in the FAI flyoffs at NARAM- 53, and used a typical BT-5 FH piston launcher and I still remember the "pop" sound.

I do belive it was the first piston launcher to use a custom machined Teflon piston head.

 

[Spacedog49Krell]

Steve:

Just how tiny are the nozzle dimensions?

I actually participated in the FAI flyoffs at NARAM- 53, and used a typical BT-5 FH piston launcher and I still remember the "pop" sound.

I do belive it was the first piston launcher to use a custom machined Teflon piston head.

If the European 10mm motors are "quasi-composite" they could burn at higher pressures than black powder motors. A piston launcher would utilize that pressure difference as an advantage. The launch "pop" would be distinctly different. Back in 1978, PlasmaJet was experimenting with 18mm and 8mm composite motors. I still have one of the 8mm motors. I wonder how it would compare to a 10mm "quasi-composite".

 

[lr64]

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.
------------
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.

 

[Alan15578]

Steve:

Just how tiny are the nozzle dimensions?

I actually participated in the FAI flyoffs at NARAM- 53, and used a typical BT-5 FH piston launcher and I still remember the "pop" sound.

I do belive it was the first piston launcher to use a custom machined Teflon piston head.

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

 

[Alan15578]

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.

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.

 

[lr64]

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.

It's not unsportsmanlike unless you're competing. It might allow you to use an end-burner motor or something like that. Competing is valid, but so is not competing. If you are already using a piston setup, a small container of powder is another piece of kit, but not very much of one.

 

[SolarYellow]

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.

So it seems worth testing heavier-wall tubing for piston tubes:
Quest 15mm
BT-20H
ST-7
BT-50H
ST-9
29MMT

Should be lighter than fiberglass, and it's definitely cheaper and easier.

I could definitely see adding a few kernels of 3F or 2F in a piston under an F15 sport model to get it going faster.

 

[lr64]

The piston doesn't actually fly, does it? If not, you could use Sonotube, some kind of pipe, etc.

 

[Art Upton]

The piston doesn't actually fly, does it? If not, you could use Sonotube, some kind of pipe, etc.

The piston moves upwards putting action on the bottom of the rocket for more velocity. It is not just a breach launcher, those are a different subject.

The piston tube must be light enough to travel upwards.

 

[Alan15578]

The piston doesn't actually fly, does it? If not, you could use Sonotube, some kind of pipe, etc.

Most "floating head" pistons fly off the launcher with the rocket and then stage or separate from the model in flight. Some competition events do not allow staging or separating and should be disqualified.

Fiberglass has much more stiffness/mass. I liked to start with old Blackshaft tubes, which held up better to the exhaust and lasted longer.

 

[Spacedog49Krell]

I prefer an evacuated closed breech sabot system.

 

[lr64]

The piston moves upwards putting action on the bottom of the rocket for more velocity. It is not just a breach launcher, those are a different subject.

The piston tube must be light enough to travel upwards.

Most "floating head" pistons fly off the launcher with the rocket and then stage or separate from the model in flight. Some competition events do not allow staging or separating and should be disqualified.

Fiberglass has much more stiffness/mass. I liked to start with old Blackshaft tubes, which held up better to the exhaust and lasted longer.

Of course you guys are right. I was thinking cylinder and typing piston. Of course, if you were putting a bit of black powder or something in, you could make up for the extra weight. See Project Orion. ;-)

 

[Alan15578]

Of course you guys are right. I was thinking cylinder and typing piston. Of course, if you were putting a bit of black powder or something in, you could make up for the extra weight. See Project Orion. ;-)

I think you you would enjoy a completely different hobby: pumpkin cannons.

 

[jsdemar]

"Spring" to boost a launch? Summer is best... thinner warm air.

 

[rcktnut]

I think you you would enjoy a completely different hobby: pumpkin cannons.

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

 

[shockie]

I'm

The problem with doing that is that it results in less guidance from the guide rod.
A very important aspect for safety is the airspeed of the rocket as it leaves the rod.
If the spring moves the rocket closer to the end of the guide rod you lose some of the guidance and could leave the rod before the rocket has built up airspeed. It must be going fast enough that air moving over the fins causes the rocket to fly stable. A spring (or even a rubber band like a slingshot) could certainly augment the acceleration, but increasing the impulse of the motor does so more simply.
It’s great that you and your grandfather are flying rockets and engaging in very interesting thought experiments.

Use a longer launch rod?