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  #11  
Old 04-05-2022, 12:10 AM
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Gus Gus is offline
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Quote:
Originally Posted by astronwolf
Floating head pistons have been banned from international competition. It's fixed pistons only. I think you can still use the floating head variant in US competition, but I haven't checked lately.

The only nation to use floating head pistons was the U.S.

Floating head pistons were banned the year after the U.S. won altitude and scale altitude at the World Championships in Ukraine.

In all fairness, though, one of the objections to floating head pistons is that our piston tubes would fly 20 - 30 feet in the air and then come dropping down on the heads and rockets of our neighboring competitors. Unlike U.S. competiton, International events have each country launching from their own narrow lane. Having piston tubes raining down on your rocket sitting on the pad was pretty annoying. Don't recall that we ever knocked anyone's rocket down, or hit someone in the eye, but they did have a point.

Floating head piston are still allowed in NAR competiton and are definitely way easier to set up than fixed heads.
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  #12  
Old 04-05-2022, 07:42 AM
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Quote:
Originally Posted by Gus
Floating head pistons were banned the year after the U.S. won altitude and scale altitude at the World Championships in Ukraine.



Now that we are all more familiar with the geography of the country, where in Ukraine was that?

Hope they can return to something as insignificant as a model rocket competition...


Bill
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  #13  
Old 04-05-2022, 10:42 AM
shockwaveriderz shockwaveriderz is offline
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Quote:
Originally Posted by Bill
Now that we are all more familiar with the geography of the country, where in Ukraine was that?

Hope they can return to something as insignificant as a model rocket competition...


Bill


Lviv in extreme western Ukraine.
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  #14  
Old 04-05-2022, 10:45 AM
shockwaveriderz shockwaveriderz is offline
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Quote:
Originally Posted by Gus
Would it be safe and correct to say that the height that a traditional floating head will fly once it leaves the piston rod, with the rocket attached, would be determined by the engine used?

Motor plays a part. Strength of fit between motor and piston tube is very important. Piston tube length and weight are very important. Piston head plays a role. Rocket weight is an important part.

If this is so, what kind of heights are we looking at ? 5ft ? 10ft? More?


For both floating and fixed head pistons the rocket generally leaves the piston tube a fraction of a second after the aft end of the piston tube hits the piston head. Almost no difference between fixed and floating heads. The old theory was that floating head pistons sailed some ways above the rod before the rocket leaves the piston. Not actually so.

I'm specifically talking about 1/4A3, 1/2A3 and A3 13mm motors.


These 3 particular motors behave very similarly on a piston. A10s are a bit different with their much quicker burn.

Different motors with different thru-time curves are going to pressurize the piston differently?


Correct

it also seems to me that wind speed would have a detrimental effect on the rocket/piston tube assembly. Anybody ever seen such a combination hit with a strong wing and noticed how much it tilts before separation of the two?


Most U.S. fliers fly a piston in a tower. Wind is rarely a problem. Many Europeans tend to fly naked, piston without a tower. Wind doesn't affect their pistons but will affect the rocket itself once it leaves the piston.


Thank you very much Gus.
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  #15  
Old 04-05-2022, 11:39 AM
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Quote:
Originally Posted by Bill
Now that we are all more familiar with the geography of the country, where in Ukraine was that?

Hope they can return to something as insignificant as a model rocket competition...


Bill

Bill,

The contest was originally scheduled to be held in Dnipropetrovsk, now known as Dnipro, in 2016. Dnipro is only about 80 miles from where the invasion took place in the Donbass region in 2014, and there was still recurrent fighting in that area.

So the contest was moved to the far west of the country, near Lviv. Even so, a number of U.S. competitors chose not to go.

After the contest my daughter Emma and I were offered the once-in-a-lifetime opportunity to accompany Matt Steele on a visit to the Youzhnoye / Youzhmash rocket design and manufacturing facility in Dnipro. This facility is better known to most of us in the west as the Yangel Design Bureau, where the Missiles of October and current Russian Satan missiles were built. Youzhnoye had a new project in mind and the director wanted to discuss it with Matt, with whom they worked in an earlier joint project to dismantle Russian nuclear missiles.

Until about 10 years before we went Dnipro had been a closed city, off limits to foreigners due to the nature of the work done there. And at the time we went, due to the nearby fighting, it was not the safest place to go.

But it was worth the risk. The facility was truly mind-boggling. We were also given a private tour of the city's incredible rocketry museum, and were treated to one of the most fantastic dinners we've ever eaten at a truly beautiful outdoor Yurt next to the Dnipro river.

Of note, in our visit to Dnipro our hosts walked us by a large rocket display in the downtown area. That display was right across from the very large memorial to local residents killed in the defense of the Donbass two years before. The memorial was a lengthy wall along the city square with photos of those lost in the fighting.

Our hearts are truly broken at what is happening in Ukraine.

Slava Ukraini
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  #16  
Old 04-05-2022, 04:41 PM
shockwaveriderz shockwaveriderz is offline
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Quote:
Originally Posted by Gus
Many of us now use a short tube (4"-6") on top of our piston tubes creating an air gap between the rocket motor and the piston head. With black powder motors this is less for performance than it is for ease of use with fixed head pistons. Added benefit is that most of the soot from the motor ends up in the buffer tubes making repeat use of the longer piston tubes more possible.

You can piston launch composite motors, like the Quest Q-Jets , or other Aerotech single use motors if you use a buffer tube to prevent chuffing. Without such a buffer tube composites have difficulty igniting in a zero volume piston.


Got any pics or diagrams?
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  #17  
Old 04-05-2022, 07:44 PM
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Everyone flying NRC in our club uses floating head pistons. They usually fly 20-30' in the air if friction is right. They're harmless when falling down, we all use 34" lengths of standard BT-5, or sometimes more. It's silly they were banned - if they're banned for NRC, I may stop flying NRC. They provide tremendous performance improvement for 13mm motors - less so for 18mm motors.

We found using Quest B4 and B6 motors in pistons worked poorly for egg lofters - they had to be held incredibly tight, usually with a zip tie, and the thrust profile didn't get them up to speed nearly as fast as the Estes B6. This suggest the early spike of the BP motors is important when using pistons.
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  #18  
Old 04-05-2022, 11:32 PM
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And....well with a heavy payload (the egg) a good thrust spike, piston or no piston, is important. The Q-Jet Bs just aren't the right motor for that application. The Cs are a different story.
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  #19  
Old 04-06-2022, 07:37 AM
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Quote:
Originally Posted by Gus
Our hearts are truly broken at what is happening in Ukraine.


Amen to that.

Thanks for the writeup.


Bill
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Please unload your question before you ask it unless you have a concealed harry permit.

: countdown begin cr dup . 1- ?dup 0= until cr ." Launch!" cr ;

Give a man a rocket and he will fly for a day; teach him to build and he will spend the rest of his days sanding...
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  #20  
Old 04-08-2022, 12:20 AM
rocket.aero rocket.aero is offline
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Quote:
Originally Posted by Ez2cDave
As for the upcoming WSMC in Austin, TX, it will be interesting to see if they bring ("smuggle" ) European motors into the USA and use them here.


We have been entirely clear that the only motors allowed for use at the World Championships next year will be NAR certified motors from Estes and Aerotech. Additionally, those motors will be provided by the organizers.
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