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  #31  
Old 04-12-2022, 12:40 AM
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Quote:
Originally Posted by rocket.aero
Our friends from overseas are experienced flyers, and most of the top-tier S7 competitors are already using Aerotech motors.

Yeah. The 10mm motors got all the glory for the lower power events.

But some countries' scale teams were hampered at times trying to use European made D, E, & F type black powder motors that often went "ka-boom". Or had very poor performance, not enough thrust. Things started to shift when at some WSMC, a couple of spare Aerotech E or F engines suitable for scale were given or traded to another country's team (possibly Poland), for their scale fliers to use. I think perhaps the next time, some were arranged in advance by request, but am not sure.

And the other countries saw how well the Aerotech engines worked, so finally some of them started to get their own...somehow (Sierra Fox Hobbies is in Italy and ships all over the place. So maybe thru them, maybe more directly. They also sell Estes engines). And I know there have been Aerotech and Estes engines sold in the UK.
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Last edited by georgegassaway : 04-12-2022 at 01:02 AM.
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  #32  
Old 04-12-2022, 07:13 AM
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I enjoyed the videos. What material are the piston tubes made of? The B6 Egglofter flight put a lot of side force on it. It bowed like a spring but came right back.
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  #33  
Old 04-12-2022, 10:57 AM
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Quote:
Originally Posted by tbzep
I enjoyed the videos. What material are the piston tubes made of? The B6 Egglofter flight put a lot of side force on it. It bowed like a spring but came right back.


My theory is that they are fiberglass, because of the length. I think a paper tube might crimp, at that length.

Dave F.

Last edited by Ez2cDave : 04-12-2022 at 06:01 PM.
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  #34  
Old 04-12-2022, 11:33 AM
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Quote:
Originally Posted by tbzep
I enjoyed the videos. What material are the piston tubes made of? The B6 Egglofter flight put a lot of side force on it. It bowed like a spring but came right back.

18mm paper body tubes from BMS. That is why they look white.

That B6 eggloft piston was 68" long (two 34" tubes, with a 19mm external coupler. And the inside edges sanded with a cone of sandpaper to round the lips so the piston head slides thru as though there is no joint at all).

It seems as it sepped, the exhuast helped to deflect the top sideways, acting upon the flat face of the top ring. The mass of the top centering ring helped it "twang" like that (plus the initial deflection cause), as I have not noticed that effect on any other 68" pistons that did not have those centering rings. Indeed that's the most extreme "twang" I've seen in flight test videos. Also, there is a chance that the piston tube also bowed some from the vertical acceleration, given the mass it was pushing and possibly the egglofter not being dead center.
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Last edited by georgegassaway : 04-12-2022 at 11:53 AM.
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  #35  
Old 04-12-2022, 06:06 PM
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Quote:
Originally Posted by georgegassaway
18mm paper body tubes from BMS. That is why they look white.

That B6 eggloft piston was 68" long (two 34" tubes, with a 19mm external coupler. And the inside edges sanded with a cone of sandpaper to round the lips so the piston head slides thru as though there is no joint at all).

It seems as it sepped, the exhuast helped to deflect the top sideways, acting upon the flat face of the top ring. The mass of the top centering ring helped it "twang" like that (plus the initial deflection cause), as I have not noticed that effect on any other 68" pistons that did not have those centering rings. Indeed that's the most extreme "twang" I've seen in flight test videos. Also, there is a chance that the piston tube also bowed some from the vertical acceleration, given the mass it was pushing and possibly the egglofter not being dead center.


George,

So, what was the performance gain with a piston tube of that length ?

I believe there is a point of "diminishing returns", at some point, right ?

Dave F.

Last edited by Ez2cDave : 04-12-2022 at 06:27 PM.
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  #36  
Old 04-13-2022, 03:39 PM
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A couple of more piston videos. I think this was B6 powered. It is a superroc. The tower had a V-shaped "wind shield" added to the top, to hlep keep the exposed upper section of the superroc form bending in the wind. After launch, you can see how the smoke is swirling downwind of the shield.

https://m.youtube.com/watch?v=9rcwE...eature=youtu.be

And this is a test of some 1/2A gliders, to be sure they did not shred due to the higher speed. And a test of an A Streamer model to be sure it flew OK.

https://www.youtube.com/shorts/0UoayOgUt9I
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  #37  
Old 04-13-2022, 06:29 PM
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Quote:
Originally Posted by Ez2cDave
George,

So, what was the performance gain with a piston tube of that length ?

I believe there is a point of "diminishing returns", at some point, right ?

Dave F.


Dave it depends on a number of factors:

Piston length
Piston diameter
Model weight
Engine used and it's thrust characteristics

For example for 13mm motors of type A3 and A10, smaller diameter piston tubes(10mm) produce more pressure than 13mm tubes do.

Higher thrust motors produce more pressure than low thrust at the same length

Egglofters due to their incresed weight benefit from longer piston tubes than lighter models do.

I have a thread over on TRF with some pressure info based upon several R&D reports.

https://www.rocketryforum.com/threa...pressor.172117/

Basically there is an optimized piston tube more or less for a particular model rocket motor.

Hth
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  #38  
Old 09-14-2022, 09:21 PM
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Quote:
Originally Posted by Ez2cDave
George,

So, what was the performance gain with a piston tube of that length ?

I believe there is a point of "diminishing returns", at some point, right ?

Dave F.


Neutron Fusion (mainly Patrick Peterson on this topic) did a series of R&D reports on this over about a 5 year span, and for the most part concluded that surprisingly even with 13mm A motors the performance gain at 68" length is not only worthwhile, but is still not quite maxing out, meaning an even longer one would be optimal. Thanks to an annoying rule inspired by our boundary pushing, though, anything beyond 68" was banned. We did another R&D exploring an intriguing workaround--telescoping multi-tube design that meets the rule at time of launch (34" tall), but extends to 3x34" during launch, just could not get consistent/reliable enough performance out of it to make it worth using.

I even explored (R&D only, could not use in contest) having Euclid make a custom order of tubes at whatever their max spindle/tooling length could support but was overruled by my wife when I mentioned I might be ordering about 500 tubes/lifetime supply, though those would only have been about 50" apiece.

Our hypothesis was that for 13mm the max benefit would probably be something under 3x34 because of the weight of the tubes but for 18mm B it might be at least 4-5 lengths.

Having said all this, though, and having probably more firsthand experience working with multi-tube pistons than just about anyone, I would generally not recommend them versus 34" for anyone other than the uber competitive types. They are not very difficult to prep/use, but do require a bit of (inexpensive) special purpose launch equipment--no way would you ever attempt to "fly naked" just using a support rod. It also takes a good bit of time/effort to master the process to the point where you get consistent and reliable performance.
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