Airbrake piston heads

[Sewdhull]

Anyone used these at all?

 

I see they have been used successfully to reduce some noise, they also look to be likely to reduce the shock forces in the gearbox.

 

I realise they may make no difference at all to anything but I find it interesting so any experiences would be welcome.

[Speedbird_666]

I used a Lee Precision Airbrake piston on a build a few years ago.

 

Made only the slightest bit of difference to the noise (more...'thuddy'...) and I was paraniod that the air brake bit might shear off at some point (it was the delrin version). Nicely engineered otherwise.

 

Never used one since though - I much prefer XT POM piston heads from @ak2m4

[Adolf Hamster]

For a springer they have some logic to them, but i would have reservations about using them in an aeg given their intended function is to run counter to the needs of sector gear engagement.

[Pseudotectonic]

I doubt very much the 5 mm layer of air is going to dampen much energy from an incoming piston at 300 mph unless there are videos proving otherwise

 

Seems to me it is more for AOE correction

[Adolf Hamster]

18 minutes ago, Pseudotectonic said:

I doubt very much the 5 mm layer of air is going to dampen much energy from an incoming piston at 300 mph unless there are videos proving otherwise

 

Seems to me it is more for AOE correction

 

Its the potential for rebound, or settiling under pressure.

 

And a varying aoe is exactly what you dont want

[Sewdhull]

The piston heads I've seen don't seal so much as restrict the airflow out of the cylinder head, perhaps aoe is unaffected or only if there is insufficient time for the air to escape. I recall calculating an unrestricted cylinder taking 1ms to travel 70mm with an 80N spring. 

If there's not much sound reduction it's likely the piston head still reaches the cylinder head but at a lower speed.

I take on board the issues with bounce and aoe 

 

38 minutes ago, Pseudotectonic said:

I doubt very much the 5 mm layer of air is going to dampen much energy from an incoming piston at 300 mph unless there are videos proving otherwise

 

Seems to me it is more for AOE correction

It's a layer of air under pressure and 300mph seems a little high 🙂, but it's the energy that matters anyway. 

 

I'll do some sums, I know you guys love sums

Edited January 1, 2024 by Sewdhull

[Adolf Hamster]

1 hour ago, Sewdhull said:

perhaps aoe is unaffected or only if there is insufficient time for the air to escape

 

That's the core of my reservations.

 

Now granted there are use cases, eg running a dmr where reduced piston slap is good and reduced rof is bad, where the airbrake can be of benefit.

 

That said, i don't consider piston slap to be a particularly big issue at least from a noise perspective, if you truly care about silence then you might as well skip a few steps and jump straight to the logical end of such a quest which is a suppressed hpa.

 

1 hour ago, Sewdhull said:

I'll do some sums, I know you guys love sums

 

Yes please, we do indeed love sums here

 

i don't doubt the concept should do something on paper, but wether or not that something is meaningful is an interesting question.

[Leo Greer]

Never messed with one myself, but from what I’ve gathered, they become harmful in FA above a certain point (15-20, depending on build), due to increased drag. The gains seem to be minimal. I can ask the guys over on ASF for more info if the conversation persists, since there’s a few guys who’ve worked extensively with the idea.