Shooting the breeze Best fittings sponsors UKAHFT  
Go Back   Shooting the breeze > The Chat > General Airgun Chat

General Airgun Chat Chat and banter that doesn't fit anywhere else...

Reply
 
Thread Tools Display Modes
  #11  
Old 26th August 2016, 06:04 PM
Nomads HFT Nomads HFT is offline
Senior Member
 
Join Date: Sep 2015
Location: Worcester
Posts: 114
Default

Today I tested one of my piston seals for friction at 20C and 46C.

At 20C, the static friction was 6.07N (Newtons), the kinetic (sliding) friction 4.38N

At 46C, the static friction was 10.6N, the kinetic friction 7.35N

I had a second seal in my TX cooking in the greenhouse, and when acclimatised to 46C, the muzzle velocity was the same as at 20C.

For comparison, Rob's unsized seal was nearer 23N at 40C (much higher), down to under 5N when sized.

Worth bearing in mind that the kinetic friction figures quoted exist only for a very short period of time at the very start of the stroke; when the cylinder air pressure increases, they rocket.
__________________
Nomads HFT
Reply With Quote
  #12  
Old 27th August 2016, 09:36 AM
biwain's Avatar
biwain biwain is offline
Member
 
Join Date: Aug 2015
Member of: Newbury
Location: mexborough
Posts: 67
Default

Aren't we confusing friction and resistance?

Friction is unpredictable and the guns we are shooting are virtually friction free when they leave the factory, after all the manufacturers have been at it 8 hours a day for the last 300 years!

Then we get our hands on them and bguger em up.

They pack them with a thick gooey grease for a reason. To create a constant resistance whilst managing recoil.

Now we require, and try to strive for a little less recoil, after all these are perfect sporting rifles and are not specifically designed for our purpose.

So to "tune" a gun we are trying to reduce spring compression and thereby recoil whilst preserving kinetic energy

To remove all the resistance from the working parts creates uncontrollable recoil and inconsistency and will certainly be temperature sensitive.

A car becomes very unpredictable if you just rely on the springs, so they add shock absorbers to create resistance and manage the recoil of the springs. A bit more technical as you haven't got a constant, but a similar principle.

So it all comes down to optimizing the resistance of the piston and the predictability of that constant velocity to make it do the exact same thing time after time.

Sadly, when you transfer or convert any energy you lose efficiency. We require a small amount of compressed air for our ultimate goal and that's why you need a boring PCP.
__________________
Because I'm without a intelligent name
Reply With Quote
  #13  
Old 27th August 2016, 12:13 PM
RobF's Avatar
RobF RobF is offline
My Empire of Dirt
 
Join Date: Mar 2010
Member of: Southampton Buccaneers, Parkstone, South Dorset
Location: Poole, Dorset
Posts: 10,643
Default

Quote:
Originally Posted by Nomads HFT View Post
Today I tested one of my piston seals for friction at 20C and 46C.

At 20C, the static friction was 6.07N (Newtons), the kinetic (sliding) friction 4.38N

At 46C, the static friction was 10.6N, the kinetic friction 7.35N

I had a second seal in my TX cooking in the greenhouse, and when acclimatised to 46C, the muzzle velocity was the same as at 20C.

For comparison, Rob's unsized seal was nearer 23N at 40C (much higher), down to under 5N when sized.

Worth bearing in mind that the kinetic friction figures quoted exist only for a very short period of time at the very start of the stroke; when the cylinder air pressure increases, they rocket.
very interesting. The new rig is on long term test. It's not getting touched for a good while to see its temp sensitivity with the sized seal.

Steve pope told me before the comp that it sounds like seal fit issues.
__________________
BFTA/NSRA County Coach
CSFTA Chairman/BFTA Rep
Reply With Quote
  #14  
Old 29th August 2016, 07:36 AM
oyster oyster is offline
Member
 
Join Date: Aug 2016
Member of: Canterbury Airgun Club
Location: Kent
Posts: 57
Default

Using my improved .22 HW97 during the wind free and rising temperature of 27 August midday, my point of impact altered progressively to a bit more that half a mildot. As conditions and the gun got warmer, poi dropped noticeably over 35 yds. Yet another variable to consider!
__________________
HW77K; HW100, HW77, HW97K, LGV, BSA Spitfire
Reply With Quote
  #15  
Old 29th August 2016, 08:55 AM
Conor's Avatar
Conor Conor is offline
Never has been banned from sales
 
Join Date: May 2009
Member of: Nelson & Nomads airgun club
Location: Ardboe, Co.Tyrone.
Posts: 2,805
Default

Quote:
Originally Posted by oyster View Post
Using my improved .22 HW97 during the wind free and rising temperature of 27 August midday, my point of impact altered progressively to a bit more that half a mildot. As conditions and the gun got warmer, poi dropped noticeably over 35 yds. Yet another variable to consider!
I hate it when it moves half a mil dot.
__________________
He who never made a mistake never learned!
He who never missed never shot!
Reply With Quote
  #16  
Old 29th August 2016, 09:35 AM
RobF's Avatar
RobF RobF is offline
My Empire of Dirt
 
Join Date: Mar 2010
Member of: Southampton Buccaneers, Parkstone, South Dorset
Location: Poole, Dorset
Posts: 10,643
Default

Quote:
Originally Posted by oyster View Post
Using my improved .22 HW97 during the wind free and rising temperature of 27 August midday, my point of impact altered progressively to a bit more that half a mildot. As conditions and the gun got warmer, poi dropped noticeably over 35 yds. Yet another variable to consider!
That is the variable we are looking at
__________________
BFTA/NSRA County Coach
CSFTA Chairman/BFTA Rep
Reply With Quote
  #17  
Old 29th August 2016, 09:54 AM
airborn68's Avatar
airborn68 airborn68 is offline
Senior Member
 
Join Date: Apr 2011
Member of: Ponte & Hull & District Ft (secretary)
Location: UK, Hull. East Yorkshire
Posts: 406
Default

I don't think I will have the pleasure of shooting in 40c + temps but I did suffer from a significant power drop in temps below 3c running the Aussie seals.

Jon
Reply With Quote
  #18  
Old 29th August 2016, 05:54 PM
Sake-San's Avatar
Sake-San Sake-San is offline
La Veille Alliance
 
Join Date: Oct 2014
Member of: l'Association Francaise de Field Target
Location: Dordogne, France
Posts: 386
Default

As if springers weren't frustrating enough, do yourselves a favor and fit an o-ring piston
__________________
The Auld Alliance
Reply With Quote
  #19  
Old 29th August 2016, 06:03 PM
vinny's Avatar
vinny vinny is offline
WHFTA 2015 World Champion
 
Join Date: Mar 2014
Member of: M.A.D
Location: essex
Posts: 691
Default

Quote:
Originally Posted by Sake-San View Post
As if springers weren't frustrating enough, do yourselves a favor and fit an o-ring piston
Hmmm, fitted nick g kit ( o ring piston ) with sake, s lube regime and no fps temp swings happy days , just need to sort my stock inletting now , nearly there
__________________
H.G.H , spring power is fun

FTP900 MTC connect,Welhamanium internals -sorted
HFT500, ACZ stock MTC connect
TX200 Mk3 CS1000 stock, hawke vantage sf , Nick G internals, Sake-San's lube regime.
Steyr ?, maybe , they cant all be wrong?
Reply With Quote
  #20  
Old 30th August 2016, 08:08 PM
Sake-San's Avatar
Sake-San Sake-San is offline
La Veille Alliance
 
Join Date: Oct 2014
Member of: l'Association Francaise de Field Target
Location: Dordogne, France
Posts: 386
Default

Quote:
Originally Posted by vinny View Post
Hmmm, fitted nick g kit ( o ring piston ) with sake, s lube regime and no fps temp swings happy days , just need to sort my stock inletting now , nearly there
But, you are a modern, progressive, open minded HFT champ, with a highly developed learning agility.
The closed monastic order of FT springer monks is somewhat different. Consistency and a stable POI would necessitate the penance of putting stones in our sandals
__________________
The Auld Alliance
Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
anybody take the Coriolis effect into account? Tone Hunter / Field Target 14 27th January 2015 06:00 PM
Magnus Effect & Airgun External Ballistics PeteM General Airgun Chat 49 12th October 2010 09:16 PM
Temperature shift RobF Polls 53 28th February 2010 10:39 PM
Strange effect of moving a cheek piece Baltipal General Airgun Chat 10 19th January 2009 06:45 PM


All times are GMT. The time now is 06:29 AM.


Powered by vBulletin® Version 3.8.4
Copyright ©2000 - 2017, Jelsoft Enterprises Ltd.
shooting-the-breeze.com Skin design and concept by Attitude