Snap G's

[Earl Haury]

Dean

Presently I've the sample rate set to 10/sec so as to log an entire P05 (speed, altitude, volts, aileron, G).  Snap duration is on the order of 0.6sec and there's typically only one data point at the max, before mid-snap, it appears that the "spike" ramp up-down is on the order of 0.2sec, and yes - the remainder is half or less. We shouldn't read too much into this quick look. For the next session I plan to increase the sample rate (40/sec available) so that the load profile is more quantifiable during a snap. Keep the thinking cap on - I welcome the brain storming.

Earl
  ----- Original Message ----- 
  From: Dean Pappas 
  To: discussion at nsrca.org 
  Sent: Friday, January 28, 2005 10:23 AM
  Subject: RE: Snao G's


  Let me add another two cents worth ...
  Earl,
  What is the sampling rate on your data logger?
  Can you see if the maximum 13-Gs at 100 MPH was sustained for the entire half second or so that it took to complete the snap,
  or was it a short spike (like 0.1 second)  and then sustained at say half of that value, for the rest of the snap.
  Of course, if the data logger samples once a second, we have almost no way of knowing.

  Later,
          Dean

  Dean Pappas 
  Sr. Design Engineer 
  Kodeos Communications 
  111 Corporate Blvd. 
  South Plainfield, N.J. 07080 
  (908) 222-7817 phone 
  (908) 222-2392 fax 
  d.pappas at kodeos.com 

    -----Original Message-----
    From: discussion-request at nsrca.org [mailto:discussion-request at nsrca.org]On Behalf Of David Lockhart
    Sent: Thursday, January 27, 2005 11:14 PM
    To: discussion at nsrca.org
    Subject: Re: Snao G's


    Ed,

    A couple answers I can think of (and I'm sure there are more possibilities) -

    - Flight speed - for F3A at 150 meters, 100 mph is a pretty fast pace.  70-75 mph is on the the slow side.  I know I tend to fly at low 80s with my Vivats.

    - snap wasn't/isn't really a snap.

    - I do know of several planes coming apart on either the 1.5 snap / 4/8 or the 1.25 snap / 1.25 opp roll in F3A.

    - Most of the F3A flying I saw did have a reduced entry speed to the 1.5 snap.

    - Average weight of F3A plane is lighter (but same spar strength) resulting in less load on the tube/spar structure?  (compared to average weight of planes damaged to date on the Rev Avalanche).

    Regards,

    Dave
      ----- Original Message ----- 
      From: Ed Deaver 
      To: discussion at nsrca.org 
      Sent: Thursday, January 27, 2005 6:07 PM
      Subject: Re: Snao G's


      So, if I am interpreting these numbers(realize only one day and flight) correctly.  Beings the straight and level pos snap at 100mph(not unusual speed) was -13G's and the Rev avalance at approximately 95mph was -13G's, then the forces are about the same.  

      So, if we can slow the rev avalanche down to 70mph then the G's would only be -7.  

      This seems to go along with previous arguments that speed is the key.

      My question is, if the G's on flat and level snaps are approximately the same, with approx equal speeds, as the rev snap, then why hasn't FAI pilots been breaking planes with the 1.5snapopp 4/8????  

      Before anyone says it, I have seen many of these 1.5 snaps flown with some speed, so they weren't just puttputt into it.

      Thanx Earl.  Interesting stuff

      ed


      Earl Haury <ehaury at houston.rr.com> wrote:
        FWIW, I took a quick look at some snap G's yesterday. Equipment was a Quique YAK (140 size) fitted with an Eagle Tree Systems datalogger with G sensor. I only gathered data from one flight - so take that into consideration.

        Flat and level pos snaps @ (nominally) 100mph = 13G, dropping the speed to 70mph = 7G. (A normal pull to vertical @ 100mph = 7G.)

        An Avalanche with a neg snap at the top measured -5G @ 50mph.

        A Rev Avalanche with a pos snap at the bottom measured 13G @ 95mph. (Masters maneuver - intentionally flown fast.)

        An Avalanche from the top (push - F05) with a neg snap and a half at the bottom measured -14G @ 90mph. 

        (I normally measure around 5G on upline and downline snaps with my Partner.)

        All snaps were executed with rapid / high degree elevator lead and % reduction of elevator during rotation.

        I may look at this further as the mood strikes. As expected, controlling speed into snaps is easier on your airplane. None of the observed loads (in my opinion) should damage a well constructed aerobatic model (wouldn't want to ride in it though).

        Earl
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