Snap G's

[Earl Haury]

I agree with Dave in that 100mph is too fast. For a first pass I simply tried to capture some basic data at the extremes (the reason for using the YAK). 

I still plan to look at this in more detail, including the forces for a variety of "non-snaps". It's surprising how much time is involved in designing a flight plan to encompass the areas of interest, flying the plan correctly (really need a caller), ensuring that "markers" are flown to aid data identification, and then analyzing the data. Of course multiples of each element must be flown to asses repeatability and reproducibility.

As I'm comfortable with the loads imposed during the P/F05 flights, I'll focus on the Masters Avalanche with a variety of sizes, speeds, snap positions, snap intensities, and "non-snaps". Still a lot of stuff. Now if it quits raining. Oh, and I can remember how to do a non-snap.

Earl



----- Original Message ----- 
  From: David Lockhart 
  To: discussion at nsrca.org 
  Sent: Thursday, January 27, 2005 10:13 PM
  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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