Webra 1.45 Prop

[David Flynt]

Thanks.  Very interesting.  

David
  ----- Original Message ----- 
  From: David Lockhart 
  To: discussion at nsrca.org 
  Sent: Sunday, July 10, 2005 8:18 PM
  Subject: Re: Webra 1.45 Prop


  Re-post from myself, some time ago.

  Regards,

  Dave


  --------

  I've been repitching APCs for years - and in general not had a problem with
  springback/memory - but I have found that the technique is critical.  Using
  the Prather pitch gauge, I feel comfortable saying I can repeatedly measure
  prop pitches within 1/8" pitch - which I feel is pretty much the pushing the
  precision of the gauge.  I would say that 10-20% of the blades I twist do
  have some amount of springback (1/8 to 1/2") in the first 24 hrs - but I've
  not seen them springback anymore after that, and it is rare that I have one
  springback as much as 1/2".

  I mark every prop front/back of the blade where I am going to heat with the
  heatgun and where I am going to apply the twist.  I use a good heat gun, a
  thick cotton towel or sock, and a large set of channel lock pliers.
  Basically, I slowly heat the prop blade near the hub with the heat gun
  (alternating front/back, concentrating on the thicker areas of the blade),
  and when the blade is hot enough, it will twist without too much pressure.
  For the APC 15.75-13 3 blade, I heat at Station 5 (of the Pitch gauge, which
  is 2.5" from prop center) and then wrap the sock around the blade and hold
  the prop at station 7 (3.5" from prop center) to apply the twist - I put the
  other 2 blades on my leg and do the twisting bit in my lap.  (For 2 bladers,
  I use 2 pair of pliers).  The sock is too keep the teeth of the pliers from
  scarring the prop.  When the desired pitch is achieved, you can either cool
  the prop in cold running water (and move onto the next blade) or let it cool
  overnight (don't mess with the prop while it is cooling).

  The basics are pretty simple - but it does take some practice to get good at
  using the Pitch Gauge and being able to get consistent readings from the
  Pitch Gauge.  Heating the prop slowly (I spend 4-5 minutes before twisting
  on the 15.75-11) is better than heating it fast - think slow cooked prime
  rib, not "black and blue".  You want the prop warm on the surface and at the
  core - then it will twist easier and have less memory.  If the prop is not
  evenly heated, the pitch will tend to wander as it cools - not good.  It
  usually takes me 1 heating cycle, about 1 major twist, and a couple minor
  "tweaks" during the first couple minutes of cooling to get the pitch change
  I want.  On occasion, I do need to reheat a blade and tweak the pitch a bit.
  Some of the props I twist get a little bit of whitish discoloration when
  heated, some develop the whitish coloration after I twist them, and some
  don't show any change at all.  Near as I can tell, the prop is at about 200
  degrees when I twist (using an InfraRed temperature gun).

  I used to quench the prop in cold running water (very important to cool both
  sides equally) and repitch each blade consecutively in one session.  At this
  time, I'm having better luck letting the prop air cool - the pitch seems to
  wander less.  I then let the prop sit overnight and check again the next day
  and make minor pitch adjustments if needed.  I've got a couple 13.5-11.5N
  prototypes I made back in 1992 that were the result of twisting/reshaping
  and they are still at 11.5" pitch, after 12 years, and hundreds of flights.
  And I've got some prototype 17-13Ns that are 5 years old with hundred of
  flights and still ok.

  Regards,

  Dave Lockhart
  DaveL322 at comcast.net
    ----- Original Message ----- 
    From: David Flynt 
    To: discussion at nsrca.org 
    Sent: Sunday, July 10, 2005 3:06 PM
    Subject: Re: Webra 1.45 Prop


    Curious -- how does one repitch a prop?  Is it machined?

    Thanks,

    David
      ----- Original Message ----- 
      From: RUDDERCABL at aol.com 
      To: discussion at nsrca.org 
      Sent: Sunday, July 10, 2005 12:03 PM
      Subject: Re: Webra 1.45 Prop


      In a message dated 7/10/2005 2:22:10 PM Eastern Standard Time, rcaerobob at cox.net writes:
        The choices are pretty subtle, and not real obvious unless you're willing to try "weird stuff"....like the Master Airscrew 16 x 10.  Proving to be a great choice.  So is the "GRS" (looks like a Mejzlik) 16 x 11, and the Mejlik itself.  Then, of course, the APC's, but Fred refuses to retool and reduce the 13 pitch three blade (Completely understable considering the "fickleness" of US).  Lockharts' repitching works VERY well, and I've had the 10, 11, and 12 pitch.  All work very well on the OS 1.60 piped.
      Bob

      Perhaps the APC 15x13w would work . It worked well on my 1.40RX. I also have one that Dave Lockhart repitched to 10 that I will be trying soon on an 1.40L.

      Robert Gainey
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