3-bladed props for OS160FX

[Claudio Garcia Rosa]

Thanks Dean & Dave
For the inputs on de-pitching the 153/4x13 prop.

I will practice with a broken 17x13 2b.

Regards.
Claudio

----- Original Message -----
From: David Lockhart <DaveL322 at comcast.net>
To: <discussion at nsrca.org>
Sent: Monday, November 15, 2004 9:54 PM
Subject: Re: 3-bladed props for OS160FX


> Claudio,
>
> Below I've posted some info I've written before - I think most of it has
> been on this discussion list before.  In short, progressive twisting is
not
> needed - a single twist near the root is sufficient.
>
> --------
>
> 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: Claudio Garcia Rosa
> To: discussion at nsrca.org
> Sent: Monday, November 15, 2004 7:06 PM
> Subject: RE: 3-bladed props for OS160FX
>
>
> Gracias Dean,
>
> Just to see if I´ve understood,
> I must twist the blade about 1-1/2" from the root untill it reaches the
12"
> pitch?.
> Or must I twist it progressively from the root to the tip ?
>
> Saludos.
> Claudio
> ----- Original Message -----
> From: Dean Pappas
> To: discussion at nsrca.org
> Sent: Monday, November 15, 2004 7:05 PM
> Subject: RE: 3-bladed props for OS160FX
>
>
> Saludos Claudio,
> First you need a pitch gauge, and then a monokote hot air gun. For this
size
> prop, I actually use 2 heat guns, to warm the thick blade root. You will
> probably have to apply heat for 30 ~ 60 seconds with two heat guns. Warm
the
> blade about 1-1/2" from the root, and twist the blade until it cools. You
> will need something to prevent burning your hands, like a block of wood
that
> has a narrow hole in it. The blade can be restored to its original shape
by
> warming, if and when you need several tries to achieve the dewsired pitch.
> It will take practice to keep from bending the blade along its length,
while
> just twisting it.
>
> Try practicing on a small, disposable, two-bladed prop!
>
> Have Fun,
>
> 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 Claudio Garcia Rosa
> Sent: Monday, November 15, 2004 4:59 PM
> To: discussion at nsrca.org
> Subject: RE: 3-bladed props for OS160FX
>
>
> Hello Dean,
>
> I have the same prop.
> Can you please tel me how to de-pitch it to 12 ?
>
> Thanks in advance.
> Claudio
> ----- Original Message -----
> From: Dean Pappas
> To: discussion at nsrca.org
> Sent: Monday, November 15, 2004 6:42 PM
> Subject: RE: 3-bladed props for OS160FX
>
>
> Try the stock 15-3/4 X 13 APC.
> You migh de-pitch it to a 12.
>
> 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 randy10926 at comcast.net
> Sent: Monday, November 15, 2004 4:41 PM
> To: discussion at nsrca.org @nsrca.
> Subject: 3-bladed props for OS160FX
>
>
> So what 3 bladed prop would you use on an OS160FX?
>
> Any reason to think a bolly carbon prop is better than an APC on this
> engine?
>
> Randy
>
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