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 on: Today at 02:42:16 PM 
Started by Alfred Welch - Last post by frank mccune
    Hi Alfred:

    I do not think that the 53 Stunt had anything other than a flat head.  About that time, Duke came out with his No. 2 head to keep up with the K&B engines.  These are very rare!!!!!  I think that you are asking about the stock head for 1953.

     I have a No. 2 head on a Stunt .35 but I have not had a chance to fly it yet to determine if there is any advantage.  Will post results later.  I wonder if the No. 2 head will make no nitro fuel run better than the stock head.

                                                                                         Good luck,


 on: Today at 02:40:12 PM 
Started by Bill Little - Last post by Bill Mohrbacher
I did a series of article on the Stunt 35s for Engine Collectors Journal and did some work on the bypass sizes:


The bypass on a Fox engine is a space that connects the bottom of the case to the intake port.  It is a cavity on the left side of the case.  When the round liner is slipped into the case, the bypass space is created.  For some time, stunt fliers, first on the ISKY Bulletin Board and now on the Stuka Stunt Works BB have talked about newer Fox Stunt 35s suffering from the Fox “Burp”.  This occurs when using a side mounted engine (as on a profile model) just after the model is climbing away from the inverted position at the bottom of an outside loop.  The engine hesitates for an instant (the Fox Burp), then picks up while in the meantime the pilot has had a heart attack.   I don’t remember this problem, but I was flying with early 1960’s or older Fox 35s and didn’t usually set them for a 2-4-2 break.  Anyway, the cure has been to insert a piece or something, usually wood, into the bypass opening to reduce its cross section.     
Since I had and will have engines apart, I thought it might be good to see what the Fox bypasses have looked like over the years and document their dimensions.  Fig. 19 shows the bypass cavities of the 1951, ‘52/’53, ‘54, and ’55 engines looking from the head down.  Fig. 20 shows the tops of the bypass cavities looking in through the exhaust stacks; the dark area at the top of the cavity is really the fillet, not just a shadow.  You can see the narrow rounded top and fillet on the 1951 Permold case; a very generous fillet on the 1954 engine and a wider cavity on the 1955 engine. 

I used an ID Pin Gage to measure bypass depth and bypass width (Fig. 21).  There is a taper in the side walls of the cavity, but by holding the gage in about the middle I got close to an “average” value.  I measured diametrically across the cylinder bore into the bottom of the bypass cavity and then subtracted the cylinder bore to arrive at the bypass depth.  Then I just multiplied the width by the depth to get the bypass cross section.  I know I should calculate it by using the section of a ring, not a rectangle, but since I will use the same calculation, the results ought to be comparative.

      WIDTH        DEPTH          DIAM.   DEPTH   X-SECTION
1951      .514”          1.010”         .886”   .124”      .064”2
1952      .583”          1.005”         .886”   .119”      .069”2
1954      .575”          1.050”          .886”   .164”      .094”2
1955      .615”          1.025”         .886”   .139”      .086”2

OK, there are the results all documented.  There is a 25% difference between the 1955 and 1952 bypasses, but we’ll wait and see more measurements and try and find out from the fliers where the trouble occurs.  It is great to be retired and get paid by someone like the PE to do this stuff!

The BYPASS ADDENDUM (after I finished the stunt series)

Now I’ve measured bypasses from the first Permold engines through the current model, 1948-2011.  Part II of this series explains why I did this and the “Fox Burp”.  Fig. 21 shows an accepted method for stuffing the bypass and eliminating the burp (thanks to Dennis Vander Kuur). 

Looking at all the data and realizing I measured basically as cast surfaces and engines that may have come from different molds, I would conclude:

-The Permold engines, 1948 through 1951 had essentially the same bypass dimensions
-The first die cast engines, 1952-1954 had wider bypasses and the 1954 was definitely        deeper
-The 1955-2011 bypasses were wider than 52-54, but the 55-2011had about the same    bypass width. It looks like there may have been 2 different dies for the bypass depth,    one set producing .150” depths and another .130”  depths.

Now someone can run some tests and see if any of these engines really are more “burp prone” than others!

      WIDTH        DEPTH          DIAM.   DEPTH   X-SECTION
1948      .520”          1.014”         .875”   .139”      .072”2
1951      .514”          1.010”         .875”   .135”      .069”2
1952      .583”          1.005”         .875”   .130”      .076”2
1954      .575”          1.050”          .875”   .175”      .101”2
1955      .615”          1.025”         .875”   .150”      .092”2
1968      .620”          1.025”         .875”   .150”      .093”2
1970      .630”          1.025”         .875”   .150”      .094”2
1972      .630”          1.025”         .875”   .150”      .094”2
1973      .630”          1.025”         .875”   .150”      .094”2
1975      .630”          1.005”         .875”   .130”      .082”2
1980      .620”          1.005”         .875”   .130”      .081”2
1998      .625”          1.020”         .875”   .145”      .091”2
2011      .625”          1.010”         .875”   .135”      .084”2

 on: Today at 02:34:59 PM 
Started by frank mccune - Last post by frank mccune
     Hi Eddy:

     Thanks for the tip! I wonder if it can handle the current draw of the buffer?  I will check!

                                                                            Be well my friend,


 on: Today at 02:24:11 PM 
Started by Dennis_Bieber - Last post by John Leidle
   My Saitos came with Hanger9  4 stroke plugs & I now use them in my 2 strokers.

 on: Today at 02:01:14 PM 
Started by wwwarbird - Last post by Dan Labine
Hi Wayne.

Sent you a message..Also changed my email


 on: Today at 01:55:20 PM 
Started by Crist Rigotti - Last post by Fred Underwood
One thing I did not test today was using a different prop.  Mike Scott was out flying today with his Cobra 2826/10 930Kv 4S Edge/Hubin set up in an airplane a little larger than mine but almost the same weight and his motor temps, with a tightly cowled motor and minimum exhaust air outlet was running motor temps about 105 F.  He was using an APC 12 x 6 cut down to 11 3/4 at 8900?rpm, while I'm using an APC 13 x 5.5 cut down to 12 running at 9600 rpm.  Next time out I'll try using a 12 x 6 cut down like Mike was flying.  I could be running a prop that puts too much load on the motor.  We'll see.

I appreciate everybody's input and maybe we can all learn something together getting through this.

It looks like you have tried the easy cooling suggestions except the turbo spinner, and have moved to the other end of the problem, heat generation.  I was hoping to see some of the variables other than just prop for comparison.  Mike's variables, particularly amps/watts and the factors contributing might be enlightening or, differences between your current plane and prior where you used the same motor, prop, batteries. 

With more weight/wing loading, might you be using more gain rpm or time in gain on the Igor setup vs Hubin and then more watts used.

Thanks, just trying to learn as you suggested.

 on: Today at 01:48:56 PM 
Started by Bill Little - Last post by frank mccune
     Hi Bill:

     Yes, you can.  I think that the .29 and the .35 cylinders have the same o.d.! I have some new p&c from a 1958 C.S. that I was hoping to put into a .35 Stunt but no go.  The o.d. on the C.S. are greater than the Stunt.
      I have a 1949 and a 1951Fox .35 Stunt engines and they are great for Stunt.  No Burp!


 on: Today at 01:46:03 PM 
Started by Bob Heywood - Last post by Motorman
Perhaps it's time to rekindle the Rossafox lol.


 on: Today at 01:22:30 PM 
Started by Bill Little - Last post by rustler
I've heard it said that you can keep old Fox 35's going with parts from newer models, - a tribute to a continuous line since 1948.
Maybe the same applies to 29's? Or even, - it it's just a case of thick or thin cylinders, maybe a 35 p/c would really cheer your 29 up  Wink (Guess that would also mean a different head).
I think the real answer is you'll have to check.
Let us know?

 on: Today at 01:15:43 PM 
Started by Robert Zambelli - Last post by Jim Kraft
I use to fly the company products pipeline with the pipeline flyers. One day we saw something in the air that we could not identify. It was probably 200 to 300 feet away and the sun was flashing off of it. We turned around and went back to see what it was. It turned out to be one of those aluminized party balloons.

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