At the Nats, I was impressed by the engine runs that Burt Brokaw and Eric Conley were getting with their piped Nelsons.  I was able to pick up a used Nelson .40 Pylon engine and it is not going to be just 'plug and play'.  Main problem is that the carb is just an air cutoff, with no fuel metering.  The fuel goes through a normal needle valve/spray bar.  I'm not sure how they run these things in Pylon and the engine that I got was for event 428 (which is now discontinued and so I wasn't able to read the rules for a description), but it seems that they were run on suction, with a max of 15% Nitro and using the tuned muffler which Eric has written about in other threads, so it should be adaptable to Class 1 pretty easily.  So I got in contact with Eric to get a couple of questions answered, and we decided that it might make an interesting thread in case anyone else has a similar application, rather than just a series of emails between us.

So my initial questions for Eric are -

1.  First off, is this the Nelson that you are using?  When I inquired about the ability to idle and fly with a reliable mid-range, the fellow that I was talking to recommended this engine rather than the one he was actually selling.  He claimed it would idle and fly at mid-range very well, even with the crude 'carb' that is currently fitted.

2.  What are you using for carbs on these?  I did look through some old posts concerning Nelsons here on SH, and found reference to Perry's in a discussion of the 'big case' .36.  Is that also the carb you use in Class 1? I want to fit something with low-end metering, at least and wonder how much carb bore this engine will stand, using suction fuel feed.

3.  What prop do you use?  I won't be trying to 'reverse crank-shaft' this one but a starting point for diameter, pitch and material (glass, wood, carbon, etc) would be helpful.

4.  This engine has a Nelson plug (naturally).  I haven't pulled the head, but it doesn't look like a button type, so other plugs appear to be no-go.  Is there more than one type of Nelson plug?  I am only familiar with the Nelson conversion heads that are available for 1/2A combat engines that allow use of a Nelson plug (I think it's called an "HD").

5.  I know you use the muffler, and that is my intention also, but just out of curiosity, have you tried the engine open-faced?  Do you know of any Pros and Cons?

If anyone else has any info or other questions, please feel free to add to this discussion.  Thanks in advance to Eric.

Hi Mike

I do not use "social media" and I do not normally visit any "forums" the reasons for which I will not go into here.  However I welcome questions and comments from others and am more than willing to help anyone in any way that I am able.  I just prefer to do it with direct contact.  In spite of that, Eric has persuaded me to post on this forum in response to your post.  So here goes:

1)  The FISE Nelson .40 Pylon engine is what I am using for Class I carrier.  I am not familiar with the carb that you have described so cannot help you with that.

2)  The carb that I am using in Class I is a Magnum .91 carburetor that Henry Nelson recommended to me and he installed a sleeve for me on the outside of the carb throat so that it fits perfectly into the carb boss on the engine.  The way this sleeve is designed, it only fits into the engine one way so depending on your engine installation the sleeve may need to be installed "backwards" in order to put the throttle arm on the correct side of the engine (as I had to do on one of my models).  This carb has a throat ID of .430 so must be run on pressure.  I use "muffler" pressure using the pressure tap on the "tuned" muffler that came with the engine from Henry.  I also use a one-way check valve in the pressure line which does two things.  First, it prevents fuel from flowing into the muffler during the "fueling" process.  Second, it results in a much higher tank pressure since the pressure pulses are totally "additive".  As a result of all these factors it is necessary to use a very fine thread remote needle valve assembly.  I use the needle valve assembly from an OS carburetor that was designed for use on OS .15 size engines.  I have also tried one that was designed for .25 size OS engine carburetors but it was a little more sensitive than I liked.  

As for running this engine on suction, I tried using a ST carb with .350 bore but had problems getting reliable throttle response throughout the throttle range.  I have had some success running this engine on suction using a Perry carb with .315 bore.  If you really want to stay with suction I would recommend this setup.  The only reason that I developed the system that I am using was because I was feeling the "need for speed".  The down side of the way I am running it is I have given up some reliability for a little extra speed.  Due to the very high tank pressure, even the slightest pin-hole leak anywhere in the system and it is big trouble amigo.  But on the other hand when it is all working as advertised it is very satisfying.

3)  I recommend using APC 9-6 props.  They are available in right and left hand rotation so if you ever decide to try a reverse crank it is a piece of cake to convert.  I have experimented with different diameters and different pitch props of different materials but always came back to the APC 9-6.  For me it is the best compromise of performance, availability, cost, and consistency.

4)  I highly recommend staying with the Nelson one-piece plugs.  They are still available and they are still the lowest cost plug that I am aware of.  If you use an after-market head that will accept a common 1/4-32 plug you will not only pay more for the plugs but you will also lose some performance because the Nelson plugs seal at the bottom instead of at the top as other plugs do.  Nelson makes a "large hole" plug sometimes referred to as a "hot" plug and also a "small hole" plug that is usually referred to as a "heavy duty" plug and is what is used by the combat guys and some of the speed guys.  Henry recommends the "large hole" plugs for carrier but I have used both and can't tell much difference but am currently using the "large hole" plugs.

5)  There are three very good reasons that I am using the Nelson "tuned" muffler on all my Nelson carrier engines (except for the .15):  PERFORMANCE, PERFORMANCE, AND PERFORMANCE.  I tried very hard to get the same performance without using the tuned muffler.  I was eventually able to get the same airspeed by using lots of Nitro and trimming the prop diameter down.  The problem was that the acceleration as so poor that my high speed times were much slower.  With the same prop and fuel the tuned muffler is worth approximately 2000 RPM.  The weight and drag of the "tuned muffler" is a non-issue when compared to the performance boost, plus being able to use stock props and cheaper fuel.

Hope at least some of this may be helpful to you.  If you or anyone else wishes to contact me directly here is my contact information:
Burt Brokaw
lecreit@msn.com
520-743-3003  hm
520-360-6552  cell

     H O L Y    C O W,    I didn't think I was that persuasive. Eric