Steel FP 20s rule OK?

[Andrew Tinsley]

Hi,
    I am a fan of the FP20 BBTU. Was distressed when Towers ran out of FP20 piston/liners! I then found a supplier who had stock.........Whoopee!
Sent off for 3 sets, when they arrived, it turned out they were steel liners..............Oh well, you live and learn, the supplier did say old stock!
     
    I then thought of a couple of Cougars that I have (the UK Cougar by Stoker, not the US version). These had upright steel FP 20s that were getting a bit tired. So use the surplus steel liners in those hack planes. Simple job done!

    It then occured to me "how best to run them?" Do you go the traditional 4-2-4, using the mods advocated by Leonard Neuman (think it was specific venturi diameter and a low back pressure muffler amongst other things?). Leonard thinks very highly of steel FP 20s modified thus. On the other hand, there is nothing to stop you going the high rev/low pitch route with this engine, even try the E2030 muffler, it may not work as a mild pipe but so what?

     Whichever way you go, the fuel will need to be a high castor type. OK which is the best way to run an upright steelie FP 20, there must be lots of experience out there,

Regards,

Andrew.

[Brett Buck]

    It then occured to me "how best to run them?" Do you go the traditional 4-2-4, using the mods advocated by Leonard Neuman (think it was specific venturi diameter and a low back pressure muffler amongst other things?). Leonard thinks very highly of steel FP 20s modified thus. On the other hand, there is nothing to stop you going the high rev/low pitch route with this engine, even try the E2030 muffler, it may not work as a mild pipe but so what?

   Leonard has no idea whether they were better before or after the modification. He has never run one stock, and  as far as I can tell doesn't grasp the basic concept behind it. I ended up very frustrated trying to explain it.
   
   The muffler will work like a pipe just like it does on the ABC version.

   In the spirit of full disclosure, I have only run or helped people a few times with the steel versions. They appeared to work about like the ABCs, but not nearly as consistently.

    Run it just as described for the ABC, but use at least 50/50 castor. Break it in for a long time on the bench.

     Brett

[Andrew Tinsley]

Thanks Brett,
 I thought they may behave as the ABN version, so I may even get the benefit of the E2030 pipe! That is interesting! I think that the major worry was the upright position. I got the impression from Dan's write up that the "magic"  run didn't go all that well in the upright position.

Thanks again,

Andrew.

[Phil Spillman]

I've used both kinds of set ups. For my money the iron ones work best of all! I use my same stunt fuel ie 10 11 11 or 5 12.5 12.5 etc! I have run both 9 X 4 and 9 X 5 of APC and MAS varieties! This engine is pure magic on the Sterling Profiles and the Flite Streake. Purchase FP .20 to .25 Venturis at .25" ID. If more power is wanted gradually ream them out with a tapered reamer. Go slow and do not use drill bits as they remove too much metal too fast.

Phil Spillman   

[Bill Little]

My first BBTU FP 20 was a steel liner.  It worked great!  I have not used my ABN FP 20s as much, so I am waiting to see just what difference it will make.  ALWAYS use the 3030 muffler and an APC 9-4 with stock venturi.  It is just a dead steady engine set up.  Baffles me to this day!

Big Bear

[Greg McCoy]

Rather than start a new thread, I'll ask here.

How do the FP 20 clones function compared to the FP 20? I do have a Magnum 20. Should be able to follow the same set up and get good results.

[Andrew Tinsley]

Hello Greg,
                 Are you sure that it is a Magnum 20 and not a Magnum 25? I am fairly certain that the FP Clone manufacturers NEVER made a 20 version. When Towers discontinued the FP20 piston and liner I checked the clone manufacturers and I am sure there was no 20!
  Some folk say that the FP25s don't run very well or downright poorly in BBTU mode. Dirty Dan used to convert FP25s to FP20 spec! I have heard other people say they do run as well as the FP20!
  I can't understand why the FP25 and clones are dubious in this respect, after all they are effectively bored out 20s. Unless the increase in gas flow upsets the pipe effect of the E 2030 silencer, they should run in a similar manner. I do have a NIB Thunder Tiger GP25, maybe I will get round to trying it in BBTU setup. Anyone else got any experience of FP25s and clones?

Andrew.

[Greg McCoy]

I just looked, it's a Magnum GP, marked 21 on the bottom side.

[Andrew Tinsley]

Hi Greg,

   I am pretty sure that the Magnum GP 21 is not an FP clone! For a start the FP series never had a 21 capacity engine. I am floundering a little here. Is the Magnum GP21 an original engine design or is it a clone of something else?

Andrew.

[dennis lipsett]

Thunder Tigre, who made those engines under the Magnum name for Hobby People made some different displacement engines the 21 was one and the 44 is another one that comes to mind. They also make the TT42 which is also an odd displacement but nonetheless a great running engine.
dennis

[Brett Buck]

 I am pretty sure that the Magnum GP 21 is not an FP clone! For a start the FP series never had a 21 capacity engine.

   To be strictly technical, the "20" FP is actually a 21. I flew mine in WAM "A" Stunt for years without knowing that - but it was over the limit.

     Brett

[Steve Fitton]

For what its worth, the BB setup worked quite well with my steel liner FP 25 as well.  Not having an FP 20 at the time, and stumbling across a new 25 at a King Orange some years back, I tried it in my Veco Tomahawk and it worked very well indeed.  I had some issues with the rpms wandering slightly around in flight, but never enough to disturb flying the pattern.  I won quite a few trophies with that little plane untill the wing fell apart, but the engine has been preserved for the next small plane project.

[Bill Little]

For what its worth, the BB setup worked quite well with my steel liner FP 25 as well.  Not having an FP 20 at the time, and stumbling across a new 25 at a King Orange some years back, I tried it in my Veco Tomahawk and it worked very well indeed.  I had some issues with the rpms wandering slightly around in flight, but never enough to disturb flying the pattern.  I won quite a few trophies with that little plane untill the wing fell apart, but the engine has been preserved for the next small plane project.

Hi Steve,

I remember flying that one at Huntersville and it turned me on to building my own *wind plane* Tomahawk!

Big Bear

[Brett Buck]

For what its worth, the BB setup worked quite well with my steel liner FP 25 as well.  Not having an FP 20 at the time, and stumbling across a new 25 at a King Orange some years back, I tried it in my Veco Tomahawk and it worked very well indeed.  I had some issues with the rpms wandering slightly around in flight, but never enough to disturb flying the pattern. 

    That's pretty much what the ABC version does, too. It's wandering in and out of resonance from the muffler. That's why I think the 20 is a little better. But almost all the small engines I tried (those available for cheap in the early/mid 90s) were pretty good performers as long as you left them stock, and found the right, low pitched, prop. Basically run them as they were intended.

I won quite a few trophies with that little plane untill the wing fell apart, but the engine has been preserved for the next small plane project.

     That was the other problem we noted - once we got the engines running right, the overall performance went through the roof. And the wings started folding/stress cracking/falling apart with alarming regularity. The worst structural designs, the Ringmaster in particular, would just fly apart at some point.   Same thing happened when we started running TP motors in regular stunt planes. Every TP airplane I have ever had, aside from the current Infinity, has had some sort of structural problem in the wing. Matt Neumann's airplane just blew apart at the 2001 TT, and it was built very conservatively. But he was far from the first. That's why a lot of the current airplane are built like tanks - not only does it make it more consistent to fly, it also keeps it from falling apart in a year and a half.

    Brett