Hello,
  I have found the Thunder Tiger GP42 to be amazingly good as a stunt engine. Slightly more power and every bit as good as an LA46. This coupled with better build quality (e.g. true ABC) makes this an excellent buy at a very reasonable price.
  It looks as though the engine is an FP40 clone, which has been slightly stretched in capacity. If this is so, why does it behave like an LA46, rather than the "difficult" FP40. Are the "numbers" for the GP42 very different from the FP40? I don't even know if the GP42 has a boost port, they have been so reliable and wear free, that I have never taken one apart, let alone put a timing wheel on one.



Just curious,


The Thunder Tigre 42 is not a clone of the FP 40, no parts are interchangable and it is not an ABC but an ABN. The box is slightly misleading.
That said it does not share the same timing as any of the OS engines and in fact has according to other
more interested users better timing more suited to our needs.
This does not mean that it is a great 4/2/4 engine but it is  a well behaved tractable powerplant. It holds a needle setting almost perfectly for the flight, starts instantly, and is almost a miser on fuel. And as you pointed out it has a little more oomph then the LA46.
It probably was not popular simply because of the requirement to go to .018 lines. I believe that those conditions have changed and it just might be time for more people to discover this powerplant.
I certainly like mine.
dennis
Andrew.

P.S. I suspect the odd venturi fixing has put people off!

Hello Gordon,
  My GP42s, converted to C/L and complete with venturi, NVA and plug, weighs out at 8.5 ounces. So that isn't too far from your ideal. I am still curious as to why this particular engine is so stunt friendly. Are there any engine experts out there, who can shed any light on this?

Regards,

Andrew.

Hello Randy,
  you comment that the GP42 is not as good as an LA46 for the money, takes me by surprise. What I am seeing is the reverse. The advantages that I observe with the GP42 are as follows.

1/ Rock solid engine run from start to finish, it is as good as my FP20s with BBTU.

2/ One (at most two!) flip starts.

3/ Relatively small changes in performance between choice of props (within reason).

4/ Very insensitive to tank height, makes the inside to outside performance almost a non issue.

5/ Can fly a somewhat heavier plane.

6/ 15 to 20% better fuel economy.

  I am not making out that it is a world beater but the above advantages over the LA46 are real, some more than others. I have run three LA46s and three GP42s on a variety of planes. I got so intrigued, that I was swapping the two engine types between the same plane in the same flying session. Could be a good reason why my flying suffers, too much tinkering!
  There was no doubt in my mind that the GP42 was noticeably better on all counts, 5/ could be difficult to prove and may be subjective, but a flying friend tried the two engines on a porker and came to the same conclusion as myself. Now it is either a brave man or a fool who would argue with someone like yourself. I have used the setup that seems to be the consensus for the LA46 and found it to be an excellent budget stunt engine. I tried the GP42 a year or three ago, when Dennis made his original post (I just happened to have a new one on the shelf). My experience is closely in line with Dennis. Perhaps I need to look carefully at the LA46 setup that I am using, if I don't have that quite right, then it could account for our different perceptions. By the way, I made sure I was comparing like with like, even down to using the same silencer. When I convert my new GP42 I shall even use the same OS venturi, just to be sure.
  As far as cost is concerned, the Tower price for a GP42 is $63 and an LAS46 is $80. So by the time the GP42 has been converted to stunt, it may cost just a few dollars more. I would take the GP42 on quality grounds alone.

Regards,

Andrew.

P.S. If you think I have too many motors and planes for my own use, then you would be correct. I use the majority of "my" fleet to encourage local youngsters to take up control line stunt. I have even got some promising pilots and a couple who are actually building!

Andrew. 

Hello Randy,
  Thank you for your response, I have never tried a 3 blade prop on either engines (They tend to be expensive and with youngsters flying the planes, broken props are fairly common!). Excuse me for appearing to be a stubborn in my claims for the GP42. I was an experimental physicist in a past life and I try to be scrupulously honest when doing any back to back testing. If you found the GP42 didn't fly heavier planes, then I accept that as fact. My comments on the topic were subjective (and I hope I made that clear). Everything else, I stick to, it isn't easy to dispute things with someone so much more experienced than myself! The differences are not huge, but definitely there, at least on my engines. Perhaps you would be kind enough to spell out the best set up for an LA46 in say a Cardinal. I like a constant speed run rather than a 4-2-4. I currently run a standard FP40 venturi (.285")with OS NVA, APC 11x4 (rough field!), launch at about 10,300, Enya no3 plug and standard muffler, oh and plastic clunk tank. For fuel I am using 5% nitro and 22% oil, the oil is 50% castor and 50% synthetic. Maybe this doesn't suit the LA46 too well ? I am more than happy to try out any suggestion. I realise that I could improve things with a lightweight tube muffler and maybe a cut down APC 12.25x3.75 prop, but I would run into lots of "pecking" on the field we use.
  I am just plain curious as to the differences I am seeing! The chances of 3 dud LA46s and 3 extra good GP42s are pretty unlikely. Maybe the setup I am using just favours the GP42? Perhaps I should just stop fretting and enjoy life!

Best Regards,

Andrew.