This mostly directed to Randy but also to all of you who fly Randy's products. Questions: if one was to graduate to a SV-11 and was only interested in a side exhaust, which runs better, the PA .61 or PA .65 ? And because I have one, would a T&L Tigre .60 have guts to power ship ? or should one go with Tim the tool man Taylor "more power" and just get the new PA .75 on a pipe ? ( but I'd rather have a side exhaust on a .61 or .65) Thanks for your replys.
Any of those are sufficient for the airplane. The PAs are generally much higher quality and usability than any ST and far more durable/reliable, but the ST60 is more than adequate in terms of power, if it's running correctly.
I can't answer the 61 vs 65 question with any authority, haven't seen many PA side exhaust/muffler engines. I would guess that they run about the same and the 65 has a tiny bit more power. In either case you have far more than enough power. All the direct comparisons of the same engine, muffler vs, pipe, we have noticed that they run well either way, but you give up a fair bit of performance using the muffler. It's not really a power thing, it's a controllability issue. Bear in mind that these size airplanes are what we used to fly, 30 years ago, with ST46s. Getting any 60 to put out enough power is not the issue - it's how well you control the power. You can better take advantage of the larger much more "powerful" engines with the controllability provided by tuned pipes. It works fine with a muffler, but we have tried it several times (using PA and RO-Jett rear-exhaust engines on mufflers) and it was clear that you give up a pretty fair bit of performance.
And there is some pretty good evidence that the bigger, more grossly overkill you get with muffled engines, the harder they are to get to run just like you want - once again, you have to somehow control the overkill power, and with only a needle valve, it can get pretty touchy. I wouldn't expect much problem with an SV-11 and a 61/65 but we have seen more than a few examples of people putting gianter and gianter motors in the same sized airplanes (like a muffled 91 in a 700-square-inch airplane) on the theory that "I have a 91, why do I need a pipe?" and winding up having to make hair-trigger needle adjustments. If it changes by 1% of its capacity that's a huge change in the speed of the airplane. Windy had that problem (among others) at the NATs a few years ago. But it makes sense and corresponds to what we all knew back in the 70's and 80's when people were running only muffler engines - you need to match the airplane to the engine carefully or you either run out of power, or you can't control the engine and it either puts out way too much or way too little. PA61/SV-11, not a problem.
The PA75 on a pipe (using David's setup) is the only engine that I would consider switching to right now, as I really like the run characteristics. It's not because of added power nearly as much as you can run it detuned to the point it runs as evenly as an electric motor. Of course it was semi-intentional that it runs a lot like mine so obviously I like it.
If they are all a wash, cost and functionality-wise, it's really a no-brainer that the best system of those you have listed (and the one that will limit you less in the future) is the piped 75. It's the gold standard, literally. But any are sufficient to fly an SV-11 with good performance.
Brett
Topic: PA Engine & Plane (Read 2479 times)