GMS 76 vs TH 75

If the GMS 76 and the TH 75 (both made by GMS) have the same displacement, why does the GMS produce 2.5HP while the TH only 2.2HP? One is ringed and the other is ABC, but that much difference?

Why do engine makers advertise horse power at these crazy high RPM's? The operating range with the suggested props is no where near peak HP. e.g TH 75 2.2HP at 15600RPM, yet operating ranges is between 10-13K.

Lastly, which of the two is a better engine. I like the gold plating on the GMS, looks royal!

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I have always preferred GMS versions over the Tower. Every one I have seen and used ran better.

The gold color is anodizing and will tuen slightly bronze over time and heat.

The new Tower may even be a renamed supertigre, which may also be made by GMS. If it is the Supertigre, then the GMS is even that much better. The large ST engines were dogs compared to just about any other brand.

Reply to
Paul McIntosh

That's not much difference. One is probably tuned for more torque or to be easier to use, or both.

They assume (probably correctly) that most folks buying engines see the TWO POINT THREE HORSEPOWER and don't see the itty bitty print mentioning that it was at 50,000 RPM and that the motor only held together for 1 second...

Reply to
Tim Wescott

I have a couple of O.S. FX engines and I just got done breaking in and flying a GMS .47 over the last week or two. The GMS engine revs at a noticably higher maximum RPM. You can hear the pitch difference between my GMS .47 and my O.S. .46 FXi in flight.

I haven't measured either with a tachometer, but I wouldn't be surprised to see the GMS at a maximum usable RPM rate 1,500 or 2,000 rpm faster than the O.S.

Reply to
Ed Paasch

Let me give you my take on this HP question. Back in the good old days model magazines that reviewed engines always included the curves of HP and torque versus RPM. Typically the torque starts out high at low RPM and it falls off as RPM goes higher. On the other hand, the HP climbs as the RPM increases and generally peaks ant then falls off at the high end of the RPM range. In the case that you mention, this peak HP takes place at a high RPM of 15,000. Since thrust is directly proportional to HP, with the right propeller you will get the most thrust at 15,000. For a sport flyer like me I would prefer to operate at 12,000 RPM. If I were into pylon racing I would be at 15,000.

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That is about average for the GMS and OS engines.

Reply to
Paul McIntosh

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