I'm running an OS 50 SX-H in one of my planes and I've got a bunch of 10x8 props hanging around. I've been using 11x7's and they seem to work fine but would like to use these other props. Are the 10x8's too small to run with this engine?
No, that is a good size prop for that size entine, but OS says not to ues this engine in a plane. I am not real familiar with it but there must be a reason.
Just guessing, and speaking in general... Helis run a very narrow rpm range under load. It's possible that the SX-H is ported to make good power only in this narrow band. Also, heli engines run hotter because the head isn't out in the open airflow. Last, the carb is likely to be different, again because it can be optimized to run well in only one specific, very narrow power band.
The head and plug can be changed out to solve head heat problems. The carb can be swapped out for something more appropriate. There isn't much you can easily do to change the port timing. (But you knew that.)
Depends on the plane. What is it used for? A 10-8 should not overload a 50, but it is a tad large. (Your 11-7 to me is a .60 size prop.) If your plane is a go-fast type, then the 10-8 should work well. If it's pulling power you need, the 10-8 will very probably be a bit disappointing.
Try one and see. I suggest a slight bit richer than normal on the first try as that prop may tend to unload a good bit in the air.
It would cost more than just buying the appropriate engine in the first place. You cannot do any port cutting on a nickel plated cylinder with out a high risk of the plating flaking off later.
Please reread what I said........there are OTHER WAYS besides that you can alter port timing. Now , I am NOT going to get into a lengthy thread among "armchair experts" on this subject.......... next thing you will tell me is I cannot run wheel bearings without any grease in them. Im done with it now.
Aaah yes! 11x5, 11x6, 10x7 in that order will fly that model. The 10x8 will certainly fly it, but not like the 3 I mentioned. Vertical and acceleration will be way down with the 10x8.
Here's a link to some thrust and airspeed figures to .46-50 size engines:
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Scroll way down to the bottom of the page and find your prop sizes. You can quickly see why the 10x8 is not ideal for any glo engine.
How about a short one, then, to help us non-experts? My list of engine changes is pretty short: shimming the head; tuning the pipe; ... A rather short list, as you can see. What are some of the many ways you can change port timing?
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