Prop changes when increasing weight/high altitude
12-25-2006, 05:58 PM
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Prop changes when increasing weight/high altitude
I have an Alpha 40 trainer, which has the Evolution .46 3-blade prop. A couple questions arise from living in a high altitude environment, (5,550ft), and wanting to mount a cheapo point and shoot camera to take .mpg videos for fun...
I met a guy at one of the local fields who happened to have an Alpha 40 also, and he commented that the 3-blade Evolution system prop is far from ideal in his experience, and that I should go with a 2-blade prop, and of course forgot the size and pitch that he recommended.
But for the "rules of thumb"- What is a good 2-blade prop choice for a 40 size trainer? How will high altitude affect the optimal choice? How will an increase in weight affect the optimal choice?
I met a guy at one of the local fields who happened to have an Alpha 40 also, and he commented that the 3-blade Evolution system prop is far from ideal in his experience, and that I should go with a 2-blade prop, and of course forgot the size and pitch that he recommended.
But for the "rules of thumb"- What is a good 2-blade prop choice for a 40 size trainer? How will high altitude affect the optimal choice? How will an increase in weight affect the optimal choice?
12-25-2006, 08:03 PM
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RE: Prop changes when increasing weight/high altitude
Longer props are more effecient than shorter ones. Two bladed are better than three. In fact big props turning slow are much better than small props turning fast.
The prop size depends on the engine you're using and how it should be loaded for it's horse power. There should be a few in it's range that you can use. Use the longer choices that have lower pitch. This will get you up to flight speed fastest but will also have a little slower speed than a long prop with a deep bite. Maybe a 8x6 to 9x6 to 10x4.
What engine are you using?
Dan
The prop size depends on the engine you're using and how it should be loaded for it's horse power. There should be a few in it's range that you can use. Use the longer choices that have lower pitch. This will get you up to flight speed fastest but will also have a little slower speed than a long prop with a deep bite. Maybe a 8x6 to 9x6 to 10x4.
What engine are you using?
Dan
12-25-2006, 09:40 PM
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RE: Prop changes when increasing weight/high altitude
Its the standard Evolution .46 that comes with the Alpha trainer. It seems like a good engine, but it comes with a 3-blade, unknown dimension prop that takes about 60 seconds from broken prop to ready to fly. If I remember correctly, the 3-blade has a 10" radius, but with what I've heard from another guy with an Alpha, the 3-blade isn't as efficient as a 2-blade, and he didn't have anything good to say about the 3-blade anyways.
I'm also looking into not only what works best, but what direction to go when I am increasing weight, and flying at a higher altitude than sea level. My priority isn't with top speed- I am more interested in shorter takeoffs, high drag at idle, higher thrust at low speeds, and generally within the high altitude, low speed, higher weight envelope.
I'm also looking into not only what works best, but what direction to go when I am increasing weight, and flying at a higher altitude than sea level. My priority isn't with top speed- I am more interested in shorter takeoffs, high drag at idle, higher thrust at low speeds, and generally within the high altitude, low speed, higher weight envelope.
12-25-2006, 10:04 PM
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RE: Prop changes when increasing weight/high altitude
Well I was picking pretty small ones for that engine. A quick Google search led me here. http://h1071118.hobbyshopnow.com/pro...?prod=EVOE0460
They state they used a 11x6 for getting the numbers for the engine specs. That's a pretty fair length prop for a .46 to .60 engine. I would go with that. You might also experiment with a 12x6 prop if you can get one but you'll start to deal with ground clearence and prop tip damage issues. It might load it down too much. I would go with the 11x6. That's a fair sized prop and doesn't have a deep bite. Like a 11x8 or etc would. This will give you good acceleration in a good strong running .46.
Dan
They state they used a 11x6 for getting the numbers for the engine specs. That's a pretty fair length prop for a .46 to .60 engine. I would go with that. You might also experiment with a 12x6 prop if you can get one but you'll start to deal with ground clearence and prop tip damage issues. It might load it down too much. I would go with the 11x6. That's a fair sized prop and doesn't have a deep bite. Like a 11x8 or etc would. This will give you good acceleration in a good strong running .46.
Dan
12-25-2006, 11:43 PM
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RE: Prop changes when increasing weight/high altitude
Excellent! Thanks for your input. The prop clearance on this trainer is limited, and I have been flying from a dirt road on occasions. The 11" is getting a bit much, 12" would be out of the question.
But, to anyone else flying at 4,000-5,000ft, if the books are saying 11x6 at sea level, would the experiments shift towards 11x5, or are rc planes not affected to the point that this becomes an issue? What other issues are there with higher altitude flights? (Thanks to kd7ost, that link had some great user manuals and diagrams specific to the engine that I didn't have, since it came with the RTF trainer)
But, to anyone else flying at 4,000-5,000ft, if the books are saying 11x6 at sea level, would the experiments shift towards 11x5, or are rc planes not affected to the point that this becomes an issue? What other issues are there with higher altitude flights? (Thanks to kd7ost, that link had some great user manuals and diagrams specific to the engine that I didn't have, since it came with the RTF trainer)
12-27-2006, 08:00 AM
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RE: Prop changes when increasing weight/high altitude
That 3 bladed prop on the Evo is meant for training only, and is purposefully designed to be inefficient. The prop is designed NOT to let the plane gain much speed no matter how much throttle you run, or even if you dive it, it acts like a brake. The idea for that prop is to fly at a very constant, low speed so the plane stays slow for new pilots. Get an APC 12X6 and the performance will increase by a HUGE amount.
JettPilot
JettPilot
