Starman
Well-Known Member
I would like the benefit of your experience and wisdom concerning propellers. First I'll post a picture of what I want and then I'll explain why I want it, then you can shoot it down.
I want one of these, only smaller
And only one fan, not counter rotating. If I use two engines later then I'll consider counter rotating.
These are my ideas: the reasons that I like this is because I'm designing a pusher, which can always benefit from a smaller diameter, and because I want to see how well I can get away with direct drive.
So, for direct drive you want the prop to be the largest possible diameter for a given RPM, and my target RPM for direct drive is 4000. For this RPM a wood prop can only be like 54" and a standard metal prop can be almost 60" (according to an online calculator).
Swept back blades are required to get the largest diameter for a given RPM.
More considerations - most of the time I think I'll be using less than 200hp but I will be able to get well over 300 and maybe over 400hp for short bursts (later I'm aiming for around 500 - 600hp). With a small diameter this requires more blades but more blades are wasted with the lower power, but ... I'll need more anyway so I live with a little less efficiency at lower power.
I've checked and I don't see anyone making swept back blades that can approach or exceed supersonic, even unaffordable ones. If there are any then let me know. Also, these blades would need to fit into a multi-blade hub, ideally one that can accept more blades later, like go from two to three to four to six blades in increments.
I designed and made a high RPM fan for a V8 once but didn't test it because I realized that where I had it riveted would cause cracks. They were made out of 1/16" stainless steel and curved to make an ideal supersonic airfoil, one that would not give up anything for being supersonic.
So, what do you think.
I want one of these, only smaller
And only one fan, not counter rotating. If I use two engines later then I'll consider counter rotating.
These are my ideas: the reasons that I like this is because I'm designing a pusher, which can always benefit from a smaller diameter, and because I want to see how well I can get away with direct drive.
So, for direct drive you want the prop to be the largest possible diameter for a given RPM, and my target RPM for direct drive is 4000. For this RPM a wood prop can only be like 54" and a standard metal prop can be almost 60" (according to an online calculator).
Swept back blades are required to get the largest diameter for a given RPM.
More considerations - most of the time I think I'll be using less than 200hp but I will be able to get well over 300 and maybe over 400hp for short bursts (later I'm aiming for around 500 - 600hp). With a small diameter this requires more blades but more blades are wasted with the lower power, but ... I'll need more anyway so I live with a little less efficiency at lower power.
I've checked and I don't see anyone making swept back blades that can approach or exceed supersonic, even unaffordable ones. If there are any then let me know. Also, these blades would need to fit into a multi-blade hub, ideally one that can accept more blades later, like go from two to three to four to six blades in increments.
I designed and made a high RPM fan for a V8 once but didn't test it because I realized that where I had it riveted would cause cracks. They were made out of 1/16" stainless steel and curved to make an ideal supersonic airfoil, one that would not give up anything for being supersonic.
So, what do you think.
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