Post by btboone on Mar 19, 2017 19:13:56 GMT -5
My goal would be to make a simple turbine engine similar to the ones used for RC planes with as much thrust as possible, yet be reasonable in size, so as efficient as possible. I'd like to get to around the 200 pound thrust range if possible. One question I have is about the design of the turbo impeller compressors. It seems to me that instead of having the vanes travel very close to the outer casing wall where that casing is stationary (thus suffering some ground effect), it might be more efficient to have an outer skin that travels with the impeller. It would look something like a piece of a trumpet bell laser welded on. In this way, the outside of the skin would not need to ride close to a wall, would be smooth, and it would not have the "eggbeater effect" that is used to describe bicycle spokes cutting through the wind. Covering spokes is so much more efficient. There would be no air leaking by the gap between the vanes and wall, so the potential for better compression might be realized. I understand that it would add a nasty manufacturing step and add a little mass, so those could certainly be reasons to not do it, but might it make the compressor more efficient? Is it a matter of manufacturing convenience that they are not made like that? Maybe things spin so fast that it doesn't even matter?
I understand that the turbos are standard things made for cars and trucks, but if we were to make some from scratch on 5th axis machines from titanium or something similar, could that potentially be a more efficient option?t Being that we are trying to ultimately deflect the air downward, maybe rethinking the compressor and air deflector to do it more smoothly than the relatively sharp corner the air needs to travel past to get from radial to axial flow has room for improvement? Also on a turbo that is bought, it appears that the outside is a set radius, say 1.000" or 25.00mm or something. Is there a way to know from an ordering number exactly what that dimension should be? Perhaps they do engineering drawings on the Internet for that? Along that line, if one were to build one from scratch, is that perfect radius the optimal shape for the curve? It seems like it should be some sort of parabola as the air gets slung outward and downward. Any insights or theories on how to get more efficient would be appreciated.
On the turbine, I notice that the model engines usually use a single blisk at the turbine, and not all of them even use the air steering vanes before the turbine. On real plane engines, they seem to use 2 or 3 turbines. I suppose they need to also power the bypass fan blades, so that might be a big difference there. I suppose it just needs to be strong enough to drive the compressor and anything extra is fluff. I would assume for maximum output modelers have found the single set of vanes then the C shaped turbine blades with no following vanes to be the most efficient? Again, insights on what would be the best setup there would be appreciated.
I understand that the turbos are standard things made for cars and trucks, but if we were to make some from scratch on 5th axis machines from titanium or something similar, could that potentially be a more efficient option?t Being that we are trying to ultimately deflect the air downward, maybe rethinking the compressor and air deflector to do it more smoothly than the relatively sharp corner the air needs to travel past to get from radial to axial flow has room for improvement? Also on a turbo that is bought, it appears that the outside is a set radius, say 1.000" or 25.00mm or something. Is there a way to know from an ordering number exactly what that dimension should be? Perhaps they do engineering drawings on the Internet for that? Along that line, if one were to build one from scratch, is that perfect radius the optimal shape for the curve? It seems like it should be some sort of parabola as the air gets slung outward and downward. Any insights or theories on how to get more efficient would be appreciated.
On the turbine, I notice that the model engines usually use a single blisk at the turbine, and not all of them even use the air steering vanes before the turbine. On real plane engines, they seem to use 2 or 3 turbines. I suppose they need to also power the bypass fan blades, so that might be a big difference there. I suppose it just needs to be strong enough to drive the compressor and anything extra is fluff. I would assume for maximum output modelers have found the single set of vanes then the C shaped turbine blades with no following vanes to be the most efficient? Again, insights on what would be the best setup there would be appreciated.
