experimental high speed plane
quorneng
Master member
ezbruh
An interesting design but I fear you are seriously misjudging the power required to reach 100mph let alone any faster.
You estimated the weight as 1.2lbs. I expect you will need a thrust to weight of at least 1:1 and you certainly won't get that from a 40mm EDF.
An EDF accelerates the air and it does so across the width of the blade. Accelerating the air generates the thrust so It follows as much undisturbed air as possible must reach the fan. The whole air intake duct should have the same area as the rotating part of the Fan, its Swept Area.
Part of the losses in any duct are due to skin friction at the inner surface creating a slow moving boundary layer. Unfortunately the boundary lay thickness is constant so small size ducts have proportionally bigger losses than big ones. The boundary layer also suggests the duct should be circular to give the maximum cross section area for the minimum surface area. Unfortunately your narrow "crescent" inlet has a lot of surface for the area provided.
Of course both the airframe's frontal area and its surface area create drag which the EDF has to over come. Everything has to be both as small and streamlined as possible.
The difficult part is how you package the fixed bits like the battery, servos and radio needed to both power and control the plane but only adding the minimum frontal and surface area. It is not easy or simple.
You best bet would be to research what are the attributes of a know "fast" EDF, what power it uses and work from there.
I could be all wrong but from my own experience I don't think so.
An interesting design but I fear you are seriously misjudging the power required to reach 100mph let alone any faster.
You estimated the weight as 1.2lbs. I expect you will need a thrust to weight of at least 1:1 and you certainly won't get that from a 40mm EDF.
An EDF accelerates the air and it does so across the width of the blade. Accelerating the air generates the thrust so It follows as much undisturbed air as possible must reach the fan. The whole air intake duct should have the same area as the rotating part of the Fan, its Swept Area.
Part of the losses in any duct are due to skin friction at the inner surface creating a slow moving boundary layer. Unfortunately the boundary lay thickness is constant so small size ducts have proportionally bigger losses than big ones. The boundary layer also suggests the duct should be circular to give the maximum cross section area for the minimum surface area. Unfortunately your narrow "crescent" inlet has a lot of surface for the area provided.
Of course both the airframe's frontal area and its surface area create drag which the EDF has to over come. Everything has to be both as small and streamlined as possible.
The difficult part is how you package the fixed bits like the battery, servos and radio needed to both power and control the plane but only adding the minimum frontal and surface area. It is not easy or simple.
You best bet would be to research what are the attributes of a know "fast" EDF, what power it uses and work from there.
I could be all wrong but from my own experience I don't think so.
ezbruh
Active member
I’m aware of this. I know just an edf isn’t enough to get it that fast which is why I proposed modding the edf to function as an axial compressor and feeding the air through a nozzle of some kind. The 40mm edf I linked is a very high power edf for its size but it won’t be enough to reach the (probably incorrectly) calculated speeds. The plane looks much larger in the images than it actually is. The wingspan is 15 inches. I ran a simulation on it at a speed of 200mph and the surface pressure on the front facing sections was pretty low and the stream lines diverted as the were supposed to so I’m not worried too much about the drag. I’ve done some research and all of the fastest edf planes are configured very similarly to mine, or rather mine is configured similarly to them. I appreciate the input and I think you’re right about me underestimating what it takes. I’m still gonna try though.
Mr Man
Mr SPEED!
Rocket Booster!
WARP drive!
Mr Man
Mr SPEED!
He’s gonna go PLAID!
Mr Man
Mr SPEED!
You mean turn it into a fuel burning jet engine?
ezbruh
Active member
no, it would heat the air to expand it further and shoot it through the nozzle
Mr Man
Mr SPEED!
Bummer😂
ezbruh
Active member
i can do both but the speed record for jet powered rc planes is waaay higher
Mr Man
Mr SPEED!
Yeah I know😂
EDFs are more about eflux velocity that performing as a compressor.
Compressing the EDF output and adding heat is just not going to do anything measurable.
EDFs will never be faster than their exhaust velocity in flight minus the total drag of the airframe. Exhaust velocity inflight is less than on a test stand due to inlet losses and other effects.
A tapered EDF thrust tube can increase velocity at speed, at the cost of reduced static thrust on the ground. Smaller EDFs do not respond as well as larger units to reducing the size of the exhaust.
Compressing the EDF output and adding heat is just not going to do anything measurable.
EDFs will never be faster than their exhaust velocity in flight minus the total drag of the airframe. Exhaust velocity inflight is less than on a test stand due to inlet losses and other effects.
A tapered EDF thrust tube can increase velocity at speed, at the cost of reduced static thrust on the ground. Smaller EDFs do not respond as well as larger units to reducing the size of the exhaust.
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