Bench Testing EDF Output Velocity

[KevinMar]

I'm working on a jet concept that uses EDF's of different diameters for VTOL flight (not what this thread is about) and I would like to ensure that the outlet velocities of the different EDFs are at least similar, if not identical.

Because if a hypothetical 90mm edf outputs 120mph airflow, and a 70mm only outputs 90mph airflow, the 70mm would be choked.

I'm going to create a rig to measure thrust, but would also like to measure airspeed for the above reasons.

The 'wind speed gauges' on Amazon only go up to about 90mph before the price increases from ~$30 to $80+. Is there a better setup than buying a wind speed gauge?

[kallend]

I'm working on a jet concept that uses EDF's of different diameters for VTOL flight (not what this thread is about) and I would like to ensure that the outlet velocities of the different EDFs are at least similar, if not identical.

Because if a hypothetical 90mm edf outputs 120mph airflow, and a 70mm only outputs 90mph airflow, the 70mm would be choked.

Not sure I understand the comment about being "choked". The efflux speed depends on a lot of things.

I'm going to create a rig to measure thrust, but would also like to measure airspeed for the above reasons.

The 'wind speed gauges' on Amazon only go up to about 90mph before the price increases from ~$30 to $80+. Is there a better setup than buying a wind speed gauge?

Pitot tube and pressure gauge.

[KevinMar]

Not sure I understand the comment about being "choked". The efflux speed depends on a lot of things.

Well if the 70mm edf has a lower maximum mass flow rate, when being fed air at the maximum velocity of the 90mm edf the 70mm will become a huge source of drag.

if the mass flow rate entering the edf is greater than what the edf can exhaust, we have an imbalance…

[kallend]

Well if the 70mm edf has a lower maximum mass flow rate, when being fed air at the maximum velocity of the 90mm edf the 70mm will become a huge source of drag.

So the 90mm is blowing its exhaust into the 70mm intake?

I think you need to explain your setup more clearly.

if the mass flow rate entering the edf is greater than what the edf can exhaust, we have an imbalance…

If more air goes in than comes out, you have a compressor.

[KevinMar]

I think you need to explain your setup more clearly.

Very fair

The EDFs would both be pointing forward, side by side.

I drew a very general diagram showing that the inlet velocity of all 3 EDFs is the same. This is all theoretical of course, but if running at 100% throttle in a steady state, the output velocity of a 90mm EDF on a bench may be different than a 70mm EDF on the bench, therefore the airflow difference could create inefficiencies.

[kallend]

If the input and output to the 90mm fan are both the same (Vo) then is it doing any work?

I'm not sure you have properly analyzed the physics of the setup.

[KevinMar]

If the input and output to the 90mm fan are both the same (Vo) then is it doing any work?

I'm not sure you have properly analyzed the physics of the setup.

ugh, tired mind drawing, this is a bit of a mess lol. Just had a midterm yesterday so please forgive my brain mushiness.

I guess my point is that all 3 EDFs are being fed air at the same speed because they are fixed on the same airframe. The speed of the airframe is a result of the summation of forces acting on the aircraft including the thrust outputs of the power units, and the aerodynamic drag. At a steady state, the forces are balanced, and the aircraft is traveling at (Vo).

Am I correct to state that simply adding EDFs of different diameters does NOT necessarily result in the thrust output being the sum of the outputs from the individual EDFs?

[Warthog]

If you are into math, this guy has it all: https://www.youtube.com/watch?v=QccRbsZVg1Y