Perry Mick wrote:

It takes 2200 RPM to taxi with the duct on, 2800 with duct off.
With the duct on and a 10 knot headwind, it took 1000' to reach 70 knots
airspeed, was airborne at 1500'. It usually takes me 1800' with no headwind.


Without the duct, acceleration was sooooo sluggish, I thought I must
have been running on one rotor. Even with the headwind it took 2000' to
reach 70 knots and it didn't seem to be accelerating. I would guess that
it may have taken 4000' to break ground, and then I doubt it would have
climbed. I probably would have ended up in the trees at the end of the
runway in ground effect.
Just from the feel of it, I would guess the duct MORE THAN DOUBLES the
thrust for static, takeoff and climb.
So I broke off the unducted takeoff 2000' down the runway and taxied
back to the hangar. The engine was almost overheated. Immediately
de-cowled, put the duct back on and went flying! (that's when I got the
ducted data above for comparison).
So sorry guys. I guess you just don't understand what that duct is doing
for me. As far as I can tell there is just no way a 38" fan turning 5000
RPM will ever get off the ground in a reasonable manner unless you have
about 400 HP available and maybe a variable pitch mechanism. I think
it's a combination of capturing the tip losses and the venturi duct
shape that makes it a success at more than doubling the thrust of
stand-alone fan.
I was hopeful it would work and I could shed 30 to 40 lbs. but I'm
afraid I will have to leave the unducted fan experiments for the 400 HP
racing crowd.

There is one other question in my mind. Are the fan tips approaching super
sonic velocities and absorbing all the HP or are the fan blades wide enough to generate as much thrust as possible? In other words, where is the HP going?


Perhaps Vance can answer this question.
I still think you need to broad band that duct. Make a more streamlined
lower drag duct such as found on turbo fan jets with a smaller diameter opening and use the variable geometry opening. I still think it can be done with an inflatable rubber lip.


Marc de since you are on here now perhaps you can help Perry extend the speed range of his ducted fan. In other words reduce the high speed drag from the duct with out losing too much low speed thrust.
Paul Lamar

With the duct you are "sucking down the inlet face of the duct at static
for a forward thrusting pressure area term, but at high forward speed
the inlet flow is overpowering that "suction" and you have an added drag
component
With the duct removed you are aparrently "sucking down " the significant
"base"
area on your plane, What rpm can you get at static? are you really making
horsepower? Why does it work with the Subaru which is not that much
bigger than yours (Or do Subaru's just make more power than Wankels (;<)!!
Vance

Ah So! Vance has a point here Perry. What he is saying the fan is causing
a low pressure all over the back side of your cowl which translates into high
drag. In other words the negative pressure vectors are perpendicular to the
cowl surface so the backward facing components of the vectors are adding
up to a lot of drag.

I forgot about that Vance. Good point.

Paul Lamar

As I've said before, I am not making that much power. Prop analysis and
fuel burn indicate maybe 120 HP which agrees with Mazda specs. Stock
porting 1986. The potential is there for 180 HP on two rotors, so I'm
waiting for Jerry to get this PPort thing worked out.
As far as the Subaru guy, do I remember correctly that he is not flying
that configuration any more? The VEZ is a 600 lb. airplane while the LEZ
is a 1000 lb. airplane. I think he was turning maybe 3500 RPM and I'm
turning 5500 so his prop was still much larger than mine, around 50
inches I think it was? I'm guessing his plane must have been a runway
hog but it did ok once in the air.
Those goofy antique subarooo piston engines just can't turn up the rpm
like our superior rotary turbines Vance.
Perry

Perry, I also think you can make some drag reductions on your current duct.
The one on the left is your current duct more or less and the one on
the right is lower drag because it is less cone shaped. In other words
the departure angle on the outside surface of the duct is less acute.
Any negative pressure vectors back there will have a high drag components.
Both ducts are designed to have the same inlet areas and the same
out let areas. 

Paul Lamar
 
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