I'm reading my mail on the web, so combined a couple messages into one:
previously I wrote:
I do all my calculations and data in knots just to be
consistent. My ASI is in knots. Doing everything in knots makes my
plane seem slower than it really is. It's can do 145 mph, but
normally
does about 130 mph. My next experiment will be with pitch on the
prop. I have good climb rate, maybe I can trade a little of that for
speed.
Paul wrote:
That may slow the RPM and lose HP. What are the prop tip speeds now?
You need those inflatable lips and a high speed duct.
Try a truck or tractor inner tube.
That is true. My current RPM range full throttle is 4800 to 5400.
The vector sum velocity at 5300 RPM is about 900 fps tip speed,
so I think I'm currently operating at about the max rpm range for
my duct diameter of 37.5 inches. So to increase pitch and get more
speed, I will have to add power also to stay in the same RPM
range. I'm only operating at about 110-130 HP range if I believe
my Mazda HP chart, or, if I believe my prop analysis program vs.
my actual flight data I'm really down about 10 HP from the Mazda
numbers, around 100-120 HP. Which is believable since my engine
is probably not producing as much power as it would when new.
Now we all know this engine is capable of more power than that,
even at my lower RPM range. Eventually I'll get there, with some
engine mods. Ed Anderson is seeing a power increase by changing
from an '86-87 era 13B (which is what I have) to a '91.
Vance wrote:
I agree that the duct looks great , and the overall impression is very
positive.
However after looking at the pictures, I am still convinced he could
gain at least
10 mph by leaving the duct home.
Probably true, but for 10 mph I'd rather leave the duct on, have shorter
takeoff, better climb rate, and no ground cooling problems. I think to
run this engine direct-drive you need a duct because of the RPM of
the rotary engine. To get rid of the duct would require a PSRU.
I've had 120 trouble-free hours of flying fun so far. I know if I
remove
the duct I have ground cooling problems, that I don't really want to
deal
with right now. If I put on a PSRU and prop, I'll have to deal with
the ground cooling problem at that time.
Incidently I looked at the high res pictures on
Perry's page, and the detail is great - but unless you are very
patient, you
better have DSL or a cable modem - Vance
Sorry 'bout that. I don't have a digital camera, but a friend of mine
from work has one, and we took those pictures one Saturday morning
last July. I left them full res for the detail. Some of them are from
the
air, he was in the backseat snapping away.
Paul wrote:
I tend to agree with Vance. Charlie Airesman has had great results with
a direct drive soob. The rotary would be even a smaller package than
the soob so less of an extension shaft length would be required
for the same blockage factor.
You are right, but in order to use the rotary, would have to get
significant power out of it at 3500 RPM. My LongEZ is a larger
and heavier plane than the VariEZ. It doesn't help that my plane
is overweight anyway.
Perry have you tried any high speed taxi test without the duct
to measure the acceleration?
Not for a long time. I can roll down the taxiway at 10 knots with
about 1900 RPM ducted, it takes a lot more when there is no duct.
I think the duct will have to stay until I get a PSRU on order. But
I'd rather sneak in a few more experiments before I do that.
Assuming I'm doing 145 mph now at 5300 RPM and 120-130
HP, it would be interesting to see how it would do with 5500 RPM
and 150 or 160 HP. The design is such that the duct can be easily
removed and a PSRU bolted on. My ducts have always been behind
the wings, so there is no effect on the basic Long-EZ design. Just
cowl changes would be required. Incidentally, the weight of a
PSRU and the weight of my duct is about a wash.
I built that new engine mount and test stand, but I still have to
build new intake manifolds, exhaust, etc. And now I'm thinking
I should roll a turbocharger into the design while I'm at it.
This is all probably going to take several months, so my plane
will stay in it's existing state for probably the next several
months or even a year or two. It's so fun to fly I can't stand
to take it down for mods anymore. If I can't fly at least once
a week I get withdrawal symptoms :-).
--
Perry J. Mick
Duckt N7XR
http://www.ductedfan.com