My ideas may not be the complete list of
information that could be recovered. Mr Lipps would know much more. Perhaps you
could get Mr Lipps to comment? Paul was it? I enjoyed his talk at Jean this
year. Thank you for that effort.
My pleasure.
I just did a key-word search through our
current “All Paul Lipps” issue of CONTACT! Magazine, for the word
“thrust”.
www.ContactMagazine.com/backissu.html
Here’s one short paragraph where
Paul mentions static thrust. All other mentions (and formulas) of thrust are
related to dynamic thrust.
SINGLE BLADE MYTH
One of the myths that has been
propagated in the aviation community, to the point that it is
“gospel”, is that the most efficient prop is a single blade; all
higher number of blades falling further and further short of this paragon. Did
you ever consider that a single-blade prop, developing thrust on only one side
of the plane as it revolves, would cause the engine to cone violently in its
mounts as it is twisted by the prop? The European’s latest turbo-prop
transport, the A400-M, has eight-blade
props! The Boeing MD-900 helicopter has a five-blade rotor. A popular
regional turbo-prop airliner has a five-blade prop. Hasn’t anybody filled
these plane-makers in on the errors of their ways? In a recent edition of
Kitplanes, the author of an article on props uttered the same fallacy. He
maintained that multiple blades interfere with each other. When I pointed out
to him that at 200 mph and 2800 RPM, the blades on my three-blade prop follow
three distinct helical paths through the air, and each blade is 25” ahead
of the previous blade at the same point of rotation, he rather lamely explained
that in static conditions interference occurs. STATIC? Who uses static thrust?
Airplanes are meant to fly, not pull tree-stumps!
I know from several conversations with
Paul that he cares very little about static thrust.
Propeller thrust might be useful in
designing propellers.
At a gathering we had some time back, we
had two nearly identical Corvair engines running on separate test stands. They
had completely different props on them, one made for a Pietenpol, the other for
a single place Sonerai. They both spooled up nicely to 2700 RPM. The Sonerai
prop made a lot of wind for sure. The Piet prop made so much wind one
couldn’t hardly stand or breathe behind it.
Here’s a shot of me, behind my test
rig, running the Sonerai prop at full tilt.
http://www.experimental-aviation.com/Corvair/Images/WCCC/Event/TuftTest.jpg
If we had thrust measuring equipment
I’m certain it would show us that the other engine/prop combination was
easily making 2x the static thrust I was making.
Bug picture, what does that really prove?
Could I bolt the Pietenpol prop to the
Sonerai and expect 2x thrust at altitude? No way. I’d probably climb like
crazy but max out at 110 mph.
What does it tell us about the engines? If
we could measure HP we could be sure that they were making the same power...
but what does these static thrust measurements tell us about HP output?
We did swap props however. My friend ran
my Sonerai prop on his engine and got the same RPM. I didn’t put his prop
on my engine however. But for me, his ability to swing my prop on his engine at
the same static RPM tells me that the engines were making identical power.
Thrust told us nothing.
It is hard to imagine a prop dyno not
recovering thrust information.
A prop dyno as opposed to a water brake?
I’m having difficulty seeing the
need for knowing static thrust at all, that’s why I asked the question in
the first place.
So if it’s hard for you to imagine a
prop dyno not giving static thrust info, please tell me what one can gain from
knowing this information?
For experiencing propeller stall.
Ok... I’ve seen countless little red
biplanes hang from their prop at airshows; certainly the prop is
“stalled”, and knowing that the engine/prop combination can produce
thrust to counter the gross weight in order to allow the plane to hover is
useful information to this small group of pilots. But how many of us really
need that info?
For comparing one prop to another.
Yes, you can compare one to another for a
given situation, that being making wind while not moving. But that does that
really tell us???
Say for example you have XYZ prop
installed in a plane you have countless hours in. You measure the static thrust
at 350 lbs at 2250 prop RPM. Now
you install an ABC prop that your buddy says should work better for you and you
get 280 lbs at 2250... or you get 385 lbs at 2340 RPM. What do we now know about prop ABC? Is it
better or worse than prop XYZ? Bear in
mind, we know everything there is to already know about XYZ, but what
have we learned about ABC now that we know what each prop produces in the
matter of thrust?
Lately for making movies in a side view
of blade flexing in single rotor installations.
Ah... yes, running a prop on the ground
can tell you a lot of things. That’s why I have such a rig.
But measuring thrust had no part of the
revelations from said prop in the video.
Pat