CMP.WERNER@UTEXAS-20.ARPA (09/26/84)
From: Werner Uhrig <CMP.WERNER@UTEXAS-20.ARPA>
[ just read this in the local paper ]
General Electric unveiled an unducted fan engine recently at the
International Air Show in Farnborough, England. A propfan engine
like this one, which the company says is more fuel efficient, may
power future jet-liners. An Wmerican plane manufacturer is already
testing the design. The engine's two bands of short propeller blades rotate in opposite directions.
[ a photo accompanying these lines shows a rather fat looking engine pod,
tapering to a rather thin tail-end (might be my misconception due to the
perspective). At the tail are 2 circular sections with 8 prop-blades each,
looking somewhat like shark-fins.
2 requests for comments:
1. am I mistaken that it always seems that such announcements are always
done overseas, England, France, Germany, mostly, and never in the US?
are all air-shows of importance in Europe?
2. these 2 bands of counter-rotating prop-blades remind me of the blades in
my mixer. Now when I try to imagine the air-flow between them, I can't
help but think that they must be interfering with each other something
fierce. How can one prop try to pull the air into a clock-wise circular
motion and not be interfered with by another prop right behind, trying to
force the airflow into a counterclockwise rotation? On a Cessna 310
pull-push configuration, there is, at least, the length of the passenger
cell between the 2 props, but in this case it doesn't look like more than
inches.
[ when the blimp was visiting Austin 10 days ago for the Auburn-game,
I went up to take a closer look while he was doing his 3-day PR-stuff
of taking dealers and other folks that Goodyear would like to ingratiate
for rides - right, I was not one of those - and I had my first REAL taste
of the disadvantages of the new "Austin Airport Radar Service Area" (ARSA)
- THEY WOULDN'T LET ME IN BELOW THE 4000ft HAA upper limit
of the control zone. And the blimp, of course was down there at 2000ft. ...
Boy, I hate blimps and ARSAs and other traffic and controllers and ....((-:
well, I wasn't sure if anyone has any ideas on how to tempt a blimp to leave
an ARSA, or how to shoot one down to inspect it closely on the ground then ...
]
-------ron@BRL-TGR.ARPA (09/26/84)
From: Ron Natalie <ron@BRL-TGR.ARPA> With regards to overseas product announcements. I think you hit the nail on the head. There aren't any trully national airshows in the United States with the exception of Oshkosh. While GE probably considers the work experimental, I don't think they place themselves with the EAA. The last show of note was TRANSPO (I don't recall what year 74?) in D.C. (well actually it was at Dulles). Why doesn't the US have any airshows? -Ron
mat@hou4b.UUCP (10/04/84)
With regards to the counter-rotating unducted fan ...
Yes, the two fans interact. No, they don't interfere. The
fans are not supposed to pull the air around and around ... they are
supposed to push it BACK (cuz thats what makes the plane go forward ...)
The counter-rotating fans reduce torque effects, which apparently are
more severe with the unducted fan than with conventional ducted fans.
The whole point of the ducts is to avoid all the interesting effects that
occur around the tips of prop blades, while still getting as much momentum
into the airstream as possible.
[Back to Freshman Physics]
Note momentum, not energy. Energy goes as the square of velocity, and
momentum as the first power. Conservation of momentum holds -- so that going
moving twice as much air at half the speed will take half as much power. The
speed in question is the difference between the speed (relative to the
aircraft) that the gasses come in at and the speed they leave at; when talking
about the energy, it is the differences in the squares of the speeds. (NB
Power is energy/unit time...)
If instead of pushing exhaust gasses and propwash, you are pushing
against something that is (almost) infinitely massive (like the earth) all
of your energy goes into the thing that is moving. It follows that as the
mass of what you are pushing against (or ejecting) goes down, the amount of
energy you lose in it goes up. This is one advantage that fans have over
straight jets ... they move a greater mass, and so have to speed it up less
to get a given momentum out of it.
--
from Mole End Mark Terribile
(scrape .. dig ) hou4b!mat
,.. .,, ,,, ..,***_*.