Bob,
Partly right. With axial flow engines you need a
relatively distortion free flow/pressure field at
the compressor face to avoid compressor stall.
These engines are centrifugal compressor types which are much less sensitive.
Now calculate the flow velocity at the inlet of
one of these engines. I gave you the mass flow of
0.66 Kg/sec which on a Standard sea level day is 0.541 cubic meters/sec.
The diameter of the inlet on an AMT Titan at the
start of the venturi leading to the compressor is
10 cm or 0.1 meters. The area is 0.0079 square
meters. The velocity to get 0.541 cubic meters of
air through that is 68.5 meters/sec.
At the compressor face the diameter is 7 cm or
.07 meters for an area of .0039 square meters
which gives a velocity of 142.4 meters/sec.
I highly doubt the engine will notice airflow at
+/- say 5 meters/sec arriving near the inlet.
Also look at lots of helicopters say like the
AW189. See how the engine inlets, even on a
helicopter that can cruise at 150 knots do not
take advantage of any ram air effect.
These inlets will also act as inertial separators
for birds, rocks, ice etc. The atmospheric
pressure at sea level is around 1000hPa. The
pitot pressure at 100KIAS is only 16.2 hPa, at
150 knots say 35hPa. Not much total pressure change at the inlet.
Now on a jet cruising at 30,000 + feet where the
pressure is 300 to 200 hPa and IAS of 250Knots
the pitot pressure is 101.25 hpa which is large
compared to atmospheric pressure, so there you
want the inlet facing the oncoming flow to get a
useful supercharging effect. particularly when
the pressure ratio in the engine may well be over 30 to get good fuel economy.
Mike
At 12:25 PM 5/16/2016, you wrote:
jet performance is highly dependent on ambient pressure/flow at the inlet.
During descent this is reduced, unless he has
inlet scoops which realign themselves to the direction of travel.
On Mon, May 16, 2016 at 12:17 PM, Mike Borgelt
<<mailto:[email protected]>[email protected]>
wrote:
By your own numbers the 3 engine full thrust of
120 KG exceeds the weight so he'll still hover.
Anyway why does the engine thrust decrease as he descends more rapidly???
Nobody has said anything about practicality. It
is just a fun project by a bloke who seems to be
doing nicely out of his day business which is the water pump type flyboard.
He also gets some nice publicity. I think I'd
vaguely heard of the water type device but I now
know a lot more about it. As do a lot of other people I suspect.
Mike
At 09:46 AM 5/16/2016, you wrote:
On Mon, May 16, 2016 at 8:58 AM, Mike Borgelt
<<mailto:[email protected]>
[email protected]> wrote:
More here:
<http://www.guinnessworldrecords.com/news/2016/4/confirmed-franky-zapata-sets-new-farthest-hoverboard-flight-record-in-france-427011>http://www.guinnessworldrecords.com/news/2016/4/confirmed-franky-zapata-sets-new-farthest-hoverboard-flight-record-in-france-427011
If he was at close to full thrust he wouldn't
have engine out capability, which is one of the
major problems of all vertical lift aircraft.
Do the numbers. With the platform tilted at 15
degrees off vertical he still gets a vertical
thrust component of 96.6% of hover.
He also gets 26.6% horizontal component.
Presumably if he loses an engine he goes vertical and slows down.
I don't see anything impossible here.
Mike
à "Presumably if he loses an engine he goes vertical and slows down."
More like "Presumably if he loses an engine he
goes vertical and goes down...... hopefully at a speed that is not fatal.
Of course as the vertical speed downwards
increases, the engine thrust decreases significantly..... not a good picture.
It looks like a manufactured blurb to attract
investors.... (who don't understand much physics).
It resembles the blurb for the compressed air
car that made ridiculous performance claims. Promotional rubbish.
This might have some glimmer of truth, but
unless jet technology improves by about 500% it
is not going to deliver any practicality, no matter how glossy the brochure is.
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Borgelt Instruments - design & manufacture of
quality soaring instrumentation since 1978
www.borgeltinstruments.com
tel: 07 4635 5784 overseas: int+61-7-4635 5784
mob: 042835 5784 : int+61-42835 5784
P O Box 4607, Toowoomba East, QLD 4350, Australia
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