Modern day propeller fighter - hypothetical

I recall seeing GE tested scimitar shaped pusher prop engines, I think
it was on a 727.

I seem to recall it being on the right engine of a DC-9. I wonder what became
of that idea.


"Unducted fans" or "propfans" were, I believe, tested on both a 727
and an MD-80. See for instance

http://www.jsc.nasa.gov/er/seh/profan.html (contemporary article from
midway through the program)


http://www.aerospaceweb.org/question...on/q0067.shtml (survey
article; pix)


http://www.aviation-history.com/garb...g/udf-2_f.html


The goals were, I think, a combination of fuel efficiency and some
internal simplifications.


I'm not exactly sure why they aren't much in use. Hypotheses I've
read include greater risk to the passenger cabin from uncontained
failures (I wonder if it is coincidence that both the testbeds were
the sort of jets with aft-mounted engines); undesirable "propeller"
image; noise; and parallel improvements in high-bypass turbofans of
the usual ducted design.

Cheers,
--Joe

"Ad absurdum per aspera" wrote in message
om...
I recall seeing GE tested scimitar shaped pusher prop engines, I
think
it was on a 727.

I seem to recall it being on the right engine of a DC-9. I wonder
what became
of that idea.


"Unducted fans" or "propfans" were, I believe, tested on both a 727
and an MD-80. See for instance

http://www.jsc.nasa.gov/er/seh/profan.html (contemporary article
from
midway through the program)



Thanks for these links. They all seem to think that a Mach 0.85 for a
scimitar blade contra-rotating coaxial "prop-fan" is possible and
indeed fuel efficient. Given that there was in a German 1940s study
suggesting 584 mph with twin piston engines I think its fairly
believable. I find the idea of a Mach 0.85 diesel or spark ignition
engine fascinating.

There is also the Soviet An 70
http://www.geocities.com/CapeCanaver...5/antonov1.htm I would be
interesting to read what the Russian desginers thought that they
gained with this designe of a straight jet or prop. I know that a
C-17 got bogged at a Sarajevo airport on a bit of wet grass and that
this lack of grunt is due to the use of jets instead of props.

Either way the Russians are ready to go apparently!

Another fascinating possibility is the use of SOFC (Solid Oxide Fuel
Cells). Many people beleive these will match piston engines in cars
in terms was weight. If turbo supercharged they should have an
amazing efficiency of 85%. They opperate at 800C at which point the
metal oxide membranse can conduct oxygen ions (instead of hysrgen
ions) and thus burn hydrocarbon fuels. The high temperature (still
only 1/3rd that of a pertrol engine) means that no catalyst is needed.
They are running in the lab at 60% efficient unburdened but becuase
they exhaust at 800-1000C they can be trubo-supercharged and excess
shaft power extracted.

These SOFCs should achieve the same power to weigh ratio of petrol
engines and thus be able to propell aircraft. Potentialy their engine
and cell life will be so high that they compete with gas trubines.
They would require only modes cooling and would require light
propellors since no piston torgue vibarations would be present.



I'm not exactly sure why they aren't much in use. Hypotheses I've
read include greater risk to the passenger cabin from uncontained
failures (I wonder if it is coincidence that both the testbeds were
the sort of jets with aft-mounted engines); undesirable "propeller"
image; noise; and parallel improvements in high-bypass turbofans of
the usual ducted design.

Cheers,
--Joe

I think there were some noise issues (not major), blade safety I
think could be handled (the scimitar shaped much add unusual
stresses), then there is the issue of gear boxes. These are high
maintain items. (The only geared turbo fan in sevice is that unit
(Allison) on the BAE avro regional/ BAE146 series jet I think)

It will be interesting to see if Pratt+Whitney's PW8000 geared
turbofan for airbus changes the anti-gearbox mindset.










http://www.aerospaceweb.org/question...on/q0067.shtml (survey
article; pix)


http://www.aviation-history.com/garb...g/udf-2_f.html


The goals were, I think, a combination of fuel efficiency and some
internal simplifications.

In article ,
"The Enlightenment" writes:
Those sorts of performances I think were achievable with piston
engines.

The Luft46 web site lists a few German pusher prop aircraft that were
projected as replacements for then current Lufwaffe aircraft.
Achieving as much as 584 mph on an ordinary 1750HP Jumo 213 V12 piston
engine seems to have been accepted.

Quite frankly, that's bat****.
cue the every 3 months lecture on the Speed/Power relationship for
the thrust of propeller driven airplanes.
To cut to the chase - a constnt power output engine, like a recip, or
the propeller side of a turboprop, produces less thrust the faster you
go. Assuming 85% propeller efficiency across the board, your 1750 HP
Jumo is producing 2790# of thrust at 200 mph, 1490# of thrust at 375
mph, and at 584 mph, 955# of thrust. (It's actually a lot worse than
that - the efficiency of the prop goes way down beyond about 450-500
mph at Sea Level.

This scimitar prop aircraft is one of the fastest at 584mph.
http://www.luft46.com/dornier/dop252.html

Even assuming that there are _no_ transonic effects on the airframe
(Which there will be), and two engines, the Equivalent Profile Area of
the drawing below is 3.55 sq ft. (That's Drag Coefficient * Reference
Area).
A P-51 works out to a profile area of about 4.66 ft.
This Dornier cattywampus is more that twice the size of a P-51.
The claims are rediculouss on the face of it. The SS Scientific Branch
might believe such horse****, but real life physics wins every time.


(And the Scientific Branch certainly _did_ believe such horse****.
They sent a specialist in Infrared Photography to Spitzbergen to
photograph the British Home Fleet at Scapa Floe through the Hole into
the Hollow Earth.)

The advantage would be fuel efficiency and the lack of refractory
alloys needed for the engine. The cost of making high octane fuel is
exorbitant compared to make Jet fuel.

I recall seeing GE tested scimitar shaped pusher prop engines, I think
it was on a 727.

And it wasn't operating at 85% efficency at that Mach Number, either.
The thrust numbers I posted above are best case.

--
Pete Stickney
A strong conviction that something must be done is the parent of many
bad measures. -- Daniel Webster

"Peter Stickney" wrote in message
...
In article ,
"The Enlightenment" writes:
Those sorts of performances I think were achievable with piston
engines.

The Luft46 web site lists a few German pusher prop aircraft that
were
projected as replacements for then current Lufwaffe aircraft.
Achieving as much as 584 mph on an ordinary 1750HP Jumo 213 V12
piston
engine seems to have been accepted.

Quite frankly, that's bat****.
cue the every 3 months lecture on the Speed/Power relationship for
the thrust of propeller driven airplanes.
To cut to the chase - a constnt power output engine, like a recip,
or
the propeller side of a turboprop, produces less thrust the faster
you
go. Assuming 85% propeller efficiency across the board, your 1750
HP
Jumo is producing 2790# of thrust at 200 mph, 1490# of thrust at 375
mph, and at 584 mph, 955# of thrust. (It's actually a lot worse than
that - the efficiency of the prop goes way down beyond about 450-500
mph at Sea Level.

You make one oversight though it is perhaps mine:

1 There are actualy 2 Jumo 213Js on this aircraft driving coaxial
contra-roting props so this automatically doubles the thrust.
2 I believe the Jumo specification is incorrect. Takeoff power is
1750 but with MW50 water methanol injection to allow overboost it is
someting like 2250hp. Likewise at high altitudes a Nitrous Oxide "Ha
Ha" system can bring power up to about 2150 hp because of the extra
oxgen in the NO and its anti-knock properties. Both systems were
fitted to the TA152

(for some reason I can get onto google but certainly the TA152H Jumo
213 could produce 2250hp I don't know if it was a J though)

Thus without boost an equivalent thrust of 900kg - 2000lbs is
available and that would presumably be maintained to quite a high
altitude where the atmoshere is at least half of sea level density and
probably less. With boost more like 2500lbs.

Incidently Anthony Kays book lists the following thrusts of the Jumo
004B1 jet as used in a Me262.

900kg sea level static
730kg seal level 559 mph (a test chamber result I suspect, German
test chambers were excellent and so good they were used by the allies)
320kg at 10000m




This scimitar prop aircraft is one of the fastest at 584mph.
http://www.luft46.com/dornier/dop252.html

Even assuming that there are _no_ transonic effects on the airframe

It DOES have swept wings and 584mph is not at the high end of
transonic. The AVA at Goetingen (German Equavalent to NACA) did a lot
of supersonic research in the mid 30s.

(Which there will be), and two engines, the Equivalent Profile Area
of
the drawing below is 3.55 sq ft. (That's Drag Coefficient *
Reference
Area).
A P-51 works out to a profile area of about 4.66 ft.
This Dornier cattywampus is more that twice the size of a P-51.
The claims are rediculouss on the face of it. The SS Scientific
Branch
might believe such horse****, but real life physics wins every time.

A pusher aircraft has less drag becuase there is no high velocity
airflow over the airframe that is turbulent to boot. This on its own
suggests higher speed.


(And the Scientific Branch certainly _did_ believe such horse****.
They sent a specialist in Infrared Photography to Spitzbergen to
photograph the British Home Fleet at Scapa Floe through the Hole
into
the Hollow Earth.)

Sounds like the one where a Jewish doctor cut of Hitlers testicals
that was circulated in the war.


The advantage would be fuel efficiency and the lack of refractory
alloys needed for the engine. The cost of making high octane fuel
is
exorbitant compared to make Jet fuel.

I recall seeing GE tested scimitar shaped pusher prop engines, I
think
it was on a 727.

And it wasn't operating at 85% efficency at that Mach Number,
either.
The thrust numbers I posted above are best case.

85% for a scimitar shapped contra-rotating prop is good but I think
achievable.


--
Pete Stickney
A strong conviction that something must be done is the parent of
many
bad measures. -- Daniel Webster

(Nev) wrote:

Some of the latest developments in propeller aircraft has fascinated
me. It also brought up an interesting hypothetical question; mostly
when reading about modern day warbird replicas.

With relatively easily available technology off the shelf (no rail
guns or laser cannon please). Lets say a reasonable development budget
of oh say $300 million. The question is are we capable of producing
superior prop aircraft than the great fighters of WWII and what
configuration would it take?

[snip]

If we were to design a new prop, gun armed aircrafy would it
essentially look pretty similar to a carbon fibre, turbo-prop P-51
Mustang or would it be some bizzare split wing, dual rear engined
travesty?

Bizarre, hardly. Have you taken a look at the Beech Starship?

http://www.bobscherer.com/Pages/Starship.htm and
http://www.brunton.net/starship.html

Seems like that would be a reasonable starting point for such a fighter.
Advanced composite construction, modern avionics and flight controls, and
sexy as hell.

/------------------------------------------------------------\
| George Ruch |
| "Is there life in Clovis after Clovis Man?" |
\------------------------------------------------------------/

George Ruch wrote in message . ..
(Nev) wrote:

Some of the latest developments in propeller aircraft has fascinated
me. It also brought up an interesting hypothetical question; mostly
when reading about modern day warbird replicas.

With relatively easily available technology off the shelf (no rail
guns or laser cannon please). Lets say a reasonable development budget
of oh say $300 million. The question is are we capable of producing
superior prop aircraft than the great fighters of WWII and what
configuration would it take?

[snip]

If we were to design a new prop, gun armed aircrafy would it
essentially look pretty similar to a carbon fibre, turbo-prop P-51
Mustang or would it be some bizzare split wing, dual rear engined
travesty?

Uh, it WAS a modernized Mustang- the Piper Pa-48 Enforcer of the '80s:

http://www.aerofiles.com/piper-pa48.jpg

.... and rejected too...

Rob

In article ,
Nev wrote:

If we were to design a new prop, gun armed aircrafy would it
essentially look pretty similar to a carbon fibre, turbo-prop P-51
Mustang or would it be some bizzare split wing, dual rear engined
travesty?

Do you think the Embraer ALX and Pilatus PC-21 look like a
Piper PA48 Enforcer (only with nose gear and yes - I know
it's not really a Mustang)? If something like 4 x 20 mm is
enough, it seems that configuration works well. If you
want something like a Oerlikon KCA, GAU-8 or even Oerlikon
35/1000 a pusher prop might be indicated.
--
Urban Fredriksson http://www.canit.se/%7Egriffon/
A king and an elephant were sitting in a bathtub. The king said, "pass
the soap" and the elephant said, "No soap, radio!"

(Nev) wrote in message m...
Some of the latest developments in propeller aircraft has fascinated
me. It also brought up an interesting hypothetical question; mostly
when reading about modern day warbird replicas.

With relatively easily available technology off the shelf (no rail
guns or laser cannon please). Lets say a reasonable development budget
of oh say $300 million. The question is are we capable of producing
superior prop aircraft than the great fighters of WWII and what
configuration would it take?

To keep the discussion relatively focused we'll put in a couple of
rules:

1. Mission: Air superiority/dominance during WWII. Land based. It
should be able to clear the skies of any and all opposition at all
ranges and altitudes.

2. Must be a propeller aircraft.

3. Only armanent allowed are guns/cannons. No guided missiles. I guess
dumb firing rockets will be ok since they were used during WWII.


With the above two exceptions all of modern technology is allowed to
be used for example composite materials, radars, titanium armour,
fly-by-wire (will dynamic instability benefit the agility of a prop
plane?) advanced aerodynamic configurations (rear mounted engines). To
make matters really intesting helicopters are fine. Just as long as
the driving force isn't a jet.

If we were to design a new prop, gun armed aircrafy would it
essentially look pretty similar to a carbon fibre, turbo-prop P-51
Mustang or would it be some bizzare split wing, dual rear engined
travesty?

About 15 yrs ago BAe messed around with a project called SABA ('small
agile battlefield aicraft') one of the designs touted was a v.
lightweight pusher UDF propellor craft with about a 2 ton warload.
Looked pretty cool. I think it was mainly an anti-tank craft designed
to fill the void between attack helicopters and full-blown ground
attack aircraft.

David

About 15 yrs ago BAe messed around with a project called SABA ('small
agile battlefield aicraft') one of the designs touted was a v.
lightweight pusher UDF propellor craft with about a 2 ton warload.
Looked pretty cool. I think it was mainly an anti-tank craft designed
to fill the void between attack helicopters and full-blown ground
attack aircraft.

David

Sounds a lot like the Rutan ARES.


Ron
Pilot/Wildland Firefighter