Safety of winch launch vrs. aero tow?

Actually, I read somewhere that the US Navy is converting its steam
catapults to linear electric motors to get finer control over the launch. I
also suspect that it reduces the manpower required to operate the "cat".

Bill Daniels

"Bob Johnson" wrote in message
...
Hi Bruce --

That's a very welcome correction to my hazily-remembered version of a
second-hand report of what the 454 c.i. engine torque/hp/rpm chart looks
like. This is the kind of info I was looking for and thanks for providing
it!

In all our past kicking around of the ideal winch prime mover, here's one
that sounds silly but might rate at least an engineering investigation --
a
recip steam engine! If I recall correctly, the steam engine develops max
torque at stall.

What got me thinking about that was the fact that the Navy gets 66,000 lb
Super Hornets flying in about the same three seconds that it takes us to
get
airborne. And they do it with steam, not because it's handy, but that's
probably the only practical way to get it done.

BJ

Bruce Hoult wrote:

In article ,
Bob Johnson wrote:

Our engine is petrol fueled. Despite Google's best efforts, I have not
yet located a Torque/HP/RPM curve for our very common 7.4 L engine,
but
have heard that it develops max torque and HP at about 3000 RPM and
further that the curves are fairly flat at this point.

You are making some totally contradictory and inconsistent claims there.

If max torque and max HP occur close together then they must both drop
off precipitously after that.

If the torque curve is flat then HP will be increasing linearly with
RPM, max torque and max HP will be very far apart.

It is quite likely that you do have maximum torque at around 3000 RPM,
but if for example the torque curve is flat enough that the torque at
the 5000 RPM redline is still 60% or more of that at 3000 RPM then that
(redline) is exactly where maximum power will be.

-- Bruce

in article , Robert Ehrlich at
wrote on 2003/10/30 4:11:

Bob Johnson wrote:

I 'member a time only a couple of years ago that I experienced the
dreaded aerotow line break at 200 ft and 60 kt over the...fence.

This raises the interesting question of the height loss during a 180
degree turn in a glider or an airplane with a dead engine.

The considerations are not so different for a power plane or a glider, but
the parameters are different. See the cites/sites below in their entirety at
the inlcuded URLs for the discussion as applied to Genral Aviation ASEL
types:

--------------------

Should You Turnback?
or
The Possible `Impossible' Turn
by
David F. Rogers, PhD

Copyright (C) 1991 by David F. Rogers. All rights reserved.


"Most of us fly single engine aircraft. If the engine quits
on takeoff, should you attempt to turnback to land on the
runway? The turnback problem is extremely complex. Like many
complex problems, there is no single right answer. Each
situation must be judged individually. Thus, the answer is
a qualified maybe or the classical `it depends'. It depends
on the Conditions, the Aircraft, the Altitude, the
Proficiency of the pilot and on Planning. CAAPP for short."

http://web.usna.navy.mil/~dfr/flying/possible.html

================================================== ==========

The Possible `Impossible' Turn

David F. Rogers
United States Naval Academy
Annapolis, Maryland 21402

Copyright 1994 David F. Rogers, All rights reserved.
Originally published in the AIAA Journal of Aircraft, Vol. 32,
pp. 392-397, 1995 with permission.

"Turning back after engine failure during the take-off phase
of flight in a single engine aircraft is examined using a
simplified analytical model. The important parameters are
identified. The analysis shows that the optimum flight path
is teardrop shaped with a 45-degree bank angle at stall
velocity during the turn. The effects of engine failure
altitude, wind direction and velocity, and bank angle on
the required runway length are examined. The results show
that the typical recommendations for general aviation
single engine aircraft are not optimum."

http://web.usna.navy.mil/~dfr/flying/aiaa1col.pdf

================================================== ==========

I love it! The boiler could provide the permanent thermal off the top of the
launch too!

Ian

"Bob Johnson" wrote in message
...
Hi Bruce --

That's a very welcome correction to my hazily-remembered version of a
second-hand report of what the 454 c.i. engine torque/hp/rpm chart looks
like. This is the kind of info I was looking for and thanks for providing
it!

In all our past kicking around of the ideal winch prime mover, here's one
that sounds silly but might rate at least an engineering investigation --
a
recip steam engine! If I recall correctly, the steam engine develops max
torque at stall.

What got me thinking about that was the fact that the Navy gets 66,000 lb
Super Hornets flying in about the same three seconds that it takes us to
get
airborne. And they do it with steam, not because it's handy, but that's
probably the only practical way to get it done.

BJ

Bruce Hoult wrote:

In article ,
Bob Johnson wrote:

Our engine is petrol fueled. Despite Google's best efforts, I have not
yet located a Torque/HP/RPM curve for our very common 7.4 L engine,
but
have heard that it develops max torque and HP at about 3000 RPM and
further that the curves are fairly flat at this point.

You are making some totally contradictory and inconsistent claims there.

If max torque and max HP occur close together then they must both drop
off precipitously after that.

If the torque curve is flat then HP will be increasing linearly with
RPM, max torque and max HP will be very far apart.

It is quite likely that you do have maximum torque at around 3000 RPM,
but if for example the torque curve is flat enough that the torque at
the 5000 RPM redline is still 60% or more of that at 3000 RPM then that
(redline) is exactly where maximum power will be.

-- Bruce

OK, the threads on this topic are branching out pretty good, so again I feel the
need to post that most if not all of the collected wisdom in the world concerning
ground launch in all of its phases is already available in one place.

This place is between the covers of one slim volume by the same name and was
authored by the great Derek Piggott. I just Googled "ground launch piggott" and
up popped maybe a half dozen people who wanted to sell me one. The first was NSM,
our National Soaring Museum:

http://www.soaringmuseum.org/estore/...353463656.html

Get one today! (Book, that is)

And after you read it, don't go out and "do this at home" as they say. Get
somebody that knows how to show you the ropes (har, har) and then the book will
make much more sense.

Disclaimer--- I own stock in both Piggott Enterprises and NSM.

Just kidding

BJ

Brian Case wrote:

If someone wanted to do the world of ground launch a great favor, they would
start a web site where the collective wisdom of the world could be displayed
so that anyone wishing to undertake winch launch could go there and get an
education.

Ok it may not be the collective wisdom of the world. But there is
quite a bit of information on winch launching at:

http://www.northwestsoaring.com/sitemap.shtml

Let me know if I am missing anything really important about Winch
Launching here.

Brian Case
CFIIG/ASEL

Gonna take a California Governor-sized battery and alternator combo down there
in the nuclear engine room!

Using my handy-dandy winch horsepower spreadsheet, solving for required
launching force is an incredible 218,000 pounds and over 50,000 horsepower! Of
course the engines are in full AB, but still ---

Other numbers are a "ground run" of 306 ft and a peak acceleration of 3.3G in
2.4 sec.

I can see that they have already provided the Super Hornet with a pretty stout
nosegear. That's where their "cg hook" is, I believe.

BJ

Bill Daniels wrote:

Actually, I read somewhere that the US Navy is converting its steam
catapults to linear electric motors to get finer control over the launch. I
also suspect that it reduces the manpower required to operate the "cat".

Bill Daniels

"Bob Johnson" wrote in message
...
Hi Bruce --

That's a very welcome correction to my hazily-remembered version of a
second-hand report of what the 454 c.i. engine torque/hp/rpm chart looks
like. This is the kind of info I was looking for and thanks for providing
it!

In all our past kicking around of the ideal winch prime mover, here's one
that sounds silly but might rate at least an engineering investigation --
a
recip steam engine! If I recall correctly, the steam engine develops max
torque at stall.

What got me thinking about that was the fact that the Navy gets 66,000 lb
Super Hornets flying in about the same three seconds that it takes us to
get
airborne. And they do it with steam, not because it's handy, but that's
probably the only practical way to get it done.

BJ

Bruce Hoult wrote:

In article ,
Bob Johnson wrote:

Our engine is petrol fueled. Despite Google's best efforts, I have not
yet located a Torque/HP/RPM curve for our very common 7.4 L engine,
but
have heard that it develops max torque and HP at about 3000 RPM and
further that the curves are fairly flat at this point.

You are making some totally contradictory and inconsistent claims there.

If max torque and max HP occur close together then they must both drop
off precipitously after that.

If the torque curve is flat then HP will be increasing linearly with
RPM, max torque and max HP will be very far apart.

It is quite likely that you do have maximum torque at around 3000 RPM,
but if for example the torque curve is flat enough that the torque at
the 5000 RPM redline is still 60% or more of that at 3000 RPM then that
(redline) is exactly where maximum power will be.

-- Bruce

In article ,
Bob Johnson wrote:

In all our past kicking around of the ideal winch prime mover, here's one
that sounds silly but might rate at least an engineering investigation -- a
recip steam engine! If I recall correctly, the steam engine develops max
torque at stall.

That is true, and it is also true of many electric motors.

Unfortunately, I suspect that if they are strong enough with the glider
flying at 60 knots then they will be far *too* strong at the start!

-- Bruce

I believe a German club has recently built themselves a DC winch using
dozens of automotive type batteries. Haven't heard how they have done
with it, though.

BJ

Bruce Hoult wrote:

In article ,
Bob Johnson wrote:

In all our past kicking around of the ideal winch prime mover, here's one
that sounds silly but might rate at least an engineering investigation -- a
recip steam engine! If I recall correctly, the steam engine develops max
torque at stall.

That is true, and it is also true of many electric motors.

Unfortunately, I suspect that if they are strong enough with the glider
flying at 60 knots then they will be far *too* strong at the start!

-- Bruce

Yes, but would you get up at 3am to stoke it

At 20:24 30 October 2003, Tango4 wrote:
I love it! The boiler could provide the permanent thermal
off the top of the
launch too!

Ian

'Bob Johnson' wrote in message
...
Hi Bruce --

That's a very welcome correction to my hazily-remembered
version of a
second-hand report of what the 454 c.i. engine torque/hp/rpm
chart looks
like. This is the kind of info I was looking for and
thanks for providing
it!

In all our past kicking around of the ideal winch
prime mover, here's one
that sounds silly but might rate at least an engineering
investigation --
a
recip steam engine! If I recall correctly, the steam
engine develops max
torque at stall.

What got me thinking about that was the fact that
the Navy gets 66,000 lb
Super Hornets flying in about the same three seconds
that it takes us to
get
airborne. And they do it with steam, not because it's
handy, but that's
probably the only practical way to get it done.

BJ

Bruce Hoult wrote:

In article ,
Bob Johnson wrote:

Our engine is petrol fueled. Despite Google's best
efforts, I have not
yet located a Torque/HP/RPM curve for our very common
7.4 L engine,
but
have heard that it develops max torque and HP at
about 3000 RPM and
further that the curves are fairly flat at this
point.

You are making some totally contradictory and inconsistent
claims there.

If max torque and max HP occur close together then
they must both drop
off precipitously after that.

If the torque curve is flat then HP will be increasing
linearly with
RPM, max torque and max HP will be very far apart.

It is quite likely that you do have maximum torque
at around 3000 RPM,
but if for example the torque curve is flat enough
that the torque at
the 5000 RPM redline is still 60% or more of that
at 3000 RPM then that
(redline) is exactly where maximum power will be.

-- Bruce

Yes, but would you get up at 3am to stoke it

Who would't want to stroke the wench at 3am?

There once was a non-BGA soaring site/club in East Anglia in the UK. The
operator was named Fred, but the surname escapes me and I believe he passed
away in the 1980's. By all accounts he operated a steam winch though I
never met him nor saw it in action. I believe that operation was dwindling
and may have ceased operations about 1980. Any stories out there?

Frank Whiteley

"Bob Johnson" wrote in message
...
Hi Bruce --

That's a very welcome correction to my hazily-remembered version of a
second-hand report of what the 454 c.i. engine torque/hp/rpm chart looks
like. This is the kind of info I was looking for and thanks for providing
it!

In all our past kicking around of the ideal winch prime mover, here's one
that sounds silly but might rate at least an engineering investigation --
a
recip steam engine! If I recall correctly, the steam engine develops max
torque at stall.

What got me thinking about that was the fact that the Navy gets 66,000 lb
Super Hornets flying in about the same three seconds that it takes us to
get
airborne. And they do it with steam, not because it's handy, but that's
probably the only practical way to get it done.

BJ

Bruce Hoult wrote:

In article ,
Bob Johnson wrote:

Our engine is petrol fueled. Despite Google's best efforts, I have not
yet located a Torque/HP/RPM curve for our very common 7.4 L engine,
but
have heard that it develops max torque and HP at about 3000 RPM and
further that the curves are fairly flat at this point.

You are making some totally contradictory and inconsistent claims there.

If max torque and max HP occur close together then they must both drop
off precipitously after that.

If the torque curve is flat then HP will be increasing linearly with
RPM, max torque and max HP will be very far apart.

It is quite likely that you do have maximum torque at around 3000 RPM,
but if for example the torque curve is flat enough that the torque at
the 5000 RPM redline is still 60% or more of that at 3000 RPM then that
(redline) is exactly where maximum power will be.

-- Bruce