motorgliders as towplanes

A physicist acquantance who wrote a book on Newton and aerodynamics said
that the mathematics was taken over from electrical theory because the
equations balanced, but that they don't explain what is cause and what is
effect. That's the feeling I get when you start talking about something
called theta as if it were proof.

Seems to me we have a new theology going here -- something akin to
pre-milleniumism versus post-milleniumism.


At 13:29 20 March 2009, wrote:
You guys have proven 2 fundamental truths.

1) In any engineering discussion. If you don't define terms at the
start, you just chase yourself around in a circle.

2) Pilots don't need to know much about aerodyanmics to fly well.

Oh yeah,

3) Flight instructors explain these things more to make a point than
to be accurate :-)


Todd Smith
3S

On 20 Mar, 14:38, Doug Hoffman wrote:
The Real Doctor wrote:
On 20 Mar, 01:39, Doug Hoffman wrote:
And lift(as we are using the term) without gravity is not possible.

Aircraft in a 90 degree bank can still produce lift ...

Without gravity how will you get the glider into a bank (or even to
move)? *Answer = not possible.

An engine. You'll notice that I wrote "aircraft" and not "gliders"...

Ian

On Mar 19, 6:08 pm, Doug Hoffman wrote:

I just wish the US would perform its conversion to metric units for
*everything*. The sooner the better. But that job is being handled by
our highly efficient government. Don't hold your breath. :-)

Kind of a hijack, but what I wish is that aircraft hardware
manufacturers would get their crap together and produce a coherent
metric equivalent of the AN system of common aircraft hardware.

The magic of the AN hardware system is not that they offer any
particularly high strength (they don't; for the most part AN bolts are
equivalent to Grade 5 hardware store bolts) or any particularly high
precision (again, they're about the same as the bolts at Ace or True
Value). The magic is that AN bolts have just enough thread for a nut
and somewhere between 0" and about 0.125" of washers, and that they
come in length increments of 0.125". Those two elements let you create
a nice, tidy bolted joint of virtually any practical grip length, and
not have the threaded portion of the bolt loaded in shear, and not
have a bunch of threads hanging out of the nut. Furthermore, common AN
hardware is very attractively priced, for the most part you can buy
them from any of several aircraft parts outlets at the same or even
lower prices as Grade 5 bolts at a mom&pop hardware store.

By contrast, metric aircraft hardware has no coherent system of
markings, thread lengths, and grip lengths. It averages twice or
thrice the cost of AN hardware when you can find it, and is available
from only a few outlets. When you need a replacement bolt for your
European aircraft, you have virtually no choice but to order it
directly from the manufacturer at huge markups and with huge shipping
charges.

I like the metric system, and I like metric hardware. I appreciate
that even American cars are, by and large, assembled with metric nuts
and bolts these days. But given the choice between about $500 worth of
AN hardware per aircraft and twice or thrice that in metric nuts and
bolts that offer no greater utility, hmmm, I think I'll go with the
less expensive option.

End rant.

Thanks, Bob K.
http://www.hpaircraft.com/hp-24

Bob Kuykendall wrote:
On Mar 19, 6:08 pm, Doug Hoffman wrote:

I just wish the US would perform its conversion to metric units for
*everything*. The sooner the better. But that job is being handled by
our highly efficient government. Don't hold your breath. :-)

Kind of a hijack, but what I wish is that aircraft hardware
manufacturers would get their crap together and produce a coherent
metric equivalent of the AN system of common aircraft hardware.

The magic of the AN hardware system is not that they offer any
particularly high strength (they don't; for the most part AN bolts are
equivalent to Grade 5 hardware store bolts) or any particularly high
precision (again, they're about the same as the bolts at Ace or True
Value). The magic is that AN bolts have just enough thread for a nut
and somewhere between 0" and about 0.125" of washers, and that they
come in length increments of 0.125". Those two elements let you create
a nice, tidy bolted joint of virtually any practical grip length, and
not have the threaded portion of the bolt loaded in shear, and not
have a bunch of threads hanging out of the nut. Furthermore, common AN
hardware is very attractively priced, for the most part you can buy
them from any of several aircraft parts outlets at the same or even
lower prices as Grade 5 bolts at a mom&pop hardware store.

By contrast, metric aircraft hardware has no coherent system of
markings, thread lengths, and grip lengths. It averages twice or
thrice the cost of AN hardware when you can find it, and is available
from only a few outlets. When you need a replacement bolt for your
European aircraft, you have virtually no choice but to order it
directly from the manufacturer at huge markups and with huge shipping
charges.

I like the metric system, and I like metric hardware. I appreciate
that even American cars are, by and large, assembled with metric nuts
and bolts these days. But given the choice between about $500 worth of
AN hardware per aircraft and twice or thrice that in metric nuts and
bolts that offer no greater utility, hmmm, I think I'll go with the
less expensive option.

End rant.

Hi Bob,

Yes. There may be some niche areas like aircraft hardware that would at
least require legacy support for a period of years. Makes me wonder
what Boeing/Cessna and others are doing now and plan to do in the future
in that respect.

Regards,

-Doug

Btw, American designed cars and trucks do more than just assemble with
metric fasteners. Nominal dimensions are typically, e.g., 100 mm for a
bracket width instead of 4.0". We call that "hard metric" design. Some
user interface items like wheel lug nuts may still be SAE.

On Mar 20, 4:58*pm, Doug Hoffman wrote:
Bob Kuykendall wrote:
On Mar 19, 6:08 pm, Doug Hoffman wrote:

I just wish the US would perform its conversion to metric units for
*everything*. *The sooner the better. *But that job is being handled by
our highly efficient government. *Don't hold your breath. *:-)

Kind of a hijack, but what I wish is that aircraft hardware
manufacturers would get their crap together and produce a coherent
metric equivalent of the AN system of common aircraft hardware.

The magic of the AN hardware system is not that they offer any
particularly high strength (they don't; for the most part AN bolts are
equivalent to Grade 5 hardware store bolts) or any particularly high
precision (again, they're about the same as the bolts at Ace or True
Value). The magic is that AN bolts have just enough thread for a nut
and somewhere between 0" and about 0.125" of washers, and that they
come in length increments of 0.125". Those two elements let you create
a nice, tidy bolted joint of virtually any practical grip length, and
not have the threaded portion of the bolt loaded in shear, and not
have a bunch of threads hanging out of the nut. Furthermore, common AN
hardware is very attractively priced, for the most part you can buy
them from any of several aircraft parts outlets at the same or even
lower prices as Grade 5 bolts at a mom&pop hardware store.

By contrast, metric aircraft hardware has no coherent system of
markings, thread lengths, and grip lengths. It averages twice or
thrice the cost of AN hardware when you can find it, and is available
from only a few outlets. When you need a replacement bolt for your
European aircraft, you have virtually no choice but to order it
directly from the manufacturer at huge markups and with huge shipping
charges.

I like the metric system, and I like metric hardware. I appreciate
that even American cars are, by and large, assembled with metric nuts
and bolts these days. But given the choice between about $500 worth of
AN hardware per aircraft and twice or thrice that in metric nuts and
bolts that offer no greater utility, hmmm, I think I'll go with the
less expensive option.

End rant.

Hi Bob,

Yes. *There may be some niche areas like aircraft hardware that would at
least require legacy support for a period of years. *Makes me wonder
what Boeing/Cessna and others are doing now and plan to do in the future
in that respect.

Regards,

-Doug

Btw, American designed cars and trucks do more than just assemble with
metric fasteners. *Nominal dimensions are typically, e.g., 100 mm for a
bracket width instead of 4.0". *We call that "hard metric" design. *Some
user interface items like wheel lug nuts may still be SAE.- Hide quoted text -

- Show quoted text -

While we're 'Ranting'.... Bob, that would be nice, wouldn't it? It
took me 2 tries to get the right bolt from Grob when I went throught
my control system a few years ago.
DON'T get me started on US auto makers. I have two Dodge Trucks. I
HATE the fact that evey time I get under one to work on it, I need to
take BOTH metric and SAE tools. Pick a STANDARD! My favorite example
was an exhaust stud on a 1998 Olds Intrigue. Engine side - SAE
exhaust flange side - metric.
Rant off.
I feel better now.

On Mar 20, 1:32 am, The Real Doctor wrote:

Physicists, and particularly
school physics teachers, traditionally get terribly upset by the idea
of centrifugal force.

Ian

Physicsists make equally snarky comments about engineers, Ian. My
engineering dynamics professor at UC, Berkeley was adamant in
opposing the perpetuation of the centrifugal force myth. It's phony
physics and can lead to seriously erroneous conclusions.

Myles

On 21 Mar, 05:21, Myles wrote:
On Mar 20, 1:32 am, The Real Doctor wrote:

Physicists, and particularly
school physics teachers, traditionally get terribly upset by the idea
of centrifugal force.

Physicsists make equally snarky comments about engineers, Ian. *

Indeed. Bu hey, the mathematicians despise us all.

My
engineering dynamics professor at UC, Berkeley was *adamant in
opposing the perpetuation of the centrifugal force myth. *It's phony
physics and can lead to seriously erroneous conclusions.

It's a perfectly useful tool if applied correctly. That normally means
within a moving axis system, and getting there is not always simple.
You always have to decide whether it's going to be easier overall to
use the difficult model with the simple setup (stationary axes) or the
simple model with the difficult setup (moving axes).

It's the same in fluids - normally we model a glider by holding it
still and letting the air move past, but that's not always the best
way, or the easiest way. Mind you, I'm a typical lazy engineer, so for
me best = easiest in about 99% of cases.

Ian

On 21 Mar, 03:17, Uncle Fuzzy wrote:

While we're 'Ranting'.... Bob, that would be nice, wouldn't it? *It
took me 2 tries to get the right bolt from Grob when I went throught
my control system a few years ago.

You think that;s bad? Try getting specialist fasteners for old Polish
gliders. Or, on the ground, getting fasteners in the odd 5mm-but-not-
M5 thread that Citroen used. I've seen refurbished original Citroen
nuts and bolts at €4 per item - not per set!

Ian

At 11:44 21 March 2009, The Real Doctor wrote:

You think that;s bad? Try getting specialist fasteners for old Polish
gliders. Or, on the ground, getting fasteners in the odd 5mm-but-not-
M5 thread that Citroen used. I've seen refurbished original Citroen
nuts and bolts at =804 per item - not per set!

I have to keep my Whitworth wrenches on hand when working on my
Austin-Healey 100. Some of the basic stuff that came out of the parts
bins, like suspension and transmission, uses Whitworth hardware, while the
rest works with SAE stuff. It's still possible to buy Whitworth threaded
fasteners, but you have to know where to look. Are there any British
gliders left that are old enough to have used Whitworth hardware?

Jim Beckman

Myles wrote:
On Mar 20, 1:32 am, The Real Doctor wrote:

... My engineering dynamics professor at UC, Berkeley was adamant in
opposing the perpetuation of the centrifugal force myth. It's phony
physics and can lead to seriously erroneous conclusions.

Yeah, yeah, centrifugal force is a reaction to a centripetal force, I
know the difference,.... I don't care. The layman understands the former
term and not the latter. To the typical student, I'll use the term
"centrifugal". If he's a physicist, I'll say "centripetal". :-)

Tony V.