For the real engineers here

In article , Bertie the
Bunyip says...

Jim Logajan wrote in
:

Maxwell luv2^fly99@live.^com wrote:
In article , Maxwell says...
If you dislike being called a forger, then stop doing so.

You are convicting yourself of lying every time you poast claim I'm
forging you.

Your name isn't Maxwell and you are obsessed up the gonzo.

Maxwell doesn't understand we all already know how to distinguish your
posts from his and he is obsessed up the gonzo.

Could you post a guide? I'm a bit confused at times myself..

Maybe we start indexing them. Maxwell(1), Maxwell(2), Maxwell(3) etc.

--

"Tis an ill wind that blows no minds"

Maxwell luv2^fly99@live.^com wrote in
:

In article , Bertie the
Bunyip says...

Jim Logajan wrote in
:

Maxwell luv2^fly99@live.^com wrote:
In article , Maxwell says...
If you dislike being called a forger, then stop doing so.

You are convicting yourself of lying every time you poast claim
I'm forging you.

Your name isn't Maxwell and you are obsessed up the gonzo.

Maxwell doesn't understand we all already know how to distinguish
your posts from his and he is obsessed up the gonzo.

Could you post a guide? I'm a bit confused at times myself..

Maybe we start indexing them. Maxwell(1), Maxwell(2), Maxwell(3) etc.


That would confuse Maxwell. He can only count to two.

Better leave it the way it is.


Bertie

wrote:

I'm thinking of a clean glider, one that might weigh 1500 pounds and
has a glide angle of say 1 in 25. At 50 miles an hour, that would mean
in an hour's time it might descend two miles (of course scale it
reasonable numbers, I chose those for ease of calculation). That means
it's losing about 1500 * 5280 * 2, or about 16 million foot pounds of
energy an hour.

Now if I add an engine swinging an 8 foot diameter prop, maybe as a
pusher, the question is, how big an engine for cruise only? A
horsepower is 550 foot lbs a second, or about 2 million foot pounds
an hour. If all of that is correct, it suggests with a 50% efficient
prop a little 16 horsepower engine could pretty much keep this thing
at constant altitude.

It passes the reasonableness test as far as I can see. Any serious
disagreements?

For those of you who do things in metric units? I went to school a
long long time ago, and here in the US I can buy a little Briggs and
Stanton (spelling?) engine with a horsepower rating, not a kilowatt
one.

well, seems to be correct. still, let me add some annotations:

- i'd calculate directly using power instead of energy. the installed power
you need is simply weight*sink speed/efficiency; in a formula:
P = W*w/eta = m*g*v/(E*eta) with the glide ratio E = Lift/Drag, m the mass
and g the gravitational acceleration

- i prefer SI units, for the simple benefit tp be able to calculate without
conversion factors. this eliminates a quite likely source of mistakes (ask
NASA...). a few years ago, while working in the US, i failed to calculate
the mass of a simple sheet of aluminum (don't laugh!); i had several
numbers for the material's density, but none in the combination of units
for volume and mass that i needed; so i decided it was safer to go via SI
and convert the mass back to ounces...

- the conversion hp-kW is simple: 1 kW = 1.34 hp (= 1.36 german PS) or
roughly 4/3 hp


cheers
uli

On Jun 26, 4:09 am, Uli wrote:
wrote:
I'm thinking of a clean glider, one that might weigh 1500 pounds and
has a glide angle of say 1 in 25. At 50 miles an hour, that would mean
in an hour's time it might descend two miles (of course scale it
reasonable numbers, I chose those for ease of calculation). That means
it's losing about 1500 * 5280 * 2, or about 16 million foot pounds of
energy an hour.

Now if I add an engine swinging an 8 foot diameter prop, maybe as a
pusher, the question is, how big an engine for cruise only? A
horsepower is 550 foot lbs a second, or about 2 million foot pounds
an hour. If all of that is correct, it suggests with a 50% efficient
prop a little 16 horsepower engine could pretty much keep this thing
at constant altitude.

It passes the reasonableness test as far as I can see. Any serious
disagreements?

For those of you who do things in metric units? I went to school a
long long time ago, and here in the US I can buy a little Briggs and
Stanton (spelling?) engine with a horsepower rating, not a kilowatt
one.

well, seems to be correct. still, let me add some annotations:

- i'd calculate directly using power instead of energy. the installed power
you need is simply weight*sink speed/efficiency; in a formula:
P = W*w/eta = m*g*v/(E*eta) with the glide ratio E = Lift/Drag, m the mass
and g the gravitational acceleration

- i prefer SI units, for the simple benefit tp be able to calculate without
conversion factors. this eliminates a quite likely source of mistakes (ask
NASA...). a few years ago, while working in the US, i failed to calculate
the mass of a simple sheet of aluminum (don't laugh!); i had several
numbers for the material's density, but none in the combination of units
for volume and mass that i needed; so i decided it was safer to go via SI
and convert the mass back to ounces...

- the conversion hp-kW is simple: 1 kW = 1.34 hp (= 1.36 german PS) or
roughly 4/3 hp

cheers
uli
I wouldn't argue with you about using SI units in professional
communications -- I do that all of the time -- but in this case I
started out with English units and it was easy to stay within them.
Also, and importantly, the question I asked was more easily understood
by most pilots here, and the more useful answers came back in the same
units. First rule of communication -- speak the language the spoken to
are most likely to understand!

It would have been fun to give the airspeed in furlongs per fortnight,
or for the spectroscopically inclined, nm/sec.

I do appreciate your comments, thanks. Now let's give the thread back
to the little boys with their spray cans.

On Jun 26, 4:09 am, Uli wrote:
wrote:
I'm thinking of a clean glider, one that might weigh 1500 pounds and
has a glide angle of say 1 in 25. At 50 miles an hour, that would mean
in an hour's time it might descend two miles (of course scale it
reasonable numbers, I chose those for ease of calculation). That means
it's losing about 1500 * 5280 * 2, or about 16 million foot pounds of
energy an hour.

Now if I add an engine swinging an 8 foot diameter prop, maybe as a
pusher, the question is, how big an engine for cruise only? A
horsepower is 550 foot lbs a second, or about 2 million foot pounds
an hour. If all of that is correct, it suggests with a 50% efficient
prop a little 16 horsepower engine could pretty much keep this thing
at constant altitude.

It passes the reasonableness test as far as I can see. Any serious
disagreements?

For those of you who do things in metric units? I went to school a
long long time ago, and here in the US I can buy a little Briggs and
Stanton (spelling?) engine with a horsepower rating, not a kilowatt
one.

well, seems to be correct. still, let me add some annotations:

- i'd calculate directly using power instead of energy. the installed power
you need is simply weight*sink speed/efficiency; in a formula:
P = W*w/eta = m*g*v/(E*eta) with the glide ratio E = Lift/Drag, m the mass
and g the gravitational acceleration

- i prefer SI units, for the simple benefit tp be able to calculate without
conversion factors. this eliminates a quite likely source of mistakes (ask
NASA...). a few years ago, while working in the US, i failed to calculate
the mass of a simple sheet of aluminum (don't laugh!); i had several
numbers for the material's density, but none in the combination of units
for volume and mass that i needed; so i decided it was safer to go via SI
and convert the mass back to ounces...

- the conversion hp-kW is simple: 1 kW = 1.34 hp (= 1.36 german PS) or
roughly 4/3 hp

cheers
uli
I wouldn't argue with you about using SI units in professional
communications -- I do that all of the time -- but in this case I
started out with English units and it was easy to stay within them.
Also, and importantly, the question I asked was more easily understood
by most pilots here, and the more useful answers came back in the same
units. First rule of communication -- speak the language the spoken to
are most likely to understand!

It would have been fun to give the airspeed in furlongs per fortnight,
or for the spectroscopically inclined, nm/sec.

I do appreciate your comments, thanks. Now let's give the thread back
to the little boys with their spray cans.

I wouldn't argue with you about using SI units in professional
communications -- I do that all of the time -- but in this case I
started out with English units and it was easy to stay within them.
Also, and importantly, the question I asked was more easily understood
by most pilots here, and the more useful answers came back in the same
units. First rule of communication -- speak the language the spoken to
are most likely to understand!

my direct answer wasn't in another "language"; it was pretty straight, i
think. the formula i suggested is independent of units; so it can used also
if one calculates with imperial units.

you asked for an answer by "real engineers"; that's what you got.

i'm sorry if i confused anyone by giving additional information...

Liar.

Liar. You're talking to yourself.

On 2008-06-25, wrote:
I'm thinking of a clean glider, one that might weigh 1500 pounds and
has a glide angle of say 1 in 25.

That's not really a 'clean glider' - that's less than the performance of
an old wooden glider like a Slingsby Skylark. Modern training gliders
like the Puchacz have a glide of 30:1.

Now if I add an engine swinging an 8 foot diameter prop, maybe as a
pusher, the question is, how big an engine for cruise only?

As a point of reference, the Ventus 2ct (a 'turbo', no it's not
turbocharged, but for some reason self-sustainers are called 'turbos'
here) is a 2 seat glider which is genuinely clean (around 45:1 glide),
with an all up weight of 600kg (around 1300 lbs or so), has a 20
horsepower engine. So you're in the right order of magnitude. It doesn't
have an 8 foot prop either (it's a teeny little 5 blade prop IIRC, and
the whole engine/prop retracts just behind the cockpit).

--
From the sunny Isle of Man.
Yes, the Reply-To email address is valid.

Sure bertie, cuz you know everyone, and you know everything.

You're damn near as smart as LeChaud.