Propellors vs Rotors

[Don W]

Can someone explain to me why 300HP applied to a large rotor
at ~700 RPM is enough to lift a 2000lb helicopter straight up,
but the same 300HP applied to a smaller diameter propellor
at ~2600 RPM can not even come close to allowing a 2000 LB
airplane to climb vertically?

This is really bugging me. BTW, does anyone have any idea
what the thrust produced by the propellor of the hypothetical
300 HP (say LYC-IO540 powered) airplane would be? Obviously
the thrust produced by the 300HP helicopter exceeds 2000 LBs.

TIA,

Don W.

[Alan Baker]

In article >,
Don W > wrote:

> Can someone explain to me why 300HP applied to a large rotor
> at ~700 RPM is enough to lift a 2000lb helicopter straight up,
> but the same 300HP applied to a smaller diameter propellor
> at ~2600 RPM can not even come close to allowing a 2000 LB
> airplane to climb vertically?
>
> This is really bugging me. BTW, does anyone have any idea
> what the thrust produced by the propellor of the hypothetical
> 300 HP (say LYC-IO540 powered) airplane would be? Obviously
> the thrust produced by the 300HP helicopter exceeds 2000 LBs.
>
> TIA,
>
> Don W.

It's got everything to do with the amount of air they move and the
difference in efficiency between moving a little air at high speed or a
lot of air at lower speed.

Let's look at this qualitatively.

In order to lift an object by moving air, you need to create enough
force. Force is equal to a change in momentum with respect to time. That
is, you can think of force as being equal to changing the momentum of a
constant mass at a constant rate of acceleration (F = ma), *or* you can
think of it as applying a constant speed change to a flow of mass (F =
m/s * v). But as long as multiplying the two together gives you the same
total force, it does matter from a momentum perspective.

But! From and energy and power perspective it matters a lot.

Kinetic energy is proportional to the mass being moved but also
proportional to the *square* of the speed you move it at.

So if you go from rotor moving x mass per second at y speed to a
propellor moving x/2 mass per second at 2y speed, then your power goes
down by half from the change in mass, but *up* by four from the change
in speed. IOW, move half the mass to achieve the same force and you need
to use twice the power.

Does that help?

--
Alan Baker
Vancouver, British Columbia
"If you raise the ceiling 4 feet, move the fireplace from that wall
to that wall, you'll still only get the full stereophonic effect
if you sit in the bottom of that cupboard."

[Bill Daniels]

"Alan Baker" > wrote in message
...
> In article >,
> Don W > wrote:
>
>> Can someone explain to me why 300HP applied to a large rotor
>> at ~700 RPM is enough to lift a 2000lb helicopter straight up,
>> but the same 300HP applied to a smaller diameter propellor
>> at ~2600 RPM can not even come close to allowing a 2000 LB
>> airplane to climb vertically?
>>
>> This is really bugging me. BTW, does anyone have any idea
>> what the thrust produced by the propellor of the hypothetical
>> 300 HP (say LYC-IO540 powered) airplane would be? Obviously
>> the thrust produced by the 300HP helicopter exceeds 2000 LBs.
>>
>> TIA,
>>
>> Don W.
>
> It's got everything to do with the amount of air they move and the
> difference in efficiency between moving a little air at high speed or a
> lot of air at lower speed.
>
> Let's look at this qualitatively.
>
> In order to lift an object by moving air, you need to create enough
> force. Force is equal to a change in momentum with respect to time. That
> is, you can think of force as being equal to changing the momentum of a
> constant mass at a constant rate of acceleration (F = ma), *or* you can
> think of it as applying a constant speed change to a flow of mass (F =
> m/s * v). But as long as multiplying the two together gives you the same
> total force, it does matter from a momentum perspective.
>
> But! From and energy and power perspective it matters a lot.
>
> Kinetic energy is proportional to the mass being moved but also
> proportional to the *square* of the speed you move it at.
>
> So if you go from rotor moving x mass per second at y speed to a
> propellor moving x/2 mass per second at 2y speed, then your power goes
> down by half from the change in mass, but *up* by four from the change
> in speed. IOW, move half the mass to achieve the same force and you need
> to use twice the power.
>
> Does that help?
>
> --
> Alan Baker
> Vancouver, British Columbia
> "If you raise the ceiling 4 feet, move the fireplace from that wall
> to that wall, you'll still only get the full stereophonic effect
> if you sit in the bottom of that cupboard."

Good explanation.

This is why I've been trying to get glider tug guys interested in gearing a
small engine to a large slow prop.

Bill Daniels

[COLIN LAMB]

Can someone explain to me why 300HP applied to a large rotor
at ~700 RPM is enough to lift a 2000lb helicopter straight up,
but the same 300HP applied to a smaller diameter propellor
at ~2600 RPM can not even come close to allowing a 2000 LB
airplane to climb vertically?

Think of the airplane as a boat. Take a 30 foot boat and put in 300 hp
motor and a 6" propellor. It will not move the boat much. But put on a 2
foot prop and low rpm and you will move the boat quite nicely. Air is like
water.

Colin

[[email protected]]

> In order to lift an object by moving air, you need to create enough
> force. Force is equal to a change in momentum with respect to time. That
> is, you can think of force as being equal to changing the momentum of a
> constant mass at a constant rate of acceleration (F = ma), *or* you can
> think of it as applying a constant speed change to a flow of mass (F =
> m/s * v). But as long as multiplying the two together gives you the same
> total force, it does matter from a momentum perspective.

Alan:
Does this mean that a helicopter in hover is continuously pushing
down a mass of air equal to the weight of the aircraft? The corollary
is that a rotary wing or fixed wing aircraft in unaccelerated flight is
displacing a mass of air equal to its weight, i.e., it is not flying
because of low pressure above the wing but because of the upward force
on the airfoil from the displacement of air downward. True?
Russell Thorstenberg
Houston, Texas

[Peter Dohm]

"Don W" > wrote in message
. net...
> Can someone explain to me why 300HP applied to a large rotor
> at ~700 RPM is enough to lift a 2000lb helicopter straight up,
> but the same 300HP applied to a smaller diameter propellor
> at ~2600 RPM can not even come close to allowing a 2000 LB
> airplane to climb vertically?
>
> This is really bugging me. BTW, does anyone have any idea
> what the thrust produced by the propellor of the hypothetical
> 300 HP (say LYC-IO540 powered) airplane would be? Obviously
> the thrust produced by the 300HP helicopter exceeds 2000 LBs.
>
> TIA,
>
> Don W.
>
I am not a helicopter guy, so please don't expect my to carry this thread
very far; but I'll try at the most basic level.

Lift as generated by throwing air downward in order to maintain the
altitude, or the constant rate of ascent or descent, of an object is based
upon a momentum equation--rather than an energy equation. Therefore,
throwing twice as much air downward half as fast will support the same
weight; but will require about half as much energy per unit time, or about
one half the horsepower. Remember that horsepower is a measure of energy,
or work, per unit of time.

The helicopter is thus supported on the downwash from its rotor, producing a
vertical thrust at least equal to its weight (actually more when hovering)
and literally glides forward in response to tilt.

I stopped for a moment to dress in my flame retarding coveralls in
anticipation of the response to my use of the word "glide"; however that is
what it does. It even recovers a little efficiency, compared to its
hovering condition, by virtue of continuously transitioning onto new and
undisturbed air. At its most "efficient" speed, a helicopter might be more
than half as efficient as a really atrocious airplane.

OTOH, in the case of an airplane propeller, we need to make the energy
equation work--while the wings deal with the momentum equation. We can
choose a wingspan appropriate for the intended weight and cruising speed and
a wing area to meet our stall speed requirements, determine the expected
drag in cruise, choose a propeller disk area and number of blades
appropriate for reasonable efficiency in cruise, and match the result to an
engine, and possibly a PRSU since the propeller disk area determines the
diameter and the maximum RPM. Finally, determine that the available power
can supply sufficient thrust for take-off and climb. Traditionally, small
airplanes produce a maximum static thrust on the order of one fifth of their
weight when tied in place, and much less in cruise. The propeller, of
course, constantly transitions into new and undisturbed air and its
efficiency improves from zero at the start of the take-off roll to an
acceptable figure in cruise.

One size does not fit all.

BTW, a 700 rpm rotor is pretty small and may be really inefficient--even by
helicopter standards!

I hope this helps.

Peter

[COLIN LAMB]

>BTW, a 700 rpm rotor is pretty small and may be really inefficient--even by
>helicopter standards!

The Schweizer 300 (formerly Hughes 269C) has a rotor rpm power on of 442 to
471 rpm. Power off range is 390 to 504 rpm. Esceed these limits and you
are quite likely to break something.

The Schweizer has 190 hp and gross weight is 2050 lbs.

Colin

[wright1902glider]

At the risk of opening up a huge can of worms, I have 2 questions and
one statement:

1. If a helicopter makes lift by displacing air downward with its
rotor:

Rotor blades are airfoil shaped (I've seen 'em) just like airplane
wings. Therefore airplanes fly by displacing air downward with their
wings? There's something wrong with your logic Sir Maxim. It would
seem that we killed this theory about 104 years ago with Will & Orv's
little wind tunnel. Recall, the flat inclined surface displaced more
air than any of the airfoil surfaces as measured by the vane balance.
However, it also made less lift than any of the airfoil surfaces at a
similar AOA. Ergo, an airfoil makes lift not by displacing air
downward, but by producing a condition where the air flowing across its
upper surface travels faster, and therefore has less pressure, than the
air flowing under its lower surface. Therefore, an airfoil wing does
not "fly" by displacing air downward, but rather exploits a zone of
differential pressure caused by a difference in the speed of the
airflow. And since a helicopter rotor blade is a long skinny wing
flying around in a circle, it produces lift just the same as an
airplane's wing does. I can only think of 2 machines that fly by
displacing air downward. Those would be ballistic rockets/missles, and
the Harrier jet in vertical or hovering flight.

2. A helicopter glides forward on an inclined cushion of displaced air:

A helicopter flies in a chosen direction due to the cyclic change in
rotor blade pitch impatred by an inclined swash plate. What's a swash
plate do? Well, imagine a doughnut smashed between 2 dinner plates. The
dinner plates are fixed to the fuselage and do not rotate. The doughnut
rotates at the same rate as the rotor head. When you tilt the dinner
plates, you also tilt the doughnut. Now if the doughnut is attached to
the rotor blade pitch-control horns by rotor blade pitch-change links,
the links will go up and down relative to the fuselage as the tilted
doughnut spins. This pushes and pulls on the rotor-blade control horns,
constantly changing the pitch of the blade as it flys around in a
circle. If you tilt the dinner plates forward, the blade flys at a
lower AOA in the front 1/2 of the rotor disk than it does at the back
1/2. Since its producing more lift in the back 1/2 than in the front
1/2, the blade flies higher in back. Stay with me here. As the blade
flies higher, its coning angle relative to the rotor head increases to
a greater angle than it does in the forward 1/2 of the rotor disk..
Therefore, its line of thrust relative to the fuselage is not vertical,
but is actually inclined forward. A helicopter "pulls" itself forward
through the air, more or less.

3. Rotor blades turning at 700 rpm vs. a prop turning at 2600 rpm.

Well, helicopter rotors don't turn that fast. Most are somewhere in the
300-350 rpm range. A Boeing Vertol CH-47's rotors only turn at 255 rpm,
or so I've heard. If I'm not mistaken, Hughes once built some kinda
giant tip-thrust powered test-freak that had a rotor speed of about 16
rpm. I've seen the videos, but I can't recall the name.

I could of course be completely and totally wrong about all of this. It
might just be fairies and Leprachauns.

Harry

[COLIN LAMB]

"Therefore, an airfoil wing does not "fly" by displacing air downward, but
rather exploits a zone of differential pressure caused by a difference in
the speed of the airflow."

Does this mean that airplanes cannot fly upside down, or does the shape of
the wing change when the airplane rolls over?

Colin

[wright1902glider]

> Does this mean that airplanes cannot fly upside down, or does the shape of
> the wing change when the airplane rolls over?
>
> Colin

Good question. In most aircraft, the airfoil shape does not change.
However, assuming that an airplane maintains level flight at +5 degrees
AOA relative to the horizon, and then rolls over upside down, what is
its new AOA? That would neg. 5 degrees. Gravity aside, the plane would
fly in a downward direction because the air flowing over the "upper"
surface of the airfoil would still be traveling at a higher rate
relative to the "lower" surface.

Of course, if a pilot rolls her plane over and then pushes forward on
the stick, that would produce a positive AOA relative to the horizon.
How much would be enough to increase the flow over the "lower" surface
of the wing (now sunny-side up) than on the "upper" surface? I dunno.
Push the stick forward till we quit flying down toward the dirt.

Some planes, and some helicopters, have semetrical airfoil wings. They
achieve a differential airspeed/pressure by flying at a positive AOA.

So why is AOA so important? If the leading edge is up, and the trailing
edge is down, doesn't that mean that the wing is still forcing air down
as it travels through the air? Maybe somewhat, but that's not where the
magic is. Its all about the relative difference in airspeed and
therefore air pressue. Since AOA directly effects airflow over the
wing, is it not reasonable to think that it alone could produce enough
of a difference in speed/pressure to sustain flight?


Old Regallo wings could/would change shape. Google "luff-dive"
sometime. Things get ugly in a hurry when your airfoil reverses its
loveley curved shape and slams you into the ground with over 300 lbs of
force. Been there. Done that. Lived.

By the way, I'm not professing to know much more about aerodynamics
than what was discovered in the Wright wind tunnel. But I'm pretty well
convinced by those results that most airplanes do not stay in the aloft
by forcing air downward.

Now here's a simple 19th Century way to prove the point. Attach a
length of yarn to the "lower" surface of a slow-flying plane. Watch the
yarn and see what direction it takes in flight. Is it straight back? Or
is it down? If air is indeed being forced downward by the wing,
shouldn't we be able to see the results in the yarn?

Harry

[Peter Dohm]

----------------------much snipping-------------

> If I'm not mistaken, Hughes once built some kinda
> giant tip-thrust powered test-freak that had a rotor speed of about 16
> rpm. I've seen the videos, but I can't recall the name.
>

Fairchild-Hiller once built something like that, supposedly with ram jets in
the tips, and Hughes may have as well; although I am fairly sure that the
rotor speed was within the normal range for helicopters.

There was also a propane fueled pulse jet powered single blade helicopter of
the strap-onto-the-pilot variety several years ago. ( I even had a "blurb"
about it--and a related APU for gliders--which may still be buried among
other books and catalogs.) Although I don't know if it ever flew out of
tether...

Peter

P.S.: As to the original post: the pilot shops at most airports have
passable texts to introduce the theory of helicopters, and a lot of
accomplished helicopter pilots and mechanics used to hang around on
"rec.aviation.rotorcraft: so that lurking over there could pay dividends...

[Alan Baker]

In article . com>,
wrote:

> > In order to lift an object by moving air, you need to create enough
> > force. Force is equal to a change in momentum with respect to time. That
> > is, you can think of force as being equal to changing the momentum of a
> > constant mass at a constant rate of acceleration (F = ma), *or* you can
> > think of it as applying a constant speed change to a flow of mass (F =
> > m/s * v). But as long as multiplying the two together gives you the same
> > total force, it does matter from a momentum perspective.
>
> Alan:
> Does this mean that a helicopter in hover is continuously pushing
> down a mass of air equal to the weight of the aircraft?

No. It means that it is continuously changing the velocity of a mass
flow of air.

Let's say the helicopter has a mass of 1000 kg. To hover, it requires a
force of 9800 Newtons be exerted upward on it. Therefore, the rotors
must exert a force of 9800 Newtons downward on the air. If we assume to
speed at which it makes the air flow -- say 50 meters per second -- then
we can calculate the mass flow involved.

F = M(ass)/s * v; or M/s = F/v = 9800/50 = 196 kg/s.

So if the helicopter is moving the air downward at 50 meters per second,
then the amount of mass to which it must impart that velocity is 196
kg/s. If it only moves the air downward at 10 meters per second, then it
must be moving 980 kg/s at that speed.

Every one knows "F = ma", but few realize that "F = m/s * v" is equally
valid. The same force that will accelerate a fixed mass at a give rate
can also change a mass flow's velocity by a fixed amount.

> The corollary
> is that a rotary wing or fixed wing aircraft in unaccelerated flight is
> displacing a mass of air equal to its weight, i.e., it is not flying
> because of low pressure above the wing but because of the upward force
> on the airfoil from the displacement of air downward. True?

It's not an either/or situation. Both are true. It flies because of the
low pressure and the low pressure (among other things) directs air
downward.

> Russell Thorstenberg
> Houston, Texas

--
Alan Baker
Vancouver, British Columbia
"If you raise the ceiling 4 feet, move the fireplace from that wall
to that wall, you'll still only get the full stereophonic effect
if you sit in the bottom of that cupboard."

[Richard Lamb]

wright1902glider wrote:

> Now here's a simple 19th Century way to prove the point. Attach a
> length of yarn to the "lower" surface of a slow-flying plane. Watch the
> yarn and see what direction it takes in flight. Is it straight back? Or
> is it down? If air is indeed being forced downward by the wing,
> shouldn't we be able to see the results in the yarn?
>
> Harry
>

Thank you, Harry!

[COLIN LAMB]

"Attach a length of yarn to the "lower" surface of a slow-flying plane.
Watch the yarn"

Is this why they invented wing walking? How do I do that on a low wing
monoplane?

Colin

[[email protected]]

>This pushes and pulls on the rotor-blade control horns,
>constantly changing the pitch of the blade as it flys around in a
>circle. If you tilt the dinner plates forward, the blade flys at a
>lower AOA in the front 1/2 of the rotor disk than it does at the back
>1/2. Since its producing more lift in the back 1/2 than in the front
>1/2, the blade flies higher in back. Stay with me here. As the blade
>flies higher, its coning angle relative to the rotor head increases to
>a greater angle than it does in the forward 1/2 of the rotor disk..
>Therefore, its line of thrust relative to the fuselage is not vertical,
>but is actually inclined forward.

Except the swash plate is not inclined forward in forward
flight. It's inclined to the right in forward flight, if the rotor
turns counterclockwise as seen from above, as in most American
'copters.
The rotor is a gyroscope, and trying to tilt one edge of it
will result instead in tilting the edge 90 degrees away in the
direction of rotation, like any other gyro. The rotor blades reach
their maximum pitch on the left side of the machine, and the blades
reach their maximum flap at the rear, tilting the disc forward. The
advancing blade on the right has minimum pitch and the front of the
disc is lowest.This is a happy coincidence, since we also need a lot
more AOA on the retreating blade to partly make up for its much lower
airspeed through the air compared to the advancing blade on the right.
Assymetrical lift has to be dealt with or the machine will roll over as
soon as it move forward, so the retreating blade's higher pitched AOA,
the blade's small downward flap approaching the retreating side and
rising flap approaching the advancing side also contributes to AOA
changes, and the lead/lag hinges on many rotors allow the blades to
accellerate on the retrating side and decellerate on the advancing side
at and therefore reduce some of the airspeed difference. Symmetrical
airfoils are used to minimize vibration caused by center of pressure
changes with AOA changes.
Helicopters are a lot more complex than they seem.

Dan

[Al]

The 300 hp in the helicopter is moving it's wing fast enough to lift the
Helo. The
fixed wing engine is also moving it's wing fast enough to lift the aircraft.
The Helicopter itself need not move forward, so the lift appears vertical,
but the wing is indeed climbing at a shallow angle, just like the fixed
wing.

Al


"Don W" > wrote in message
. net...
> Can someone explain to me why 300HP applied to a large rotor
> at ~700 RPM is enough to lift a 2000lb helicopter straight up,
> but the same 300HP applied to a smaller diameter propellor
> at ~2600 RPM can not even come close to allowing a 2000 LB
> airplane to climb vertically?
>
> This is really bugging me. BTW, does anyone have any idea
> what the thrust produced by the propellor of the hypothetical
> 300 HP (say LYC-IO540 powered) airplane would be? Obviously
> the thrust produced by the 300HP helicopter exceeds 2000 LBs.
>
> TIA,
>
> Don W.
>

[Richard Lamb]

ELIPPSE wrote:
> Well, the way I hears it, the low pressure on the wing is produced by
> the Coanda effect as air travels up and over the wing, not because of a
> change of velocity.The velocity change hypothesis has been disproven
> over and over! The mass of air displaced downward is the result (read:
> reaction) to the air having clung-to and been moved around the surface
> by the Coanda effect. Lift is caused by a pressure difference, not the
> downwash. There is no such force as suction, and downwash doesn't
> generate lift.
>

http://jef.raskincenter.org/published/coanda_effect.html

scroll down to OTHER PARADOXES

[Don W]

Alan Baker wrote:

> Don W > wrote:
>
>>Can someone explain to me why 300HP applied to a large rotor
>>at ~700 RPM is enough to lift a 2000lb helicopter straight up,
>>but the same 300HP applied to a smaller diameter propellor
>>at ~2600 RPM can not even come close to allowing a 2000 LB
>>airplane to climb vertically?
>>Don W.
>
<snip>

>
> So if you go from rotor moving x mass per second at y speed to a
> propellor moving x/2 mass per second at 2y speed, then your power goes
> down by half from the change in mass, but *up* by four from the change
> in speed. IOW, move half the mass to achieve the same force and you need
> to use twice the power.
>
> Does that help?
>

Yes Alan, it does. I had just not thought of it that way. Now that
you point it out, it makes perfect sense. This is what I think you
said:

force = d (mv)/dt =>
force = d (m)/dt * d(v)/dt => force = d(m)/dt * (v1-v0)

In English: force is equal to mass flow rate times the difference
in velocity before and after the propellor.

Ek= 1/2 (mv^2) -and-
Power = d(Ek)/dt => Power = d(m)/dt * (v1-v0)^2

In English: Power is the rate of change of the kinetic energy of
the airflow which is equal to the mass airflow times the square
of the difference in velocity before and after the propellor.

Is that correct? If so, it says that for fuel efficiency you
want as big a prop as you can fit turning slow. That also makes
sense because the parasitic drag on the prop goes up as the
square of the blade velocity as well.

<big grin>

I think something fundamental just just clicked.

Don W.

[Don W]

Peter Dohm wrote:

> "Don W" > wrote in message
> . net...
>
>>Can someone explain to me why 300HP applied to a large rotor
>>at ~700 RPM is enough to lift a 2000lb helicopter straight up,
>>but the same 300HP applied to a smaller diameter propellor
>>at ~2600 RPM can not even come close to allowing a 2000 LB
>>airplane to climb vertically?
>>
>>This is really bugging me. BTW, does anyone have any idea
>>what the thrust produced by the propellor of the hypothetical
>>300 HP (say LYC-IO540 powered) airplane would be? Obviously
>>the thrust produced by the 300HP helicopter exceeds 2000 LBs.
>>
>>TIA,
>>
>>Don W.
>>
>
> I am not a helicopter guy, so please don't expect my to carry this thread
> very far; but I'll try at the most basic level.
>
> Lift as generated by throwing air downward in order to maintain the
> altitude, or the constant rate of ascent or descent, of an object is based
> upon a momentum equation--rather than an energy equation. Therefore,
> throwing twice as much air downward half as fast will support the same
> weight; but will require about half as much energy per unit time, or about
> one half the horsepower. Remember that horsepower is a measure of energy,
> or work, per unit of time.

This makes sense to me now.

> OTOH, in the case of an airplane propeller, we need to make the energy
> equation work--while the wings deal with the momentum equation. We can
> choose a wingspan appropriate for the intended weight and cruising speed and
> a wing area to meet our stall speed requirements, determine the expected
> drag in cruise, choose a propeller disk area and number of blades
> appropriate for reasonable efficiency in cruise, and match the result to an
> engine, and possibly a PRSU since the propeller disk area determines the
> diameter and the maximum RPM. Finally, determine that the available power
> can supply sufficient thrust for take-off and climb. Traditionally, small
> airplanes produce a maximum static thrust on the order of one fifth of their
> weight when tied in place, and much less in cruise. The propeller, of
> course, constantly transitions into new and undisturbed air and its
> efficiency improves from zero at the start of the take-off roll to an
> acceptable figure in cruise.

Nit picking here, but the propellor is actually doing a lot of work
even when the aircraft is not moving. It just does not translate
into useful work on the airplane. You are thinking of the work as
thrust * velocity (airplane) which is correct from the viewpoint of
the airplane, but not the system. The prop is moving plenty of air,
dust, leaves etc. although that does not help you get where you are
going.

> One size does not fit all.
>
> BTW, a 700 rpm rotor is pretty small and may be really inefficient--even by
> helicopter standards!
>
> I hope this helps.
>
> Peter

Yes it does. Thanks.

Don W.

[Don W]

Hi Colin,

I cant remember what the max rotor rpm on the R22 Beta is although
I have a few hours in them. I just make sure that both guages
stay in the green arc and that little light and the annoying horn
don't come on ;-).

Don W.

COLIN LAMB wrote:

>>BTW, a 700 rpm rotor is pretty small and may be really inefficient--even by
>>helicopter standards!
>
>
> The Schweizer 300 (formerly Hughes 269C) has a rotor rpm power on of 442 to
> 471 rpm. Power off range is 390 to 504 rpm. Esceed these limits and you
> are quite likely to break something.
>
> The Schweizer has 190 hp and gross weight is 2050 lbs.
>
> Colin
>
>

[Alan Baker]

In article >,
Don W > wrote:

> Alan Baker wrote:
>
> > Don W > wrote:
> >
> >>Can someone explain to me why 300HP applied to a large rotor
> >>at ~700 RPM is enough to lift a 2000lb helicopter straight up,
> >>but the same 300HP applied to a smaller diameter propellor
> >>at ~2600 RPM can not even come close to allowing a 2000 LB
> >>airplane to climb vertically?
> >>Don W.
> >
> <snip>
>
> >
> > So if you go from rotor moving x mass per second at y speed to a
> > propellor moving x/2 mass per second at 2y speed, then your power goes
> > down by half from the change in mass, but *up* by four from the change
> > in speed. IOW, move half the mass to achieve the same force and you need
> > to use twice the power.
> >
> > Does that help?
> >
>
> Yes Alan, it does. I had just not thought of it that way. Now that
> you point it out, it makes perfect sense. This is what I think you
> said:
>
> force = d (mv)/dt =>
> force = d (m)/dt * d(v)/dt => force = d(m)/dt * (v1-v0)
>
> In English: force is equal to mass flow rate times the difference
> in velocity before and after the propellor.
>
> Ek= 1/2 (mv^2) -and-
> Power = d(Ek)/dt => Power = d(m)/dt * (v1-v0)^2
>
> In English: Power is the rate of change of the kinetic energy of
> the airflow which is equal to the mass airflow times the square
> of the difference in velocity before and after the propellor.
>
> Is that correct? If so, it says that for fuel efficiency you
> want as big a prop as you can fit turning slow. That also makes
> sense because the parasitic drag on the prop goes up as the
> square of the blade velocity as well.
>
> <big grin>
>
> I think something fundamental just just clicked.
>
> Don W.

Looks correct to me, Don. Glad to have helped.

--
Alan Baker
Vancouver, British Columbia
"If you raise the ceiling 4 feet, move the fireplace from that wall
to that wall, you'll still only get the full stereophonic effect
if you sit in the bottom of that cupboard."

[Don W]

wright1902glider wrote:

> At the risk of opening up a huge can of worms, I have 2 questions and
> one statement:

Consider it opened ;-)

> 1. If a helicopter makes lift by displacing air downward with its
> rotor:
>
> Rotor blades are airfoil shaped (I've seen 'em) just like airplane
> wings. Therefore airplanes fly by displacing air downward with their
> wings? There's something wrong with your logic Sir Maxim. It would
> seem that we killed this theory about 104 years ago with Will & Orv's
> little wind tunnel. Recall, the flat inclined surface displaced more
> air than any of the airfoil surfaces as measured by the vane balance.
> However, it also made less lift than any of the airfoil surfaces at a
> similar AOA. Ergo, an airfoil makes lift not by displacing air
> downward, but by producing a condition where the air flowing across its
> upper surface travels faster, and therefore has less pressure, than the
> air flowing under its lower surface. Therefore, an airfoil wing does
> not "fly" by displacing air downward, but rather exploits a zone of
> differential pressure caused by a difference in the speed of the
> airflow. And since a helicopter rotor blade is a long skinny wing
> flying around in a circle, it produces lift just the same as an
> airplane's wing does. I can only think of 2 machines that fly by
> displacing air downward. Those would be ballistic rockets/missles, and
> the Harrier jet in vertical or hovering flight.

I'm not familiar with the particular experiment, although I have seen
the wind tunnel you are referring to. It is at the Air Force museum
in Dayton Ohio.

> 2. A helicopter glides forward on an inclined cushion of displaced air:
>
> A helicopter flies in a chosen direction due to the cyclic change in
> rotor blade pitch impatred by an inclined swash plate. What's a swash
> plate do? Well, imagine a doughnut smashed between 2 dinner plates. The
> dinner plates are fixed to the fuselage and do not rotate. The doughnut
> rotates at the same rate as the rotor head. When you tilt the dinner
> plates, you also tilt the doughnut. Now if the doughnut is attached to
> the rotor blade pitch-control horns by rotor blade pitch-change links,
> the links will go up and down relative to the fuselage as the tilted
> doughnut spins. This pushes and pulls on the rotor-blade control horns,
> constantly changing the pitch of the blade as it flys around in a
> circle. If you tilt the dinner plates forward, the blade flys at a
> lower AOA in the front 1/2 of the rotor disk than it does at the back
> 1/2. Since its producing more lift in the back 1/2 than in the front
> 1/2, the blade flies higher in back. Stay with me here. As the blade
> flies higher, its coning angle relative to the rotor head increases to
> a greater angle than it does in the forward 1/2 of the rotor disk..
> Therefore, its line of thrust relative to the fuselage is not vertical,
> but is actually inclined forward. A helicopter "pulls" itself forward
> through the air, more or less.
>
> 3. Rotor blades turning at 700 rpm vs. a prop turning at 2600 rpm.
>
> Well, helicopter rotors don't turn that fast. Most are somewhere in the
> 300-350 rpm range. A Boeing Vertol CH-47's rotors only turn at 255 rpm,
> or so I've heard. If I'm not mistaken, Hughes once built some kinda
> giant tip-thrust powered test-freak that had a rotor speed of about 16
> rpm. I've seen the videos, but I can't recall the name.

Rotorway's Exec 162F main rotor turns 520 RPM at 100%. The tail rotor
is turning 2600 RPM at 100%. I tried to find info on the Robinson R22
and R44 but didn't find it. IIRC it was in the same range. I would
expect that larger helicopters would use larger main rotors turning
somewhat slower to avoid supersonic tip speeds.

> Harry

Don W.

[COLIN LAMB]

Hi Don:

Yes, we are taught that if the rpm gets too low, we are dead. If the rpm
gets too high, the gearbox is blown. Keep the rotor in the green or you may
not walk away - and you have 1.75 seconds to drop the collective when the
engine quits in the Schweizer - even less in the Robinson.

But, where else can you pay $200 per hour to move one foot away from where
you started and work up a sweat doing it, all while having a big grin.

Colin

[Richard Riley]

Or, as a very good aero guy told me

"It is better to annoy a lot of air a little than to annoy a little air
a lot." :)

[Smitty Two]

So what am I missing in this? I can see there might be some cost, ground
clearance, and possibly vibration issues involved in putting a twelve
foot diameter prop on my RV. But hypothetically speaking, are there
other, perhaps more important, reasons not to make the prop bigger and
the engine smaller and slower?

[ELIPPSE]

Calling things which don't agree with your own notions "fairy tales" as
Denker does doesn't make it wrong. It's always easier to invoke
name-calling rather than to be able to demonstrate how something is
wrong; we have enough of that in politics! Anyone who has worked with
the Coanda effect can easily show, mathematically and demonstrably, how
all of what takes place in lift occurs, even the upwash ahead of the
wing. This whole idea that explaining lift based on lift's reaction,
downwash, rather than the action which caused the downwash, is the real
"fairy tale". So we have lift from Bernoulli, longer distance above to
below, circulation, and on and on.

[Bill Daniels]

This is a little like the reporter asking President Lincoln how long a mans
legs should be. "Long enough to reach the ground", the Civil War president
replied.

So, what are the problems with a big prop?

High tip speeds limit cruise performance.
Long landing gear legs.
Larger "P" factor.
Requirement for a PRSU if the engine is to turn fast enough to produce
reasonable HP.

On the upside:

MUCH greater eficiency
Lower noise - if the RPM is low enough.
Greater acceleration during ground roll leading to better short field
performance.
Better climb rates.

A big slow prop should be good for a STOL airplane (Glider tug) and maybe
not so good for a cruiser. If I wanted maximum range on minimum fuel and
wasn't too concerned about cruise speed, I'd look at something like a
touring motorglider with a big, slow prop.

Bill Daniels

"Smitty Two" > wrote in message
...
> So what am I missing in this? I can see there might be some cost, ground
> clearance, and possibly vibration issues involved in putting a twelve
> foot diameter prop on my RV. But hypothetically speaking, are there
> other, perhaps more important, reasons not to make the prop bigger and
> the engine smaller and slower?

[Richard Lamb]

ELIPPSE wrote:
> Calling things which don't agree with your own notions "fairy tales" as
> Denker does doesn't make it wrong. It's always easier to invoke
> name-calling rather than to be able to demonstrate how something is
> wrong; we have enough of that in politics! Anyone who has worked with
> the Coanda effect can easily show, mathematically and demonstrably, how
> all of what takes place in lift occurs, even the upwash ahead of the
> wing. This whole idea that explaining lift based on lift's reaction,
> downwash, rather than the action which caused the downwash, is the real
> "fairy tale". So we have lift from Bernoulli, longer distance above to
> below, circulation, and on and on.
>

There is a minor problem withe the "Longer on top" theory...


http://jef.raskincenter.org/published/coanda_effect.html

scroll down to OTHER PARADOXES

[Don W]

Hi Colin,

I was having a lot of fun in the Robinson until I made the mistake
of looking through the NTSB accident database. Wow! Those things
have a _much_ higher accident rate for the hours flown than
other helicopters. The main rotor loss of control accident rate
was 4x higher than the next worse helicopter (Bell 204).

(oddly enough, the Bell 206 had the lowest loss of control accident
rate for the hours flown at .015 fatal LOC accidents per 100K flight
hours.)

This is based on data taken from 1981 - 1994, and can be found
on page 12 of the following PDF:

http://www.ntsb.gov/publictn/1996/SIR9603.pdf

Scary stuff!!

Don W.


COLIN LAMB wrote:
> Hi Don:
>
> Yes, we are taught that if the rpm gets too low, we are dead. If the rpm
> gets too high, the gearbox is blown. Keep the rotor in the green or you may
> not walk away - and you have 1.75 seconds to drop the collective when the
> engine quits in the Schweizer - even less in the Robinson.
>
> But, where else can you pay $200 per hour to move one foot away from where
> you started and work up a sweat doing it, all while having a big grin.
>
> Colin
>
>

[Don W]

Smitty Two wrote:

> So what am I missing in this? I can see there might be some cost, ground
> clearance, and possibly vibration issues involved in putting a twelve
> foot diameter prop on my RV. But hypothetically speaking, are there
> other, perhaps more important, reasons not to make the prop bigger and
> the engine smaller and slower?

Smitty,

You just asked the $24 question that I am dying to find out the answer
to. Seems to me that thrust is thrust, and thrust is what makes
airplanes go fast, but I'll bet I'm missing something here, and someone
will set me straight.

Don W.

[[email protected]]

Don W wrote:
> Smitty Two wrote:
>
> > So what am I missing in this? I can see there might be some cost, ground
> > clearance, and possibly vibration issues involved in putting a twelve
> > foot diameter prop on my RV. But hypothetically speaking, are there
> > other, perhaps more important, reasons not to make the prop bigger and
> > the engine smaller and slower?
>
> Smitty,
>
> You just asked the $24 question that I am dying to find out the answer
> to. Seems to me that thrust is thrust, and thrust is what makes
> airplanes go fast, but I'll bet I'm missing something here, and someone
> will set me straight.
>
> Don W.

A larger, slower prop will provide better takeoff and
climb, but unless its blades are variable in pitch (as in a
constant-speed setup) your forward velocity will be lower in cruise.
You can't swing a large prop anywhere near fast enough to allow the
engine to develop its horses unless that prop has a low pitch, while a
smaller, higher-pitched prop will "slip" more easily at low forward
speeds. The smaller fixed-pitch prop compromises more easily.
WW2 fighters like the Corsair had huge props (14 feet or
so?) that turned at 1300 for takeoff and around 900 in cruise. The low
cruise RPM was necessary to keep the tip speeds within reason. A (tip
speed) squared plus B (forward speed) squared equals C (total tip
speed) squared. The prop's blade angles at the tip in cruise were more
than 45 degrees to maintain a workable AOA.

Dan

[Richard Lamb]

Don W wrote:

> Hi Colin,
>
> I was having a lot of fun in the Robinson until I made the mistake
> of looking through the NTSB accident database. Wow! Those things
> have a _much_ higher accident rate for the hours flown than
> other helicopters. The main rotor loss of control accident rate
> was 4x higher than the next worse helicopter (Bell 204).
>
> (oddly enough, the Bell 206 had the lowest loss of control accident
> rate for the hours flown at .015 fatal LOC accidents per 100K flight
> hours.)
>
> This is based on data taken from 1981 - 1994, and can be found
> on page 12 of the following PDF:
>
> http://www.ntsb.gov/publictn/1996/SIR9603.pdf
>
> Scary stuff!!
>
> Don W.
>
>
> COLIN LAMB wrote:
>
>> Hi Don:
>>
>> Yes, we are taught that if the rpm gets too low, we are dead. If the
>> rpm gets too high, the gearbox is blown. Keep the rotor in the green
>> or you may not walk away - and you have 1.75 seconds to drop the
>> collective when the engine quits in the Schweizer - even less in the
>> Robinson.
>>
>> But, where else can you pay $200 per hour to move one foot away from
>> where you started and work up a sweat doing it, all while having a big
>> grin.
>>
>> Colin
>>
>


When you finally find out what's really going on,
helicopters are about the scariest machines ever made.

Some argue - second to "nuclear reactors built by the lowest bidder",
but that doesn't detract much from the claim...

If they were not so - unbelievably useful -
they would never be built.

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

Rotor rpm decay rate is a function of rotor inertia.

Robinson R-22 grosses 1370 pounds.

At an average 3300 pounds gross, the Bell 206 over twice as heavy.
And Bell makes special comment on the 206 high inertia rotor system.
Turbine time too.

Even a die-hard fixed wing fanatic has to admit,
that's a hell of an airplane.


Have fun having fun!


Richard

[Peter Dohm]

-------------snip------------

> Better climb rates.
>
Quite possibly, but definitely steeper climb angles


> A big slow prop should be good for a STOL airplane (Glider tug) and maybe
> not so good for a cruiser. If I wanted maximum range on minimum fuel and
> wasn't too concerned about cruise speed, I'd look at something like a
> touring motorglider with a big, slow prop.
>

I agree completely,
Regrettably, I am still a bit of a speed freak.... ;-)

Peter

[COLIN LAMB]

The Robinson requires more training time than the Schweizer. I think I
calculated that you have about 1.75 seconds to go into autorotation in a
Schweizer if the engine quits, but less than a second in a Robinson. With
practice, the 1.75 seconds is a piece of cake. I have never flown a 206,
but they sound wonderful.

Going through the FAA rotorcraft book (free on the internet), there are 8 or
9 easy ways to get into trouble with a helicopter. The gyrocopter, on the
other hand, only has a a couple - and those can be remedied. However, the
gyrocopter cannot hover.

Colin

[Cameron Carter]

Well ,for ****s sake, I thought ducks were made of depleted mercury!

Cam

"ELIPPSE" > wrote in message
oups.com...
> Well, the way I hears it, the low pressure on the wing is produced by
> the Coanda effect as air travels up and over the wing, not because of a
> change of velocity.The velocity change hypothesis has been disproven
> over and over! The mass of air displaced downward is the result (read:
> reaction) to the air having clung-to and been moved around the surface
> by the Coanda effect. Lift is caused by a pressure difference, not the
> downwash. There is no such force as suction, and downwash doesn't
> generate lift.
>

[Cameron Carter]

When You look up, does gravity push?

Cam

[wright1902glider]

GET BACK IN THERE! 'YA DAMN WORMS!

Yea, rotor wash is real. I've been in it... under an AS Puma slow
orbiting just over wet pine trees, 100 ft. from a Bell 412, 212, 214,
206, 222, Boelkow 105C, AS AStar, AS Twinstar, Hughes 500C getting out
of a Bell 206-B3, Robinsin R44, Bell 206-L1, and numerous other
encounters that I can't quite remember over the years. My Dad was a
helicopter A&P.

Yea, a significant portion of the air surrounding a hovering helicopter
is moved downward, just as fixed-wing props throw back a pretty good
blast. So I guess it is possible that fixed wings do deflect some air
downward, though I've never felt it while flying hang-gliders. And
that's still not what makes wings work. Its one of the things that
makes them less efficient.

Wilbur Wright struggled with this very issue for months while
attempting to develop his propeller theory. And Wilbur's theory is that
propellers are not "screws", no or they fans. They're airfoils and not
rotating "aero planes". Not that you can't propel a plane or SkyCar
with a ducted fan, but thats reaction-thrust from my understanding. A
propeller is a wing traveling in a corkscrew path through air. Some of
the energy consumed by the prop makes lift and pulls the aircraft
forward. Some of the energy consumed by the prop pulls the air
backward. Developing a prop that puts enough energy into pulling the
plane forward and not just swishing the air around is the trick. Its
kinda like trying to turn a bolt with a wrench in space. Your arm can
turn the wrench in reference to you, or it can turn you in reference to
the wrench. In reality, space arms and propellers are pretty good at
doing some of both.

Wilbur and Orville used the largest props that would fit on their
airframe. In 1903 those were 8' 6" each and turned between 300 and 350
rpm depending on how hot the engine was. At an average of 8.56hp (the
engine only made 11.78hp for a few seconds dead cold), the twin props
produced an average of 96 lbs of thrust. or 11.22 lbs of thrust per hp.
Not bad on the first try.

Getting back to the original issue, here's another experiment. Hold a
peice of paper vertically. Grasp its lower edge with your thumb and
forefinger. Now let the paper drape over your wrist so that the free
edge hangs down and away from you. Now blow along the upper surface of
the paper. DO NOT let any part of your breath blow under the paper. See
what happens. Hmmmmmmm. What's holding that paper up? All of the air
that it, the sheet of paper, is throwing downward, all on its own,
because it instinctually "knows" that this is the correct behavior for
good little sheets of paper that get blown on? Hold your other hand
under the paper as you blow. Any air moving downward? And what's the
paper doing? Hmmm?

BTW, addressing my previous statement about AOA, some planes can
definately climb nose-down in upright flight. Amazing, but the B-52 is
one of them. I was reminded of this 2 days ago while watching the
Hitler Channel. Looks goofier than hell.

The original Wright 16" wind tunnel did not survive history. However,
the original balances and test airfoils did and are currently at the
Franklin Institute in Philly. Orville stored them in a box for years
and almost threw them out once. Thanks for shaking that box Orv. There
are numerous reproduction wind tunnels in museums. I'm planning to
build one myself. Nick Engler had blueprints for one on his website
http://first-to-fly.com/Adventure/Workshop/lift_and_drift.htm

Harry "rotor-ramp-rat" Frey

[Don W]

Hi Harry,

wright1902glider wrote:
> GET BACK IN THERE! 'YA DAMN WORMS!

;-)

> The original Wright 16" wind tunnel did not survive history. However,
> the original balances and test airfoils did and are currently at the
> Franklin Institute in Philly. Orville stored them in a box for years
> and almost threw them out once. Thanks for shaking that box Orv. There
> are numerous reproduction wind tunnels in museums. I'm planning to
> build one myself. Nick Engler had blueprints for one on his website
> http://first-to-fly.com/Adventure/Workshop/lift_and_drift.htm
>
> Harry "rotor-ramp-rat" Frey

I misunderstood what I was seeing at the Air Force museum. You
are correct that it is a 3/4 scale replica constructed under Orville
Wright's guidance sometime before WWII.

http://www.centennialofflight.gov/wbh/loc_wb_pdf/pdf_files/wind-tunnel.pdf

This link also refers to the balances and experiments you are talking
about.

Thanks for correcting me.

BTW, I think that the discussion about the way wings work
is fascinating although slightly off the original topic.

IIRC the diplacement of the air molecules around a wing can be
conclusively demonstrated by multiple smoke streams in a wind
tunnel, or by mutiple dye streams in a water tank. I remember
such demonstrations in the lab back at good ole Wichita State
U.

I've only got one such photo available right now, and it is on page
141 of "Fluid Mechanics" 5th edition by Ray Binder. It shows a
symmetric airfoil at approximately 20 degrees AOA. In the photo
_all_ of the smoke streams (e.g. both the ones above the airfoil
and the ones below) that are disturbed by the airfoil end up
lower than they started out. This shows that a symmetric
airfoil at positive AOA pushes the air below it down, and _also_
pulls the air above it down. The net result is a slight downward
displacement of a _lot_ of air including air that is ~2x the chord
away from the airfoil.

I'll try to see if I can find similar photos on the web because I
think it will enliven this discussion to the general benefit of all
the participants (including me).

Don W.

[Richard Lamb]

wright1902glider wrote:

> GET BACK IN THERE! 'YA DAMN WORMS!
>
Hi Harry,
snipped in places...
>

> Wilbur and Orville used the largest props that would fit on their
> airframe. In 1903 those were 8' 6" each and turned between 300 and 350
> rpm depending on how hot the engine was. At an average of 8.56hp (the
> engine only made 11.78hp for a few seconds dead cold), the twin props
> produced an average of 96 lbs of thrust. or 11.22 lbs of thrust per hp.
> Not bad on the first try.

96 pounds of thrust from 11 horse?

What did that whole rig weigh?



> what happens. Hmmmmmmm. What's holding that paper up? All of the air
> that it, the sheet of paper, is throwing downward, all on its own,
> because it instinctually "knows" that this is the correct behavior for
> good little sheets of paper that get blown on? Hold your other hand
> under the paper as you blow. Any air moving downward? And what's the
> paper doing? Hmmm?

But you Cheated!

Very localized pressure field resulted above the paper, and so what?

You sped up the air above the paper by blowing it.
(cheater)



> BTW, addressing my previous statement about AOA, some planes can
> definately climb nose-down in upright flight. Amazing, but the B-52 is
> one of them. I was reminded of this 2 days ago while watching the
> Hitler Channel. Looks goofier than hell.

BIG Lift Fairies!

[[email protected]]

>under the paper as you blow. Any air moving downward?

>>None directly below the paper. There *is* air moving down
behind the paper<<

Here is another interesting way to think about air and lift - stolen
from basic Chemistry.

Don't think in terms of flow but of "vibration" of the individual air
molecules. At any temperature above absolute zero there will be
movement, or "vibration" of the fluid molecules. With no "flow" the
probability of each molecule of air being in a particular place can be
visualized as a sphere of decreasing density. Around a solid body at
rest the impacts of these air molecules will be at a given even rate
all about the surface. The "pressure" exertided is the same at all
points. Move either the surface or the air molecules (induce flow) and
the relative shape of that variable density sphere will change with
respect to the surface and the average impact vector of each will also
shift . If there is a net difference in the "flow" about the solid
then there will also be a corresponding change of impact, and impact
average vector, of the air molecules about the solid . This leads to
an imbalance that results in varying pressure at each point and the
resulting movement of the solid.

Thinking this way it's possable to see how both Newton and Bernouli
explain exactly the same thing, just with different, but equal,
mathmatical models. Kind of like the different ways of mathmatically
expressing a simple line.

Thinking this way helps to "see" how density and temperature change
lift, how skin drag works, how the boundry layer is formed and even how
things like humidity and viscosity change things.

I've probably done a really poor job of describing how I visiualize
this so I may have confused things much more than I intended.
================
Leon "Brownian Motion" McAtee

[Peter Dohm]

> snipped in places...
--------------and snipped some more-----------
> >
>
> > Wilbur and Orville used the largest props that would fit on their
> > airframe. In 1903 those were 8' 6" each and turned between 300 and 350
> > rpm depending on how hot the engine was. At an average of 8.56hp (the
> > engine only made 11.78hp for a few seconds dead cold), the twin props
> > produced an average of 96 lbs of thrust. or 11.22 lbs of thrust per hp.
> > Not bad on the first try.
>
> 96 pounds of thrust from 11 horse?
>
Actually from the 8+ horsepower. Based on 1 horsepower = 1 pound of thrust
at 315 knots, the figure sounds like a reasonable static thrust value. The
thrust may have been a little less in flight.

> What did that whole rig weigh?
>

I vaguely remember reading something like 600 pounds, plus the pilot of
course. Orville and Wilbur were both small and slight, so the gross weight
was probably only a little more than 700 pounds...

[COLIN LAMB]

>At any temperature above absolute zero there will be movement, or
>"vibration" of the fluid molecules.

Does that mean the airplane will quit flying at absolute zero?

Colin

[Richard Lamb]

Peter Dohm wrote:

>>snipped in places...
>
> --------------and snipped some more-----------
>
>>>Wilbur and Orville used the largest props that would fit on their
>>>airframe. In 1903 those were 8' 6" each and turned between 300 and 350
>>>rpm depending on how hot the engine was. At an average of 8.56hp (the
>>>engine only made 11.78hp for a few seconds dead cold), the twin props
>>>produced an average of 96 lbs of thrust. or 11.22 lbs of thrust per hp.
>>>Not bad on the first try.
>>
>>96 pounds of thrust from 11 horse?
>>
>
> Actually from the 8+ horsepower. Based on 1 horsepower = 1 pound of thrust
> at 315 knots, the figure sounds like a reasonable static thrust value. The
> thrust may have been a little less in flight.
>
>
>>What did that whole rig weigh?
>>
>
>
> I vaguely remember reading something like 600 pounds, plus the pilot of
> course. Orville and Wilbur were both small and slight, so the gross weight
> was probably only a little more than 700 pounds...
>
>

700 lbs / 96 thrust = .137 - which is a wee bit below the .20 rule of thumb.

Might consider catapult launch?

[Peter Dohm]

"Richard Lamb" > wrote in message
link.net...
> Peter Dohm wrote:
>
> >>snipped in places...
> >
> > --------------and snipped some more-----------
> >
> >>>Wilbur and Orville used the largest props that would fit on their
> >>>airframe. In 1903 those were 8' 6" each and turned between 300 and 350
> >>>rpm depending on how hot the engine was. At an average of 8.56hp (the
> >>>engine only made 11.78hp for a few seconds dead cold), the twin props
> >>>produced an average of 96 lbs of thrust. or 11.22 lbs of thrust per hp.
> >>>Not bad on the first try.
> >>
> >>96 pounds of thrust from 11 horse?
> >>
> >
> > Actually from the 8+ horsepower. Based on 1 horsepower = 1 pound of
thrust
> > at 315 knots, the figure sounds like a reasonable static thrust value.
The
> > thrust may have been a little less in flight.
> >
> >
> >>What did that whole rig weigh?
> >>
> >
> >
> > I vaguely remember reading something like 600 pounds, plus the pilot of
> > course. Orville and Wilbur were both small and slight, so the gross
weight
> > was probably only a little more than 700 pounds...
> >
> >
>
> 700 lbs / 96 thrust = .137 - which is a wee bit below the .20 rule of
thumb.
>
> Might consider catapult launch?
>
>
In a way, they almost did--sending it down a greased slide....

Remember that they had nearly 12 HP when first started--which gave them a
decent start slightly down hill and into the wind. All in all, I agree that
the whole enterprise was a little crazy. I am glad they succeeded, and
further engine development must have followed quickly.

[[email protected]]

Some of you will remember this photo from Flying Magazine
years ago:

http://www.grc.nasa.gov/WWW/K-12/airplane/Images/downplane.gif

There's definitely something going on behind that airplane.
The vortices are clearly visible, and the downwash trench is plenty
deep. There's debate as to whether that trench is due to vortex action,
or if the vortices are a result of the downwash. In any case, lots of
air has been displaced, and if Newton was right, there has to have been
some sort of reaction.
The air flowing off a trailing edge is angled down slightly
with respect to the airplane's flight path. The layer over the wing has
more speed and therefore more net energy, and its momentum carries both
it and the lower layer downward.
Aircraft, both fixed and rotary winged, have been used to
prevent frost in orchards on clear nights by flying low over them to
drive down the warmer air above them.

Dan

[Smitty Two]

In article >,
T o d d P a t t i s t > wrote:

..
>
> There is one thing going on in this photo that should be
> acknowledged, no matter how you view it. The jet has
> significant nose up and has its engines pointed somewhat
> down. There is some contribution to the downward airflow
> from the thrust produced by those engines.
>

How do you know the plane is nose up if you don't know from where the
picture was taken? Personally, I can't tell much about the plane's
attitude in relation to the earth, its path relative to the clouds (i.e.
above or through,) nor its distance from the clouds at the moment of the
photo.

[Richard Lamb]

Smitty Two wrote:
> In article >,
> T o d d P a t t i s t > wrote:
>
> .
>
>>There is one thing going on in this photo that should be
>>acknowledged, no matter how you view it. The jet has
>>significant nose up and has its engines pointed somewhat
>>down. There is some contribution to the downward airflow
>>from the thrust produced by those engines.
>>
>
>
> How do you know the plane is nose up if you don't know from where the
> picture was taken?

By looking at it!

If that's a real photo, this aircraft has got some deck angle...

[Smitty Two]

In article . net>,
Richard Lamb > wrote:

> Smitty Two wrote:

> >
> > How do you know the plane is nose up if you don't know from where the
> > picture was taken?
>
> By looking at it!
>
> If that's a real photo, this aircraft has got some deck angle...

Fer christ's sake, not necessarily so, if the camera was at a lower
altitude than the subject plane. I, personally, do not know where the
camera was in relation to the subject, so I, personally, have *no idea*
what the plane's attitude was. And if you don't know where the camera
was, neither do you.

[Andy Asberry]

On Tue, 14 Mar 2006 22:26:39 -0800, Smitty Two
> wrote:

>In article . net>,
> Richard Lamb > wrote:
>
>> Smitty Two wrote:
>
>> >
>> > How do you know the plane is nose up if you don't know from where the
>> > picture was taken?
>>
>> By looking at it!
>>
>> If that's a real photo, this aircraft has got some deck angle...
>
>Fer christ's sake, not necessarily so, if the camera was at a lower
>altitude than the subject plane. I, personally, do not know where the
>camera was in relation to the subject, so I, personally, have *no idea*
>what the plane's attitude was. And if you don't know where the camera
>was, neither do you.


Well, if I remember training correctly, a plane that appears below the
horizon is at a lower altitude. This one is definitely below the
horizon. The angle of attack relative to the camera is about zero. I
believe the plane sliced the top of the cloud and is climbing toward
the camera plane. Climbing=increased deck angle?

[Richard Lamb]

Andy Asberry wrote:
> On Tue, 14 Mar 2006 22:26:39 -0800, Smitty Two
> > wrote:
>
>
>>In article . net>,
>>Richard Lamb > wrote:
>>
>>
>>>Smitty Two wrote:
>>
>>>>How do you know the plane is nose up if you don't know from where the
>>>>picture was taken?
>>>
>>>By looking at it!
>>>
>>>If that's a real photo, this aircraft has got some deck angle...
>>
>>Fer christ's sake, not necessarily so, if the camera was at a lower
>>altitude than the subject plane. I, personally, do not know where the
>>camera was in relation to the subject, so I, personally, have *no idea*
>>what the plane's attitude was. And if you don't know where the camera
>>was, neither do you.
>
>
>
> Well, if I remember training correctly, a plane that appears below the
> horizon is at a lower altitude. This one is definitely below the
> horizon. The angle of attack relative to the camera is about zero. I
> believe the plane sliced the top of the cloud and is climbing toward
> the camera plane. Climbing=increased deck angle?

Thought I saw some of the bottom of that wing!

[Smitty Two]

In article et>,
Richard Lamb > wrote:

> Andy Asberry wrote:
> > On Tue, 14 Mar 2006 22:26:39 -0800, Smitty Two
> > > wrote:
> >
> >
> >>In article . net>,
> >>Richard Lamb > wrote:
> >>
> >>
> >>>Smitty Two wrote:
> >>
> >>>>How do you know the plane is nose up if you don't know from where the
> >>>>picture was taken?
> >>>
> >>>By looking at it!
> >>>
> >>>If that's a real photo, this aircraft has got some deck angle...
> >>
> >>Fer christ's sake, not necessarily so, if the camera was at a lower
> >>altitude than the subject plane. I, personally, do not know where the
> >>camera was in relation to the subject, so I, personally, have *no idea*
> >>what the plane's attitude was. And if you don't know where the camera
> >>was, neither do you.
> >
> >
> >
> > Well, if I remember training correctly, a plane that appears below the
> > horizon is at a lower altitude. This one is definitely below the
> > horizon. The angle of attack relative to the camera is about zero. I
> > believe the plane sliced the top of the cloud and is climbing toward
> > the camera plane. Climbing=increased deck angle?
>
> Thought I saw some of the bottom of that wing!

Yeah, seeing the bottom of the wing is a dead giveaway that an airplane
is climbing, regardless of the observer's attitude with respect to the
earth or the other plane. I guess I missed that day in ground school
when they told us that all planes above us (bottom of the wing visible)
were climbing and all those below us (top of the wing visible) were
descending.

And I thought I was in a roomful of pilots. Who needs an AI and all that
other junk anyway, when you can just look out the window at the clouds
and tell what's going on? Sheesh.