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Oct 28, 2020, 10:25 AM
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aeronaut999's Avatar

Magic!


Quote:
Originally Posted by funfly2
'Leaf Blower-Powered' Vehicle:

https://www.youtube.com/watch?v=PY-4K4e5s6w
PS did anyone else notice the magical transformation of the wheels of the vehicle around 0:10?

PPS I wonder if he tried to see how fast he could go if he threw away the umbrella and simply aimed the leaf blower backwards?
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Oct 28, 2020, 10:38 AM
Launch the drones ...
Thread OP
Absolutely correct - lift never sucks.
Oct 28, 2020, 03:46 PM
An itch?. Scratch build.
eflightray's Avatar
Tornados never suck, they only push.

I don't think anyone ever said lift was just by sucking, but that lift include high and low pressure differences.

.
Oct 28, 2020, 04:08 PM
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Thread OP
Quote:
Originally Posted by eflightray
Tornados never suck, they only push.

I don't think anyone ever said lift was just by sucking, but that lift include high and low pressure differences.

.
Everything has high and low pressure diffs.

However - heavier than air flight - also has a Newtonian reaction to its action of accelerating air downward - a reaction we call lift.
Oct 28, 2020, 05:31 PM
Registered User
richard hanson's Avatar
If the air is accelerating downward I am amazed!
What causes the acceleration?
is it jet propelled
Does it finally stop accelerating?
Could it be that something just just pushed the air and it bunched up into a high pressure wave
Which had nowhere else to go
And maybe whatever shoved it, really didnt shove in the opposite direction
The result might be
Wait for it
A difference in pressure?
I have never seen air accelerate
Not even a fart
It is decelerating immediately upon release
Thank goodness!
Last edited by richard hanson; Oct 28, 2020 at 05:36 PM.
Oct 28, 2020, 05:57 PM
Launch the drones ...
Thread OP
Quote:
Originally Posted by richard hanson
If the air is accelerating downward I am amazed!
What causes the acceleration?
is it jet propelled
Does it finally stop accelerating?
Could it be that something just just pushed the air and it bunched up into a high pressure wave
Which had nowhere else to go
And maybe whatever shoved it, really didnt shove in the opposite direction
The result might be
Wait for it
A difference in pressure?
I have never seen air accelerate
Not even a fart
It is decelerating immediately upon release
Thank goodness!
I disagree ... for instance, if the air is accelerated by a turbo fan - and you redirect the exhaust but leave the prop part where it was before you redirected the exhaust ... the pressure diffs will not change around the props - BUT - the thrust is redirected.

Proving that pressure diffs have nothing to do with the reactionary Newtonian thrust created by the action of having accelerated all that air.

IOW ... In this example using turbo fans - you can keep the pressure diffs about the prop unchanged - while you change the thrust vector by redirecting the exhaust.

Simply redirecting the exhaust - is all you need to do - to change the lift vector - the props, and all their pressure diffs - they don't contribute to the lift vector. They only accelerate the air - where it goes - determines the lift vector.

Lift doesn't suck.

(And a wing ... is just a prop that isn't rotating.)
Last edited by Tim Green; Oct 28, 2020 at 06:03 PM.
Oct 28, 2020, 06:34 PM
Registered User
richard hanson's Avatar
I dig all that but the air is accelerating internally
Once unrestrained, it is decelerating
Last edited by richard hanson; Oct 28, 2020 at 07:07 PM.
Oct 28, 2020, 07:17 PM
Everything is broken
JimZinVT's Avatar
And in the case of the fart, diffusing.... surprisingly rapidly

Yes, I did notice the mop bucket magically attained low friction skateboard wheels and steerable trucks. Still, it seemed like he was moving faster than the thrust from an electric leaf blower might push him. I'd wager there were some off-screen cinematic liberties taken.
Last edited by JimZinVT; Oct 28, 2020 at 07:24 PM.
Oct 28, 2020, 08:03 PM
Registered User
Coupez's Avatar
Quote:
Originally Posted by Tim Green
... for instance, if the air is accelerated by a turbo fan - and you redirect the exhaust but leave the prop part where it was before you redirected the exhaust ... the pressure diffs will not change around the props - BUT - the thrust is redirected.
You've measured them?

Otherwise, how do you know this is true?
Oct 29, 2020, 06:11 AM
Registered User
Looks like he was getting the Death wobbles.
Oct 29, 2020, 06:15 AM
Registered User
Quote:
Originally Posted by richard hanson
If the air is accelerating downward I am amazed!
What causes the acceleration?
is it jet propelled
Does it finally stop accelerating?
Could it be that something just just pushed the air and it bunched up into a high pressure wave
Which had nowhere else to go
And maybe whatever shoved it, really didnt shove in the opposite direction
The result might be
Wait for it
A difference in pressure?
I have never seen air accelerate
Not even a fart
It is decelerating immediately upon release
Thank goodness!
Hate myself for getting back in to this,.

If an air molecule changes direction, does that count as an acceleration?
Oct 29, 2020, 06:43 AM
Registered User


Some Planes can POWERBACK on their own!! Here an MD80 (1 min 50 sec)

A pressure difference is created but it is the airstream force and direction that makes the plane move, brake, reverse and/or fly.


.
Oct 29, 2020, 08:26 AM
Registered User
Coupez's Avatar
Quote:
Originally Posted by funfly2
...it is the airstream force and direction that makes the plane move, brake, reverse and/or fly.
Based on that assumption, please why an increase in angle of attack makes a wing stall. By your theory it should just snowplow more air down...
Oct 29, 2020, 09:22 AM
Registered User
Quote:
Originally Posted by Coupez
Based on that assumption, please why an increase in angle of attack makes a wing stall. By your theory it should just snowplow more air down...
No it doesn't, for the same reason a stalled prop produces less thrust.

.
Oct 29, 2020, 09:41 AM
Registered User
richard hanson's Avatar
And a one anda two------


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