Propulsion of the Mars-based helicopter

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watheyak

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not trying to be 'that guy' but yup it is wrong (and they know).

Understanding how a wing generates lift isn't simple. The Bernoulli description is simple to show students or to use or in a website but kind of does a disservice because it isn't correct. Bernoulli is important for stall speed, laminar flow and drag, all important to aircraft designers but you don't create lift by it alone.

Airplanes fly with symmetrical airfoils, airplanes fly inverted, look at a 747, the inboard section of the wing is flat on the top and curved on the bottom, missiles fly with symmetrical wings all of these are opposite of how 'Bernoulli lift' would work. Lots of other examples out there.

better NASA page for lift https://www.grc.nasa.gov/www/k-12/airplane/lift1.html

Mike K

P.S. now figure out why the shower curtain pulls in not out.....
Well said. I taught flight students for many years. I'd go through simple demonstrations of Bernoulli and Newton, explain how it's really just Newton for simplicity's sake. Then I'd show them the real answer-

390141F0-2C68-41B4-A49F-71DD6A9DB62E.png


Also an over-simplification...
 

Blast it Tom!

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Well said. I taught flight students for many years. I'd go through simple demonstrations of Bernoulli and Newton, explain how it's really just Newton for simplicity's sake. Then I'd show them the real answer-

View attachment 463787

Also an over-simplification...
True, but you could've saved some space putting in matrix form! :p
 
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G_T

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Ok, so add a third reason - average air velocity inside the shower greater than outside the shower. Doesn't need to be a vortex BTW. Anyway, I'm not in the habit of taking cold showers!

If you dive even deeper, you might find electrostatic reasons as well.

Gerald
 

OverTheTop

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Airfoil shape-induced pressure differential results in upward force on the wing.
Correct, but it is a minor component of the force. Angle of attack produced most of the force. Having an airfoil helps (Mr Bernoulli's principle) and also keeps the airflow laminar (think efficient) to reduce power requirements.

Understanding how a wing generates lift isn't simple. The Bernoulli description is simple to show students or to use or in a website but kind of does a disservice because it isn't correct. Bernoulli is important for stall speed, laminar flow and drag, all important to aircraft designers but you don't create lift by it alone.
not trying to be 'that guy' but yup it is wrong (and they know).

Understanding how a wing generates lift isn't simple. The Bernoulli description is simple to show students or to use or in a website but kind of does a disservice because it isn't correct. Bernoulli is important for stall speed, laminar flow and drag, all important to aircraft designers but you don't create lift by it alone.

Airplanes fly with symmetrical airfoils, airplanes fly inverted, look at a 747, the inboard section of the wing is flat on the top and curved on the bottom, missiles fly with symmetrical wings all of these are opposite of how 'Bernoulli lift' would work. Lots of other examples out there.

better NASA page for lift https://www.grc.nasa.gov/www/k-12/airplane/lift1.html

Mike K
^^^This. Correct IMHO :).
 
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RocketScientistAustralia

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A helicopter blade is just a wing that rotates. It is the force generated by accelerating that mass of gas downwards that lifts the vehicle upwards. Equal and opposite. I seem to remember that even hovering a modest helicopter takes roughly 750kW of power to get sufficient mass flow.

On Mars the pressure is less than 1% of what we have here, so to accelerate enough mass to lift the chopper requires larger blades (diameters and width) and much higher RPM. Gravity there is only about 37% of what it is here, so that makes the task a little easier. If the vehicle has a mass of say 3kg, then on Mars it only needs a bit over 1kg of thrust (although it still has 3kg of inertia ;) ) to get it off the ground.
Whole lot of mixed units there. The mass of an object is not the same as the weight. Weight is through the action of gravity on a mass. The 3kg mass of the theoretical helicopter is still 3kg on any planet. The force required to lift a 3kg helicopter on Earth is 3x 9.8(gravitational constant for Earth)= 30 approx Newton’s. on Mars gravity is 1/3 so 10 Newton’s. 😀
 

OverTheTop

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Whole lot of mixed units there. The mass of an object is not the same as the weight. Weight is through the action of gravity on a mass. The 3kg mass of the theoretical helicopter is still 3kg on any planet. The force required to lift a 3kg helicopter on Earth is 3x 9.8(gravitational constant for Earth)= 30 approx Newton’s. on Mars gravity is 1/3 so 10 Newton’s.
Correct. I had thought of writing kilograms force for the lift, but kept is simple. A little too simple it seems :). Edited to improve clarity.
 

gtg738w

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Correct, but it is a minor component of the force. Angle of attack produced most of the force. Having an airfoil helps (Mr Bernoulli's principle) and also keeps the airflow laminar (think efficient) to reduce power requirements.
You can’t really say that shaping produces a minor component of the force. Anything moving through a fluid creates a pressure distribution on its surface and the net force & moment is the integral of that. Airfoils are just shapes that have more useful pressure distributions. That’s it, the forces are 100% from surface pressure. Doesn’t matter if it’s a wing, a rotor blade, a propeller or even a wind turbine. You can call it lift or turn your paper sideways and call it thrust. How you generate that pressure distribution is the secret sauce. Surface shaping and angle of attack both have significant effects.
 

OverTheTop

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Surface shaping and angle of attack both have significant effects.
Agreed, but as usual it is the application that determines which is more significant. For an aircraft wing it is usually the AoA and the dynamic pressure providing the lift. When you have an asymmetric airfoil wing that is close to zero AoA then it is the Bernoulli effect that produces more significant lift than AoA.

In rocketry we operate around zero AoA and either have no airfoils or symmetric, so lift is almost entirely produced by changes in AoA.

I think we are both on the same side of the fence ;).
 

rharshberger

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Agreed, but as usual it is the application that determines which is more significant. For an aircraft wing it is usually the AoA and the dynamic pressure providing the lift. When you have an asymmetric airfoil wing that is close to zero AoA then it is the Bernoulli effect that produces more significant lift than AoA.

In rocketry we operate around zero AoA and either have no airfoils or symmetric, so lift is almost entirely produced by changes in AoA.

I think we are both on the same side of the fence ;).
Sounded more like a conversation between Wilson and Tim Taylor....🤪
 

RocketScientistAustralia

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>>>>>----->

Are you referring to an African or European Swallow?

Zeke
Obviously it’s more expensive to swallow European beer in Africa and African beer in Europe. Apart from price and availability the African Swallow and the European Swallow are the same thing. Says so in the reading notes for my Big Blue Book. Or Red.
 

watheyak

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Obviously it’s more expensive to swallow European beer in Africa and African beer in Europe. Apart from price and availability the African Swallow and the European Swallow are the same thing. Says so in the reading notes for my Big Blue Book. Or Red.
And our Big Blue Books are proof that we've done plenty of field research into the matter.
 
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