How to properly design a VTOL/ADAV helicopter-plane?

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Re: How to properly design a VTOL/ADAV aircraft-helicopter?




by Christophe » 01/11/22, 11:14

The P180 I talked about a few days ago...its particularity is to have 30% (I think) of the lift that is created by the fuselage!

Pipistrels are also very good in terms of aero and finesse: https://www.pipistrel.fr/

These are planes with the extension of a quasi motorcycle glider (they also manufacture them), there is an electric version which must work much better than the Airbus e-Fan fire...

Screenshot 2022-11-01 at 11-13-38 Stage-Velis-electro-scaled.jpg (JPEG image 2560 × 1008 pixels).png
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Re: How to properly design a VTOL/ADAV aircraft-helicopter?




by Christophe » 01/11/22, 11:20

And if the, your, VTOL has a low ground speed (< 150 km/h), it will be necessary to consider the multiplane...

Even if there are things to complain about (especially at the end of the video where they transport a car...), this configuration seems to me not bad for short trips at reduced speed:

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Re: How to properly design a VTOL/ADAV aircraft-helicopter?




by Remundo » 01/11/22, 11:47

indeed Christophe, I am considering a bi-plane, but original. : Idea:

besides, I was going to talk about bi-planes soon,

and then later wingtip vortices.
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Re: How to properly design a VTOL/ADAV aircraft-helicopter?




by Remundo » 01/11/22, 15:09

A few words about bi-plane aircraft (and more generally multiplanes)

The principle is to multiply the wings, to the extreme as below

plane_quadriplane.gif
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For technical reasons at the beginning of aviation, the bi-plane became popular, as the Wright brothers' first aircraft was a biplane:

Wrightflyer.jpg
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The bi-planes have a popular success in the United States, but also in Italy like for example this copy of the Fiat CR. 42 Falcon

avion_biplane_falchi.jpg
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Some other concepts are considering longitudinal multiplanes like the SE 200 by SE Aeronautics this one :

avion_triplane_longitudinal.jpg
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Bi-plane aircraft have the advantage ofhave better lift and easier takeoffs, they are even appreciated in aerobatics, for their maneuverability, or for folklore because some venture on the wings in full flight.

Another feature is that the wings are shorter, so they flex less. In addition, they are often stiffened by trellises.

MAIS multiplane aircraft have greater drag, their smoothness is more mediocre. In particular with aubane wings, they overconsume when cruising. Care must be taken that one wing does not create turbulence degrading the lift of the other.

In an ADAV/VTOL approach however, this is not a possibility to be excluded. to facilitate the transition from helicopter flight -> airplane which requires lift at low horizontal speed.

In addition to aircraft wing configurations:
The Aircraftman
Wikipedia
The Mignet Formula
Presentation of high-lift devices
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Re: How to properly design a VTOL/ADAV aircraft-helicopter?




by Remundo » 01/11/22, 17:04

Christophe wrote:The P180 I talked about a few days ago...its particularity is to have 30% (I think) of the lift that is created by the fuselage!

This is something that interests me too.

the "tadpole" fuselage appears to be a good compromise between penetration in the air and lift generated.

fuselage_tetard.gif
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more according to this page of interaction.free.fr, this kind of profile would have virtues to maintain a laminar flow around the fuselage, and thus reduce drag.

In my opinion, the bottom of the "tadpole" fuselage should be flattened a little and the tail should be brought back to a low position to improve lift.

In the absence of a propeller at the nose of the aircraft, round the nose further to improve the Cx while increasing the volume in the cabin.

body_less_trainee.png
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Learn more about least drag bodies
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Re: How to properly design a VTOL/ADAV aircraft-helicopter?




by Christophe » 01/11/22, 17:58

Yes you want to re-invent the glider what... : Mrgreen:
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Re: How to properly design a VTOL/ADAV aircraft-helicopter?




by Christophe » 01/11/22, 18:01

Remundo wrote:and then later wingtip vortices.


Just close the biplane... 8)
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Re: How to properly design a VTOL/ADAV aircraft-helicopter?




by Remundo » 01/11/22, 18:42

it is planned too : Idea:
Christophe wrote:Yes you want to re-invent the glider what... : Mrgreen:

no, an ADAV, not specifically a glider

But as the ADAV is intended to fly in cruise like an airplane, some inspirations of the glider may be there.

On the other hand, not the wingspan of the glider which is a handicap when landing (large surface area required on the ground).

You also need a suitable cabin volume, the glider generally neglects that.
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Re: How to properly design a VTOL/ADAV aircraft-helicopter?




by Remundo » 01/11/22, 22:38

A few words about anti-vortex fins

At the end of the wing occur amusing phenomena, but harmful for the progress of the plane. Those are the marginal vortices.

First you have to explain the origin of this phenomenon : the wing progresses through the air, but the underside of the wing has a higher pressure than the top of the wing.

marginal_eddies.jpg
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Thus, marginally, air particles bypass the wingtip from the lower surface to the upper surface. The speed of the wing and the turbulent nature of the flow then generate vortices.

Even a small plane generates noticeable vortices

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One way to reduce wake vortices is to curl the wingtip to make it difficult for fluid particles to pass through; this gives fins (or fins according to the French term), but the Anglo-Saxon term winglet is the best known.

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here are some winglet ideas

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these wake vortices are far from negligible and dissipate part of the propulsive energy of the aircraft. Worse, they destabilize planes crossing the vortex of a preceding plane and can create accidents. The phenomenon is feared and monitored at airports.

Aerodynamically, the fin adds a little drag, but the decrease in swirl ends up being beneficial. Airbus after long hesitation, equipped its planes with fins and declares to reduce consumption by 3,5%, which is interesting thanks to such a simple wingtip addition. Boeing long before Airbus was talking about the same figure.

Note that the tips of the propeller blades are also affected by vortices

HeliceTourbillons.png
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and curved shapes at the end of the blade (raked wingtip) strive to reduce them.

helice_anti_tourbillon.jpg
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Re: How to properly design a VTOL/ADAV aircraft-helicopter?




by Remundo » 02/11/22, 14:29

Propeller propulsion


We'll start by thinking independently of the propulsion system about what creates advancement.

The principle is that of action-reaction: any force exerted by a body 1 on a body 2 simultaneously generates a reciprocal force exerted by body 2 on body 1, equal in intensity and in the opposite direction.

This is easy to imagine between 2 solid bodies, but it is not limited to solid bodies. The field which interests us is in particular that exercised by "the taking of support on a fluid".

You can lean on a fluid provided you accelerate it backwards.
Throwing momentum backwards will create a reaction force that pushes forwards.

propeller_propulsion.jpg
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We will reason on the figure above, where V0 is the upstream velocity of the device, and V1 the downstream speed of the device noted A.

For a slice of fluid of infinitesimal mass dm which passes through the device during the infinitesimal time dt, the fundamental principle of dynamics gives:
eq1.png
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By asking Dm = dm/dt the mass flow rate of fluid through the device (in kg/s), the force of the fluid on the device is quickly expressed
eq2.png
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This equation is also valid for a wind turbine, a wind turbine will brake the fluid with a speed V1 lower than V0, on the contrary in propeller mode, the device accelerates the fluid backwards and we have V1 > V0

if we remove the vectors, here is the expression of the force F fluid on the device, in reaction to his backward shuffling.

eq3.png
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Beyond the aerodynamic questions which have already been mentioned, it is also necessary choose a system that has a good propulsive efficiency.

Propulsive efficiency is in principle the ratio between 2 powers:
PA: the power received by the device, which is the product of the force on the device and the speed V0 of the device
Pcin: the kinetic power supplied to the fluid between the upstream and downstream of the device, which is Dm x (V1²/2-V0²/2)

Here are the resulting formulas:
eq4.png
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We will try to express very simply the propulsion efficiency of the device as a function of the speeds:

eq5.png
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so there appears a rather light formula: PR = 2 / (1+ V1/V0) that should be analyzed.

Contrary to intuition, the fact ofviolently accelerating the fluid will result in very poor propellant output, although the propeller force will be intense.

To fix the ideas, if V1 = 4 x V0, we have RP = 0,4 = 40%, 60% of the device's power is wasted.

Si V1 = 2V0 : RP = 0,66; it's better but not very good.

Si V1 = V0 : RP = 1 = 100%, the performance is ideal... but there is no longer any fluid force on the device!

We are therefore in a paradox or rather a compromise to be found: to have good propulsive efficiency, V1 must be close to V0, just a little above.

But if we take the force of the device F = Dm x (V1 - V0), we realize that we will have to increase Dm to keep the force.

In simpler terms, you will have to stir a lot of air, but without accelerating it much.

And technically, it amounts to having a large propeller, which stirs a large tube of fluid by accelerating it gently.


We will try toexpress propulsive efficiency from wing strength FA : where F is the helix force and A the section (in m²) stirred by the device.

As a preliminary, we can express the speed V of the fluid at the level of the propeller by equalizing the power which it applies to the fluid with the kinetic power recovered by the fluid.

eq6.png
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by simplifying the equations by Dm(V1-V0), there comes a simple formula:

eq7.png
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Speed V location of the fluid on the device is the average of V1 et V0

This will be used to calculate the mass flow rate of fluid Dm = A x ro x V where ro is the density of the fluid (in kg/m3):

eq8.png
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