Ulm and light aircraft of the future

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Cuicui
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by Cuicui » 14/02/09, 13:38

chatelot16 wrote:what remains to be invented is to do in the same genre but easy to build

It is a real motor glider with air brakes, which can travel quickly and also make gliding with the engine cut to save fuel.
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Michel Kieffer
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by Michel Kieffer » 14/02/09, 15:31

Chatelot, side by side or tandem?

The fundamental equation is:

Equation: P.rh = ½.ro.v3 (SMT.Cfe + drag induced by lift)

At cruising speed, the drag induced by the lift is low compared to the SMT.Cfe product. We are therefore more interested in the SMT.Cfe product

See the explanations in the document " how to achieve our goals » http://cocyane.chez-alice.fr/aeronautique.html
See definition of these terms below.

Unlike the automobile, which references the aerodynamic efficiency coefficient (CEA) "Cx" to the frontal projected surface S, in aeronautics, we refer to the CEA "Cfe" to the wet surface SMT. However, the S.Cx product is identical to the SMT.Cfe product

So, tandem or side by side?

Insofar as the aerodynamics are correct (no flow of the boundary layer), the Cfe of these 2 config are identical, the difference will then be made on the SM of the fuselages. We deduce that the best configuration is that which leads to the minimum SM. Let's determine the SM tandem fuselage and side by side, well, we get pretty much the same thing. In one case, we are narrower but the fuselage is longer, in the other case we are wider but the fuselage is shorter.

Conclusion: in terms of aerodynamics, side by side or tandem, it's the same!

There remains a configuration that saves 10 to 14% of the fuselage SM: the side by side offset by 0,3m, which allows to significantly reduce the width of the aircraft without extending the fuselage too much. That said, 10% on the fuselage represents about 3% on the SMT (total wet surface), so nothing to revolutionize the subject ... We must act on other things.

Michel

Definition of the above terms:

Ro = air density = 1,2 kg / m3 (on the ground)
V = speed in m / s
SMT = total wetted area
SM = wet surface
Cfe = equivalent coefficient flat plate
m = mass
g = 9,81 m / s2
P = power in watts
Rh = propeller or propulsion efficiency
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by chatelot16 » 14/02/09, 16:20

thank you for these precision

so side by side offset!

anyway it has practical advantages: no need for 2 independent dashboards, simplification of orders

but I do not digest this story of S.Cx = SMT.Cfe

of course when we change the dimension cx remains constant if we change all the dimensions at once, and when all the dimensions change in the same proportion the frontal surface and the wet surface also change in the same proportion (squared)

but the notion of frontal area is useful because when we decrease it without changing the length we hope that the cx also remains constant: in general cx even decreases so the gain is greater than the decrease in surface

on the other hand when we decrease the wet surface by increasing the frontal surface we can be afraid that the smt increases

it's not even a fear, it's a certainty: when we take an arrow-shaped fuselage, if we transform it into a sphere of the same volume, we reduce the wet surface a lot but there is no chance that smt remains constant: it will increase more than the wet surface decreases

of course it is quite possible that badly screwed up tandem is less efficient than dimensions with a super profiled dimension

this notion of wet surface must be useful somewhere but it is not for the fuselage that it seems interesting

I will rather see the significant wet surface for the wings, or the frontal surface is not very significant
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by Michel Kieffer » 14/02/09, 16:26

Wing surface and / or elongation?

Table corner reasoning. In practice, everything is a matter of optimization between the parameters Sa, Cz, A, e, Cfe, SMT, ro, Rh, speed…

The power of an aircraft is used to overcome 1) parasitic drag and 2) drag induced by lift.

At high speed, 80 to 90% of power is absorbed by 1. How to reduce this drag? by seeking to have the best possible Cfe as well as the lowest possible SMT. How to reduce SMT? Compressing the crew is difficult, we then have the possibility of reducing the wing SM and therefore the wing surface (Sa). How? 'Or' What ? Develop efficient high lift devices to increase the lift coefficients (Cz) at low speed, which allows us to reduce the Sa.

At low speed, for example at minimum fall speed, 75% of the power is absorbed by the term 2. The power absorbed by the drag induced by the lift = Sa.Cz2 / pi.Ae
Sa = wing area
Cz = lift coefficient
A = elongation
E = Oswald coefficient

How to reduce these streaks?

If we want a fast plane (about 200 km / h) and not very greedy, we need good flaps (therefore a high Cz max) which must be compensated by a correct elongation. This is to avoid degrading the drag induced by the lift at low speed.

An MCR or the HKW (this is the name of our ULM VLA, we finally found it) are representative of this category. Ours being also optimized for low powers, ecology requires!

… And if we want a rather slow plane (about 140 km / h) and not very greedy, we must favor a low Cz max which imposes a rather high Sa. We also add a correct elongation so as not to degrade the drag induced at low speed too much. A high Sa implies that it is not necessary to have good flaps to maintain the 65 km / h.

Michel Barry's SOURICETTE or SOURIBULLE (no shutters but large Sa) represent this category of appliance.

Michel
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by Michel Kieffer » 14/02/09, 16:40

SMT.Cfe ... illustrations

First of all, let us reason S.Cx:
We have a given aircraft available in 2 versions: 1) thick wings 2) thin wings. In the first case, S (projected area) is high, in the other case, S is lower. We fly these 2 devices and we discover that their speeds are identical. Conclusion, aerodynamic efficiency (EA) is not influenced by S (projected surface).

Another example, we have the same aircraft in 2 versions: 1) short fuselage 2) long fuselage. We fly these 2 devices and we discover that their speeds are different despite identical S's. Conclusion, EA is disconnected from S (projected surface).

These 2 examples illustrate the inadequacy of the parameters S (projected surface) and Cx.

However, the above reasoning with the SMT.Cfe product works very well!

Michel
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by Other » 14/02/09, 17:08

Hello
chatelot16 wrote:
Cuicui wrote:Image
The Sinus, a high-performance Ulm: 210 km / h when cruising with reduced power.
View:
http://www.zenulm.eu/sinus_details.htm
See also Virus from the same manufacturer, with slightly shorter wings, fast cruising 240 km / h
http://www.zenulm.eu/virus_perf.htm


thank you: it shows that I do not dream it already exists

what remains to be invented is to do in the same genre but easy to build



Nice plane, but did you look at the price?
an average pilot works approximately 100 hours annually

Before building an airplane there are several things to consider
what use will the guy make, travel, shoot locally, muscular piloting? how many hours per year (to make 100 hours with the wrong weather, you have to go at least twice a week on voluble days and available.
A pilot who flies little very far becomes a pilot with little ability who will be caught on a short runway or on a return from a voyage in high wind, an airplane it takes several years to build it and 10 seconds to break it by a wind crooked
We must also consider the cost and the time available for construction, the place to do it, then comes the long construction (I built 2) then do the weights and centering (easy) do the tests and all the tests of maximum load and then establish the slimites maximum speed minimum takeoff distance minimum landing, try many propellers ect.

The advice I give to those who want to build is to prepare their choice according to use.
Ideally a guy should work for hours on different planes to find out exactly what he is looking for.
There is nothing more disappointing than the guy who builds an airplane thinking that he will learn to pilot it.
when he tries other planes he will regret having spent a long time in a model he did not know.
We don't build an airplane to fly, we build an airplane to fly it and we ask it for special qualities that we don't find on commercial airplanes.
No one is building a more economical Cessan 150 to buy it.

Andre
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by chatelot16 » 14/02/09, 17:49

fully agree

building before flying is the best way to build anything and be disappointed before you finish learning to fly

beautiful things like the previous image make me dream, but I do not even ask about the price anyway beyond my means

when I analyze the principles, it is to better understand what exists, and maybe possibly in a few years when I have finished something more down to earth, make reduced models radio controlled, equipped with good measuring instrument to serve prototype
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by Other » 15/02/09, 00:05

Hello


beautiful things like the previous image make me dream, but I do not even ask about the price anyway beyond my means


A virus like the photos above costs around 100000 Euros
An old Champion like this one 85hp engine costs 16000 Euro
it flies a160kmh and takes off a little longer, but for the price difference you can fly for many hours and it is much more robust than the Virus ..

Andre

Image
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by Capt_Maloche » 15/02/09, 00:18

Is this yours André? :D
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"Consumption is similar to a search consolation, a way to fill a growing existential void. With, the key, a lot of frustration and a little guilt, increasing the environmental awareness." (Gérard Mermet)
OUCH, OUILLE, OUCH, AAHH! ^ _ ^
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by Other » 15/02/09, 01:14

Hello
Capt_Maloche wrote:Is this yours André? :D

No it's not mine I had an identical one made a 950 hours
He was a guy who started coming to see me before buying a plane, at the beginning there was a discussion similar to that of the forum and he wanted to buy a racing car like Mustang, Quickie, I advised him to start with a conventional plane and this is the model he bought. I gave him his training on it, now he's buying another duck Quickie 2 photo above, he gained experience and is doing very well.

Mine is the D11 with a big engine it is the plane on ski photos above 2040 hours made with ..

Andre
End of January 2009 engine warm-up
Image
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