In the development of the theme of ornithopters,
I would like to tell how you can solve such engineering problems with a high degree of uncertainty of the result.
And so, our flywheel is the largest such device on the planet. The nearest fully flying machine weighs 3 times less. How did the two young engineers manage to create an apparatus that many consider impossible? There is a certain algorithm for this, which is a compilation of classical engineering, TRIZ and personal experience.
1. Statement of the problem.
Most of the engineers involved in this task, sought to repeat the flight of birds or insects, or invent some absolutely incredible designs, very far from the principles of aerodynamics. The first approach is doomed to failure, since creating an adaptive wing like an bird's eye or an insect is an extremely complex engineering problem that cannot be solved at this stage of technological development. The second approach is primitive, since most of the proposed methods for creating aerodynamic forces have nothing to do with the laws of the environment.
In this regard, we have simplified the task and reduced it to the following: how to create the aerodynamic forces necessary for the flight based on the existing aerodynamic theory. It is based on the classical theory, deeply studying it, you can come up with something new. Based on the laws of subsonic aerodynamics, we were able to derive the flight equation of the flywright, which describes the field of possible velocities and masses in which such an apparatus can exist. This allowed to proceed to the next stage - modeling.
Cx, Su, Cf - coefficients of resistance, lift force of friction resistance, respectively (in the flywalk Cx - negative, since it is thrust)
coefficient And this is the coefficient of wing aerodynamic perfection (this includes elongation, MAR and shape of the tips)
vo is the ratio of flight speed and swing speed to 0.75 span of the console.
dalta_alfa and alfa_A are differential and amplitude wing angles (dynamic angles of attack)
2. Information and energy model.
To go from the general theory of flight to the design of a specific vehicle, we had to create a mathematical model of the movement of a wing segment — an infinite span along a harmonic trajectory. It sounds difficult, but if you simplify, the idea is to try to simulate exactly what parameters the wing must have in order to create the necessary forces for the flight. And here we used 2 models:
- model of an ideal wing (this is a model of a wing, where each section corresponds to the specified parameters)
- model of a hard or real wing.
These two models became the basis for determining the field of possible combinations of parameters, thereby reducing the degree of uncertainty in solving a problem many times.
The model itself is not a set of formulas written on a piece of paper, it is a mathematical algorithm with wide capabilities that allows you to estimate the range of parameters used, correct existing assumptions according to the experimental data obtained.
In fact, this model has the following structure:
- energy model is a model of interaction of the desired characteristics with environmental parameters
- information model - model of the relationship of parameters with each other.
Such models were created not only for aerodynamics, but the dynamics and design.
In fact, this is a kind of "time machine" that allows you to stay simultaneously at all stages of the project. Thus, the whole task comes down to the fact that through the improvement of the model, you begin to make predictions on the behavior of the real prototype model.
The more experimental data you get, the more accurate and better the prediction is. Such a dynamic model and allowed us to bring the flight model.
3. Experience and analytics.
The biggest mystery of the flywalker is its aerodynamics. As in the course of the experiment, we identified significant discrepancies between classical theory and test results.
The aerodynamics of the flywalker is an extremely difficult thing to understand and describe. Simply put - it is not clear how it flies at all.
And that's the thing:
If we consider the perfect wing (bird wing, as a standard), then it is capable in each of its cross sections to have its optimal characteristics, which allows them to spend energy very efficiently.
But if we take hard wings, like on our model, then the fun begins here. Most of the wing is in the area of stall, which is extremely unprofitable from an energetic point of view (high resistance and low lift), but if we look at the actual flight characteristics (direct measurements of thrust and lift), it turns out that time averages lift and thrust are quite acceptable (aerodynamic quality 10-12). Why so?
Here begins a completely different aerodynamics. You see, all modern aviation science is based on the fact that the aerodynamic plane is in a uniformly accelerated or uniform flow and the values of the aerodynamic coefficients are very stable. But if now we take a non-uniformly accelerated motion, then the air begins to manifest itself quite differently, the effect of the added masses manifests itself. What is the effect? Attached masses are conditional masses assigned to a moving object in order to correct its dynamic properties when moving in a viscous medium. However, it seems to me that this phenomenon can also be considered differently, that air, like water, is capable of exhibiting the properties of conditional viscosity increase during accelerated motion. Those. the air behaves like a non-Newtonian fluid, only it does not become “solid”, but becomes more elastic.
This phenomenon can reveal to us a completely different direction of aerodynamics, which is currently little studied (only in the area of the mach of the blade of the helicopter). There may be secrets to improve the aerodynamic characteristics of existing aircraft and the creation of fundamentally new methods of flight, such as waving.
It is a strictly scientific approach and the creation of an appropriate mathematical apparatus, as well as many, many hours of eliminating design flaws that allowed us to realize the flight.
In fact, this algorithm is applicable to absolutely any engineering task associated with the creation of fundamentally new things.