TAKE OFF AND LANDING WITHOUT ROLLING (TOLWIR)
During the last poll performed on a population representing Cro-magnons, our ancestors, the question « In order to secure your survival would you rather: fly like a bird or run like a horse » was answered at 95% by « Fly* ! ».
*As the glorious French Air Force used to say « Rise up and conquer »
In this beginning of the 21st century, even though survival and more can be simply ensured by going to the nearest mall, if we take into account the traffic composed of automobiles circulating in the 2D world, it is easy to imagine that the answer would remain the same : « Fly* ! »
That’s why, in this beginning of the 21st century, it seems that a new idea to popularize the usage of aircrafts is quickly spreading across the planet. This way, you and I could vogue around in the 3D world.
In this article, we would like to present a new single place aircraft that uses NO rolling and NO rotary wing for take-off and landing: the Xplorair* PX200
*International patent approved
A brief State of the Art
On this illustration below you will find a sample of the technological breakthroughs capable of vertical lift off or very small rolling take-off:
Without contest, the most mature technology remains the rotary wing and more precisely the helicopter application. It is ranked high up in first place when discussing vertical take-off. The second place is occupied by the aircrafts using the reaction from fluidic thrust, flow deviated toward the ground. In this technology, 2 applications can be distinguished: those using a large flux with small speed (helicopters) [they have the best propulsion efficiency], or those mastering « small » flux but at very high speeds (jet or turbine engines) [they have the higher cruising speeds]. In both cases the technologies require very complex mechanisms and a closely controlled maintenance. Nevertheless, there might be a third principle to dig into, it is known since the beginning of the 20st century as: the Coanda effect, named after its Romanian finder, Henri Marie Coanda.
The Coanda effect?
First we would like to remind (sorry for the ultra experts in this domain!) that for a given profile there is a lift coefficient Cl (performing the work) and a drag coefficient Cd (dragging its feet), these two parameters characterize a wing. But, since no one or nothing is perfect after a certain angle of attack the wing loses its efficiency while the lift drops. On the picture to the left you will see one of the numerous solutions that was experimented on. It allows maintaining lift at high angles of attack and therefore higher Cl by sucking the layers of air flow on the suction face of the wing. This technology was abandoned for multiple reasons.
On the picture below, we can see that the flow remains « attached » to the suction face even though the angle of attack is high (in this picture greater than 70°, and can reach angles up to 130° based on NASA test results). The picture is a numerical simulation based on tests performed in a wind tunnel at l’ISAE-ENSICA.
These tests were supervised by sophomore students from the Fluid mechanics Department. They are a confirmation that the Coanda effect can be used efficiently to deviate high speed jet flows on high angles of attack.
The Xplorair PX200, vertical take-off and landing vehicle is built around this Coanda effect.
And the Thruster engine?
One of the applications of the Coanda effect was achieved by Boeing in the 70’s with the YC14. It allowed to reduce significantly the rolling distance (from 1500m to 900m) because the architecture generated a greater lift. The only inconvenience is that the specific architecture was relatively frozen and reduced the propulsion force, and therefore the cruising speed.
On these pictures below, we will note that the air deflectors spread the hot flow from the jet engines, allowing the flow to « wet » a maximum of the suction layer and therefore create a greater lift. This explains that, on the global view of the aircraft (to the left), we can see a removable surface deployed only during take-off and landing, this is a foreseen technology, by NASA for the year 2025.
The PX200 needs to solution the problem of « performance neutralization » where:
Greater lift = reduced cruising speed
The idea is to integrate a brand new engine in the wings, the brand name of this engine is deposited as the Thermoreacteur© (called Thermoreactor in this paper). The resulting architecture will allow us to better use the Coanda effect during the take-off and landing phases all the while insuring that this same Coanda effect does not « parasite » the high cruising speed.
Furthermore, the new propulsion system will respect the following specifications:
- 1- Generate a flux of high speed, high flow burned gas, through a jet pipe of box section. The exhaust section is adapted to wet a large surface of the suction face of the wing.
2- Display a compact geometry and therefore a high power ratio per volume unit
3- Generate a gain in specific fuel consumption of at least 20% compared to actual state of theart turbine engines.
4- Minimize maintenance requirements.
5- Most of all, be in line with the most progressive acoustic norms such as they are imagined for the years 2025/2030
At first sight there is enough challenge to this new development to send us “back to school” in order to answer all these specifications! Nevertheless, let us not forget that we are part of the aeronautic field of play... And we will show that there actually is a realistic opening toward a sky of possibilities.
First of all, our list of specifications requires a gain in specific fuel consumption. This field of studies is the playground to never seen before advances proposed by the countries on the western coast of the Atlantic Ocean. We will comment the illustration below available on the internet on the DARPA web-site:
The engine manufacturers daily feed off the Brayton cycle to design the actual turbine engines. But they also know that the thermodynamic efficiency is fairly low since 75% of the calories are evacuated in the atmosphere, participating in part to global warming, not talking about the kerosene consumption...
This is one of the reasons why the Humphrey cycle is in the spot light, the consumption gains announced by the DARPA are simply breathtaking. The illustration here under explains that for a compression ratio of 17, the thermodynamic efficiency gains are close to 15%.
Based on American experts, the specific consumption would be reduced by up to 30 or 50% ! Nevertheless for our study, we prefer to limit this gain to 20% indicated by all our simulations and other calculations performed as of today. We would like to mention that our technology designed to perform the Humphrey Cycle is very different from the one used by the American consortium Rolls Royce, Pratt&Whitney*, General Electric and Alliant Techsystems and their tens of millions dollar budget to design a prototype for the year 2014 !
The Thermoreactor technology
The technology aims at achieving the thermodynamic of the Humphrey cycle, in other words combustion in constant volume, in contrary from the Brayton cycle used by all the actual turbine engines where the combustion is at constant pressure (isobar). What is the advantage? For the same quantity of fuel, the Constant Volume Combustion (CVC) allows a greater increase in pressure than when using isobar combustion. The exhaust temperatures are also much lower...
For example, in the Brayton cycle, if the pressure after compression (called P2) is 5 bars it will remain sensibly the same throughout the combustion phase (not counting the charge loss or the combustion efficiency). On the other hand for CVC (Humphrey), if P2 is the same 5bars, the pressure at the end of the combustion (called P3) will be P3 = 6xP2 = 30bars !
We can explain this by mentioning that for isobar combustion the Cp (Specific heat at constant pressure) is the main parameter, whereas in a CVC the main parameter is the Cv (Specific heat at constant volume). When introducing the Mayer’s equation that gives Cp-Cv=r (r is 287 for the air), we show that the temperature will be much greater in constant volume (Cv) than in isobar (Cp) and in consequence the pressure will be much greater at the end of combustion in constant volume.
The basics are laid down, but in order to answer all the specifications listed above, we still need to « draw » the combustion chamber that will achieve this advantage.
The combustion chamber’s architecture is as follows:
The design of the Thermoreactor’s combustion chamber (patent deposited and published on the WIPO) can also be used in isobar mode when the valves are static in a nozzle form (upper illustration). In this mode the Thermoreactor can work as a classic combustion chamber. In the other mode, the valves are synchronized in rotation (lower illustration) to create the CVC. Of course the constant volume combustion will be used mainly during cruising for an aircraft application in order to satisfy the fuel consumption specification.
A few applications
We are aiming our efforts on the single place aircraft as our preferred application (« He who can do more can do less ») the given brand name of this project is the Xplorair© PX200 that stands for Personal Xplorair 200km/h. One of the advantages of the Thermoreactor is its compact size, small enough to be fitted within the wing. One Unit of Propulsion (UoP) has an outer geometry of 25cm x 10cm x 10cm; it will produce either a continuous power or a relatively modest pulsation power. During take-off or in continuous mode, one UoP develops a propulsive force of Fprop=170N.
Since we have decided to limit the total mass of the PX200 to 300 kg, we have planned to use a total of 20UoP within the front wings and in the back tail of the aircraft as shown on the picture below.
On this illustration of the PX200, 7 Thermoreactors are fitted in each of the front wings and 6 Thermoreactors are in the back tail. This adds up to 20 Thermoreactors developing, at take-off, a lift of 20x170N = 3400N.
To start, during take-off, all 20 Thermoreactors are activated to lift the PX200 during 4 minutes (1/15th hour) to a maximum altitude of 2500meters (the bio-fuels do not like « cold weather »). This represents a consumption of about 15kg of fuel for take-off. Then, during Cruise the consumption is about:
15 liters per 100 km at 200 km/h
Based on our last simulations in cruising mode, with a Cd between 0.025 and 0.030, only one Thermoreactor at the tip of each front wing will be sufficient to have the PX200 reach its 200km/h (55m/s). We also notice that having this blowing at the tip of the back wing allows us to not need Winglets...Furthermore, in order to reduce acoustic levels within the pilot’s cabin, all throughout the cruising, the engines will be activated in priority in the back tail.
Note: Of course, it is possible to reach higher peak speeds by activating more than 2 Thermoreactors. In these conditions, the maximum speed equation is: VMaxi # 140.(N)1/2 (km/h) with N = number of pairs of Thermoreactors activated .
Therefore if we activate all 20 Thermoreactors: VMaxi > 600 km/h! But of course beware of the consumption and therefore flight endurance....
About the concept of take-off and cruise
In take-off mode, the Thermoreactor is fitted within the front wings. The back wing and the lower wing rotate until the lower wing is positioned at the exhaust of the Thermoreactor’s nozzle, allowing the Coanda effect to take place. The jet of exhaust air is deviated toward the ground and insures lift-off not purely vertical but at a certain slanted angle. In a more general term this Take-off is WITHOUT rolling (TOLWIR*)
* Take Off and Landing WIthout Rolling