Re: Trainer Jet WIP
Posted: 06 May 2013, 14:39
Do it! You'll love it
So, moving swiftly onwards and upwards from that. A quick amount of research and testing suggested that the plane will be a 'mid-wing' configuration and not high or low because it carries many more aerodynamic advantages.
So we're now moving on to aerofoils.
So, the aerofoil is what gives the plane lift. It, like every other component is selected out of compromise based on certain factors, and a lot of the time it's not which shape generates the most lift. It can be the most benign stall conditions, the best lift-drag ratio, thickness for internal storage and so on. But all are selected because it generates the correct amount of lift at minimum drag when the aircraft is in cruise.
Here's the ones I have selected, known as NACA 6 digit aerofoils. The aerofoil needed a lift coefficient of 0.31, therefore I have selected NACA 641,412 as it generates a good amount of lift for minimum drag at the required coefficient. But, this may be too thick an aerofoil to carry over the entire length of the wing, so I have selected a slightly thinner aerofoil, 64A410 to be used at the wingtips, providing minimal drag for maximum lift across the largest speed range possible.
Wing Root. 641-412
Wingtip. 64A410
I've also needed to decide what type of high lift device is needed. For that I've picked out a leading edge slat, which delays stalling effects over the wing by providing fast moving air over the top surface through a slot. And a slotted flap, which provides a greater down wash, larger wing area and a higher angle of attack. The flap itself has its own leading edge slat to make sure it doesn't stall too soon.
The anatomy of the devices looks like this:
You can see the small 'slot' in front of the main flap, called the vane and how in theory it will re-accelerate air through the gap between it and the main flap
This has required a new program, called 'Ansys Fluent', to check the aerodynamics of the aerofoil. I include this because later on it ties in with 3D modelling. Here's some of the results.
Where this sequence of images show the stalling properties of the wing with the flaps down at increasing angle of attack, 10-14 degrees. The colour plots show the amount of turbulence indicating stalled flow.
These are unusual results; a stall develops over the rear section of the wing and is transitioned into strong wake turbulence at a higher angle of attack only to then re-develop. While there is a possibility of simulation error a likely cause could be the effectiveness of the flap vane at varying angles of attack, which is a significantly negative, delaying the effects of a stall. As a result with increasing wing angle of attack the vane will become more effective at providing clean air through the slot gap. This is shown in area A, where separation and turbulence originates from the main wing elements, but pushed away from the flaps where the slot gaps are positioned. While this may indicate that the maximum angle of attack possible is 13 degrees, it may still be firmly in a stalled condition. Pressure plots varying from 9 degrees upwards to 13 appear to confirm that in fact 11 degrees is the maximum usable angle of attack.
And some steamlines showing flow direction around the leading edge slat. If you look you can see a lot of circulation inside the slot gap until the aerofoil reaches a certain angle of attack. That's not good, requiring a redesign
Next up. The wing shape, and some...actually interesting looking simulations
So, moving swiftly onwards and upwards from that. A quick amount of research and testing suggested that the plane will be a 'mid-wing' configuration and not high or low because it carries many more aerodynamic advantages.
So we're now moving on to aerofoils.
So, the aerofoil is what gives the plane lift. It, like every other component is selected out of compromise based on certain factors, and a lot of the time it's not which shape generates the most lift. It can be the most benign stall conditions, the best lift-drag ratio, thickness for internal storage and so on. But all are selected because it generates the correct amount of lift at minimum drag when the aircraft is in cruise.
Here's the ones I have selected, known as NACA 6 digit aerofoils. The aerofoil needed a lift coefficient of 0.31, therefore I have selected NACA 641,412 as it generates a good amount of lift for minimum drag at the required coefficient. But, this may be too thick an aerofoil to carry over the entire length of the wing, so I have selected a slightly thinner aerofoil, 64A410 to be used at the wingtips, providing minimal drag for maximum lift across the largest speed range possible.
Wing Root. 641-412
Wingtip. 64A410
I've also needed to decide what type of high lift device is needed. For that I've picked out a leading edge slat, which delays stalling effects over the wing by providing fast moving air over the top surface through a slot. And a slotted flap, which provides a greater down wash, larger wing area and a higher angle of attack. The flap itself has its own leading edge slat to make sure it doesn't stall too soon.
The anatomy of the devices looks like this:
You can see the small 'slot' in front of the main flap, called the vane and how in theory it will re-accelerate air through the gap between it and the main flap
This has required a new program, called 'Ansys Fluent', to check the aerodynamics of the aerofoil. I include this because later on it ties in with 3D modelling. Here's some of the results.
Where this sequence of images show the stalling properties of the wing with the flaps down at increasing angle of attack, 10-14 degrees. The colour plots show the amount of turbulence indicating stalled flow.
These are unusual results; a stall develops over the rear section of the wing and is transitioned into strong wake turbulence at a higher angle of attack only to then re-develop. While there is a possibility of simulation error a likely cause could be the effectiveness of the flap vane at varying angles of attack, which is a significantly negative, delaying the effects of a stall. As a result with increasing wing angle of attack the vane will become more effective at providing clean air through the slot gap. This is shown in area A, where separation and turbulence originates from the main wing elements, but pushed away from the flaps where the slot gaps are positioned. While this may indicate that the maximum angle of attack possible is 13 degrees, it may still be firmly in a stalled condition. Pressure plots varying from 9 degrees upwards to 13 appear to confirm that in fact 11 degrees is the maximum usable angle of attack.
And some steamlines showing flow direction around the leading edge slat. If you look you can see a lot of circulation inside the slot gap until the aerofoil reaches a certain angle of attack. That's not good, requiring a redesign
Next up. The wing shape, and some...actually interesting looking simulations