When designing an airplane meant to cruise at transonic speeds (or supersonic speeds), I heard that one should look at the isobars on the main wing in order to assess if the shape, sweep angle and other airfoil parameters are suitably chosen. I also read that the better configuration yields isobars that are parallel to the leading edge. I already know that there are several techniques to get the isobars aligned with the leading edge (area ruling, adapting the sweep angle, extra care in the design of the junction between the fuselage and the wing), but why is this configuration better than another one? What does it improve?
The aim of parallel isobars on the wing is to generate quasi two-dimensional flow.
Let's say, the layout is set. You shaped the wing in a way to 'force' the isobars to be parallel with the sweep - the entire span. You now (should) have the same pressure distribution in every single profile of your wing. This eases your calculations extremely!
I finally found several arguments to answer this question from different sources.
Sweep and Mach Number from Airbus
This argument is developed in an Airbus magazine from 1985. To grasp it it is important to understand the purpose of swept wing. By sweeping the main wings one introduces an angle between the leading edge of the wing and a line perpendicular to the fuselage axis. Let's consider two airplanes, one with swept wings (A) and one with straight wings (B).
One of the most important parameters is the Mach Number experienced by the wings. It is measured normal to the leading edge of the wing which means that for the two airplanes flying at the same Mach Number, the Mach Number seen by wings of (B) is larger than the one seen by the wings of (A). This allows to fly at higher speed because it delays the large increase in drag (drag divergence) and other effects linked to the Mach Number around the airfoil.
However, if the isobars on the wing are not aligned with the leading edge, they are following a less swept pattern which tends to reduce the benefits from the sweep angle of the main wing because the effective sweep angle is smaller and the Mach Number around the wing should not be computed normal to the leading edge but normal to the isobars close to the leading edge.
From a theoretical point of view it would even be better to have isobars not aligned with the leading edge but having a larger sweep angle. However this never happens due to boundary conditions at the root and the tip of the wing.
All this is also explained here.
Finally, this last source deals also with the matters but does not justify the need for the isobars to be parallel to the leading edge. It deals more with the shock on the wing and the ways to weaken it and thus reduce the drag.
When designing an airplane meant to cruise at transonic speeds (or supersonic speeds), I heard that one should look at the isobars on the main wing in order to assess if the shape, sweep angle and other airfoil parameters are suitably chosen. I also read that the better configuration yields isobars that are parallel to the leading edge. I already know that there are several techniques to get the isobars aligned with the leading edge (area ruling, adapting the sweep angle, extra care in the design of the junction between the fuselage and the wing), but why is this configuration better than
Another enthusiast question. I watch a lot of the National Geographic Channel's "Air Crash Investigation", for better or worse, and it seems accident investigators make tremendous use of the Cockpit Voice Recorder "CVR" and Flight Data Recorder "FDR" to determine the chain of events leading up to- or the root cause of an accident. One of the more recent episodes of ACI (Season 12 Ep. 13... beneath the mid-Atlantic. Even after the recovery, there were concerns one of the drives had failed. That ACI episode also mentioned that the Airbus A330-203 in that accident came equipped with a system
Here is a $C_L$ / $AoA$ curve that I took from Wikipedia. The better textbooks say that a stall is that condition in which a further increase in angle of attack will result in a reduction of lift. The point at which that transition happens is known as the critical angle of attack. Theoretically, sustained flight is possible at angles beyond the critical angle of attack - take a look at the chart. If the airplane can sustain level flight at point $A$, it can sustain level flight at point $B$. Is there a practical way that I can demonstrate sustained flight on the backside of the lift
When I extend my flaps to 10 degrees, what exactly is the 10 degrees measuring? Is this referring to the angle of the flap blades themselves, the new angle of the wing chord, the change in the new critical angle of attack or something else?
In aeroelasticity, there are three main phenomena that one should take care of: divergence, aileron reversal and flutter. Each of them has an associated speed at which the phenomenon might start to occur. During wind-tunnel tests it is possible to increase the flutter speed to have access to the divergence speed first by using some small masses smartly placed on the wing. This is due to the fact that usually flutter speed is smaller than divergence speed. Is it always the case for aircraft (without additional masses on the wing)? If not do you have any example? If yes do you have
I was flying on Porter Airlines and they had an info card about how similar the Bombardier (I still say DeHavallind) Dash 8 Q400s are to the Bombardier CSeries they have ordered are. There was a cool overlay photo to show relative sizes and shapes: Looking at that image, it got me wondering about the straight vs angled wing. Straight vs angled tails, etc. I get that a jet is faster than a turbo prop. Cseries cruise speeds are: Mach 0.78 (828 km/h, 447 kn, 514 mph) Dash8 Q400 cruise speeds are: 414 mph (667 km/h) 360 knots Those are pretty close and yet that is a pretty radical
On some Hawker Hunters, there is a zig-zag on the leading edge of the wing, as shown below. Why do only some Hawker Hunters have this feature, and what is it for?
There are a couple of American military aircraft (the retired F-14 and the B-1 come to mind immediately), that have variable swept wings. I know that they keep the wings full out (roughly perpendicular to the body) during take off and landing, and they have the wings swept back for high speed flight. But I've never really understood why? I assume that at lower speeds the wings out configuration creates more lift. But, why does sweeping the wings back help at high speed? For bonus points: how does the performance gain make up for the cost in weight and complexity created by having
Is it possible to rent a float plane with a private pilot's license? Flying floats is one of the main attractions for me to learn to fly. However, after some searching on the internet I can only find wheeled aircraft that are available for rent in my area. Am I missing something? Are there flying clubs or partnerships that have float planes available? I would love to fly floats but owning a seaplane is not in the cards for me at this point in my life.
Without getting into the mess of redesigning existing Flight Data Recorders, I have a simple proposal that I think would help in deep water crashes. I propose that several floating cushion sets... would help find water crashes sooner, but if you add a simple USB memory stick in the center, then have data similar to the current FDR's being fed into it, then finding one of the floaties would give... would be the wiring needed to connect to the main FDR or the nearby data splitter. But just putting a few in the tail section alone would end this madness of having to find FDR's on the seabed to get