I think you’re wrong here and the wing sweep has nothing to do with it.
Try NASA descriptions of it, i do not invent anything but report on their own findings which dates from previous to X-1…
http://history.nasa.gov/SP-367/chapt5.htm
The question as to whether one may delay the drag-divergence Mach number to a value closer to 1 is a fascinating subject of novel aerodynamic designs. What this really suggests is the ability to fly at near-sonic velocities with the same available engine thrust before encountering large wave drag. There are a number of ways of delaying the transonic wave drag rise (or equivalently, increasing the drag-divergence Mach number closer to 1). These include
(1) Use of thin airfoils
(2) Use of sweep of the wing forward or back
(3) Low-aspect-ratio wing
(4) Removal of boundary layer and vortex generators
[110] (5) Supercritical and area-rule technology
http://history.nasa.gov/SP-367/chapt5.htm
The critical Mach number (at which a sonic point appears) and the drag-divergence Mach number are delayed to higher values; Sweepforward or sweepback will accomplish these desired results.
http://history.nasa.gov/SP-367/chapt5.htm
Figure 91.- Effects of sweep on wing transonic drag coefficient.
http://history.nasa.gov/SP-367/chapt5.htm
Cola
You have to be careful while showing graphs such as this one, people can easely simplify and think this is IT while it is not Critical Mach.
This kind of wave drag is minimal compared to what defines the Critical Mach and doesn’t really affects performances, it is a bow shock and these can occur in diverse places in the airframe, there is one in leading edges at supersonic regimes too.
It can cause nuisances to aerodynamicists though, with buffeting and other unwanted results on control surfaces.
The nineteenth century was also a time of experimental work on supersonic flow. Perhaps the most important event was the proof that shock waves were not just a figment of the imagination —they really existed in nature. This proof was given by the physicistphysician-philosopher Ernst Mach in 1887. Mach, while a professor of physics at the University of Prague, took the first photographs of shock waves on a body moving at supersonic speeds. Shock waves are normally invisible to the naked eye. But Mach devised a special optical arrangement (called a shadowgraph) by which he could see and photograph shock waves. In 1887, he presented a paper to the Academy of Sciences in Vienna where he showed a photograph of a bullet moving at supersonic speeds. Using his shadowgraph system, the bow shock and trailing edge shock were made visible (as shown below). This historic photograph allowed scientists, for the first time in history, to actually see a shock wave. The experimental study of shock waves was off and running.
http://history.nasa.gov/SP-4219/Chapter3.html
The Critical Mach is defined by the appearence of the compressibility effect running over (and under) the wing surface from leading edge to trailing edge, with associated creation of shock waves, respectively; start and end of the transonic region.
64 RESEARCH IN SUPERSONIC FLIGHT AND THE BREAKING OF THE SOUND BARRIER
http://history.nasa.gov/SP-4219/Chapter3.html
Wing sweep minimizes the area in the Mach scale where the effects of compressibility occurs (transonic, start higher in the Mach scale and ends earlier) as well as lowering pick drag coefiscient values in transonic and supersonic.
This is directly related to:
This.
May i ask the wingsweep of Su-27+, F-15C+, F-18, Gripen, MiG-29, F-35, and Tejas to complete my list ?
Thanks
Geeeeeee.
I’ll see what i can do, i got tons of doc to dig in and it might take time.
F-35 is 33* as previously quoted, I think Gripen is 45* though by memory I might have it wrong.
That of F-15 is 45* though its wing aerodynamic is a little particular…
No leading edge slats/flaps but a profile optimized for lowest possible wave drag at high speed and best possible turning performances at 30.000 ft.
These are design points responding to the requierement of the time.
Scorpion82
Su-27 was 42° and MiG-29 40°, for the rest I don’t know out of my head.
Thanks, seems consistent with their respective performances, considering they both use multi-shock inlets.
In the case of F/A-18 and F-18 previous to it, this is yet another special design (as F-104) it comes from Northrop experience with moderately sweep but thinner wings of the F-5/F-20 serie, they generally still had lower Mach built-in and the resulting flight envelop was also optimized for lower speed maneuvrability.
I can’t really find a figure for it but it is said to be 20* at quater chord.
Here is an interesting document from NASA.
This is the “simple” version but valid regardless, one can have an idea of the increased drag brought by a reduction of wings weep in transonic and supersonic.
http://history.nasa.gov/SP-367/chapt5.htm
For comparisons:
F-35 have a wingsweep of 33*, F-16 40*, F-22 42*, Rafale 48*, YF-22 48*, Typhoon 53*, Mirage 2000 58*.
This scale compares equal THICKNESS RATIOS but still give a very good idea of what to expect as transonic and supersonic performances, THICKNESS RATIOS also have an effect in drag.
http://www.hq.nasa.gov/pao/History/SP-468/ch10-4.htm
Figure 10. 12 – Conceptual effect of wing sweepback angle and airfoil-section thickness ratio on variation of wing drag coefficient with Mach number.
In the case of F-22, NASA defined a particular supercritical wing profile with for design point that “The lowest weight possible would be obtained with a common structural box design that uses variable surfaces on the leading edges and trailing edges to optimize the aerodynamic performances for transonic/supersonic cruise, and transonic maneuvers“.
http://www.nasa.gov/centers/dryden/pdf/88410main_H-1957V1.pdf
The team spent 6715 wing tunnel hours for low speed stability and control vs 4000 hours for high speed drag and S-C, and 5405 for propulsion aerodynamic.
From YF-23 to F-22:
Sweep angle is reduced from 48* to 42*.
Wing surface remains unchanged at 840 sq ft.
Wingspan increased from 43 ft to 44.5 ft.
Although not immediately apparent to the uninitiated observer, the external geometry of the F-22 changed significantly from the YF-22 prototype. Specifically, the wingspan was increased, the wing leading-edge sweep was decreased, the vertical tails were reduced in area and moved aft, and the horizontal-tail surfaces were reconfigured. These changes were considered significant enough to warrant specific tests of the F-22 in the same unique Langley facilities as the YF-22.
Highlights of Research by Langley for the F-22
http://oea.larc.nasa.gov/PAIS/Partners/F_22.html
Now call me what you wish but I can’t see any sign of an optimization for a higher Mach than YF-23 in F-22 aerodynamic features, quiet the opposite as it seems that everything was done to improve handling at lower speeds vs Maximum Mach.
The overall wet area increased as well as Critical Mach pick value.
“It’s funny how you permanently use 36kft as a tropopause altitude, which is actually a tropopause at standard atmosphere.”
Yes there is a reason I said that – because anything above 36kft and 20km+- has the same standard atmosphere temperature around -56 deg C… so we know that the Mach relation will be identical to the GS in that entire range. All we need to know is above 36kft and it comes down to the same thing. All A/C that we compare will fall in this bracket…
No it doesnt work this way at all.
AGAIN you still don’t tell things are they are.
Design are optimised for a given ceilling including inlets, engines and aerodynamics.
So comparing types at a standard altitude for which they aren’t optimised is not the correct way to it.
AGAIN we have non-standard standards.
Using this standard of yours, a Rafale reaches M 2.247 at the same altitude.
This means that your methodds manages to BLUR Design Maximas as well as Optimisation design points.
Airspeeds doesn’t give you the Maximum Designed Machs at the “same” altitudes.
Not for the airframe.
Not for the engine.
This is not the standard way to compute Maximum performances for flight-testing and the 1976 ICAO standard is there to help with the matter of comparison without resorting to flight-testing aircrafts at the tropopause.
You just got biten by just ignoring this.
Your point is fantasist and have for only purpose to validate a theory which is based on non-standard values, now would you mind providing us with a link to this interview please?
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