Shape of nose cones
Discussion
Why do subsonic passenger planes (ie a 747) have relatively blunt nosecones? wouldn't a concorde type point nose cone be more aerodynamic?
I realise that the length of the concorde nose helps with the trans-sonic shock wave dispersal before the leading edges of the flight surfaces, but i would still have thought that a pointy cone would be better that a blunt cone at 500 knots.
2 pics to illustrate
I realise that the length of the concorde nose helps with the trans-sonic shock wave dispersal before the leading edges of the flight surfaces, but i would still have thought that a pointy cone would be better that a blunt cone at 500 knots.
2 pics to illustrate
In terms of drag, the shape at the "front" of an object is actually way less important than the shape at the back!
Due to compresability effects, a blunt nose actually becomes effectively tapered as the air closer to to it slows down more and more. far more important is to obtain efficient pressure recovery at the back end, where the displaced air streams must rejoin.
And for commercial airframes, the most usable volume per any given size is important, hence wide body cabins packing as many passengers as possible into a given length (which is restricted by the airport facilities etc), again, naturally leading to a wide/blunt nose.
Once supersonic, the shape for min drag becomes complicated, as the air has no time to get out of the way, and hence high drag is caused by poor frontal shapes. Concordes pointed nose acts as the primary shock location for the entire rest of the airframe at M2. and it needed to have the primary flight data sensors well ahead of the airframe out of the shock cone to get accurate readings, required to control the inlets, engines and flight control surfaces, hence the long pitot boom on the end of the nose (compared to the short stubby ones sticking out the side of the 747 airframe someway behind the nose)
Then, we get to radar. Modern planes have lots of radar, for air traffic control and weather reporting, and generally that radar, not fitted to concorde, needs to be up front, and have a reasonable field of view, so a rounded radome is typically used.
Finally, we get to cockpit visibility. Concorde was poor for visibility, and needed a complex drooping nose to allow the pilots to see the runway. Modern widebody jets needs better visibility and lower costs, so the cockpit is set up front and often high up, something difficult to do with a long pointy nose.
So the answer is
1) they don't need pointy noses
and
2) There are lots of good reasons NOT to have one as well
;-)
Due to compresability effects, a blunt nose actually becomes effectively tapered as the air closer to to it slows down more and more. far more important is to obtain efficient pressure recovery at the back end, where the displaced air streams must rejoin.
And for commercial airframes, the most usable volume per any given size is important, hence wide body cabins packing as many passengers as possible into a given length (which is restricted by the airport facilities etc), again, naturally leading to a wide/blunt nose.
Once supersonic, the shape for min drag becomes complicated, as the air has no time to get out of the way, and hence high drag is caused by poor frontal shapes. Concordes pointed nose acts as the primary shock location for the entire rest of the airframe at M2. and it needed to have the primary flight data sensors well ahead of the airframe out of the shock cone to get accurate readings, required to control the inlets, engines and flight control surfaces, hence the long pitot boom on the end of the nose (compared to the short stubby ones sticking out the side of the 747 airframe someway behind the nose)
Then, we get to radar. Modern planes have lots of radar, for air traffic control and weather reporting, and generally that radar, not fitted to concorde, needs to be up front, and have a reasonable field of view, so a rounded radome is typically used.
Finally, we get to cockpit visibility. Concorde was poor for visibility, and needed a complex drooping nose to allow the pilots to see the runway. Modern widebody jets needs better visibility and lower costs, so the cockpit is set up front and often high up, something difficult to do with a long pointy nose.
So the answer is
1) they don't need pointy noses
and
2) There are lots of good reasons NOT to have one as well
;-)
davepoth said:
I have a good reason why. Consider the raindrop. It's soft - softer than the air that's hitting it once it's at speed - so the air pushes it into the shape that forms the least resistance. The air doesn't make it pointy.
Look at aircraft like the Brewster Buffalo, the Gee Bee racers and the early Grumman fighters. There was a mistaken belief in the early 30's that the teardrop was the optimum aerodynamic shape, the Mitsubishi A6M 'Zero' proved that theory wrong...
Compare the Grumman F4F to the later F8F and you can see the evoloution of a longer, narrower fuselage.
As for hypersonic nose cones, they are bulbous purely for thermal reasons. They keep the shockwave far enough ahead of the nose cone to stop it melting.
Tango13 said:
davepoth said:
I have a good reason why. Consider the raindrop. It's soft - softer than the air that's hitting it once it's at speed - so the air pushes it into the shape that forms the least resistance. The air doesn't make it pointy.
Look at aircraft like the Brewster Buffalo, the Gee Bee racers and the early Grumman fighters. There was a mistaken belief in the early 30's that the teardrop was the optimum aerodynamic shape, the Mitsubishi A6M 'Zero' proved that theory wrong...
Compare the Grumman F4F to the later F8F and you can see the evoloution of a longer, narrower fuselage.
As for hypersonic nose cones, they are bulbous purely for thermal reasons. They keep the shockwave far enough ahead of the nose cone to stop it melting.
The science behind that is that at subsonic speeds friction drag is the most important drag (assuming no turbulence) so the shape with the smallest wetted area compared to frontal area (the fineness ratio, effectively) is going to have the least drag at subsonic speeds, which is why a jumbo jet is blunt.
However, past the speed of sound pressure drag becomes more significant, so you want a higher fineness ratio, which is why Concorde was pointy.
Eric Mc said:
Tango13 said:
As for hypersonic nose cones, they are bulbous purely for thermal reasons. They keep the shockwave far enough ahead of the nose cone to stop it melting.
Yes, the blunt body principle - as seen on space capsules.
Eric Mc said:
You can even fly them to a certain extent. Both the Gemini and Apollo capsules had an offset centre of mass which allowed the descent path to be altered slightly - which in turn extended or shortened the flight patch profile.
I can imagine the astronauts shuffling across from one side to the other...
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