History, Politics And Current Affairs

LM put up an instagram story labelled Skunk Works, which flashed silhouettes of some well known Skunk Works projects such as the SR-71. Plus the two below. Are those something we know what they are? One of them looks like something hypersonic, the other a stealth combat aircraft design?

Top one is the X-59 QueSST ("Quiet SuperSonic Technology"). First flight is planned for sometime in 2023.
Not hypersonic, projected speed is around Mach 1.4.

James1978 wrote: ↑Sat Jul 01, 2023 9:36 pmTop one is the X-59 QueSST ("Quiet SuperSonic Technology"). First flight is planned for sometime in 2023.
Not hypersonic, projected speed is around Mach 1.4.

Beat me to it, so here's an article. Long nose doesn't really help at very high speeds.
Annoyingly I half recognise the other aircraft as well.

Pdf27 wrote: ↑Sat Jul 01, 2023 9:44 pm

James1978 wrote: ↑Sat Jul 01, 2023 9:36 pmTop one is the X-59 QueSST ("Quiet SuperSonic Technology"). First flight is planned for sometime in 2023.
Not hypersonic, projected speed is around Mach 1.4.

Beat me to it, so here's an article. Long nose doesn't really help at very high speeds.
Annoyingly I half recognise the other aircraft as well.

Of course you do, it was hidden in plane* sight.
(*cheap shot dad joke opportunity, so I wasn’t going to turn it down)

Article speculating about NGAD in relation to the second one:
https://www.thedrive.com/the-war-zone/s ... silhouette

Great article. Current airliners are flying at M0.9, and air travel is under attack from the usual suspects. Flying at M1.6 will use almost 4 times as much fuel, and reduce journey times by 40%. Sounds like a tricky marketing exercise.

warshipadmin wrote: ↑Sat Jul 01, 2023 11:11 pmGreat article. Current airliners are flying at M0.9, and air travel is under attack from the usual suspects. Flying at M1.6 will use almost 4 times as much fuel, and reduce journey times by 40%. Sounds like a tricky marketing exercise.

It's aimed at the private jet crowd - they're using vastly more fuel already, so the people doing this assume that they'll be happy to burn even more and lobby to clamp down on air travel for the masses so they can keep flying.

isn't the high-subsonic/transonic area (M0.8-1.2) actually draggier than low supersonic?

You can optimise the shape to move the peak Cd around, but you are still fighting v^2 so it looks a bit more of a peak on paper than it does in terms of thrust.

This shows the idea

https://aerodyn.org/files/drag/gifs/drag_rise.gif

Here's one with some actual aircraft which probably shows it more clearly. The B-70 is the only one where the Cd isn't clearly higher at all supersonic points.


The other side of things is the lift coefficient (Cl) - lost of your drag is directly tied to making lift, so you want to be operating in a region of high Cl/Cd.

Key takeaway here is is that there's a zone around (B) where with some careful design you can run at high Cl but the transonic rise in Cd hasn't kicked in yet. Essentially all subsonic airliners try to run in this region. Anything running supersonic has to deal with the poor Cl in region (E), even if the Cd is starting to drop a bit.
Note that this chart is for a classic aerofoil - delta wings work a bit differently, so I'd expect a different Cl chart for them. This would potentially explain why the B-70 was supposedly so efficient at high speed - in reality the transonic efficiency may have been very poor. I have half a memory of Concorde having the same problem - being unable to make it trans-Atlantic at subsonic speeds.

I hate to say it but my first reaction to the outlines was.... lawn dart

@pdf27 BZ, that's great data, is there a simple explanation for the B->C->D changes? I didn't do supersonic airfoils at uni, in fact what's the reason for the increasing Cl at low M?

warshipadmin wrote: ↑Wed Jul 05, 2023 12:15 am@pdf27 BZ, that's great data, is there a simple explanation for the B->C->D changes? I didn't do supersonic airfoils at uni, in fact what's the reason for the increasing Cl at low M?

Essentially what happens is that when you start getting into the transonic region (A-ish) you've got small patches of sonic air in parts of the wing (the top surface from memory). They give you locally better lift without really starting to build up shock waves, and this effect is strongest around (B). That's the condition in the top image above, and as you can see the air is quite curved going over the wing which is fundamentally where you get lift from.

As the speed increases you start getting this effect on other surfaces as well which reduces your lift, as well as increasingly strong shocks which increase drag. (C) will be the heart of the buffeting region associated with the Sound Barrier. This is the middle image above - you've got a very big shock wave being towed (hence high drag) and the air isn't being turned by the wing very much so you don't have much lift.

By the time you get to (D) you're more or less through it. You don't quite get the bottom image until you're fully supersonic, but it gets pretty close by the time you're at (D).

This is all my memory from 20 years ago (yeah, I'm feeling old now) so might be a big shaky, but I'm fairly sure the fundamentals are right.

Ah, Hmm. Thank you.