Ever heard of a Turbine-Based Combined Cycle (TBCC) engine design? It’s a pretty fun concept that can conceivably provide air-breathing propulsion from take-off to hypersonic speeds. Basically you combine a turbojet and a ramjet/scramjet—read this thread for more info... #AvGeek
First, why can’t you just use a turbojet to get to hypersonic speeds? There are many complications that limit the top speed and efficiency of a jet engine, most notably the elevated temperatures of high speed flight. But turbojets/fans are generally limited to Mach numbers ~2.5
What about rockets? Rockets will certainly do the trick, but there are the obvious issues that rockets are (usually) expendable, they are less efficient than air-breathing engines, you generally won’t use a rocket to fly subsonic, and there is probably more of a safety concern.
Enter ramjets and scramjets. These are air-breathing concepts that can operate up to M~7 (ramjet) and M~20+ (scramjet). There are no internal moving parts, just compression from shocks, then you light the exhaust almost like an afterburner. Fun! Image
One problem with scramjets/ramjets is it’s like “lighting a match in a hurricane” plus you need supersonic flow for them to start (really M>3). So aside from the technical challenges, if you’re parked on a runway with nothing but a scramjet you might as well walk. Image
Most scramjet tests have employed an air-dropped vehicle with a first stage rocket to get to supersonic speed
This is the reason for interest in TBCC engines. What if we could get moving to M~3-4 with a jet engine and then turn on a ram/scramjet? Then you could just about get into orbit (this has been proposed)! Image
The SR-71 almost used a TBCC depending on how you want to define things. The shared flow path diverted air between a ramjet bypass and the jet engine core. At the top speed of M~3.2 the ramjet was providing 80% of the thrust but technically the turbojet was still running.
In addition to the shared axisymmetric flowpath, there’s the crude version where you quite literally strap a ram/scramjet to the belly of a turbojet aircraft but in this design you’re paying a steep weight and drag penalty.
Will we see a full-on TBCC in the wild? Maybe—the SR-72 design is said to include a TBCC with a scramjet for hypersonic flight. The NASA X-43B would have used a TBCC. I know there are other concepts out there as well, so hopefully soon!


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Apologies to @mikeheil for taking so long to get around to this—up next will be RBCC engines (hopefully not quite so long of a wait!)

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More from @DrChrisCombs

Feb 5
Take that CFD nerds Image
From the Anderson hypersonics book Image
Read 4 tweets
Dec 14, 2023
So, if I understand correctly, it sounds like GE has successfully tested a turbine-based combined-cycle engine that incorporates: 1) gas turbine; 2) rotating detonation engine; 3) ramjet; 4) scramjet 🤯

Could in theory go from 0 to Mach 10+

Demo at full scale planned for 2024 Image
GE press release:

Some earlier reporting on the concept: geaerospace.com/press-release/…
aviationweek.com/shownews/paris…
Here's my explainer thread on turbine-based combined-cycle (TBCC) engines
Read 7 tweets
Nov 11, 2023
As we approach what may be a historic Starship flight test, this Reuters report is really, really bad

No excuses: as arguably the number one launch provider *in the world* the safety culture at SpaceX has to be better. They should be setting the standard (in a good way)

If we are going to continue giving them billions annually in taxpayer dollars, they can’t keep treating workers like disposable meat puppets


Image
And yes before you ask these numbers are much worse than industry averages Image
This is an absolutely total systematic failure that goes beyond SpaceX—NASA has some explaining to do about how they allowed SpaceX to operate in their own backyard allowing a > 20% injury rate Image
Read 4 tweets
Jul 10, 2023
If you're ever frustrated by someone with a PhD acting like a know-it-all outside their niche field of study, just remember that Albert Einstein tried to design an airfoil but it performed so poorly during testing it's flight characteristics were compared to a "pregnant duck"
HT to @milan_tomicc for reminding me of this the other day
For a bit more technical insight, bottom line is that Einstein designed this entirely using Bernoulli theory.

Stall at 12deg AoA @ 92 L/D

He later confessed he was "ashamed" and "this is what can happen to a man that thinks a lot but reads little"

Read 4 tweets
Apr 21, 2023
Am I being unreasonable in thinking that "clearing the launch pad" (that everyone knew would be destroyed) is a bit of a low bar for arguably the most successful launch company *ever*?

Sorry for having higher expectations for SpaceX?

The whole thing feels half-baked and rushed
I really want SpaceX to do well

We NEED SpaceX to do well

SpaceX has a great track record of success

There are tons of insanely smart, hard-working, talented people there

NASA needs Starship to put boots on the moon

So I expect more than what we got yesterday
When some brand new startup or a university rocket club sends their rocket into a death spiral at T+4min we all pat them on the back and say "space is hard" and "you'll figure it out"

I hold SpaceX (and NASA) to a much higher standard. SpaceX is better than this. It wasn't ready
Read 5 tweets
Mar 11, 2023
WE DID IT!!!

MOO-K SEVEN

HEIFERSONIC
I HAVE NO IDEA WHAT WE LEARNED BUT I'M EXCITED
Some quick notes about this images: first, this is from a technique called schlieren imaging and what you are seeing are density gradients in the flow. helps to visualize shock waves, expansion fans, etc.
Read 6 tweets

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