Antonio wrote:
Afterburning is not the point: overall engine-airframe efficiency is.
I hear you and of course you are right. The discussion I was referring to was Concorde vs the TU144. Both had similar speeds but the TU needed the afterburners on all the time while Concorde did not, giving it the transatlantic range it had. I recall talking to Chris Orlebar (whose Concorde book is quite well known) about this and of course the factor with those two planes was that they were cruising at similar speeds, but the TU is significantly bigger. So yes, it is the overall engine-airframe combination which does the job. This does not change the fact though that in this case, the afterburning the TU needed, also because it’s engines were most probably not strong enough to keep the TU flying without them, caused a massively higher fuel flow.
Antonio wrote:
even on your Mooney, you may have the best engine efficiency at WOT, but depending on altitude and weight, WOT will not be the most efficient power setting of the airframe-powerplant combination.
Absolutely right. To figure out range/efficiency sweetspots for any airframe is something which is a pretty hard work but usually yields very unexpected results :) And WOT hardly ever plays into that where range is concerned, but almost always when speed is. It depends what you are looking for.
Antonio wrote:
Which one is more efficient?
I would say it will depend on which airframe they are fitted on :)
I have to say the Hermeus project looks quite interesting. Scram jet operation is not exactly new, but it also has a lot of potential. I will be watching out for them.
Antonio wrote:
Afterburning is not the point: overall engine-airframe efficiency is.
Let’s just say the thermodynamics of afterburning are really unfavorable. While you’re technically correct, an afterburner starts with such a design disadvantage that it’s unlikely to beat at efficiency an engine more suited to extract the same power with the help of a turbine.
Antonio wrote:
Which one is more efficient?
Without compensating for weight (and especially pax capacity), the comparison is not very relevant.
Hermeus’ goal is the practical application of large scale hypersonic piloted and non-piloted aircraft using efficient turbo-scramjet technology developed and funded entirely privately.
A certain amount of BS is to be expected in a project that has to cater for investors, present or future. There is more so in the former video than the latter.
The videos have been made by a third party but I am sure Hermeus had to approve them before they were released, and as a result of that negotiation process, the video producer managed to release some extremely interesting tech insight ( @Mooney_Driver will like the performance part by the Hermeus engineer) that would otherwise not have been readily available. I am grateful for that.
Unlike a lot of other projects, (boom and Aerion included) Hermeus is very practical about using low-cost, readily available, even run-of-the-mill , no BS hardware to demonstrate their technology concepts in the most efficient manner. They have excelled at that, demonstrating turbo-scramjet operation, and reasonable prototype progress including procurement of ten J85 and F100 engines and construction of a ground test “full”-scale taxi prototype with a very low budget of around $100m. Compare that with some of the budgets for similar NASA projects.
I am concerned at the high percentage of corporate BS in the videos 
Dan wrote:
most efficient
PLease dont try to convince us that you care about Carson speeds and the likes in your RV with your huge mpg and mogas…we know you don’t care unless you are trying to cross an ocean against a headwind :)
But yes, seriously it is a fascinating subject…some thinking along those lines in these videos , hopefully not too big of a thread diversion. The first one is along project description, the second one is probably more detailed, hands-on, interview
Antonio wrote:
but depending on altitude and weight, WOT will not be the most efficient power setting of the airframe-powerplant combination
Thanks for that @Antonio, this is a fascinating subject…
Having to balance a multiple factor of “time” aka “speed” against a factor “most efficient” in a supersonic design gotta be arduous to say the least
Mooney_Driver wrote:
without the power of afterburning.
Afterburning is not the point: overall engine-airframe efficiency is. Few people around here know more about performance than you do:even on a prop, even on your Mooney, you may have the best engine efficiency at WOT, but depending on altitude and weight, WOT will not be the most efficient power setting of the airframe-powerplant combination.
This requirement to look at airframe-powerplant-flight conditions in an integrated way is more the case on a supersonic or hypersonic aircraft. You can have an efficient afterburner like the well proven J-58 at Mach 3 or the modern version like Hermeus’ Chimera turbo-ramjet.
The 60-YO J-58 afterburning turbojet at Mach 3.2 used about 20000lbs fuel per hour (times two for the twin-engined SR-71)
Compare that with the more modern non-afterburning and even turbofan-engined Boeing 727 at similar weights with about 10000lbs/hr total for the three engines at mach .75
Which one is more efficient?
Antonio wrote:
NASA is working on a demonstrator that should dramatically reduce the sonic boom.That is also Boom’s idea.
You’ll forgive me for not holding my breath. Attempts to do this have been going on for decades, also in the military where stealth is a great thing.
maxbc wrote:
The fact that Boom is still burning money making prototypes after the Rolls debacle is a strong indicator of this.
Exactly. The art in this business is probably not how to actually produce something but how to make people believe you might just be able to pull off what everyone else has failed to do. Hope springs eternal and with it money.
Peter wrote:
VCs make money by getting on board a “ship” at a particular value point, and jumping off the ship at a higher value point.
Which is a well proven business model. Get the money, pay yourself a good salary out of it, then reluctantly retire once it’s clear it won’t work and start the next one.
LeSving wrote:
A larger aircraft would need at least 2 x PW/GE F100/F110 sized engines (F-15/F-16 engines),
There is one thing which gets forgotten often when talking of Concorde: The technological breakthrough which made Concorde viable was that it could sustain supersonic flight without having the reheats on! The TU144 never succeeded in that and hence its range was massively shorter than Concorde. In order to make one viable airframe, this will be one of the paramount challenges! You need a supersonic capable engine which can accelerate the airplane to SS speed and a wing and airframe which is capable of staying supersonic without the power of afterburning.
Also one bit which Concorde had to keep the Olympus engines happy was a variable inlet. This was another technological marvel which allowed to decelerate the air influx sufficiently that the engines would not choke on them. The Vulcan, which also used Olympus engines did not have these inlet vanes. But most probably you are right in that the most likely engine for a plane like that would have to come from the military. And maybe also get air to air refuelling capability, then maybe the military might be interested too.
All in all, Concorde was a totally wonderful airplane and probably the technologically and aerodynamically best airplane ever designed. Its technology and the cooperation between BAE and Sud Aviation was the foundation for today’s Airbus. Many technologies developed then found their way into later projects. Concorde was undoubtedly a masterpiece of excellence which should have been developped further and kept going. To replace it however is going to be very likely to reproduce the financial disaster Concorde became to it’s developers.
However, VCs make money by getting on board a “ship” at a particular value point, and jumping off the ship at a higher value point.
This is nothing to do with creating wealth or anything else but the process is a lot harder if the underlying idea is totally bogus. And VCs tend to know how to do the basic assessment process.
Peter wrote:
If what LeSving describes re the engine options is the whole story (and I have no reason to think it isn’t) then how can these projects get funding?
There is just so much money floating around today that I’m not even surprised. Even after last year’s Tech crash. Especially for silly ideas (but not only). Remember Virgin Hyperloop had raised about 500M$ total on an idea that you could prove impossible in less than 10s (because of basic physics).
The fact that Boom is still burning money making prototypes after the Rolls debacle is a strong indicator of this.
