Overture Boom 2

[TugboatEng]

I wanted to put this in one of the aerospace groups but I'll let those stay technical.

Is my understanding correct that aerodynamics and flight characteristics don't scale? I know this is true for boats in water. If my understanding is correct, building small flying models does not contribute to knowledge of the full scale aircraft.

It seems that Overture is burning their budget building small test aircraft to prove concepts that were well understood 60+ years ago.

Maybe this is a failure in the making.

 

[3DDave]

Test results do scale but results require corrections for temperature and density and, of course, scale. One of the major reasons is to validate the design methods.

Ever been to the David Taylor model testing basin? They test tiny ships and racing yachts, among others, there. It's at the Carderock Division of the Naval Surface Warfare Center. I visited there when I was a little kid and later in high school.

Scaled Composites, founded by Burt Rutan, is in business on just that premise.

The Overture claim is that they are building an aircraft that produces a smeared sonic signature, more of a sustained thud than the sharp crack of the typical sonic boom. This is novel in aviation and is to overcome the previous primary reason for resistance to supersonic flight over inhabited areas.

OTOH, it fails to overcome several economic problems with supersonic flight and for that reason it is very likely to fail in the commercial passenger market. Over the last several decades passenger jets have been going slightly more slowly; this is to maximize efficient operation of the ever larger turbofan engines. When the whole market is saying that a few percent slower is worth a cheaper ticket/ticket prices rising more slowly, then having a faster plane with a much larger ticket price seems like the wrong direction.

Maybe they have a bunch of billionaires lined up, the way they line up for super yachts.

The killer is they need a supersonic capable engine and that is going to be expensive. They appear to be developing their own; little different than the approach of SpaceX.

However, looking at the rest of what they have done - it's impressive, not the vapor that other aviation startups exist on. They have apparently built an actual demonstrator, have working designs for critical systems. I would expect the endgame is to either have the plane they want or to have significant design work that Airbus or Boeing would want to buy the company to get. Example:

Force-feedback sidesticks. For the first time on an airliner, force-feedback sidesticks allow pilots to control the plane while physically feeling both aircraft response and inputs made by the co-pilot or autopilot.

The lack of force feedback between the pilots was partially blamed for the crash of AF447 where the two pilots were giving vastly different inputs into the controls.

One thing supersonic operation leans towards is a narrow fuselage. I've been in a Concorde; the interior was rather cramped with little room for carry-on bags. I think the Concorde was larger and still only managed 2 - 2 seat arrangement.

https://www.cnet.com/pictures/look-inside-concorde/17/

 

[3DDave]

According to this:

https://simpleflying.com/concorde-vs-boom-overture/

The eventual target will be larger than Concorde but hold only 80 passengers to Concorde's 100.

After the demonstrator they expect "building a premium 55-seat airliner, longer and thinner than Concorde" which seems a reasonable goal.

Emphasis on this planes, as it is for almost every successful aircraft, is the engine comes first. If they can get a decent engine they will work out. The initial Mustang fighter plane had rather pathetic high altitude performance and was generally inferior until the US got licensed to built the Merlin engines of Rolls Royce design.

Get an engine that is cheap enough reliable enough and performant enough to drive this in supersonic flow - at least technically it's a success.

At this point the failure doesn't look like it will be on the engineering side of the company.

 

[Brian Malone]

Your question seems technical and appropriate for the Aero forums. Some aspects of scale airplane models must scale. Wind tunnel testing is still integral and essential to modern aircraft design and development. BAE Systems touts their wind tunnel expertise and services; NASA Glenn Research Center does the same. Sub-scale models of aircraft are common especially in the research fields. NASA uses them. I would be surprised if other aero companies don't.

 

[Brian Malone]

3Ddave has this covered. !

 

[3DDave]

A correction - Boom isn't going for sonic smearing; just going to avoid supersonic flights over inhabited areas like Concorde did; the main savings is, go figure, lower speed to cut fuel consumption. Someone is trying the sonic smear but I see no one has left model testing.

 

[Alistair_Heaton]

BAe still has the facilities.

There are various universities round the UK still have Mach tunnels.

And they are still being used.

The main issue is they are all full of none civilian projects for years.

 

[GregLocock]

Aero does scale, but different aspects scale differently. F1 is limited to 60% scale models, but these are distorted compared with the full size design in order that the interactions between the different surfaces is correct. The other thing you can do is use the scale model to validate your CFD, and then predict the performance of the full size vehicle in CFD with more confidence.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[dik]

I seem to recall that with scaling, the Reynolds' number doesn't scale well... This was from 60 year old work in hydrology...

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[btrueblood]

Not a failure, at least not technically, as 3D says. Scalability works if you can analyse the scale model with confidence, it gives support for full scale analysis, as Greg says.

The "smeared shock" efforts mentioned by 3DDave are best exemplified by the NASA X-59 plane. The plane has been rolled out and work is progressing towards a first flight planned sometime this year. More at NASA and Lockheed websites, but this was the most up-to-date article I found:

https://www.nasa.gov/aeronautics/nasas-x-59-progresses-through-tests-on-the-path-to-flight/

 

[3DDave]

"the Reynolds' number doesn't scale well..."

This is true. However the main reason for concern on Reynold's number is the prediction of the onset of turbulence. A main driver of the Reynolds' number is density, which is why incompressible regime testing can use tiny models of aircraft in water tunnels where the effects of density offset the change in the ratio of dynamic effects to viscosity effects.

I don't recall compressibility effects being much affected by Reynold's number but it's been a while since that was on a test. Compressibility is very driven by gamma and dynamic effects.

 

[FacEngrPE]

This document provides some of the history of the origin and use of variable density wind tunnels. Sorry the citation is too big to upload.

https://ntrs.nasa.gov/citations/19810023610[/URL]
Wind Tunnels of NASA, January 1, 1981, Page 15]

 

[drawoh]

...

OTOH, it fails to overcome several economic problems with supersonic flight and for that reason it is very likely to fail in the commercial passenger market. Over the last several decades passenger jets have been going slightly more slowly; this is to maximize efficient operation of the ever larger turbofan engines. When the whole market is saying that a few percent slower is worth a cheaper ticket/ticket prices rising more slowly, then having a faster plane with a much larger ticket price seems like the wrong direction.

I boasted a couple of years ago that I would write an article on WWII aircraft technology. The project has gotten well out of hand. One of my investigations is alternate history, and one alternate is no WWII. Basically, aircraft technology is driven by the airlines.

As you note, airlines have not gotten faster over sixty years. Turbofans are more efficient, less polluting, quieter and a bit slower. Three out of four ain't bad.

Question: Why should airliners get faster?

In Buster Keaton's movie The Navigator, they used an actual ship that was about to be scrapped, the Buford, launched in 1890. She cruised at 11[ ]knots, or 20[ ]kph, and would have needed eleven days to cross the Atlantic. In 1889, the Inman Line introduced the twin-screw ship City of New York, which could do 20[ ]knots, or 37[ ]kph, and needed six days to cross the Altantic. It's 1891 and you have a choice of ships. On a two-way trip, you save eight days. Speed matters.

Today, 500mph versus 550mph saves you hours. Does it really matter? Was Concorde an efficient transport resource, or just a fun way to spend ten thousand dollars? When you get ready to cross the Atlantic, air traffic control gives you a Mach number to fly at. This is based on you not colliding with anything. If you had the extra speed, how would you use it?

--
JHG

 

[TugboatEng]

The faster the airplane the more cramped of conditions I will tolerate. If you can get me where I want to be in 3 hours or less I'll tolerate being packed into a supersonic sardine can. I think Overture is after the wrong market. Then again, it seems a lot easier to get a few millionaires to squander their money on unlikely successes than it does to get many middle classers to do the same.

 

[hpaircraft]

The only business case that pencils out for this design is providing an extra hour and a half that oligarchs and CEOs can spend with their mistresses.

 

[TugboatEng]

They're bragging about slightly exceeding the performance of a Beech Baron...

https://supercarblondie.com/pilot-son-concorde-xb1-london-new-york-boom/

 

[3DDave]

Not really bragging - just pointing out the test program is moving along. There's a lot of work to go over all the results from each test and it may seem from the outside not much has happened since the last test flight. It's helpful to remind investors and potential customers that they are continuing to develop the aircraft.

They need to produce a complete flight envelope and this is part of that effort; one of the most important if they expect to take off and land.

 

[TugboatEng]

I understand the need to test aircraft at all speeds that it may experience, especially take off and landing speeds. The laughable moment is that the article sates that the airplane is nearing the completion of testing having achieved an airspeed or 277 mph at 10000 feet. The article was obviously paid for by the Boom team and it had nothing significant to say. That's a really bad sign.

 

[EdStainless]

The NASA test plane (I forget the number) is the sonic-smearing (thud) item.
I believe that the testing will start in late 25 or early 26.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[btrueblood]

Ed, it's the X-59, see my post 28 Aug. Testing is still supposedly slated to start this year, we'll see.