PSA: I’m writing A LOT about supersonics now, mostly because they’ve stalled int’l policy progress on aviation emissions for four years and could easily waste another four before failing. But don’t mistake my engagement as an argument that they’ll succeed. It’s what/if. (1/x)
The tech, economic, and regulatory hurdles to success are **immense**, particularly for commercial applications. And, as @jonostrower put it so well, we’re still in the “marketing and enthusiasm” phase. Just a few markers here; #avgeeks no doubt have their own. (2/x)
1) Insufficient capital, to date ~$240 raised vs by Boom’s estimated $6 billion needed. We don’t have details on how much United put in, BTW. (3/x)
2) Minimal airline support, currently JAL and United. Virgin Group was an early supporter but then decided to build its own, even beating @boomaero to the punch with its Rolls-Royce partnership. Funny how little you hear about that now. (4/x)
3) On that theme, no identified engine, only an agreement with RR to explore options (paraphrasing here). Building a supersonic engine is incredibly expensive, esp since the goal here is for a medium bypass turbofan w/o afterburners. First time through (5/x)
4) Difficult and price-sensitive market segment. Making the economics work for airlines is a huge lift, esp compared to business jet owners with deep pockets. Recall that @AerionCorp, which was ahead in partnerships and design in that easier BJ play, just went under. (6/x)
5) Sustainable aviation fuels — basically Unobtainium and too expensive for commercial supersonic applications anyway. Don’t @ me. (7/x)
7) No really just put your phone down on this. (9/x)
8) By all accounts, a fast commercial supersonic will burn 5x (ICCT) to 10x (MIT) more fuel per passenger as equivalent subsonics. That’s a huge fuel bill for airlines to eat, even independent of the climate damages. (10/x) theicct.org/publications/e…
9) The other atmospheric impacts of fast supersonics could be serious — up to 20x more damaging than subsonics due to their high cruise altitude. See MIT’s great work on this. (11/x)
10) Noise, holy moly. Sonic boom is hugely disruptive and will not be mitigated in any serious way in near-term designs. That leaves you two choices, a small niche market over water, or... (12/x)
Let ‘er rip overland and impose sonic boom as often as every 5 minutes over parts of the globe. That’s the natural result of the @united @boom vision of 500 routes, BTW. (13/x) theicct.org/publications/n…
Now, the regulatory barriers. There are no int’l standards to enable supersonics, and much opposition from the EU, airports, and civil society to them. And **you cannot fully finance a new aircraft program w/o assurances it can be certified.** (14/x) theicct.org/blog/staff/tur…
And onto the program. One of the challenges in trying to model commercial SSTs is that our reference aircraft (@boomaero Overture) changes **constantly** and w/o explanation. We’ve seen it on weights (15/x)
# of passengers (I’ve lost count, honestly) and most recently speed (MN). As @WandrMe first picked up, on Thursday Boom suddenly chopped MN 0.5 off of Overture **by press release**. That a mind-boggling change is done in such a casual fashion raises questions re maturity. (16/x)
So, in summary. Do I think commercial SSTs will succeed? Nope. Would the env impact be large if they did? Yup. Is this all a huge distraction from the real challenge of decarbonizing aviation? 💯(END)

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More from @rutherdan

19 May
I’ve spent some time now unpacking the new @IEA net-zero report. What’s the key to making aviation fully compatible with IEA's net-zero target? Hint: it’s not technology. A (slow) thread. (1/x)
To start, my reading of the report is that it identifies what will be needed to achieve net-zero emissions in 2050, not a prediction of what will actually occur. So, a critical path analysis, if you will, not a crystal ball. (2/x)
With that in mind, I'll reserve judgement on some of the modeling assumptions that I find unlikely. For example, the 2030 aviation biofuel uptakes. (3/x)
Read 22 tweets
18 May
“Alternative aviation fuels are slow to arrive, with biofuels and hydrogen-based fuels accounting for just 16% and 2%, respectively, of energy consumption by 2030.” 😳carbonbrief.org/iea-renewables…
Just so we’re all on the same page here.
A related, good briefing on an EU aviation alternative fuel mandate from @transenv and @cerulogy. It recommends a 2030 target equivalent to 5% by volume, or about one-quarter IEA’s 1.5 C assumption. transportenvironment.org/sites/te/files…
Read 4 tweets
18 May
IEA net zero aviation pathway...
Not that there will be any biofuel left to drink.
Recall that half of US corn production and 30% of our soybeans go into that 2020 bar.

iea.blob.core.windows.net/assets/0716bb9… Image
Read 4 tweets
17 May
Has the recent brouhaha over beef indicated the best climate metric for ‘Mericans? “Take that trip to London, OR eat 325 burgers. What’ll it be?”
“Frequent fliers are eating all your burgers!” Red state billboard.
Forgive me for being amused by the new burger GHG equivalent (bGHG-eq) metric, but my 2018 flying was equivalent to 9 bGHG-eq **per day** over the entire year. theicct.org/blog/staff/wor…
Read 4 tweets
2 Apr
Interesting new NASA paper out on the environmental impacts of supersonic aircraft. Worth a read — a bit shocking to see a US-funded study so pessimistic about SSTs, which were a major priority of the Trump administration. (1/x)

ntrs.nasa.gov/citations/2020…
The MIT lab that completed the study didn’t analyze specific designs like @boomaero Overture or @AerionCorp AS2, but they came reasonably close in terms of MN, seating capacity, and range. Here are the designs to track. (2/x) Image
The big takeaways are:
1) The potential SST market is smaller than advertised, and near-zero with current flight restrictions.
2) SSTs will be heavy and carbon intensive, up to 10x subsonic at MN2.2
3) Non-CO2 climate impact could be severe, esp. for higher MN designs. (3/x)
Read 12 tweets
31 Mar
Major announcement tonight that US airlines are collectively signing on to net zero emissions by 2050. Some thoughts. (1/x)
First, this is a good step by A4A. The announcement comes after international trade groups (EU, UK), alliances (oneworld), and its own members (United, American, JetBlue etc.) made similar commitments. But OK to be fashionably late to this party, dressed appropriately. (2/x)
So what is A4A wearing to the party? Broadly:

1) Drop-in alt jet fuel (SAFs)
2) Advanced aircraft R&D
3) Advanced ATM
4) Ground electrification
5) Int’l agreements, notably offsets
6) Other innovation (e.g. DAC, hydrogen) (3/x)
Read 9 tweets

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