James' World

Like everybody connected to the aviation industry, I watched the Very Light Jet (VLJ) market hype (mostly around Paul Allen’s Eclipse 500,) in 2002 and wondered how the market would shake out. After the Eclipse announcement, around 10 competitors announced they would build a VLJ, too.

VLJ’s are characterized by being lower-cost than other private jets, and being certified for single-pilot (SP) operation. However, “lower-cost” increased from $837,000 in 2002 to $3-$5 million in 2020. The key technology in 2002 was a Wiliams cruise missile engine, but that turned out to be under-powered for the Eclipse back then and the engines were upgraded to P&W. A Williams jet is used in the Cirrus Jet today.)

The Eclipse (twin P&W, 370k, ~$1M, 267 made) company was predicted to fail because of the ultralow pricing and company mfg. inexperience. And it did in 2008, although it shipped a few hundred airframes in various stages of completion. Most of the wealthy individual buyers moved on to the Cessna Mustang (twin P&WC, 340 knots, $3.3M, 469 made), which was much more expensive but had the backing of Cessna/Textron.

What’s interesting is that Eclipse reported a major deal with an air taxi, Day Jet. I was skeptical of the deal at the time, but they did receive about 20 jets and provided service until also failing in 2008, although I wonder about the dispatch rate for a v1 jet.

Besides the Cessna Mustang, another successful jet that eventually emerged was the Cirrus Vision SF50.

The Cirrus Vision SF50 (single Williams, 300 knots, $2.7M, 170 made so far) was certified in 2016 and the shipment volume winner for 2018 and 2019. It and the Embraer Phenom 100 (twin P&WC, 400 knots, $5 million) are the only VLJs currently being made, with the HondaJet available at twice the price ($5.5 million.)

(Note that Cirrus (and most small US airplane companies) are owned by Chinese companies as of 2020.)

On Apr. 18, 2019, an FAA AD was issued after 3 incidents involving AOA sensors were reported. Aerosonic, the AOA supplier, shipped bad units to Cirrus, and the SF50 fleet was grounded until replaced. The effect was the same as the 737 MAX accidents, although Cirrus had a hardware, not a mostly software, problem. It’s interesting that a ferry flight was allowed to repair it.

W: Eclipse 500, Cirrus Vision SF50, Cessna Citation Mustang (Model 510), Honda HA-420 HondaJet, Embraer Phenom 100

Textron Ceases Production of Cessna Citation Mustang

Very interesting:

“Airbus has determined that acoustic resonance is behind the destruction of four engines on its new A220 airliners in the last couple of years. The company has come up with a software fix for the condition, which caused in-flight shutdowns of the Pratt & Whitney geared turbofan engines on three Swiss flights and one on an Air Baltic aircraft.”

Engine makers commonly use remote telemetry, so I’m a little surprised it took a couple of years to pinpoint that. But I’m sure they’ll be adding acoustic sensors now.

Acoustics are a surprisingly big deal in aerospace. HondaJet’s composite fuselage rang like a bell and even passengers needed headsets, so the new Elite version focused on reducing cabin noise by 3 db (half.)

avweb.com: Software Fix Found For A220 Engine Shutdowns

Cessna T210M Wing Spar Shear between top rivets and lower I-beam Flange Narrowing Point (and Lower Forging Lightening Spotface Indentation.) The white foam may have collected water, aiding corrosion. Photo credit: ATSB. (click image to enlarge)

I’ve read thousands of airplane accident reports, but this is one of the most concerning.

The Cessna 210 (and 177) family has a complex wing design made of aluminum components with around 100 features, mostly rivet holes, that can become stress risers.

Since 2012, several spar cracks have been found, and in 2019, there was a fatal accident in Australia after losing a wing, which is not survivable. (Note that this plane was used for aerial survey grids at 200′ with full fuel plus wing tip fuel tanks and 2 pilots, for as many as 5,000 hours. Two survey planes were operated. It would be fascinating to do a teardown on the other one.)

The fatal 2019 accident in Australia appears to be a combination of corrosion on a rivet hole and metal (aluminum) fatigue, possibly combined with the round shape of the lower spar forging spotface (indentation.) Aluminum can shear instantaneously once a crack forms, though in this case the ATSB suspects previous cracking.

Cessna 210 Wing Lower Spar Forging. Photo credit: tennesseeaircraft.net.

Example of a fail-safe spar with a riveted spar web. This might have arrested the crack, but at the cost of being twice as heavy since both the top and bottom half-spars would need to be capable of carrying the load. And all bets are off with corrosion. Diagram credit: aircraftsystemstech.com.

(In the 1995 Kobe earthquake, some of the freeway supports that failed had a steel jacket around the bottom third of the concrete supports, causing a stress riser in a ring around the support. Japan subsequently updated their building code to do full steel jackets. This spar structure failure appears to be very similar if a forging spotface was involved. Under a sideways load, the weakest part would be at the curved spar cap spotface indentation, acting as a strees riser. Under a vertical load, it would still be the same location, since both the spar caps and forgings narrow in thickness at that point.)

This is a tough one to fix, let alone inspect. The spar and other attachments are no longer made, and even if they were, that’s $86,000 into an old airplane. For these to continue to fly, somebody needs to operate these outside the USA and come up with a “massive spar” modification that’s affordable, if not TSO’ed.

Cessna 210 Spar Links

Wings – Aircraft Structures
federalregister.gov: Airworthiness Directives; Textron Aviation Inc. (Type Certificate Previously Held by Cessna Aircraft Company)
tennesseeaircraft.net: 210 Wing Lower Spar Cap Bulletin Sel-57-01 Revision 1 (2012)
avweb.com: Mask Shortage Results In Cessna 210 Spar AD Extension
generalaviationnews.com: Cessna 210 spar caps subject of new Airworthiness Directive
flyingmag.com: FAA Calls for Cessna 210 Wing Spar Inspections
aopa.org: Cessna 210 owners weigh compliance options for corrosion AD
asrs.arc.nasa.gov: Smoking Rivets
nasa.gov: THE STRENGTH AND STIFFNESS OF SHEAR WEBS WITH AND WITHOUT LIGHTENING HOLES (1945)
W: Spotface
faa.gov: FAA Request for Information on Cessna 201 and 177 Airplanes
pprune.org: Cessna 210 Accident Mt ISA

1995 Kobe Earthquake Freeway Collapse

The Collapse of the Hanshin Expressway (Fukae) Bridge, Kobe 1995: Soil-Foundation-Structure Interaction, Reconstruction, Seismic Isolation
fhwa.dot.gov: Aftermath of The Kobe Earthquake