And What's Next?

By ANN Correspondent Kevin O'Brien

A teardown Sunday morning revealed why Bruce Bohannon fell short of his planned US absolute piston altitude record -- and the entire, disappointed crew breathed a sigh of relief. It was a broken, formed bracket, that prevented the wastegate from closing fully and the engine from developing full power in the rarefied air near Bohannon's 50,000 foot objective.

How come? Well, if an airplane might be broken, it makes sense to ask a mechanic you catch working on it.
 
"There's a bracket for the wastegate," Ernie Butcher explained. (Unlike most modern turbos, whose designers to reduce pilot workload and maximize efficiency with an automatic wastegate, the Flyin' Tiger's Mattituck MTX-555 engine has a manual wastegate, to give its pilot, Bohannon, maximum control). "And of coures, at about 40,000 is the time where it starts getting almost closed."

"And at 45, he really makes sure it is closed. [But] that bracket is fractured, so it didn't get quite closed, so he didn't get full power."

So that's all it was, a wastegate bracket? A little metal bracket?

"Well, that was certainly a significant part. He can go higher. He's BEEN higher."

That would be 47,067 feet, Bohannon's current FAI Absolute Altitude Record in Class C-1B, set at Flyin' Tiger Field in Texas in November, which earned Bohannon his third straight Louis Bleriot medal from the FAI (an accomplishment unprecedented in FAI's long history).

Another factor? High ambient temperatures at altitude. While the FAI corrects alitude and other records for standard atmospheric conditions, the thin, hot air had a dual effect, aerodynamically on the Flyin' Tiger's airframe, and on the Flyin' Tiger's engine. Between the wastegate's inability to fully close, and the extra degrees, the usually robust-and-a-half MTX-555 was wheezing -- at least by MTX-555 standards.

"We thought that there was no reason for this. And everything was perfect when he went up! I mean, we looked at it, we went over it, we took it apart, we inspected it. But -- you know."

Yeah.

"When you're out there on the edge sometimes...."

Well, could it have been damage that had been somehow missed? With that thorough inspection cycle, and the quality of the Exxon Flyin' Tiger maintenance crew, it seems unlikely. Still, the day before the flight, we were surprised to note that the engine had been removed. As it happened, a foreign object had FODded the turbo, and it had in turn made a mess of the exhaust; the turbo and some of the exhaust parts had to be R&R'd in very short time before the record flight. Still, we saw some of this work going on, and like everything the team does, (at least in sight of the press and public!), it took place with consummate professionalism and no drama at all. So COULD the wastegate bracket been damaged in the turbo failure, and somehow missed until the record flight, despite the inspections?

"It could have been a fracture that we didn't see." So it was possible that it was damaged in this way. It could have been that the initial failure was a tiny crack that was too small for human eyes to detect, also. The bracket failing on the record flight, though, seems more probable than a preexisting failure.

"And of course, it gets quite a bit of tension on it, when he closes the wastegate."

To lose a record because of a small alloy bracket. That's disappointing.

"To say the least."

What about the absolute world record of over 56,000 feet? Bohannon will be unlikely to attempt that in the Flyin' Tiger. The limiting factor is high-altitude physiology. While a positive pressure O2 system can sustain life to FL 500, beyond that point the pressure is so low that the nitrogen in human blood boils; you need a pressure suit or pressure cabin, which add weight and complexity.

"This plane wasn't built for that. It was an afterthought [to pursue altitude records.] He just seemed to do wo well flying it..."

It must be unbelievably cold in this thing, at forty-something thousand feet.

"I wouldn't get in it, anyway."

So, anyway, that was why the long tradition of Bruce Bohannon and te Exxon Flyin' Tiger record-breaking at airshows was interrupted this summer.

"We just found this this morning," Butcher said, looking back to his work under the control panel of the Flyin' Tiger, and no doubt wishing the reporter would shove off and let him do it. "I'm glad we found something legitimate. None of it made sense. It was SO perfect going up."

And he had done it before.

"Oh yeah. He is more motivated now than ever." Most likely, the team will tackle the record where they set the last one -- Flyin' Tiger Field, deep in the heart of Texas.

A lot depends on other things -- like sponsors. But here, the team members have no worries. The sponsors great and small have been outstanding.

"Well, Exxon -- and Mattituck -- I've been around this [business] for a long time and I've never seen two sponsors with more support. The folks that did the turbo, we sent it back in -- Kelly Aerospace -- it's just unbelievable. They're all --" and he gestured at the array of sponsor decals festooning the side of the record-shattering Flyin' Tiger, sweeping all the smaller sponsors into the circle of excellence with Exxon, Mattituck, and Kelly. "He's just got the cream of the crop here -- but then, he's a cream of the crop kind of person."

FMI: www.airventure.org