Sunday, September 25, 2011

Cessna Citation Commuter Turboprop Concept

A strange thing often occurs when scouring the web for a specific piece of information. That which one seeks remains forever hidden, while new and unrelated discoveries are made.

Some time ago, I made such a discovery. While searching for photos of the elusive Citation turboprop pusher...

...I ran across files describing an even more bizarre variation on the Citation - a 19-passenger commuter turboprop variant. Enjoy...and click the images for larger versions:

Wednesday, September 21, 2011

Reno Crash - Further Investigation

I've received several emails and comments about the likelihood of a trim tab failure causing the recent crash at Reno. Among them was this:

"I was part of the pit crew. Jimmy was a close personal freind. I've owned Race 9 (Cloudancer) since April'10. It is common practice for air racers to zero the elevator and rudder tabs so there is less drag and less chance of setting up a buzz. I know this sounds strange, but when they are in the valley of speed it takes both hands pushing forward on the stick. And when you are turning especially pylon 7 and 8 where you need 5 to 7g's to make the corner and not bust the spectator deadline you relax the forward pressure so you dont have to pull so hard. 

If you had forward trim set in the act(tab up for down elevator) the forces on the tab would be tremendous while turning. The aircraft pitched up nearly vertical but climbed very little maybe a 100 Feet, this was accompanied by a very loud whump or a burrump sound. The aircraft slowed tremendously. Pictures show a large buckle in the right side of the fuselage, this probably tripped the tailwheel uplock cable and extended the tailwheel. The inboard 2/3's of the trimtab then seperated. Just a comment about bob hannah's tab failure, he said that when he came to he was looking at his feet"

The last comment was in reference to an incident with "Voodoo" several years ago. He lost a trim tab on the course, blacked out during a 10G pull-up and woke up to find himself at 9000 feet

And about that extended tail wheel, clearly visible in a photo shot a second or two before impact - a P-51 checklist emergency gear procedure on Aerofiles sheds some light on how extreme G-forces indeed could have extended the tail wheel:

"If there is any doubt about the tail wheel being down, dive the plane a short distance and pull out with enough acceleration to down the tail wheel."

Here's hoping for a future with the air races, but without accidents like this.

Friday, September 16, 2011

Reno Crash - Trim Tab to Blame?

It is, of course, very early to speculate on the cause of the tragic crash at Reno. A disciplined examination of photos, however, reveals a possible clue.

This photo was shot by Tim O'Brien of the AP and Grass Valley Union just a moment before the crash. A sharp-eyed Russell Farris spotted an elevator trim tab that is either missing or severely deflected. If the trim tab was deflected downward at such an angle, the elevator would have been forced upward with a great deal of force. This would severely pitch the nose upward, likely with enough force to overpower even the strongest pilot.

In such a scenario, the pilot would push forward on the control stick with all his might to arrest the pitch rate. If he was unable to do so, the nose would continue to pitch further and further upward until airframe failure or ground contact occurs.

It's important to bear in mind that at the speed he was flying today, a relatively small control surface deflection would have resulted in an abrupt and extreme load factor ("G-force") on the pilot, making recovery that much more difficult.

Here's hoping the reaction of the public and media doesn't put an end to the Reno Air Races. You can bet that none of today's victims would have wanted that.