Max Q wrote:jetstar wrote:Max Q wrote:The Jetstar is an interesting aircraft with some unique design features
One of which is the stabilizer trim system, in a conventional set up in the horizontal stabilizer is attached to the rear fuselage and pivots nose up and down.
On the Jetstar the horizontal stabilizer is part of the vertical stab and is not adjustable(although the attached elevators are)
Instead the entire vertical tail ‘tilts’
forward or back, in turn changing the angle of the horizontal stabilizer
One of the Jetstar engineers subsequently went to work for Mooney light aircraft and incorporated the same feature in their single engine aircraft line
It is still being used to this day
If you look closely at photographs of the Jetstar you can see an exposed section of
highly polished aluminum at the base of the
vertical fin’s leading edge
This shows the range of movement utilized
for fore and aft trim
There are only 2 aircraft that use this type of pitch trim system, the single engine piston Mooney’s and the Lockheed JetStar.
But actually it was the other way around, Al Mooney after he left the company he helped found, Mooney Aircraft he then went to work for Kelly Johnson’s skunk works at Lockheed. He was tasked with engineering the design for the empennage section of the JetStar so he incorporated the same design he used for his Mooney airplanes. Since Kelly Johnson was the chief engineer of the JetStar I guess he liked the design because he approved it.
I cursed Al Mooney many times, probably each time I had to service the pitch trim servo unit, once every 200 hours to check the oil level, drain any water that would leak down the jack screws and grease the mechanism. The pitch trim unit had 2 motors, one main and a standby attached to a gear box with 2 large jack screws that moved the forward edge of the vertical stabilizer up or down. To access this pitch trim unit you had to crawl through an opening about 14 inches by 12 inches and place you body between all the control cables, making sure you do not put any weight on the 2” diameter fuel jettison line and then remove the cover plates to gain access to the pitch trim mechanism. I usually brought in my coffee with me because once I was in there I stayed until I finished the job so I did not have to go through all the contortions required to get comfortable again. It took about an hour and a half to do the servicing, changing a pitch trim motor took another hour or so.
I stand corrected Jetstar and thanks for the interesting follow up
It’s a unique configuration, not really sure
if there’s any advantage or disadvantage
You do end up moving a larger, heavier piece of metal for the same result as a conventional horizontal stabilizer
An advantage might be that you have an overall simpler system
Fascinating aircraft though, do you know if there are any still flying ?
I never really knew what was the advantages of the flying tail, one story I heard was this moved the flight stresses to a stronger point in the fuselage, this way they could make the empennage lighter. The pitch trim jackscrews were located in the lower front of the moving empennage.
If you look at a sideways picture of the JetStar’s empennage, the bare metal at the base has a slight bend towards the aft and at the base of the bend was the pivot point of the empennage where it attached to the airframe. This pivot point consisted of a large bolt mounted into bearings with grease fitting on them and had to be greased every 200 hours, access was through access plates on the outside of the empennage.
I have heard that there are some JetStars still flying, if in the US they would have to be either the re-engined or JetStar 2’s because the P&W powered ones would be banned because of noise regulations.
Of the original 162 production run of the P&W powered JetStar’s most were produced in the late 1960’s to the early 1970’s, so these airframes would be hitting or past the 50 year mark, and with the JetStar’s history of wing corrosion, which required expensive repairs I doubt any of these older airframes are still flying, although I did hear of one of the conversions, a late serial number was still flying.
The second production run, of the JetStar 2 was only 40 airplanes and these had better corrosion properties and some of these are still around in the US. Outside of the US, there might be some more flying.
I believe Lockheed does not support the JetStar anymore for parts, they turned it over to an outside company and parts have become real expensive if they have to be manufactured if not available from scrapped airframes.