Centerline Thrust For a Twin Jet

[tcasblue]

It is interesting that a jet with two aft mounted engines, in the same manner as a DC-9, can be a centerline thrust aircraft. But that is exactly what the Eclipse Jet is...centerline thrust. No VMC is published. And here is what was done for the newer version(Eclipse 550) to keep it in the centerline thrust category.....

"As a result of the greater weight and performance, the horizontal stabilizer will be lengthened as well. The engines, which currently have zero cant to their thrust line, will be canted 5 degrees out, slightly reducing drag near the forward edge of the nacelle. The resulting cant inward at the aft end of the nacelles will preserve the airplane's centerline thrust handling while accommodating the higher thrust."

https://www.aopa.org/news-and-media/all-news/2016/july/21/next-generation-eclipse-jet-announced

[Vessbot]

If the backs of the engines point inward (front outward), that INCREASES the distance between the thrustline and CG, which increases yaw moment when single engine, i.e., makes SE handling worse. What am I missing?

[stilton]

Since when is a DC9 a ‘centerline thrust aircraft’ ?

[tcasblue]

Since when is a DC9 a ‘centerline thrust aircraft’ ?

My wording could be misinterpreted.....the Eclipse has tail mounted engines like a DC-9 but is considered centerline thrust by the FAA.

[Pugilistic Animus]

If I ever get rich I would buy me a nice Eclipse 550. It has lots more to offer than just centerline Thrust. B Quite Amazing What they did with her

[pattern_is_full]

I think it just boils down to - the FFA can find no flying speed so slow that directional control can be lost due to an engine failure ("VMC" < VSo) and that automated corrections via the yaw damper/rudder, and FADEC, mean that the loss of an engine requires no particular pilot inputs to maintain direction control in the event of engine loss at higher speed.

The 550 engines are fairly small and low-thrust (900-1100 lbft) and are mounted on short pylons on a fuselage that also skinnies down very rapidly (thrust lever arm ~1.17m - only slightly wider that the cabin exterior). The VS and rudder are large (and on the upgrade "Canada" there is a centerline strake or VSTAB below the fuselage as well). There may be other less obvious aerodynamic effects that minimize SE yaw (tadpole fuselage, cranked wing that technically has a forward sweep, on the mean chord line).

I do note that the engines are to be brought up to a stabilized 50% on each side before brake release - just to be sure one doesn't perform a ground loop at zero airspeed. ;)

CANADA Specs (http://www.oneaviation.aero/canada-specs.html)

[bafanguy]

Since when is a DC9 a ‘centerline thrust aircraft’ ?

Well, the FAA considered it as such circa 1970; no idea what they say now. If I recall the details after all this time, I think it was because the Vmca was below the stall speed.

Coming at the time from the S/E world in license terms, when I got my first ATP with DC9 type rating the M/E rating thrown in was limited to C/L thrust. When I contacted my acquaintance in flight test at Douglas to complain, he gave me the above explanation...IIRC. That C/L limit wasn't changed until I later got a B737 type rating.

I think the B727 was the same thing ?

[aterpster]

I am rated in both the DC9-10 (1967) and 727 (1969). Neither were center-line thrust ratings. The DC-9-10 had OEI procedures. The 727 had one and two engine inoperative procedures.

[aterpster]

Well, the FAA considered it as such circa 1970; no idea what they say now. If I recall the details after all this time, I think it was because the Vmca was below the stall speed.

Coming at the time from the S/E world in license terms, when I got my first ATP with DC9 type rating the M/E rating thrown in was limited to C/L thrust. When I contacted my acquaintance in flight test at Douglas to complain, he gave me the above explanation...IIRC. That C/L limit wasn't changed until I later got a B737 type rating.

I think the B727 was the same thing ?
They must have changed their minds after i got my DC-9-10 rating in 1967 and my 727 rating in 1969.

[DaveReidUK]

It is interesting that a jet with two aft mounted engines, in the same manner as a DC-9, can be a centerline thrust aircraft. But that is exactly what the Eclipse Jet is...centerline thrust. No VMC is published. And here is what was done for the newer version (Eclipse 550) to keep it in the centerline thrust category.....

"As a result of the greater weight and performance, the horizontal stabilizer will be lengthened as well. The engines, which currently have zero cant to their thrust line, will be canted 5 degrees out, slightly reducing drag near the forward edge of the nacelle. The resulting cant inward at the aft end of the nacelles will preserve the airplane's centerline thrust handling while accommodating the higher thrust."

I think you are misreading that AOPA article. Those aren't differences between the Eclipse 500 and 550, which share the same structure, engines, thrust and weight.

[tcasblue]

I was the one who brought up the DC-9 as a example of tail-mounted engines as I figured that there may be many who were unfamiliar with the look of the Eclipse. I doubt there was ever any centerline thrust for the DC-9. Someone is either making it up or had an error on his license.

As for the 727, a lot of rudder is needed to maintain present track after an engine failure soon after V1(at least in the sim). It was a bit surprising to me coming from the multi-engine world of engines on wings as I expected it to be much less rudder input required.

I flew the Cessna 337 centerline thrust aircraft and after experiencing a power loss in cruise, it was not surprisingly, a non-event in terms of handling characteristics with it being the equivalent of reducing power by half in a Cessna 172. But, I do wonder, if the centerline thrust Eclipse, even though it has no VMC, still requires quite a bit of rudder to maintain the desired track. If so, it is a much different handling centerline thrust aircraft than a Cessna 337.

[bafanguy]

I am rated in both the DC9-10 (1967) and 727 (1969). Neither were center-line thrust ratings. The DC-9-10 had OEI procedures. The 727 had one and two engine inoperative procedures.

aterpster,

Hard to say what happened when. I only know my direct personal circumstances in 1970.

If you got your initial FAA ATP at the time you held a CPL with a regular M/E rating, you wouldn't have been affected...I guess. I only had a CPL with S/E Land at the time of my initial FAA ATP and DC9 type rating so I guess the first M/E rating I got as ink spots on my ticket was C/L thrust because they considered the DC9 to be C/L thrust. They must've overlooked that foot full o'rudder needed on a V1 cut in their definition of C/L thrust airplanes. We also had to demonstrate them in the airplane as you must have in those days...and I found the airplane much easier than the sim.

And the C/L thrust limit was removed with the addition of my B737 rating in 1971 and replaced with a "real" M/E rating. ;) That's all I know...I was just a line pilot.

[Spooky 2]

Back in the late 60's and up through the 80's the airline were hiring a lot of former USAF & USN pilots with F4 backgrounds. Their airman certificates were restricted to centerline thrust, and consequently this limiation had to be removed before they went to fly the line. Not a big deal but there was some paperwork over and above the normal checkout and since not all pilots in those early days got type rated in the new aircraft, so the IP had to be careful that the CLT limitation did not slip through the cracks. Wish i could tell you this never happened, but the fact is some pilots made it to the line without this box being checked, only to be found by some FAA inspector doing a route check sometimes months after the pilot started flying the line.

Don't recall the 727 ever being anything but a ME rating.