Can business jets go supersonic?

[skidz]

I've heard from a guy that worked with some test pilots on Learjets and citations that these airplanes can actually go supersonic at times. I know it would be illegal to go supersonic over the territory of US but does anyone know of any case of flying these suckers at supersonic speeds over the oceans or somewhere where it's not restricted?

[Clocks]

Wouldn't supersonic air entering those engines do terrible things?

[Stone Cold]

Originally Posted by skidz

I've heard from a guy that worked with some test pilots on Learjets and citations that these airplanes can actually go supersonic at times. I know it would be illegal to go supersonic over the territory of US but does anyone know of any case of flying these suckers at supersonic speeds over the oceans or somewhere where it's not restricted?

No business jet goes supersonic. I believe the fastest bizjet is the Citation X and it goes Mach .92 or so. I fly the Lear 60 and we are limited to Mach .81ish, depending on altitude.

Supposedly some companies are wanting to eventually develop a SS bizjet, but it's not even on the drawing board ($$$) as far as I know.

[SteveC]

Hope you don't mind, but I'm going to move this over to the Technical Talk forum. There are some guys that hang out there that I'll bet can really give some good insight into this topic, and they might miss it in General Topics...

(Remind me if it dies out and I'll move it back.)

[Minuteman]

Downwards, and maybe only once.. A common laundry list of problems encountered in the transonic regime is:

• Exponential drag increase. In theory, the coefficient of drag is infinite at Mach 1.0. Obviously its not, but CD does increase significantly from subsonic values. For example, say the increase is a 30% CD. To accelerate from M=0.8 to M=1.0 you'd need roughly twice as much thrust ([1.0/0.8)^2]*[1.3] = 2.03). The good news is that CD will return to lower values as the Mach number increases. So if you could dive through the transonic region, you might need less thrust to maintain supersonic flight than to break the sound barrier. But that brings us to the next problem:
  
• Change in pressure distribution around the aircraft. Shockwaves mechanically compress the air behind them which can change the location of the center of pressure on a wing (you want the CG aft of the CP for stability). When shockwaves form on the upper and lower surfaces of the wing the CP typically moves aft and you either need to move the aircraft's CG aft as well (like Concorde), or have a crazy-go-nuts flight control system to keep things in line (like the F-16). In the supersonic transition, the shockwaves can also move far enough aft to camp-out on the flight control surfaces and introduce asymmetric forces which might cause flutter or loss of control.
  
• Engine airflow. Before air enters the engine it needs to slow down, or else you'll have shockwaves standing at the face of the fan or LP compressor, which totally kills their efficiency (and ability to overcome the drag rise). Most supersonic aircraft have the ability to regulate and slow the amount of air entering the engines with alternate intakes for slow speeds, and ramps to reduce the inlet area and form shockwaves to slow the flow down to subsonci speeds before reaching the engine. I defy you to find a picture of the Sonic Cruiser that shows its inlets!

So a Learjet probably went supersonic momentarily, once, and it probably wasn't a pleasant experience and used all the gas.

See y'all in Vegas.

[tgrayson]

Originally Posted by Minuteman

you want the CG aft of the CP for stability

Actually, you want the CG ahead of the CP (or aerodynamic center, really) for stability. As an aircraft goes through the transonic range, the aerodynamic center moves rearward, increasing stability, which tends to pitch the airplane down. It's indeed helpful for the CG to move back in order to reduce the stability. A very authoritative tailplane could alleviate this, but you'd have a lot of trim drag.

[Minuteman]

Originally Posted by tgrayson

Actually, you want the CG ahead of the CP (or aerodynamic center, really) for stability. As an aircraft goes through the transonic range, the aerodynamic center moves rearward, increasing stability, which tends to pitch the airplane down. It's indeed helpful for the CG to move back in order to reduce the stability. A very authoritative tailplane could alleviate this, but you'd have a lot of trim drag.

Aww no wonder planes keep crashing! You're right.

[falconvalley]

Originally Posted by tgrayson

Actually, you want the CG ahead of the CP (or aerodynamic center, really) for stability. As an aircraft goes through the transonic range, the aerodynamic center moves rearward, increasing stability, which tends to pitch the airplane down. It's indeed helpful for the CG to move back in order to reduce the stability. A very authoritative tailplane could alleviate this, but you'd have a lot of trim drag.

Is that why some jets have a tendancy to nose over?

[tgrayson]

Originally Posted by falconvalley

Is that why some jets have a tendancy to nose over?

That's one of them and probably dominant in subsonic jets. Most jets incorporate some sort of mach trimmer that trims nose down as the mach number rises. Some of late WWII airplanes crashed due to various "mach tuck" tendencies. The standard horizontal stabilizer/elevator combination loses effectiveness once the airflow goes supersonic, which makes recovery difficult. There also may be airflow separation of the main wing due to mach effects can also decrease downwash over the tail, causing a pitch down.

[Berkut]

The DC-8 intentionally went supersonic during testing. Suffered no damage, and apparently didn't have much trouble pulling it off. It was a shallow dive from about 50,000 to 42,000 feet.

[Stone Cold]

Originally Posted by Berkut

The DC-8 intentionally went supersonic during testing. Suffered no damage, and apparently didn't have much trouble pulling it off. It was a shallow dive from about 50,000 to 42,000 feet.

There's a huge difference between what the test pilots did and what line pilots do. The OP asked what we do, and there is no bizjet that goes supersonic. If we left the engines at max power, especially in a dive, I'm sure we could do it (supersonic). It would be assinine, and we might only get one chance at it. As far as actually doing it, no, we don't!!! Have the test pilots done it...have no clue. I'm not a test pilot and operate inside the envelope!!!

[Berkut]

Originally Posted by Stone Cold

There's a huge difference between what the test pilots did and what line pilots do. I'm not a test pilot and operate inside the envelope!!!

Oh, don't get me wrong, I don't doubt that at all. But the question is, do all your brethren share that sentiment?

[Stone Cold]

Originally Posted by Berkut

Oh, don't get me wrong, I don't doubt that at all. But the question is, do all your brethren share that sentiment?

They darn well better. We are all professional pilots. None of the group I fly with will do anything out of the ordinary. And that's a great thing.

[B767Driver]

Originally Posted by tgrayson

Actually, you want the CG ahead of the CP (or aerodynamic center, really) for stability. As an aircraft goes through the transonic range, the aerodynamic center moves rearward, increasing stability, which tends to pitch the airplane down. It's indeed helpful for the CG to move back in order to reduce the stability. A very authoritative tailplane could alleviate this, but you'd have a lot of trim drag.

There are a handful of texts out there that illustrate this backwards. No wonder we get so confused.

[tgrayson]

Originally Posted by B767Driver

There are a handful of texts out there that illustrate this backwards. No wonder we get so confused.

Yes, I remember that throwing me at one time. They do show it backwards in order to demonstrate what is considered positive in the equations. The actual relative positions of the CG and AC (or neutral point) are determined by the sign and absolute distance.

Similarly, the diagrams may show curled arrows indicated a right roll, right yaw, and pitch up. They obviously aren't saying that all aircraft only roll, yaw and pitch in those directions, but merely showing what positive is. Any left roll, left yaw, or pitch down would be shown as negative values.

Authors don't realize how one skipped concept can seriously distort the understand that the reader can acquire.

[NJA_Capt]

Originally Posted by Stone Cold

No business jet goes supersonic. I believe the fastest bizjet is the Citation X and it goes Mach .92 or so. I fly the Lear 60 and we are limited to Mach .81ish, depending on altitude.

The Citation X and the G-V both went supersonic during certification testing. Neither are certified for supersonic flight. NASA also had a couple of old Lears the "accidentally" went supersonic.

[Stone Cold]

Originally Posted by NJA_Capt

The Citation X and the G-V both went supersonic during certification testing. Neither are certified for supersonic flight. NASA also had a couple of old Lears the "accidentally" went supersonic.

Oh, trust me, I believe all these jets can go supersonic and most probably have during testing. The OP was asking about normal cruise with line pilots. We don't do it.

[NJA_Capt]

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True. But we get pretty close

Originally Posted by Stone Cold

The OP was asking about normal cruise with line pilots. We don't do it.

[Stone Cold]

Originally Posted by NJA_Capt

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True. But we get pretty close

Yeah, yeah...showoff.

I did reference that in one of the posts above...thankyouverymuch!! I would like to see them develop a supersonic Bizjet...we'll see what the future holds, right?!

[Texasspilot]

Yah i think the X hit 1.1 in testing.

Also been told that the 727 could hit 1.0 in the decent.

[ppragman]

Originally Posted by Texasspilot

Yah i think the X hit 1.1 in testing.

Also been told that the 727 could hit 1.0 in the decent.

I wonder what the critical mach # is for the 727? I would expect that there would be a hell of a mach tuck at that speed, I didn't think that the 72 had a stabilator either, so recovery could be a real pain...hmmm...

[seagull]

Originally Posted by ppragman

I wonder what the critical mach # is for the 727? I would expect that there would be a hell of a mach tuck at that speed, I didn't think that the 72 had a stabilator either, so recovery could be a real pain...hmmm...

True, no stabilator, but hydraulics help a lot, and nose up trim moves the entire stabilizer on all the jets that I've flown.

[ppragman]

Originally Posted by seagull

True, no stabilator, but hydraulics help a lot, and nose up trim moves the entire stabilizer on all the jets that I've flown.

that would definately be useful. I'd hate to have to be the guy to flight test that beast to 1.0 though

[dc3flyer]

http://www.flyingmag.com/article.asp...article_id=621

[fsiflyer]

I am a Lear 60 pilot as well and myself along with every pilot in my company operates in a safe and efficient manner and always stays in the flight envelope. The chances are just not worth it. Safety first!