200 knots below Class B

[hopeful]

Hogdriver,

I think someone must have eatin too many beans before the picture was taken for your avatar. The lav just exploded.

 

[hogdriver00]

No way

No way baby! We were gettin the number.

 

[jetdriven]

naw you guys are way off. There is a SFAR which addresses the Houston Class B speed limit.

You can exceed 250 KIAS on departure from the Houston Class B if you are told the words "no speed limit"

this is to reduce congestion, and it works.

 

[FracPilot]

Speed limits

ATC does not have the authority to have you go above 250 below 10,000. If they request and you do it you can still be violated.

There is one exception to this rule. Military controllers, working military airspace, can allow you to exceed the 250 below 10k speed limit. The problem is they will not tell you when you are approaching civilian airspace so you can slow down. Another problem is that some areas that are civilian airspace but are worked by military controllers...an example of this is the area that Joshua Approach controls north of Los Angeles. You cannot legally exceed 250 below 10k unless you are within one of the Restricted areas, or within a certain area east of Palmdale Vortac(which is not depicted on our charts).

To be safe, I fly 250 or less under 10k. The only exception is departing IAH when they say "no speed limit".

 

[Postflight]

Learjet Vmo

Re: Learjet Vmo.

LJ35 (w/FC200 autopilot:
Vmo below 14,000': 307 KIAS
above 8,000': 359 KIAS
Mmo: 0.83 Mi
(above airspeeds are 300, 350, 0.81 respectively in calibrated airspeed)

LJ35 (w/FC530 autopilot):
Vmo below 8,000': 300 KIAS
above 8,000': 350 KIAS
Mmo: 0.81 Mi

LJ55b: same as FC530 equiped LJ35

LJ31a:
Vmo: 325 KIAS (all altitudes)
Mmo: 0.81 Mi

 

[CatYaaak]

Actually CE-750 Vmo is:
350kts. from 8,000 ft - 30,650 ft.
270kts. below 8,000 ft.
.

What a bummer that must be, watching Westwinds pull away (365 kts.)

 

[750driver]

What a bummer that must be, watching Westwinds pull away (365 kts.)

I just keep telling myself ..." we'll catch them down the road!" In all seriousness, it really is an operational limit, not structural. This was according to the Cessna R&D Pilots we spoke to in class.

 

[AV8OR]

Nobody was watching us pull away that day. We were one of the very last to land at BWI. It was like a ghost town.

 

[JetPilot500]

I just keep telling myself ..." we'll catch them down the road!" In all seriousness, it really is an operational limit, not structural. This was according to the Cessna R&D Pilots we spoke to in class.

At Flight Safety we watched a video of the Falcon Test pilots flying a Falcon 50. They got that thing darn close to Mach 1. Hands off the wheel with the autopilot off. No Mach-Tuck, Aileron Buzz or any adverse flying characteristics for that matter. I've been told that all Falcons actually exceed Mach 1 during flight testing. So as far as the Falcon goes, they could have a Mach .98 limit if they wanted. So I guess Mach .86 is just an "operational limit" as well.

But hey, Limits are Limits.

JetPilot500

 

[750driver]

At Flight Safety we watched a video of the Falcon Test pilots flying a Falcon 50. They got that thing darn close to Mach 1. Hands off the wheel with the autopilot off. No Mach-Tuck, Aileron Buzz or any adverse flying characteristics for that matter. I've been told that all Falcons actually exceed Mach 1 during flight testing. So as far as the Falcon goes, they could have a Mach .98 limit if they wanted. So I guess Mach .86 is just an "operational limit" as well. But hey, Limits are Limits.

JetPilot500

The Cessna engineering pilots we met in Wichita told us that the X made it past mach 1 in testing also. That was not a problem, given the proper amount of thrust. The engine output is rated at 6442lbs per side (newer models have increase thrust rating), but the Allison AE-3007C's are capable of much more power. They have obviously been limited for longevity.

I guess one of the big issues with going past mach is the effect of the shock wave pressure on the fan section. There are concerns related to repetitive fan blade stress etc. This was just one aspect and we all know there are other engineering issues that must be addressed.

I have no doubt that the Falcon can do it. That brand has always been one of my personal favorites .... kind of like a wolf in sheep's clothing

 

[bigD]

So what exactly is the limiting factor in an "operational limit"? If there's not a structural or control problem, why is the limit there?

 

[GVFlyer]

At Flight Safety we watched a video of the Falcon Test pilots flying a Falcon 50. They got that thing darn close to Mach 1. Hands off the wheel with the autopilot off. No Mach-Tuck, Aileron Buzz or any adverse flying characteristics for that matter. I've been told that all Falcons actually exceed Mach 1 during flight testing. So as far as the Falcon goes, they could have a Mach .98 limit if they wanted. So I guess Mach .86 is just an "operational limit" as well.

But hey, Limits are Limits.

JetPilot500

This is unlikely. There are several ways that Vc is determined for jet aircraft: flutter speed, Vb + 1.32 Uref, 0.8 percentage of Vd, the speed at which you can accelerate 7.5 degrees nosedown for 20 seconds then recover to Vc with no more than 1.5 G's, or the speed at which you encounter a control reversal for example. The most common limiting speed, however, is 0.07 mach below the speed where compressibility effects are encountered (this speed may be reduced to a 0.05 mach margin if rational analysis for the effects of automatic systems are used).

So, if MMO is 0.86 mach the Falcon encountered something at 0.93 mach that determined it's design cruise speed.

On the production test cards for Certificate of Airworthiness, all production jets are required to be flown at some speed above MMO to prove their controlability should jet upset occur. Initially, this speed was 0.955 mach for the GV, then the FAA relaxed the requirement to the current 0.92 mach at which all GV's are flown. At MMO, the aircraft is trimmed for hands-off flight then the speedbrakes are fully deployed and the trims are noted. There can be no roll; slight nose up pitching is allowed.

Mach tuck occurs in all jets as the transition from subsonic to trans-sonic flight (mach crit)occurs. In normal unaccelerated subsonic flight the aerodynamic center of pressure is at 25% chord. This center moves aft as you accelerate until it reaches 50% chord in supersonic flight. As a resultant of this center of pressure moving aft, the nose tucks. The rate, degree and extent to which this occurs is largely determined by the Reynold's number for the wing.

No one would intentionally take a transport category jet designed for subsonic flight beyond 1.00 mach . Subsonic wings are designed using the Navier - Stokes equation and Computational Fluid Dynamics to be just that: subsonic. Supersonic wings designed for non-compressible airflow differ significantly in strength and design. On aircraft that do not have an all-moving tail the first thing that occurs at 1.00 mach is a shock wave forms up at 50% chord on the horizontal stabilizer which negates the effectiveness of any flight control operating behind it. Subsequently, pitch control is lost.

The GV went to 1.07 mach one time during developmental test, but it was not intentional. One of the stability tests that is done during "cert " is to simulate runaway trim. In the GV, the aircraft is accelerated to Vc at 51,000 feet (0.86 mach), trimmed for hands - off flight, next the trim is run nosedown for 3 seconds, and then the test pilot is allowed to recover the resulting maneuver. After demonstrating that you can do this point, the FAA is invited to come fly the point themselves and verify it. They are to neither "demonstrate exeptional strenght or skill" to do this. They do this part well.

On the day when the GV "Made the number" the FAA test pilot from the ACO was in the left seat to verify this runaway trim point. The jet was accelerated to 0.86 mach and trimmed for hands-off flight at 51,000 feet. The trim was then run nosedown for 3 seconds. All went well until the FAA pilot was told, "You got it, recover." He was reticent to pull back on the yoke at that altitude and speed. As a result the aircraft quickly accelerated to 0.99 mach. Seeing this, FAA pilot promptly announced to the Gulfstream test pilot, "You got it!"

We learned that day that the EFIS displays only show 0.99 mach as a maximum. When the Steely-Eyed Gulfstream Test Pilot pulled back on the yoke - nothing happened. The flight test engineers in the back advised him that their instrumentation in the back was showing 1.04 mach (the real time telemetry streaming to Gulfstream flight test operations was showing 1.07 mach). The elevators were ineffective because they were operating behind a well established mid-span shock wave on the horizontal stab. The GV has a fully movable emergency stabilizer, but it is not designed for supersonic flight. A good test pilot never does add-on testing so our SEGTP elected not to use the EMER STAB and rightly thought, "We are descending. As we do so temperature will increase and with it the speed of sound. If I just hang on the aircraft will go subsonic and I will regain pitch control." Which is precisely what happened in the high 30's.

GV

 

[AV8OR]

GV,

I don't know about every body else, but that was a GREAT read. Crap, either know your stuff or you fooled the hell out of me. Either way I was impressed. Schools out.

 

[750driver]

GV,

I don't know about every body else, but that was a GREAT read. Crap, either know your stuff or you fooled the hell out of me. Either way I was impressed. Schools out.

Either GVFlyer is the best BS artist I've ever seen, or he's a former mil/ civ test pilot. I'd bet on the latter of the two. Good educational post. I can always use an aerodynamics refresher

 

[Timebuilder]

Hey, that was neat!

I take it that a second FAA inspector took a ride to get the plane certified...

 

[501261]

Hey GV,

You should consider writing some articles for the aviation rags, that's some good stuff.

 

[Muddauber]

Aero 101

Nice post, GV.

 

[LrBob]

a guy i flew with just got a 90day susp for exceeding 250knot below 10-actually he was at 4000 just departed santa monica ca
he was doing 310 horn blaring all the way-atc called him and asked his speed he said 250 pulled the pwr back dropped 200ft and went right back to 300-the way they caught him was awacs was over head and alerted on him