Tuesday, December 04, 2012

 We don't have autothrottles in the Ultra, so during long cruise legs it's fun to try to get the speed right up to redline manually, without going over - our plane will overspeed in cruise if we set the throttles to maximum continuous thrust.  Our maximum Mach is 0.755, so I'm about 6/10ths of a knot from setting off the overspeed alarm. 



Anonymous said...

On long flights at a constant power setting do you ever notice the speed creeping up as fuel burns off and (in theory) induced drag reduces as the weight goes down? Or is that sort of change lost in the noise?

Sulako said...

I notice the speed creeping up for sure - suppose we climb to FL410 at max gross weight - it'll take about an hour for the speed to get from 220 KIAS to ~230 KIAS and set off the overspeed alarm. Not sure how I'd notice induced drag - enlighten me. From what I recall, induced drag is inversely proportional to the square of the airspeed whilst parasitic drag is proportional to the square of the airspeed. I guess I mostly notice parasitic drag in the form of our max KTAS being around 430 at most altitudes and power settings.

A said...

Doesn't your drag increase because your AoA is higher with more weight? As weight goes down, Cl goes down, so Cd goes down too? That's how I think of it, anyway.

Also, at .7549 Mach, you're less than a tenth of a degree C away from .7551 Mach.

Dave W said...

Great pic! I do enjoy your posts, even the little ones - seems you've started quite a debate with this one!

I'm just a simmer learning the finer points of the E195 at the moment, every time the weather updates I have an automated woman shouting "HIGH SPEED!" at me - also I have to turn off airframe damage on the sim because of this.....

So a question, if you do inadvertently overspeed do you get shouted at and do any additional post-flight checks need to be carried out?

Thanks for blogging!

Dave from the UK

Sulako said...

Hi Dave from the UK. I'll make my funny post first:

If the overspeed warning sounds, I get the right-seat pilot to pull the "Warn" circuit breaker whilst I reduce the throttles.

Har har har :)

Actually, I'm a bit too scared to pull the circuit breaker, even though I have identified it in the simulator as the one that stops the "BEEP BEEP BEEP" from echoing throughout the cabin.

If we overspeed we don't have to carry out any additional maintenance, but having said that, we have never oversped the aircraft by more than a knot or two.

Interesting tidbit: In the Primus 1000 avionics suite which is installed in the Ultra, when the autopilot has indirect control over the airspeed (ie If I command it to descend at a specific vertical speed and we are close to our max airspeed - which we pretty much always operate at in this machine - it will reduce the descent rate once it runs up against the max allowable speed) , it gives itself a 5-knot buffer over MMO, but when it doesn't have control over the airspeed (IE straight and level flight), it gives me a 1-knot buffer. That's why I don't sweat it if I go over MMO by a knot or two - my takeaway from it is that if the autopilot is allowed 5 knots over MMO, then I'm guessing the wings won't fall off in that range. Here's hoping anyway :)

Arf said...

"I'm guessing the wings won't fall off in that range. Here's hoping anyway :)"

That would make for a memorable blog post. ;)

getjets said...

Want to wish all a "Happy New Year"..........and Hello Dave W..!!

Mark W said...

Thanks for finding the time to post something! Between work and being a dad, I know you're busy. These short posts let us know you're still out there. Did you ever read Captain Dave's Flight Level 390 blog? If so, you know he's left the scene. Not to put any pressure on you, but you're one the few remaining bloggers filling in us earthbound readers from the left seat. Keep 'up' the good work.