Do You Know What Vmc Is?

[MauleSkinner]

Interesting, do you recall what the approximate airspeeds were? I assumed it would be 100 knots or less for most types with fuselage mounted engines, which is probably below stall speed for everything except a few citations.

The only info I've got handy is for the Hawker 800...Vmca is pusblished at 115, Vmcg at112. Vref at nearly max landing weight (lower than MGW, so Vmc should theoretically increase) is 130, an additional 15 knots for 0 flaps makes 145, which should be approximately 1.3 Vs1, putting Vs1 somewhere around 112.

But the plot thickens...at lighter weights, our flap 15 takeoff (same Vmc numbers as flap 0, according to the manual) V1/Vr increase at colder temperatures...from 116 at the high-temp to as high as 122 at ISA. My guess is they're pushed up by Vmc issues, unless you can see another reason to increase runway requirements at lower temperatures.

Fly safe!

David

 

[kevdog]

The only info I've got handy is for the Hawker 800...Vmca is pusblished at 115, Vmcg at112. Vref at nearly max landing weight (lower than MGW, so Vmc should theoretically increase) is 130, an additional 15 knots for 0 flaps makes 145, which should be approximately 1.3 Vs1, putting Vs1 somewhere around 112.

But the plot thickens...at lighter weights, our flap 15 takeoff (same Vmc numbers as flap 0, according to the manual) V1/Vr increase at colder temperatures...from 116 at the high-temp to as high as 122 at ISA. My guess is they're pushed up by Vmc issues, unless you can see another reason to increase runway requirements at lower temperatures.

Fly safe!

David

Then you get into issues when you upper or lower rudder is inop. Changes Vmca.

 

[tomgoodman]

Speed is Life

Now for a 707 or a DC8, I'd imagine that Vmc might be a factor if you lose both engines on one side....can't say for certain though.

Very much so. Here's data from a very old Air Force C-135 manual:

(Sea level, 15 degrees C, two engines out on the same side, other two at full power, full rudder hydraulic power available) --- 124 kias

(Same, but only one engine out, rudder power inoperative) --- 155 kias

Vmca speeds decrease with higher temperatures and pressure altitudes.

For directional control purposes, losing rudder authority is worse than losing a second engine, as you can see. They could only estimate the Vmca for two engines out AND loss of full rudder hydraulic power --- 200 kias.

 

[Thresh]

I'd rather screw my way across the country, then blow my way.

(props vs jets)

 

[MauleSkinner]

Then you get into issues when you upper or lower rudder is inop. Changes Vmca.

Good thing I've only got one rudder

 

[siucavflight]

I'd rather screw my way across the country, then blow my way.

(props vs jets)

Is that your pic in your avatar?

 

[Midnight Flyer]

Yes, I know what VMC is. Visual meteorological conditions.

 

[siucavflight]

Thresh is going the way of iflyvfrifr

 

[Flyerjosh]

I'd rather screw my way across the country, then blow my way.

(props vs jets)

Have it how you like it... but just remember that I'll be drinking beers and sitting on the beaches hours (or even days) ahead of you...

 

[Flyerjosh]

Vmca (Minimum controllable airspeed) in the Citation is 86 KIAS. Since I don't really plan on flying below about 100 KIAS (lightest Vref is 91 KIAS and lightest rotate speed is 87KIAS for a sea level 50C OAT takeoff), I don't worry about it.

In the event of an engine failure, we pitch initially to V2 up to 400' AGL and then clean up and climb out at Venr which is the factor established single engine enroute climb speed (160 KIAS).