MD-11 Overspeed

[davidzill 8]

When I use REX, I have fast tail or headwinds, but my flight is always perfectly smooth (other than lower than normal OAT). When I use default FSX weather, I always get the overspeed about every 20 minutes in a cruise.

[Turbine777 13]

When I use REX, I have fast tail or headwinds, but my flight is always perfectly smooth (other than lower than normal OAT). When I use default FSX weather, I always get the overspeed about every 20 minutes in a cruise.

Interesting and good observation David. I'm not sure if this will help, but if you are using a saved default flight, try deleting it. I have cleared about a ton of FSX weather issues this way, and not just using FSX wx, but have seen many times where even though I use ASA or REX, the default gets corrupt and FSX seems to want to possibly share data between the two at times, rather than let the addon do it's own. I have also seen cases where using FSX weather and a saved default that it has tainted its own weather the same way.

[Orlaam 306]

I find this odd then. Why would such a dramatic and sudden drop in Vmo/Mmo occur? It seems like a poor design to let it do this. If this is how the real world MD-11 operates, then wouldn't the FMS compensate for it?The speed dropped (which it never does with real world weather), but the FMS still shows .803 as ECON. I would think it should show a new value in the FMS too.

[Guest BlueRidgeDx]

Hi Orlaam,I can't answer your specific FMS question with certainty. I can speculate however that the speed restriction is required to alleviate wing bending moments once the tip tanks are empty. With a full bag of fuel in the tip tanks, it greatly reduces the amount of wing-flex.Another look at the FCOM reveales that the transition from the unrestricted Vmo/Mmo to the lower limit should occur gradually, not instantaneously. Here's what the book has to say:"When the wing tip fuel tanks are 60% full or less, the Vmo/Mmo is 320KIAS at sea level to 30,704 feet, and .85 Mach above 30,704 feet. The transition between the two speeds begins at 90% tip fuel and varies linearly down to 60% tip fuel."So, if you're seeing an instantaneous reduction in Vmo/Mmo, I would interpret that as being potentially incorrect behavior. Then again, I know very little about the MD-11.