Sign in to follow this  
Ken.Pascoe

Bug Report : B777-300ER VMO

Recommended Posts

Howdy All

 

I've noticed that the PMDF B777-300ER VMO is modelled incorrectly. The PMDG aircrat has a VMO of 330 knots from sea level up until the MMO .89 limit is reached. This is not quite correct.

 

Owing to (I believe) the re-designed wing tips of the 300-ER, the VMO actually increases from sea level to 350 KIAS, where it meets the M.89 limit at ~FL290 (in ISA). Thus when you climb the aircraft at 320 kts, you can see the VMO steadily increase away from your selected climb speed, giving you a greater margin in the event of an overspeed occurrence.

 

I've seen climbs into jetstreams headwinds where other aircraft (including the 772 and 773) would have suffered a VMO exceedence, but the increased margin of the 300ER doesn't.

 

Is this something that has been missed?

 

Ken

 

VMO-MMO.jpg

 

 

 

Share this post


Link to post
Share on other sites
Help AVSIM continue to serve you!
Please donate today!

 

 


Is this something that has been missed?

 

Ken, it honestly does little good to post these here over submitting an actual ticket. While the developers do hang around the forum a decent amount, the only way things are guaranteed to be seen is to submit tickets via support.precisionmanuals.com.

 

If you're unsure if you're right, then here is a great place to discuss it. If you're absolutely sure, though, submit a ticket.

Share this post


Link to post
Share on other sites

The wing tip design is the same for the 200LR as the 300ER. I doubt it has any bearing on VMO. It's common for VMO to increase with altitude.

Share this post


Link to post
Share on other sites

Is this something that has been missed?

 

According to the FCOM (Vol2) VMO for all 777 models is 330 knots (it doesn't say this explicitly but refers to VMO-16 knots as 314 knots.)

 

However, the FAA Type Certificate Data Sheet for the 777 lists VMO/MMO as

 

-200: 330KIAS/M0.87

-300: 330KIAS/M0.89

-300ER: 330KEAS/M0.89

-200LR: 330KEAS/M0.89

 

KIAS is Knots Indicated Airspeed

KEAS is Knots Equivalent Airspeed

 

http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgMakeModel.nsf/0/e3a891bd1c8a006986257d8e005b93fe/ and open T00001SE.PDF

 

Indicated Airspeed and Equivalent Airspeed aren't the same above sea level ISA. At 28750 feet, Mach 0.89, Equivalent Airspeed is 330 knots but Calibrated Airspeed (very nearly the same as Indicated) is 351 knots. That tallies with Ken's observation and graph.

 

It seems PMDG have made VMO 330 KIAS when it should be 330 KEAS. Therefore the VMO indication (KIAS) should increase with altitude until Mach 0.89 becomes the lower limit.

 

The raked wingtips may well be the difference as Ken suggested, as it applies to both 200LR and 300ER.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
Sign in to follow this