Bell 407 Internal Max Weight Graph FMS28

[Wakatopatopa]

Hi guys/gals, looking at the Bell 407 OGE hover ceiling graph (FMS 28). Wondering why the MAX GW Internal line deviates to the left about 2/3rds of the way up? Effectively reducing the allowable internal weight considerably with altitude compared to what you can carry externally.

Have heard a few 'theories' from fellow 407 pilots. The most likely so far being extra safety margins for internal load as it cannot be jettisoned like external?

Thoughts?

[Ascend Charlie]

External loads are not a weight that has to be borne by the skids. They can be pickled off, to come back to a safe weight for landing on the skids.

[Wakatopatopa]

Originally Posted by Ascend Charlie

External loads are not a weight that has to be borne by the skids. They can be pickled off, to come back to a safe weight for landing on the skids.

Agreed if your external load puts you above the Max internal GW of 5250lbs at lower altitudes.....

However if you use the graph to plot internal and external loads as you get higher you'll find you can carry more externally than internally at the same altitude/OAT and still be well below the max skid weight?

[LRP]

Don't know the official Bell explanation, but it appears to coincide with the Area D limits of the Height Velocity Diagram. That envelope was only demonstrated to 5000Hd for the increased GW (FMS-28)

[Wakatopatopa]

Originally Posted by LRP

Don't know the official Bell explanation, but it appears to coincide with the Area D limits of the Height Velocity Diagram. That envelope was only demonstrated to 5000Hd for the increased GW (FMS-28)

You could be right. Just seems weird to me that if you go back to the original FM-1 performance section the older graphs allow a higher Internal Max GW than what those in FMS-28 do.....

[LRP]

It's because lawyers write the RFM. You can operate at higher GW's, you just have to do so "outside" of the HV curves. There are no aircraft modifications to operate under FMS-28. You just have to pay for the FMS in order to use the expanded envelope (add'l flight testing), and above 5000Hd, you're on your own.

[szbarn]

In Every hover chart in FMS 28 the Gross Weight line will turn left at around 5300` DA.What happens is when you get higher in weight and higher in altitude,you can`t stay out of the H/V diagram.It`s not that the 407 isn`t capable of carrying 5250 lbs at 11000`Da,you just can`t land,takeoff or do in ground effect maneuvers above 11000`DA.As a matter of fact the chart only allows you to takeoff below 4400lbs at 11,000`DA.So if you takeoff at sea level using FMS 28 at 5250 GW and plan on landing at a location that`s over 5300`DA you need to put the FMS 28 away and go with the regular chart AND make sure you have burnt enough fuel that your weight satisfies regular chart limits.

[Ascend Charlie]

Would one possibility be that adding weight to the cabin is done by adding people - and the last place to put them is on the middle row facing backwards. This pulls the cg further forward and might be the bend in the line?

Just musing, it's 20+ years since I flew a 407 and there has been a few beers tonight...