Bell 407 Internal Max Weight Graph FMS28
 

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?

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?

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.....

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.

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...