Bell 412 EP versus HP performance

[getiton]

I'm trying to understand the performance differences between the Bell 412 HP (with -3BE engines) and EP (with -3D engines). I've read other threads on general Bell 412 performance, and, aside from the different AFCS, I had thought that the main HP to EP difference was OEI performance - but have found that some AEO differences are also apparent. The graphs in the flight manual are the same for hover ceiling IGE and OGE (TOP) but differ for hover ceiling at MCP. TO distance is the same, as is AEO climb at TOP. AEO climb at MCP is different as is OEI climb at MCP, although OEI landing distance using 2.5 min power as required is the same. Why are the AEO MCP curves different? I know that the engine Tq, N1 and ITT limits are higher for the EP, but isn't AEO MCP = 81% mast Tq for both? Assuming 100% mast Tq is the same 'real' Tq for both, is it just that you can maintain 81% for a bigger Hd envelope with the -3D than you can for the -3BE? In other words, would the climb performance of an HP at engine limits be the same as for the EP when flown to the same parameters, but that the EP could then be taken beyond those parameters?

[BlenderPilot]

I have flown both, mostly above 7 or 8 thousand feet, performance is basically the same, on the only difference I would say is that when operating say at 8500 and 20C when you can get close to the N1 limit, the EP had more room to spare.

In case of an engine failure, the EP would have defintately performed a little better on one engine due to this extra N1 at altitude.

[getiton]

Thanks. You seem to confirm my conclusion that the twin engine performance appears essentially the same for ISA conditions or even at low-medium altitudes for warm conditions but hot and high is another matter due to the extended limits of the -3D engines. However, I'm now still confused as to why the OGE hover ceiling and AEO climb performance at TOP is the same for both HP and EP!
Can you also comment on how different the EP's SAS and ATT modes handle compared to the HP, particularly in more aggressive manoevres, and if there are any other notable issues, say when using the Flight Director(s) (apart from the potential availability of the 4th axis)?

[BlenderPilot]

Can you also comment on how different the EP's SAS and ATT modes handle compared to the HP, particularly in more aggressive manoevres, and if there are any other notable issues, say when using the Flight Director(s) (apart from the potential availability of the 4th axis)?

Call me insensitive, but noticed absolutely no difference between HP's on either aircraft.

[Matthew Parsons]

getiton, where are you getting the OGE hover ceiling? If it's from the WAT chart, then that is a limitation and not necessarily a capability. If that is so, then the limitation may be based on something other than power available.

[800]

The HP model has "Helipilots" (anologue autopilots) and the EP model has "Autopilots" (digital autopilots) with the option of the 4th axis (collective).

The 4th axis option does not neccessarily include "auto-hover".

The Autopilot (AP) vs the Helipilot (HP) will intercept a required track or inbound radial smoother than the old helipilot system.

Then with the EP model there is the option of single or Dual Digital Flight Directors (FD's)

cheers

800

[getiton]

Thanks Matthew; yes the hover ceiling was from the WAT charts.
Thanks 800; the info about smoother intercept is what I was after, but can you also comment about APs vs HPs in responses to, say, step inputs (like what would have to be demonstrated to validate a simulator)? I also presume the SAS/ATT OFF behaviour is the same between HP and EP.

[Squeaks]

It will also depend on which 3D engine you have: D, DE or DF. The ITT and N1 limits for the DF are significantly higher: OEI the 30 minute power is now 106.8% N1/885C, the 2.5 min limits are now 109.2%N1/940C ITT.

Don't forget there is a Cat A supplement which uses 103.5% Nr as well, for the EP. I'm not sure if this was approved for the HP: anyone know?