Enviro Mass Flow

[seanmcgillivray]

Any long term determent to using mass flow on my Enviro?

TIA.

[Bruce Byerly]

Not really but you shouldn’t need to use it.

[donv]

If you ever fly a Sundstrand airplane, don't confuse "Mass Flow" with "Max Flow" even though it's the same switch and would appear to have a similar function.

[seanmcgillivray]

Think I have an issue with the outflow valve. Sometimes the pressure drops below selected. Mass flow fixes it.

Going to do a little reading as I don't understand what Mass Flow does? Does it rob more bleed air?

[donv]

Mass Flow should just increase the air flow. So if you have a leaky cabin, it can overpower the leaks through sending in more air.

[Boduggan]

There is way more to Mass flow. If the system is a enviro mass flow is everything. If failed you will have little or no pressurization. The cabin switch its self in the cabin is for adjusting the mass air flow valve open a touch more. It’s not like using it turns on a motor, you’re simply changing the mass air flow computer to allow the valve to open wider allowing more outside air to be added to the bleed air. Increasing the volume of air to the cabin. Below 10,000 feet the idea is you can overcome the air to air exchanger and i guess ice it over and then end up with a hot cabin on landing. The mass flow in the enviro is a really simple system with only the mass flow valve and the bleed valves being just a few of the actual moving parts. Outside of a ground blower motor and re circ blower motors the back of the plane is simple and with few moving parts.

[Bruce Byerly]

Think I have an issue with the outflow valve. Sometimes the pressure drops below selected. Mass flow fixes it.

Going to do a little reading as I don't understand what Mass Flow does? Does it rob more bleed air?

Yes Mass Flo Max robs a little more bleed air and, as noted, you shouldn’t have to use it but it can be handy when things get a little leaky before maintenance is convenient.

No real downside to using it. Max Flow on Sundstrands ought to be deleted and is often disconnected on purpose as it just throws another 30% or something at a turbine already spinning thousands of rpm and begs even earlier failure imho. Those things flow more air anyway so they definitely shouldn’t need more flow to make max diff.

I have noticed on many planes the tendency for Enviro to fail to make max diff at intermediate altitudes but increase diff above 240-250 just fine. It’s kinda strange but with all of the 1980 circuitty/computers, there is plenty to go wonky on Enviro systems too. There are a bunch of planes with override switches installed to take out the computers but that’s another story. 

[donv]

What do the override switches do, Bruce?

It's been a while, but I've flown Enviro airplanes which wouldn't make max diff. The 1000s seem to be better than the 840/980 in that respect.

[Bruce Byerly]

What do the override switches do, Bruce?

It's been a while, but I've flown Enviro airplanes which wouldn't make max diff. The 1000s seem to be better than the 840/980 in that respect.

I believe they give you direct control of the valve, takes the computers out of the picture.

[Adam Frisch]

Has anyone explored a no-bleed electric air option? Is there another place for a gen on the case that could run it in back of engine? Boeing did it very successfully for the 787. Bleed air isn't "free" anyway, it robs the engines. That same power given back could prob drive another generator and you'd have a much simpler system with no monkey motion routing of hot bleed air and valves into cabin.

[schrambow]

Hi guys,
in my 980 (enviro) for the last 6 plus months, i have been using mass flow all the time above 7K or so. It would give me max differential all the way up to 28K perfectly.  I know i have a few cabin leaks and used it continuously for the past 6months, and now the bird is in the shop for a 150hour and to fix these cabin leaks.  Hopefully, they find and fix all the leaks so i don't have to use the Mass Flow, but it is a nice feature to be able to take some of the bleed air if needed due to a leaky cabin, until one can get it into a shop to fix.  If fixed, maybe i can see more bleed air to the power plant and more speed, lol? It would also be great to see alot more -5 or -10 ISA too!