Very interested in that!
If you have automatic-only alternate air how do you check that it works? An alternate air flap may not operate for years and could corrode shut without you knowing, although hopefully its operation is checked at maintenance.
That should e checked at every annual. The way they do it with my plane is they move the lever against spring resistance to see it open.
So its not a real test but it will determine if at least it opens. I guess to check it functionally is to run it up 2300 RPM and stick a piece of cardboard
in front of the air inlet to see if it opens the alternate air door. But Ive never seen anyone do that.
I guess to check it functionally is to run it up 2300 RPM and stick a piece of cardboard
in front of the air inlet to see if it opens the alternate air door. But Ive never seen anyone do that.
I wonder why 
This system does seem to have a real problem. But (as I posted in the fuel servo icing thread) the key probably lies in the use of prop TKS.
Which leads to the Q of whether the fluid gets into the air intake. On the TB20 it does. Where is the SR22 air intake?
Where is the SR22 air intake?
Donaldson Company, Inc. wrote:
The Cirrus SR22T is the newest member of the Cirrus SR22 family of composite airframe piston engine aircraft. The key feature of the four-seat airplane is the 315 HP twin turbocharged TSIO-550-K engine. Providing air to the engine is a redesigned cowl with new, dedicated NACA (National Advisory Committee for Aeronautics) induction inlets – one on each side of the lower cowl – which direct air flow into the dual Donaldson filters. This new system offers improved engine airflow and better performance.
Peter wrote:
the key probably lies in the use of prop TKS.Which leads to the Q of whether the fluid gets into the air intake. On the TB20 it does.
Peter I have a TKS system that includes prop deice. There is never any fluid in the engine compartment. I can just see what would happen if the filter element got soaked with TKS fluid. Not so much with Bracketts but with a Paper filter. The prop deice slings it away. The way the NA 210 system is set up there is no way you are going to get ice in the alternate air intake.
Ive had the system for 20 yrs and have been in all sorts of unforecasted ice from mild to severe including heavy snow never a problem.
The prop deice slings it away
Do you not get any TKS spray on the front window? I get lots in the TB20 – enough to totally prevent any icing sticking to the window, no matter how much ice there is on the wings.
If you get spray on the window then it will be going all over the cowling, though probably not into air inlets which are on the side of the lower cowling (as in the SR22).
Not so much with Bracketts but with a Paper filter
That may be true, but if you get icing inside the air duct (as evidently both the TB20 and the SR22 do) then water droplets must be getting through the filter, so the TKS fluid will too.
The way the NA 210 system is set up there is no way you are going to get ice in the alternate air intake.
That may be an unintended vulnerability.
Ive had the system for 20 yrs and have been in all sorts of unforecasted ice from mild to severe including heavy snow never a problem.
If you have prop TKS, I bet you are getting TKS fluid going right inside the air duct. The two incidents I had (see the fuel servo icing thread) were both without TKS; I thought that at -15C one cannot get icing. That’s fair enough for external parts but there is a temp rise in the air duct.
On a G2 Cirrus the air ducts (for cabin air) are not in line with the TKS panels on the wing, I don’t think the fluid will get in. On a G3 I am not sure.
A non-FIKI SR22 (like mine) will get some fluid on the windscreen from the prop, especially when it’s running in high mode. On the FIKI-version (AeroPlus’s) there’s extra sprayers in front of the windshield and an extra pump (tank is bigger too)
The air inlet for the engine is through the cowl openings, the air filter sits right behind. On the G3 it’s a NACA inlet on the right side of t he lower cowl.
An aircraft with the engine air intake anywhere in the front is definitely going to get TKS into the air duct, and one with NACA inlets on the side will get less.
The fact that the alternate air door ices up is very revealing of a big problem. It means
If an SR22T iced up its alternate air door while TKS was running suggests that the NACA inlets don’t get the TKS going in.
I am not going to pay $$ to read the COPA forum but it would be interesting to know if anybody there has any real data (temperature measurements).
I think Mooney has that data from when they tested the 252 with the new MB engine that had a NACA inlet instead of the usual scoop.
They were saying that the NACA inlet setup completely does away with icing (which was a known problem on the previous setup).
