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Bob & John,
I built my IV-P with only the spring-loaded alternate air door--IAW the
instruction manual as it existed at the time. I added a micro-switch and
annunciator light on the panel to indicate the alternate air door was open.
I don't have the ability to operate it manually. I was concerned about the
small area where the NACA inlet duct opens directly onto the air filter, so
enlarged it as much as I could without making a major alteration of the
cowl/inlet...perhaps 15% or so...during build.
I (unintentionally) validated operation of the door during flight test while
setting up my turbo boost and fuel flow. A turbo boost of 40" MP (should be
38.5") on a cool morning will pull the door open during the initial takeoff
roll, and it closes automatically before you get to 100KTS as the forward
speed builds. I thought this a fairly small margin of flow capacity, but
have "lived with it."
Over the last 14 months/300 hours, I've had the alternate air door open in
flight a few times, usually with visible ice elsewhere, but without other
visible icing on two occasions. I like my system and its function
(automatic), and the annunciator light provides visible warning of
inlet/filter icing before building up enough to cause a significant loss of
power/cabin pressure. Whether you use an automatic or manual system, my
experience is that some type of alternate air source provision is required.
Looking forward to meeting you at the LOBO workshop at Creve Coeur in
September.
Bob Pastusek
-----Original Message-----
From: Lancair Mailing List [mailto:lml@lancaironline.net] On Behalf Of Bob
Rickard
Sent: Wednesday, August 19, 2009 6:03 PM
To: lml@lancaironline.net
Subject: [LML] Re: Alternate air on IVP
John -
I am a relatively low time IV-P guy (100 hours) but a 2800 hour F-16 guy, so
take any comments with that in mind - I don't pretend to know as much as
most guys who have flown Lancairs (and built them) for years. But I have
flown up high and pressurized for many years and am comfortable doing so.
I have had occasion to use the alternate air door twice already since buying
the airplane this spring. The first time it iced up with only a trace on
the wing and I lost manifold pressure (and cabin pressure) and had to
descend (I was going down whether I wanted to or not) to let it melt - it
did, and everything was ok. I didn't know how to use the door at the time.
The second time it started to happen - an insidious decrease in MP and
increase in cabin press - I switched to alternate air and kept the motor
running (but still descended out of the weather and light ice). I have
never seen the "whole plane iced up" so I don't agree with that assessment.
Now the details - I fly long legs up high, that is why I got this airplane.
I don't fly in "weather" or icing continuously, but the occasional high
cloud is unavoidable. At those altitudes, as you are probably aware, icing
can occur anywhere in visible moisture, you never know. I have a thermal
deice system so I am not scared to fly in a cloud, and this alternate air
door is a must in my opinion. I know I can keep flying safely without ice
on the wing, but losing the motor and cabin pressure is serious stuff.
Jeff Edwards built my airplane and has a 6A servo with a switch and
indicator between the gear and flap handle. I just had to order a new servo
because this is in a relatively high heat/vibration area on the lower cowl
where the door is. I would be happy to send some pics from this install
(will be installing the new servo in 3 weeks incidentally, at the LOBO
maintenance workshop at Creve Coeur Airport (1H0) on 12-13 September. My
airplane will be the demo bird for the workshop.
Bob Rickard
N619SJ
-----Original Message-----
From: Lancair Mailing List [mailto:lml@lancaironline.net] On Behalf Of John
Barrett
Sent: Wednesday, August 19, 2009 10:01 AM
To: lml@lancaironline.net
Subject: [LML] Alternate air on IVP
I'm looking for advice on alternate air for the TSIO-550. We have set up a
manual actuator in case the spring loaded/magnet feature fails in some
fashion. I am advised now by a builder assist shop to unhook this because
the cable might hang up if the door pops open and may be more of a hindrance
than a help.
The gentleman suggests that there have been no actual incidences of air
blockage and need for the alternate air because the hole is so large with
the circular filter that you would have to cover the plane with ice to
ingest enough to plug the hole.
Having had engine stoppage three times in my Beech Sierra, I know that snow
storms can readily bring on that condition in the IO 360 with the small flat
intake under the cowl, but wonder if anyone has experience or enlightened
information on whether the manual cable pull should be installed or
disconnected on the Lancair.
Thanks in advance for your assistance.
Regards,
John Barrett, CEO
Leading Edge Composites
PO Box 428
Port Hadlock, WA 98339
www.carbinge.com
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