REFLECTOR: IO-550N intake

[Bob Jackson (Jax Tech)]

You may not want to, but I'm just saying another option is to shim your
engine down ~1/8" to get the clearance, and fly with the prop ~1/8" low in
the cowling opening (without appreciably affecting cruise performance).
There is normally that much 'slop' in the opening.  It's just something you
could experiment with adding some shims and to see if that fixes your 5/6
clearance and how much out of center you might be willing to tolerate.  If
you're unwilling to have the spinner out of center, then you can probably
bend the aluminum 5/6 tubes down pretty easily to get your 1/8 clearance.

 

Good luck,

Bob

 

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From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On
Behalf Of Don Johnston
Sent: Friday, October 07, 2011 8:10 PM
To: reflector at tvbf.org
Subject: REFLECTOR: IO-550N intake

 

The engine is aligned with the crank centered in the opening. Any shimming
at this point will result in the prop not being centered in the opening. 

So now it's either lower the 5 & 6 intake tubes or put a bubble in the
cowling.

Don

Date: Fri, 7 Oct 2011 19:32:33 -0400
From: "Bob Jackson" <bobj at computer.org>
Subject: Re: REFLECTOR: IO550-N intake

Don,

We have only ~1/8" clearance between our IO-550N 5 & 6 intake tubes and the
plenum, and the plenum top barely rubs against the bottom of the top cowling
in flight.  We did not have to bubble our top to achieve this clearance.  If
you aren't already flying maybe you should check the placement of the engine
mount on the firewall, or consider shimming it down.

Also, over time if your installation is like ours, the engine will slowly
sag at the rear an 1/8 or 1/4" -- so we've had to shim our engine mount
bottom legs on the firewall up/out a couple of times over 500 hours to keep
the prop perfectly centered in the cowling hole.  You might be able to shim
the engine mount angle down (probably 1/8" aluminum shims under the top two
engine mounts will bring your #5 & 6 intake tubes temporarily below the
upper cowling) -- then in a couple of hundred hours, as the engine sags on
the mounts, you can take the shims out and still have the prop centered.

We haven't been able to detect the effect of the change in angle of the
thrust vector caused by an 1/8" shim and tilt change (up or down) has on
cruise speed -- cruise speed doesn't seem to be particularly sensitive to
small tilt changes like that.

Bob Jackson
Turbo 'Cross Country' XL/RG
N2XF 

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