Throttle

The throttle for UL engines is a bit different than standard aviation 'stuff'.

The throttle body is on the top of the engine.  There is a spring on the throttle body that holds it OPEN.  The standard UL installation is essentially a bike type cable that draws the throttle closed.

I am going with a standard aviation type throttle.  Specifically a McFarlane locking vernier assist type.

The dimensions are not standard.

The firewall penetration is complete, and I had a 48" throttle I could use for mock up.  A fellow builder went through this a couple weeks before I did, and sent me his design and I used that as my starting point.

Ordered.  Should be less than 2 weeks to fabricate and ship.

Will need to build a custom bracket to seize the throttle end, using the rear engine hoist mount.

Almost 2 months later... we have been to California and back on vacation, and work has been nuts.  Have not had much time to work on the project.  But the throttle has turned into a comedy of errors.

• I had the throttle shipped to a package service in Blaine, WA.  I do this a lot... saves on shipping and brokerage fees.
• The plan was to pick it up on the way back from California.  We would have been down long enough that I would not pay tax on the throttle (its not huge, but every bit saved adds up).
• The package service has 24 hour lockers.  You request the locker by 2PM, the packages get loaded, and then you can pick it up whenever you want.  This service costs $1 (on top of the $3 per package).  Very convenient.
• While we were in California, the package service had a fire in their locker facility, which moved into their warehouse.  Lockers are destroyed (and anything in the lockers was not recoverable).  Super sad for the business.  They are such nice people.
• Bottom line... I couldnt pick up my throttle on the way home.  Went down a week later to grab it (and my intercooler).
• I get the throttle home, and start test fitting it.  The UL engine needs just shy of 2.5" of throttle travel.  My custom throttle has 2.38".

• Well thats not going to work... I email pictures and call McFarlane.  According the the service rep I dealt with (who was super helpful), it was made this way on purpose to "maximize the overlap at the throttle end", based upon my drawing.  Well, the throttle calls out the minimum required travel / throw of 2.5".  Bottom line:  redesigned the throttle to get 2.5" of travel.

• Above is old / new.
• New throttle is ordered, and should have it within a couple weeks.

New throttle has arrived, and boy is she a beauty!  I messed up when I ordered originally and used the non vernier form.  McFarlane was very accommodating and built the new one as a vernier control.  Also, they sent the incorrect tool last time, and sent the new one at no charge.  The service was outstanding - zero complaints.

The vernier control version of the throttle is different.  The locking mechanism ships separately and needs to be installed.  There is a big note on the locking mechanism to NOT remove the temporary shipping shaft without the throttle shaft directly following it.  Of course I did, and all the roll pins came out.  Luckily they have a video on how to put it back together... disaster averted!

The nice part about the vernier control is you can mount it from the rear.  Doesnt matter now, but that may come in handy at some point in the future.

Nex challenge is the mounting bracket on the engine.  The stock UL bracket is for a bike style cable and sleeve.  Zenith has a bracket that mounts to the engine lift point location.  I am going to something similar.

First step is to make the plate that bolts on to the lift point.

I used a shape finder to get the curve around the starter.  The throttle mount point has to be about 3" back from the plate, and on a bit of and angle.  I made a template out of paper first, then aluminum to find the center of the holes, and then transferred that onto .063 4130 steel.  I want the plate as large as possible.

I am worried about the stresses on this bracket and vibration.  The location of the mounting holes is not ideal.  I put a bend in the left hand side of the bracket, and am going to add a small arm that goes over the top of the aluminum mount for some added rigidity.

The bracket is all tacked together.  Test fit.

Throttle fully closed.

Fully open.

Seems to do the job well.  Going to add a gusset to strengthen the arm.

Gusset added and everything tig welded.  Fits well and appears very strong.  No flex at all.

The bracket needs to filing and priming / painting - but will do that when I do the next batch of parts.