Making a zero degree thrust line mount

Larry G · Mar 6, 2015

I'm in the process of drawing a print for myself using print 12351 as a reference to build up a jig to build a zero degree 1" drop. No swing out mount. Before I get much further on this and start making a jig I just want to see if I am figuring things right on this. Your comments would be helpful. Thank you

Olibuilt · Mar 6, 2015

I did about the same thing, for a O-360 but with swing out mount. You can also move the engine back an inch without any problems with firewall clearences.

Did the fabrication and most of the welding in my simple jig.

But watch out for stock cabin heat box and gascolator clearances...

Cub junkie · Mar 6, 2015

If you are going to build your mount off the airframe I recommend welding your fuselage spools up and then locate your holes for your jig from the fuselage.

Steve Pierce · Mar 7, 2015

Why not make it swing? How will you get the mags off?

Larry G · Mar 7, 2015

Hi Steve
I'm planning on electronic ignition thanks for asking though. Does the drawing look right for what I am planning.

Cub junkie · Mar 7, 2015

Swing mounts are easier to fabricate. The firewall side tubes are simple angles to fit to the "U" shaped brackets that swallow the firewall lugs. Oli's pics illustrate this. By not doing it this way you save a little weight by eliminating four AN6 bolts and associated hardware. Everything is a compromise. Your drawing thrustline looks correct to me but how important is the thrustline location on a cub? (I.E. SQ2)

Larry G · Dec 27, 2015

Well I didn't get my wing kit buy Xmass so I have been working on my engine mount jig. Been thinking about the swing out mount more.

Fabman · Dec 27, 2015

That Piper drawing is the mount for motors with less than 15Ohp, see the date is 1949. On the 150hp mount the lower bushing (the one against the motor) is longer and there is about 3/8" gap between the back side of the LA washer and the cluster. I know this because I recently tried the mount that is depicted in the Piper drawing on an O320 and the two lower tubes were touching the oil sump and a tube was touching the LH mag! I did a lot of research on the difference between the two mounts!! I looked at a bunch of different mounts and all of the one that had the LA washers at the clusters like this drawing had clearance issues!
On your drawing I would leave the washer in the same spot but bring the intersection of the tubes aft 3/8" and you shouldn't have any clearance issues!
I'll try to post some pics!

Larry G · Dec 27, 2015

Fabman said:
That Piper drawing is the mount for motors with less than 15Ohp, see the date is 1949. On the 150hp mount the lower bushing (the one against the motor) is longer and there is about 3/8" gap between the back side of the LA washer and the cluster. I know this because I recently tried the mount that is depicted in the Piper drawing on an O320 and the two lower tubes were touching the oil sump and a tube was touching the LH mag! I did a lot of research on the difference between the two mounts!! I looked at a bunch of different mounts and all of the one that had the LA washers at the clusters like this drawing had clearance issues!
On your drawing I would leave the washer in the same spot but bring the intersection of the tubes aft 3/8" and you shouldn't have any clearance issues!
I'll try to post some pics!

i will have to look into this. Will it make any difference that I am going with zero thrust and 1" lower.

aktango58 · Dec 27, 2015

having a swing out will also allow you better access to find pesky oil leaks on the back of the engine, deal with oil screens/filter assemblies, temp/press probes and all of the other things that go onto the back of an engine.

When you have a little leak back there, it will really make you mad when you have to pull the engine to change a simple gasket.

Just my thoughts, ymmv

skywagon8a · Dec 28, 2015

Larry G said:
i will have to look into this. Will it make any difference that I am going with zero thrust and 1" lower.

You are changing the engine relationship to the mount and airframe in two different directions. Thrust angle and 1" lower. What part of the engine is 1" lower, the front, the back, the whole engine? Is the thrustline offset for torque or parallel to the fuselage? These changes can create interference problems which are not anticipated. A tube angle to a cluster moving just a little bit can interfere with something. There is only one way that you can be certain that all of your clearances are adequate. The engine needs to be in place on your jig. Changing the relationship of an engine to it's mount requires lots of investigation before lighting the torch. We can tell you all sorts of ideas here but you need to do a hard test, unless you have one of those fancy computer programs which will give you the answers.

Larry G · Dec 28, 2015

Sky
What I did was push the bottom engine attach point out so it is square to the firewall then lower the two engine mount clusters down 1". The engine is parallel to the firewall. There isn't any fight thrust that I can see on any print is there.
Thank you everyone for your input anything helps. I will put my building jig on my engine that I used to build the main one.

PA 11 cub · Dec 28, 2015

I believe the whole objective on on "zero" thrust is to tilt the motor, prop up so the thrust is parallel to the airframe , wing incidence etc. No matter if you lower the back or raise the front of the engine to accomplish the objective there will be fit issues using stock type cub components. I believe with Larry G idea of lowering 1 inch he is on the right track. Keeps the nose cowling lower or maybe even equal to stock cub while keeping zero thrust. The beauty of experimental is building and or trimming cowling , exhaust , heater box etc to fit. JMHO

sportingrifle · Dec 30, 2015

Larry...thanks for sending me your drawing, I have built m fuselage repair jig that incorporates your mount. I am also hoping that it will clear a B&C alternator run off the vacumn drive pad. Time will tell! Thanks again,Kevin.

Baja · Mar 12, 2016

A ? a little off the subject ! But i have a Alaska Airframes wide body and plan to have an io-360, Question is can i make the firewall off of the stock PA 18 drawing !

Thanks

Mauleguy · Mar 12, 2016

I built a Javron wide body and the firewall does not match the stock cub firewall. I had a plywood template from the last cub I built that was stock and wanted to compare the difference. If I remember it was same height and about an inch wider on each side from centerline.

Larry G · Jan 7, 2017

I finished my engine mount and built stands for my wings. Every thing fit nice on the firewall and engine.

sportingrifle · Jan 7, 2017

I just want to thank Larry for all the work he did with this. We incorporated all his research into our jig and just finished building a "Larry Mount" as well.

It even cleared the prop governor but we abandoned the swing mount fittings as the mount wouldn't swing wit the governor on it. Cheers sportingrifle.

KelvinG · Jan 7, 2017

Larry G said:
View attachment 29588 View attachment 29589 View attachment 29590 View attachment 29591
I finished my engine mount and built stands for my wings. Every thing fit nice on the firewall and engine.

If my shop were 1/2 as clean! Well, dare to dream.

Sent from my SM-P900 using Tapatalk

hotrod180 · Jan 8, 2017

Now that's pretty!!

Making a zero degree thrust line mount

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