Fitting A McCauley Propeller on a 4-Cylinder Lycoming-Engine Glasair


Stoddard-Hamilton Aircraft does not stock a McCauley spinner installation kit for the Glasair I, II, or GlaStar aircraft. We do stock a McCauley spinner install kit for the G-III. The spinner diameter for these two sizes of aircraft are significantly different and therefore the spinner installation kit for the G-III cannot be used to install McCauley props on the 4-cylinder Lycoming powered S/H products.

Figure 1.

Figure 1 is an illustration taken from the G-III McCauley spinner installation instructions and is provided to show general configuration of the spinner mounting components. This installation is on the non-extended (compact hub) style propeller.


The McCauley prop company does not currently manufacture a compatible prop for the 4 cylinder Lycoming S/H aircraft. This is not to say that there are not McCauley props out in the field that cannot be adapted to the Glasair and GlaStar aircraft. We have worked with builders doing this and have developed techniques to do this.

Having recently helped mount a Stoddard-Hamilton spinner on a extended hub McCauley prop I thought it appropriate to get my procedures down on paper for those builders who may be contemplating a similar course of action.

NOTE: The standard non-extended hub McCauley prop requires slightly different procedures and will be handled separately.

Before beginning any new spinner-to-prop installation I find it is easiest to make a full size drawing on paper showing the side profile of the spinner and the location of the key elements of the prop and spinner installation. These elements are:

  1. location of forward end of cowling
  2. location of forward flange of crankshaft (this is also the aft edge of the prop hub)
  3. prop blade location (aft edge of blade hub so that the backplate will clear)
  4. forward end of prop hub dome (to find desired diameter of McCauley nylon frontplate)
  5. location of McCauley backplate mounting plate or mounting flange (S/H adapter mounting location)
  6. outline of the spinner dome (to get some idea of spinner interior buildup laminates that may be required)

The spinner installation system used by S/H can be broken down in three basic components:

  1. spinner dome
  2. spinner backplate
  3. spinner frontplate

The fiberglass spinner dome used on the extended hub McCauley propeller is our standard 301-0260-001 (extended hub) spinner; on the non-extended hub McCauley the 301-0260-002 (compact hub) spinner unit is used. The layers and locations for the fiberglass doubler laminates used inside the spinner dome will change from those called for in the Hartzell Spinner Installation Instructions, however.

The spinner front plate used by McCauley is a nylon unit they manufacture that is molded with a socket area that fits snugly over the hub dome of   the propeller and is designed so that the out- side diameter contacts the inside surface of the spinner. These units are available from McCauley and are available in several different diameters. To best fit the extended hub spinner dome I recommend the P/N B2800 unit.

Referring to our paper layout, determine the location desired for the front plate within the spinner dome. Since the fore and aft location of the front plate is a known location on the prop hub, fiberglass laminates can be installed inside of the spinner dome so that the spinner front plate contacts the inside of the dome at a point that coincides with the aft edge of the dome being 3/16” from the paper location of the front of the cowling.

Fitting and modifying the correct S/H backplate system is the key to making the S/H spinner work on the McCauley propeller. The backplate system used in this installation involves three parts. The built-in mounting flange on the McCauley extended hub, (used to attach the backplate to the hub of the prop), the S/H supplied (613-1492-001 2 ea.) split adapter half plate, and the builder modified backplate (611-0130-001 for extended hub installations).

The C8 and C9 McCauley extended hubs have two flanges cast onto the base area of the hub that are predrilled with 3/16” holes and can be used to attach the two halves of the S/H adapter plate. We have used AN3-4 or 3-5 bolts and AN364-1032 nuts to secure the adapter plate to the prop hub in this location.

To adapt the 611-0130-004 backplate (which was designed to attach to the Hartzell hub) to attach to the S/H adapter plates, the predrilled holes in the outer flange of the adapter plate must be centered on the round web area of the S/H backplate. The predrilled holes in the adapter plate outer flange are then used as guides to drill matching holes in the backplate. To save weight and provide extra clearance the aluminum 1⁄2” inside of the newly drilled holes in the backplate will be removed. To secure the adapter and the backplate together use AN525-8R8 screws and AN364-832 nuts.

With the adapter now attached to the prop hub and the backplate attached to the adapter begin the process of cutting slots in the spinner dome to clear the prop blades. Fabricate slots that clear the blades with the front plate contacting the inside of the spinner dome. Fiberglass laminates are now installed in the aft end of the spinner dome to allow the backplate to also contact the inside surface of the spinner dome.

NOTE: Since the slots are already cut (save the pieces of spinner removed from the slots) care must be taken to install equal numbers of laminates on all sections and pieces of the spinner dome where laminates are required.

CAUTION: Once the slots have been cut in the sides of the spinner dome the aft edge of the spinner dome becomes somewhat flexible and can be deformed by pushing too hard against the backplate or too many spacer laminates.

With both the front plate and backplate contacting the inside of the spinner dome, locate and drill spinner mounting holes between the dome and the backplate as per the original spinner instructions. A longer length screw may be required because of the extra laminate buildup on the spinner dome. Install the blade closeout pieces as shown in the original instructions.

Check the fit of the propeller with the now installed spinner on the aircraft. If necessary, fiberglass material can be removed from the spinner dome to get additional spinner to cowling clearance. If too much clearance exists (3/16” desired) the forward edge of the fiberglass cowling can be built up using fiberglass laminates.

Variations are necessary for the non-extended “compact” style hub glasair only.

I have not been directly involved with the spinner installation on this style of hub, but have consulted with an individual installing a McCauley prop from a Mooney on his Glasair II. The basic component usage is the same, however, this hub does not have the cast on mounting flange that exists on the extended hub unit. Therefore an alternative method of attaching the S/H adapter plates is required.

McCauley manufacturers a set of semi-circular spinner bulkhead mounting plates that are installed below the prop installation studs of the prop hub. The part number for these units is C-5046 (available from Prop overhaul facilities), they come two to a set, each plate picking up 3 of the mounting studs. These plates have a series of 3/16” dia. holes just outboard of the hub that are intended to bolt to matching holes in the ID of the S/H backplate adapter plate (borrowed from the G-III kit).

The McCauley frontplate needed will likely differ from that listed in the extended hub section, also the fiberglass spinner dome used with this installation will be the 301-0260-002, and the backplate used the 611-0130-002.

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Cliff Faber
Cliff worked for Stoddard-Hamilton Aircraft Inc. (the prior company that developed and produced the Glasair design) from almost its inception and was instrumental in getting the Glasair and GlaStar product lines up and running again as a key employee of Glasair Aviation. He was hired shortly after Stoddard-Hamilton moved to Arlington, Wa. in 1982 and was a key player in the development of each of the Glasair designs.