North Shop
Will: (850) 342-9929


The circular cooling inlets on our cowls are smaller in terms of square area than the square or rectangular inlets traditionally used for horizontal, opposed aircraft engines. The inlet design was influenced by a NASA funded study conducted by Mississippi State University. This results in a 40% reduction in cooling flow and the associated drag penalty. We are able to make these reductions through the use of a sealed plenum system that receives, contains and meters airflow according to the specific requirements of each engine type. Cylinder head temperatures are closer to uniform and the overall drag reduction yields speed increases of approximately 7 to 10 mph.

Our cowls are constructed with an advanced material system which ensures light weight, strength and rigidity. Without the the older style phenolic “honeycomb” paper core there are no concerns for future delamination.

The Cowlings are available for both updraft and parallel sump engines, fuel injected and carbureted IO-320 through IO-360, 200 horse power angle valve engines. The Cowling Kit includes the upper and lower cowling with pre-molded inlet scoop, three CNC machined aluminum inlet rings, oil inspection door, rubber plenum seal with seal cement, fiberglass cloth, cotton flock and full instructions. Induction filtration kits are sold separately. The RV-4 and the “Shorty” standard Van’s length RV versions all use the standard Van’s air induction.

Ram air induction:

Flying with unfiltered air may lead to costly repairs. Our systems filter “full time” using a very low restriction K&N filter that provide an additional one inch of manifold pressure over ambient at 5000′ density altitude. These systems are designed specifically for use with our cowls but may be adapted to many other aircraft. Available versions serve forward mounted, parallel sumps, and updraft, injected or carbureted engines.

Aluninum inlet rings:

Four sizes are availible, three to six inch diameter, 6061-T6 aluminum.

Waco wheel pants

South Shop
Sam: (863) 675-4493


Plenums are constructed using a high-temperature post cure epoxy system. They are available for engines 320 – 360 and may be used on many different aircraft besides those specified. Please call Sam James for inquiries concerning aircraft types. Plenums resolve hot cylinder issues, generally with an associated speed increase. Full-sized diagrams for construction of baffles are included.

Wheel Pants:

All wheel pants are of the pressure recovery type and are substantially smaller in cross sectional area than others available, resulting in a drag reduction which yields 3-5mph. They are lightweight but strong enough for operating from grass strips. All are provided with diagrams for mounting brackets.

Wing root fairings:

Fairings are available only for the RV-4. These fairings provide an intersection radius similar in appearance to a Curtiss P-40, extending the trailing edge somewhat for a clean departure.

Videos and DVDs:

Professionally produced “how to” videos guide the viewer through the basics of composites work and aircraft painting. Spend a little and save a lot. Available either directly from Sam, order from Aircraft Spruce or online at Aircraft Tech Book. Click here to order.