CHANGING YOUR PROPELLER
A propeller is designed to be compatible with a specific engine, in order to achieve maximum thrust or efficiency and reliability from the aircraft. Even though the propeller might fit another engine shaft, only the propeller manufacturer can determine whether it is suitable for use on a particular aircraft. Installation requirements are available for all McCauley props. Propellers are generally changed either to upgrade performance or to restore original performance compromised by wear and tear. Whatever the reason, changing propellers deserves careful consideration. The propeller is intimately linked to aircraft performance and operates in partnership with all other components. Many factors can enhance or impair performance.
Four ways to change propellers:
1. OEM Type Certificate
2. One-Time Field Approval
3. Experimental Certificate
4. Supplemental Type CertificateOEM Type Certificate
Any propeller that appears on the Original Equipment Manufacturer¹s (OEM) approved equipment list, on the Aircraft Type Certificate Data Sheet, is automatically approved for that application. No further paperwork is required.One-Time Field Approval
More subjective in nature, the One-time Field Approval changes for every situation and is heavily dependent on the personality and experience of the FAA representative. In general, the more reasonable the request, the more likely it is to be granted. There are only two things for certain about the One-time Field Approval:
€ It requires the endorsement of the FAA
€ It has to have some degree of technical justificationExperimental Certificate
The Experimental Certificate option is available only to experimental aircraft owners or operators. If you fall into this category, you can theoretically install any propeller you desire. However, we recommend contacting the propeller manufacturer for advice and for a list of propellers best suited for your aircraft and engine.Supplemental Type Certificate (STC)
The FAA issues an STC for propellers that have passed rigorous and extensive testing but which are not listed on the OEM¹s approved equipment list for a particular aircraft. The STC is the easiest way to modify an existing airplane in the field. Most owners, operators and mechanics who wish to upgrade propeller performance will use STCs.Single-component STCs involve a specific propeller that has been approved for a specific aircraft. For example, the single-component STC is commonly used to upgrade an aircraft from a two-bladed to a three-bladed propeller. It may also be used by owners or operators who are not satisfied with the performance of their original propeller. The combination STC involves multiple components, such as a propeller and an engine upgrade. Although less common than single-component STCs, the combination STC is gaining popularity because of the integral relationship between propeller and engine.
The STC holder may be the original propeller manufacturer, the original aircraft manufac- turer or an individual. To obtain an STC, the STC applicant often works with the FAA and the OEM, tests and evaluates the propeller, and pays for flight performance testing and stress surveys. Developing the STC for a simple, one-propeller changeover for a particular aircraft can be a significant expense. When someone other than McCauley obtains an STC with a McCauley product, the prop is usually sold directly to the STC holder for delivery to the end user. However:
- STC holders do not always work with the original propeller manufacturer prior to obtaining STC approval from the FAA. STC holders who have not worked with McCauley may not fully understand our products, their applications and how they are likely to perform on specific aircraft.
- The FAA usually does not notify the original propeller manufacturer when it grants an STC to someone other than the OEM. As a result, we have no way of knowing about all STCs approved for our propellers by the FAA.
- STC holders who do not work with McCauley while obtaining an STC for our products often neglect to inform us when the STC is granted.
Therefore, always contact the manufacturer of the STC propeller you plan to install, and ask if the OEM is aware of the STC or of any potential problems. Also, contact the STC holder directly to discuss the performance changes you should expect. Request a list of owners who have performed similar installations. Make sure everything is working properly under usual operating conditions before installing any STC conversion. To determine whether or not a problem is propeller related, use the process of elimination, changing one variable at a time. For example, a recently overhauled engine may cause vibration, which could be mistakenly blamed on a new propeller installed at the same time. If you converted from a two-bladed propeller to a three-bladed propeller immediately after an engine overhaul, try out the overhauled engine using the two-bladed propeller. If you experience vibration that was not apparent before the overhaul, you will know that it is an engine problem, not a propeller problem.
The warranty that comes with the STC conversion covers the propeller assembly. Technically, the original propeller manufacturer is responsible only if the propeller is defective. The STC holder is responsible for problems with installation adjustments. However, owners and operators may have adjustment or performance trouble that is not propeller-related, including problems with the engine, engine mounts, cowling configuration or airframe. As a result, performance varies by individual aircraft.