The A75 Continental Engine Dilemma

The following email is fairly common in my line of work.  It seems there are a number of airplanes (not just Taylorcrafts) out there with Continental A75 engines that have been substituted in place of Continental A65 engines.  This is a logical upgrade and one that for many years was considered a benign change to the aircraft. A lot of the old school mechanics and operators made such upgrades without a lot of attention to the paperwork. But in today's FAA world, we are increasingly held to a higher "paperwork" standard.

So what does one do about the A75 Continental Engine Dilemma??  The following is an example of a Taylorcraft solution.  The same or similar solution can be executed for other airplane makes such as Champs, Cubs, or others as well.

 

-----Original Message-----
From: XXXXXX
To: barnstmr
Sent: Tue, May 8, 2012 7:58 pm
Subject: Buying a Taylorcraft

Terry,

I’m purchasing a 1946 Taylorcraft. It has a Continental A75, as advertised. I understand there may be some paper work challenges. I’ve asked the A&P seller/dealer to give me some more information regarding the paper work and/or the installation of the A75 (vs. the 65).

If needed, is there a 337 or STC I could purchase that will help my local A&P with the annual. I’m not entirely sure what I’m getting into. Maybe it’s all fine....

XXXXXX

 **************************************

Dear XXXXXX,
Congratulations on your decision to buy a Taylorcraft.  These are great airplanes.  Mine is a 65 horsepower BC12D s/n 7898 (N95598) probably not too far away from yours.  Mine was licensed in April 1946.  I have dealt with the A75 issue on several other Taylorcrafts.  There are two options. But first, here is some basic information about the differences between the A65 and A75.  If you already know this, please excuse my elementary explanation.

The A75 uses all the same parts that are eligible on an A65, but an A65 can have some parts that are not eligible on an A75. Does this make sense?  Basically, the A75 has provisions for better lubrication to the piston pin area and thus Continental allowed operation of the A75 at higher RPMs. (It is legal to use the same parts in an A65 too). So it basically moves you up higher on the power curve. From a certification standpoint, Continental showed that with the added lubrication, the A75 has acceptable durability at the higher RPMs. With fixed pitch propellers, the only way to get to the higher RPMs is by shortening the blades, or flattening the pitch.  So here's your options.

option 1. Retain the 75 horsepower rating:  Because of the changes in the past few years on FAA ORDER 8100.9, an engine horsepower change greater than 10% requires an STC. So here's what we can do.    You can purchase the STC for the C85 upgrade and I will also provide paperwork to allow you to deviate from the STC by installing an A75. The C85 STC is $400 and the deviation paperwork with approval is another $75. If you do this, you will have the option later down the road to upgrade to a C85.   NOTE: one of the major costs you need to consider is your propeller.  In order to rate the engine at 75 hp, we will need to verify your propeller will allow the engine to "turn up" above 2150 RPM (or 2110 with a 71 inch McCauley 1A90) on the ground in a static (stationary) run-up. The 75 hp rating is then allowed with a tachometer red line of 2600 RPM.  There are some other details we need to discuss to cover all the bases and other options, but thats the short answer. 

option 2. De-rate the engine to 65 hp: If you find that your current propeller will not make required RPM in a static run-up, then we can de-rate the A75 engine to 65 hp.  In this case, we would need to verify it will match the propeller static run-up requirements on the 65 horsepower BC12D Type Certificate A-696.  This would not require an STC because we would not have a horsepower increase.In this case, the 65 horsepower rating would have a tachometer red line of 2300 RPM.  I would thus provide a modification specification sheet and an approval for the de-rated A75, which costs $250.


Thanks for contacting me.  Good luck.

Terry