BC12-D A65 to A75 Conversion

[CStence]

Re: BC12-D A65 to A75 Conversion

Jim,

In this instance what is gained is that the fellow's airplane is airworthy again. If I could leave the engine as is, he would have a 10HP increase which would be something too. The original problem is that the aircraft doesn't conform to the Type Certificate. This is the easiest, legal path to do that, even though he ends up with, at best, a more reliable engine (due to the better cooling and lubrication) and a thicker logbook.

EO,

I completely agree with what you are saying about Continental engines. I've done this myself several times, per Cont SB M47-16. Again however, the question is not whether I need DER, STC or other approved data to change the engine. The question is why I would or wouldn't need such data to effectively alter the airframe by installing the changed engine.

As I understand it, the job of the IA is to determine that (1) the aircraft is conditionally airworthy and (2) that it conforms to the Design Type Certificate. Nothing in what you said clearly points to why if the T-craft Type Certificate A-696 calls for an A65-8, -8F or -8J I could just go ahead and install a -12, -14 or otherwise.

Regarding CAR 4a477, I see the reference you were referring to regarding tailwheels. However, I would argue that, like FAR 23, these are guidelines for the designer of the airplane, prior to final certification. Once the Type Certificate is issued by the FAA, the whole airplane is certified in whatever manner it was presented to the FAA. THEN as an IA, at each annual, it is my job to make sure the airplane still meets the design parameters in which it was presented to, and certified by, the FAA.

[Edwin Otha]

Re: BC12-D A65 to A75 Conversion

Charles, keep up the good work and fly safe.
EO

[CStence]

Re: BC12-D A65 to A75 Conversion

Hey guys, just got my approved data from the DER, Bob Minnis. He was most helpful to work with and was prompt in his response time. His phone number is: (678) 494-0797. Email: [email protected]

Anyway, I've attached the engineering report and approved data form if anyone cares to see what it looks like.
Thanks for all the help!

[barnstmr]

Re: BC12-D A65 to A75 Conversion

Charles,
That's good news. You'll be glad you did this extra leg-work when the owner gets ready to sell the airplane. If you didn't get a DER approval, it would come back on you somewhere down the line.

[NY86]

Re: BC12-D A65 to A75 Conversion

I think you all are missing a point w.r.t. the A65-14. The engine is approved for 75 takeoff hp with a 5 minute limit. There is no way you can meet the RPM requirements for 75 hp while still meeting the static rpm requirements for the A65 in the airframe with a fixed pitch prop. You would need something like a Beech-Robi adjustable prop. If you install a fixed pitch prop that allows you to reach the 75 hp rpm you will not be able to reach 65 hp without exceeding the (65 hp) redline in level flight.

Your argument for installing the -14 in place of the -8 is that there is no hp increase as you are using the same prop and static limits as the -8.

[Edwin Otha]

Re: BC12-D A65 to A75 Conversion

Boy, this A65-14 is an elusive creature. I haven't been able to find much information on it. The closest thing I could locate was a military O-170-7. This was considered to be the same as an A75-14. Perhaps the FAA made a typo in the TC document. It shows the O-170-7 as an A65-3 per note 4 but the O-170-7 was a down exhaust and the A65-3 was an up exhaust.
Does anybody have any added information on the A65-14. It doesn't look like TCM produced them with this designation.
EO

[jim cooper]

Re: BC12-D A65 to A75 Conversion

According to recent article, The differences are: 8-no provision for starter...12- provision for starter, etc. 14-(the one your interested in) lord engine mount rather than traditional conical mount...16-vacuum pump adapter. They go on to say the best upgrade is to a 90 hp cont. but the 75 is a very good choice. TheA 75 at recommended cruise of 2350, produces 55.47 hp. The C75 produces 74.77 hp at 2275 The latter being a larger bore. They recommend the A75.( The 65 hp cont. delivers 55.42 hp @ 2150.) These figures are for engines in excellent condition. JC

[Ragwing nut]

Re: BC12-D A65 to A75 Conversion

According to recent article, The differences are: 8-no provision for starter...12- provision for starter, etc. 14-(the one your interested in) lord engine mount rather than traditional conical mount...16-vacuum pump adapter. They go on to say the best upgrade is to a 90 hp cont. but the 75 is a very good choice. TheA 75 at recommended cruise of 2350, produces 55.47 hp. The C75 produces 74.77 hp at 2275 The latter being a larger bore. They recommend the A75.( The 65 hp cont. delivers 55.42 hp @ 2150.) These figures are for engines in excellent condition. JC

The -14 you reference above is a C90-14 only which was for early Alon with vaccum system. I do not know of a a65-14 ever being built (not a conversion as discussed here) just like some people mistake there actually being an a65-12 which does not exist either

[NY86]

Re: BC12-D A65 to A75 Conversion

The -14 you reference above is a C90-14

Yeah, don't confuse the A series with the C series.

BTW, there is a spec for a C85-14 but I've never seen or heard of one.

[barnstmr]

Re: BC12-D A65 to A75 Conversion

A65-14 is a legitimate animal. the Engine TCDS for A65 series says the following...

"Model A-65-14 differs from A-65-8 only in that it incorporates special pistons, rocker arms and exhaust valves, seats
and guides."

This suggests it is similarly equipped as an A75. However one interesting difference with the A75 is that the magnetos on an A75 have staggered timing (29R/32L) and the A65-14 is the same as all other A65 series with both magnetos timed at 30 deg. If I owned this A65-14 and intended to operate it with a propeller that allows it to make the 2675 RPM, I think I might experiment with the staggered timing to see if the fuel consumption might improve.

[Ragwing nut]

Re: BC12-D A65 to A75 Conversion

A65-14 is a legitimate animal. the Engine TCDS for A65 series says the following...

"Model A-65-14 differs from A-65-8 only in that it incorporates special pistons, rocker arms and exhaust valves, seats
and guides."

This suggests it is similarly equipped as an A75. However one interesting difference with the A75 is that the magnetos on an A75 have staggered timing (29R/32L) and the A65-14 is the same as all other A65 series with both magnetos timed at 30 deg. If I owned this A65-14 and intended to operate it with a propeller that allows it to make the 2675 RPM, I think I might experiment with the staggered timing to see if the fuel consumption might improve.

I know what the TCDS says, but still don't belive it. The only reason for staggered timing should be impulse on one mag

[3Dreaming]

Re: BC12-D A65 to A75 Conversion

I know what the TCDS says, but still don't belive it. The only reason for staggered timing should be impulse on one mag

That doesn't make ant sense. The impulse makes no difference once the engine is running.

[cvavon]

Re: BC12-D A65 to A75 Conversion

All that the change it timing does is keeps the fuel burn going longer by retarding the timing on one mag witch lights the fire twice witch jest makes sure the fuel in the cylinder burns more completely and keeps the power stroke going longer witch could increase the horse power some

[lfries]

Re: BC12-D A65 to A75 Conversion

In searching for a 337 that Forest said was used to make the A75 conversion I have been buying a lot of CD's on Taylorcrafts advertised with an A-75. Just got one recorded on the FAA CD but not signed off by a DER or the FAA. I assume it is worthless as supporting documentation?

[barnstmr]

Re: BC12-D A65 to A75 Conversion

The staggered timing provides for a more complete (more efficient) fuel burn, particularly effective at higher RPM. If you can imagine this... the longer burn pulls more energy from the fuel and actually eeks out a little more power for a given set of power conditions... manifold pressure/RPM/fuel flow rate. The trade off though is higher heat from combustion (more energy) but in trade for a greater demand for cooling. Since the A75 has better oil flow in the piston, etc as discussed, Continental specified the staggered timing on the A75. But the A65 (with lesser piston cooling) has a more conservative (cooler burning) timing specification. Hope that is clearer than mud.