Regulatory Questions: Aeronca 7EC

[Boundary Waters]

The 7AC had a gross of 1220 lb. Replacing the A-65 with a C-90 plus starter, generator and battery would really wreck the useful load.

The 90-8F only weights 12 pounds more than an A-65-8 (The Factory Letter details tube changes so I'm sure that adds some weight as well. But the killer is 75 to 100 pounds of CRAP... (Oops, I meant electrical equipment.) Why, Ii's almost like putting a big block of lead in the airplane 700-ish pounders fly really nice using 50 to 55 of their 65 horses, IMHO better than 900-ish pounders with 90 hp engines. (Based on burn figures I'd say that is because the folks I know tend to cruise around at 2130 or so on an A-65 in a draggy Piper or Aeronca and they fly the C-90 in the same 50-55 hp "crease--" 52.5 just reads as a lower percent of 90 than of 65.

Aeronca built the 7AC from the end of the war until they stopped building airplanes, literally making thousands. All the 7ACs were 1220 lb gross weight airplanes. They started making 7ECs in 1950 and made hundreds before selling the rights to Champion. I'm told that all of the all of the Ohio and SOME of the Osceola Wisconsin and Minnesota built 7ECs were 1300 lb and SOME were 1450 lb AND OTHERS were 1500 lb gross weight aircraft. SOME of the Rochester built planes are LSA compliant at 1320 lb, and SOME are 1500 lb, AND...

I like simple, I like light, unless you get a hell of a deal it doesn't make any sense to me to buy something and then change it if you can buy it already configured the way you want it.

 

[JAWS]

I have done this kind of stuff, trying to appease an owner bit by bit, pound by pound. Trying to find old service documents, all in an effort to put lipstick on a pig.
Kind of fun to read, very glad to not be involved! I wish you luck!

 

[Dan Thomas]

The 90-8F only weights 12 pounds more than an A-65-8 (The Factory Letter details tube changes so I'm sure that adds some weight as well. But the killer is 75 to 100 pounds of CRAP... (Oops, I meant electrical equipment.) Why, Ii's almost like putting a big block of lead in the airplane 700-ish pounders fly really nice using 50 to 55 of their 65 horses, IMHO better than 900-ish pounders with 90 hp engines. (Based on burn figures I'd say that is because the folks I know tend to cruise around at 2130 or so on an A-65 in a draggy Piper or Aeronca and they fly the C-90 in the same 50-55 hp "crease--" 52.5 just reads as a lower percent of 90 than of 65.

The old starters and generators were heavy. Real heavy. An alternator weighs considerably less than a generator, and makes more power and does it at idle, unlike the generator. There are permanent-magnet starters now that weigh a lot less than the old Prestolites, too. But they're not cheap, especially those that fit the small Continentals. The alternator is gear-driven, not an adapted car alternator with a pulley, and the starter is highly specific to the engine as well. The only engine still in production that uses them is the O-200-D and maybe the O/IO-240, as opposed to dozens of Lycoming models that use much the same mounting across them all.

Batteries are heavy, too. Until we have a certified Lithium aircraft battery (that won't catch fire) we're kind of stuck with lead-acid for certified airplanes.

I used to cruise my A-65 at 2250 and 2300 RPM, redline. It's certified for that. It has no five-minute limitation on RPM like some larger engines. In fact, the A-75 was the same engine with a little bigger carb, some heavier piston pins and a higher redline of 2650. Now, the O-200 has a redline of 2750, and yet people fly it at 2400 and wonder why their airplanes are so slow. Here's a chunk of the cruise chart from the Cessna 150:



Look at that. At 2000 feet you can cruise at 2650 RPM. AT 4000, 2700. At 6000, 2750, which is redline. At 8000 it's back to 2700 because the altitude is costing horsepower and full throttle won't get you any more than that.

POHs seem to be just cockpit decorations, or they're absent altogether, which is illegal.

 

[Boundary Waters]

POHs seem to be just cockpit decorations, or they're absent altogether, which is illegal.

I've memorized my POH. Which really wasn't hard, since it is printed on one side of a 5 x 7 index card. (True, and an edited version of the TCDS-- deleting information not pertinent to this aircraft in this configuration-- is on the backside serving as the required "numbers.") A friend with a J-3 has an even shorter POH. (Written on the back of a postage stamp, I think it just says: "Stall - 38 mph. All other speeds - 60 mph..." but I could be mistaken .)

I used to cruise my A-65 at 2250 and 2300 RPM, redline. It's certified for that. It has no five-minute limitation on RPM like some larger engines. In fact, the A-75 was the same engine with a little bigger carb, some heavier piston pins and a higher redline of 2650. Now, the O-200 has a redline of 2750, and yet people fly it at 2400 and wonder why their airplanes are so slow.

My A-65-8 is redlined at 2350 by A-694. The chart on Continental's 1942 engine POH shows a max output of 64 hp at 2300 rpm which is either repeated or copied in the 1942 Army L-2 TM-1 I carry (yeah, its a T-craft but its the same engine) 2300 is about right as the maximum for my engine/prop/airframe combination in level flight. But I can't quite get there in a climb. A friend with a very slightly heavier, but arguably very slighly more aerodynamic PA-11 runs a C-90-8F.

(Interestingly Continental's C-90 POH offers different power curves for the C-90-8F and C-90-12F. With the -12F being just a smidge higher. I wonder if they are accounting for the power used by the generator. My A&P tells me that Muskegon stopped making A-65 parts in the mid-40's and that most, if not all, A-65s are flying around full of the A-65/75 parts that superseded them.)

Anyway, while Continental approved the C-90 for maybe 5 minutes at 95 hp, Piper never certifificated the PA-11 at that hp / rpm, so he maxes out at 2400 rpm and 82 horsepower with a McC 74x37 prop. I'm a noob, but I have a pretty good BS detector, and I get a hoot out of people saying that other people should "upgrade" an A-65 to an A-75 or A-80. The A-75 and 80 have essentially the same power curve, the 80 just allows 50 more rpm. The 75 is just a 65 with a smaller prop that spins faster producing the same torque, but once again topping out at a slightly higher rpm... (Am I missing something???)

Anyway, I can cruise my A-65-8F at say 50 to 55 hp 2100 to 2150 rpm, burning 3.8 to 4.2 gph, depending on the atmospheric conditions. My friend with the C-90-8F cruises at 55 to 60 hp 2100 to 2200 rpm while burning 4.5 to 5.0 gph in cruise. Pretty similar in my book.

 

[Dan Thomas]

Anyway, while Continental approved the C-90 for maybe 5 minutes at 95 hp, Piper never certifificated the PA-11 at that hp / rpm, so he maxes out at 2400 rpm and 82 horsepower with a McC 74x37 prop. I'm a noob, but I have a pretty good BS detector, and I get a hoot out of people saying that other people should "upgrade" an A-65 to an A-75 or A-80. The A-75 and 80 have essentially the same power curve, the 80 just allows 50 more rpm. The 75 is just a 65 with a smaller prop that spins faster producing the same torque, but once again topping out at a slightly higher rpm... (Am I missing something???)

Same torque and more RPM equals more horsepower. Smaller prop, or one with lower pitch, will allow a higher RPM. Torque (in foot-pounds) times RPM divided by 5252 equals horsepower.

The A-80 has higher-compression pistons. Around 7.5:1 instead of 6.3:1. That gives a bigger bang, which produces more torque, and along with the extra 50 RPM you get a few more horses. Those pistons are heavy; I have them here. The A-80 type certificate was cancelled (or "expired") long ago. I don't know if it was because of mechanical problems with it or because the C-85 came out.

More on small Continentals? Here's a rich place for info:
http://www.bowersflybaby.com/tech/fenton.html

 

[skyking3286]

You will find better information asking this on the National Aeronca Association Facebook page. BUT, if the plane has EVER had an engine driven electrical at anytime in its history it's ball of wax for transponder/ADS-B and that adds weight regardless. It's a fine airplane and the comments about the wood spar, nails and such are debatable and not supported by the service history. The same spars were used in the Champion Citabria. The struts are fine, the Piper ones had the AD. This thread has more misinformation than most. . .

 

[Dan Thomas]

You will find better information asking this on the National Aeronca Association Facebook page. BUT, if the plane has EVER had an engine driven electrical at anytime in its history it's ball of wax for transponder/ADS-B and that adds weight regardless. It's a fine airplane and the comments about the wood spar, nails and such are debatable and not supported by the service history. The same spars were used in the Champion Citabria. The struts are fine, the Piper ones had the AD. This thread has more misinformation than most. . .

I found cracked spars and loose nails. I also found struts rusted though. Not everything is covered by ADs and mechanics are supposed to be looking. Hard.

 

[Boundary Waters]

Same torque and more RPM equals more horsepower. Smaller prop, or one with lower pitch, will allow a higher RPM. Torque (in foot-pounds) times RPM divided by 5252 equals horsepower.

"The 75 is just a 65 with a smaller prop that spins faster producing the same torque..."

I don't think you are disagreeing with me. The 75 produces the same torque as a 65 by spinning faster. It spins faster because it has less of a load.

"topping out at a slightly higher rpm..."

Which gives it a 10 hp higher hp rating at the engine's highest certificated speed.

The A-80 has higher-compression pistons. Around 7.5:1 instead of 6.3:1. That gives a bigger bang, which produces more torque, and along with the extra 50 RPM you get a few more horses. Those pistons are heavy; I have them here. The A-80 type certificate was cancelled (or "expired") long ago. I don't know if it was because of mechanical problems with it or because the C-85 came out.

I cannot say if the A-80 had any more potential than the A-75 but if you look at the 1942 Continental POH for the A-50, 65, 75, and 80 at the settings that Continental specified all it offered was a slightly higher maximum rpm giving it 5 more hp in theory. ---- I say in theory because hp on an unloaded engine is useless. And once the propeller is hung the characteristics of the prop has far more effect on the system than a few more rpm*.

More on small Continentals? Here's a rich place for info:
http://www.bowersflybaby.com/tech/fenton.html

I particularly like his comparison of the C-90 and O-200 and how the different cam profiles effect torque in the rpm range we can most use it. As he explains, bigger is not always better.

* The Continental C-90-8F which Continental certificated at 96 hp spinning at 2625 rpm produces 90 hp at the MAXIMUM 2475 rpm that A-691 Item 311.C.10. limits it to. At 1960 rpm (just 10 rpm over the minimum limit) it produces 45 hp. We figured a McCauley 76AK-2-37 spinning at 2400 was developing 82-83 hp. Obviously a flatter or smaller diameter prop would spin faster. But it would not necessarily move more air, which is sorta the point of havin' that spinny thing up front.

 

[Magman]

I’ve also found loose nails and elongated holes.

No spar cracks though.

 

[Dan Thomas]

* The Continental C-90-8F which Continental certificated at 96 hp spinning at 2625 rpm produces 90 hp at the MAXIMUM 2475 rpm that A-691 Item 311.C.10. limits it to. At 1960 rpm (just 10 rpm over the minimum limit) it produces 45 hp. We figured a McCauley 76AK-2-37 spinning at 2400 was developing 82-83 hp. Obviously a flatter or smaller diameter prop would spin faster. But it would not necessarily move more air, which is sorta the point of havin' that spinny thing up front.

A flatter-pitched prop spinning faster generates more thrust at lower airspeed and allows the engine to spin up to get a higher HP output. That is, after all, what a constant-speed prop does in the takeoff roll and climb. It lets that engine produce more power (redline RPM) while optimizing the AoA of that propeller, and it does it in all flight regimes. A fixed-pitch prop will never reach engine redline other than in level flight, full throttle unless you're in a dive. That's how they determine what fixed-pitch prop to use on a TC'd airplane. You can't get redline in the climb, so you can't get 100% power even at sea level. You're stuck with second gear, basically.

 

[Silvaire]

A lot of numbers analysis going on here and yes, weight criticality is true for the 65 hp engine but with a C-90 it is more than capable of hauling the weight of even the legacy electrical equipment with better performance and useful load. The end result is a more complete and enjoyable aircraft. Most people are not interested in hand propping or having an awkward handheld radio strapped to the frame and a bunch of messy little battery packs laying all over the place to power everything. I can understand the nostalgia aspect but as much fun as it is to fly a J3 with the door wide open there comes a point where you just want to close the darn thing. The overall trend after 1946 was for these base model aircraft to get upgraded as that's what people wanted and so the service letters and TCDS amendments were designed to easily allow that. Over my 50 years of flying I've experienced them all and there is no way I would trade my 90 hp 7EC for a stripped 7AC nor would I consider converting my 85 hp Luscombe 8E back to an 8A as it was when it was built in '46. There's no guilt in convenience or creature comforts and no loss of enjoyment. Far more in fact as far as I'm concerned. As I said earlier, I don't think the LSA aspect carries that much weight these days, it's a different set of rules now.

 

[Dana]

As I said earlier, I don't think the LSA aspect carries that much weight these days, it's a different set of rules now.

It still carries a lot of weight for people unable to pass that one medical needed to qualify for basicmed.

 

[Silvaire]

Apologies, I just meant that basicmed has significantly reduced the number of potential buyers that are in that situation, not that it has eliminated all of them.