Ercoupers FAQ

Disclaimer: We have no professional or expert qualifications of any kind.
It's fully up to you to check any information you find here with
standard aviation industry sources such as aircraft maintenance
manuals, flying instruction books and, above all, FAA regulations!

by Ed Burkhead

What is an Ercoupe?
The Ercoupe is a 2-seat airplane that was designed by Fred E. Weick for ERCO (Engineering Research Corporation).  It was first manufactured in 1939.  Production stopped during WWII, and then in 1946, 4309 were made in a single year!  For months they made Ercoupes at a rate of >10 a day!  For a very short period production got to about 25/day on three shifts!  Ercoupes were immensely popular, but in the 1947 bust in the airplane business, only companies with 4-place planes survived.  ERCO's 4-place Ercoupe wasn't ready and ERCO stopped making airplanes.  The 2-place Coupes were manufactured by several different companies over the years: Sanders, Forney, Alon, and even Mooney (as the M-10) in the late 60s.

At the time it came out, the Coupe was a revolutionary plane. It was one of the first general aviation aircraft with a tricycle gear and the Coupe's designer, Fred Weick, owned the patent on the tricycle gear as we know it. The Coupe was a metal mono-coupe low wing design that came out in a time of tube and frame designs. It was stall proof, it was spin proof, it had no rudder pedals, and it was fast. People who actually flew the thing learned that it was a great flying airplane. If you go look at an Ercoupe on a modern airfield among Cessna 150's and Pipers Cherokees it does not look out of place, but go to a fly-in where the Ercoupe is parked among its contemporaries like Aeroncas, Cubs and Stinsons of the same vintage and it is striking how different and modern the metal-clad, low wing, tricycle gear Ercoupe looks among a sea of high wing, fabric covered taildraggers. But old time pilots thought the removal of rudder pedals was a sin, just as bad was the removal of the tail wheel.

Why fly an Ercoupe?
The visibility makes every other factory plane you get into feel like you are on the ground in a simulator. And, you can fly with the side windows down, so it’s one of the few airplane convertibles out there!

It's cheap (well, relatively inexpensive) to fly, unique airplane that will be the topic of conversation at every airport you land at, and great fun!

Why fly a Spam can when you can have fun and fly an Ercoupe?

Is it true it doesn't have rudder pedals? Why?
The Ercoupe is notable in that the design of it was an attempt at making a much safer airplane. Fred wanted to try, through good design, to remove many of the elements that were causing crashes in airplanes. Most notable about the Ercoupe is that the original was designed to be incapable of spinning. The reasons for that are because the leading causes of accidents were spins. Spins are impossible if you can't stall the wings. Fred wanted to cut down on the plane's ability to bite its owner.

If you can't hold the plane in an uncontrolled spin (autorotation), rudder pedals aren't needed to get out of the uncontrolled situation. Yet, if the design is done right, (it was on the Coupes) the plane can't be held in a spin even if the pilot uses pedals to cross-control the plane. The Ercoupes were designed so the rudder can optionally be linked to the ailerons so that the controls are always in coordination. According to Fred, he expected about half the planes to be produced with pedals, and half without. However, Fred said, the marketing department pushed the aspect of having no pedals as a key feature in the marketing. In retrospect, he said, he didn't think it was such a good marketing decision after all because of the misinformation that came from dwelling on this feature.

This plane is characteristically incapable of spinning? It can't spin or stall?
Yep, sort of. It can't be held in a spin, at any rate. If you do a sudden "departure" stall or hammerhead stall, you could fully stall the wings. But, due to the factors listed below, the plane can't be held in a condition where the majority of the wings are stalled.

Stick and Rudder, by Willie Langewiesche describes a spin as a condition where one wing is more stalled than the other and the plane auto-rotates around the more stalled wing.

An Ercoupe is characteristically incapable of spins. The FAA even allows (requires) a little plaque to be in the cockpit that explicitly says so. When a coupe stalls, the wing ends up just mushing, but with the ailerons still in control of the plane. It's designed so that a partial stall starts at the wing root and fans out in a "V" pattern. The outer 2/3rds or 3/4ths of the wing are still flying cleanly -- but the root stall upsets the airflow over the elevator, limiting the elevator's down push. Combined with a somewhat limited elevator up travel (on some models), a Coupe's tail can't be pushed down enough to stall or keep stalled the majority of the wing on any Coupe. Whether it's in coordination from linked ailerons and rudders or cross controlled by a rudder pedal kit, the Coupe can't be held in a spin. (If you fly over gross / out of rear CG, all bets are off.)

Can a Coupe do aerobatics?
You may encounter an old timer or young idiot who will tell you that, sure, Coupes can do aerobatics.  The fact is, the Coupe airframe picks up speed very fast when the nose points down and overstressed pullouts are very likely unless you are Bob Hoover.  Virtually all of the very few Coupes that have come apart in the air were known to be used for aerobatics and were likely to have been doing aerobatics when they came apart.  (There is one known incident, 40 or 50 years ago, of hidden wing damage in which the wing failed in the air.)

These aircraft were not designed to do aerobatics.

In short, DO NOT do aerobatics in any model of Coupes!

This warning is placed high in the FAQ not because there have been very many incidents.  But, there have been a few and it has become apparent that doing aerobatics in our planes is deadly.  This is also true of the other light aircraft not explicitly designed for aerobatics.  You'll see an article in the magazines to this effect every few months.  If you want to do aerobatics, get proper training and always use a plane designed for it.

How do you steer the plane on the ground if you don't have rudder pedals?
Like a car! The nose wheel is connected to the control wheel, so, on the ground, you simple steer it like a car! (pretty simple huh?)

How do you land in a crosswind?
The short answer is, you just land it crabbed. The tricycle gear can handle a great load, and since it is a tricycle, the plane naturally straightens out once your main wheels land. It's simply a different technique than using the rudder.

A normal coupe can handle a pretty good X-wind with little trouble according to the aircraft manuals. Several of the manuals listed 25 mph as the crosswind component. The manuals for the 415 and 415-C did not mention the maximum crosswind component, but they are very similar to the later models with manuals that do have crosswind numbers. The technique is simple. You hold it off until it settles down, preferably at minimum flying speed and land wings-level with your motion right down the runway centerline. You do want to reduce the forward speed to as little as possible to put the least stress on the landing gear.

How high a X-wind can a coupe handle?
Like most planes, pilots report having landed in crosswinds much higher than the demonstrated crosswind component. Some Coupe pilots say they don't think twice about 30 kt. direct crosswind component, others claim to have done even higher crosswinds. In practice, many Coupe owners are comfortable flying in crosswinds that keep them on the ground if they were flying most other light planes. Smart pilots first work their way up to the demonstrated croswind component listed in their owners manual. First they get fully competent at that level, and only then experiment as their own skill and equipment allow. Be sure your tail is at or very near regulation height of 75 inches for good crosswind behavior (see detailed discussion below).

I heard the wheels castor?
Nope. The wheels don't castor. This is a common misconception that people have. The main landing gear has a hinged L shape simply to allow good shock absorber travel, not for handling the plane in a crosswind. The misconception arises from the use of the word castor when describing how the plane lands in a crosswind. Nose wheels turn, and occasionally those who haven't paid attention still assert that a Coupe's landing gear castors.

When you touch down crabbed, there is a side-ways push on the laterally firm main gears. But the nose wheel turns like all other tricycle gear planes and provides almost no side-ways resistance. The plane just rotates (yaws) around its center of gravity to line up with the direction of motion. We hold the control loosely at touchdown so this nose wheel turning can take place freely. An egg in a saucer on the pilot's lap will stay right in the saucer.

After that initial nose wheel turn, caused by the nose wheel touching down, all Coupes use their nose wheel steering for positive control on the ground.

I rode in a Coupe on a crosswind landing and the up-wind wing lifted so high I though we'd flip!
A few people have ridden in a Coupe which, during this yaw motion, lifted the up-wind wing quite a ways -- and that ride is scary. Ten or twenty years ago, the majority of Coupes were sitting on their landing gear with the tails drooping low. Some of this was caused by aging and compressed rubber donuts in the gear (or by old Belleville springs). On many planes, this was worsened by replacing the original nose gear single-fork with a later designed (and slightly longer) double-fork.

We didn't think much of it, at first. But it was realized that this on-the-ground position gives the wings more angle of attack that was designed into the plane. Bill Coons of Lombard, Ill., went to an FAA engineer in Chicago and got shims approved for the landing gear and he passed the technique around the club. Added into the shock absorber stack, the shims return the on-the-ground attitude of the Coupe to the designed angle of attack in spite of compressed rubber gear donuts, aging springs, or a longer nose gear fork. Subsequently much of the fleet has gotten maintenance and/or shims as needed to raise the tails on the ground to the designed 75 inches and no-lift angle of attack.

With the tail at the right height, the Coupe's crosswind landing behavior is the best in the industry, bar none.

So why the H tail?
A well behaved plane acts the same in all power setting, from full power to windmilling. The H tail gets the rudders out of the slipstream of the prop, thus reducing the amount of correction you need to have when taking off at full power. The engine is also mounted at a slight cant to counteract the P-factor on climb out.

What is the "split" tail?
The split tail is a cutout in the center of the elevator, in the area where most of the slipstream passes the elevator. It's not completely cut out, but for a bit more than a yard in the middle there's not much elevator surface. Since the slipstream follows the fuselage to narrow as it goes back, the cutout matches the slipstream fairly well.

In keeping with the design philosophy of having the same behavior and trim from no power to full power, the "split" elevator accomplishes this pretty well. To get the same authority as earlier models had, the split elevator is allowe 20 degrees of up travel (compared to 13 degrees on the C model and 9 degrees on the D model). Some later models also had a pre-loaded spring added to the system so the pilot feels a "stop" at 65 mph to give warning this is as slow as you should normally glide, but additional pressure allows the full up elevator and touchdown near 50 mph.

This is a very smart and valuable improvement to the Coupe design. It was first introduced with the E model and many C, CD and D models have incorporated it with FAA approval. Get the FAA approval first (as with all other modifications) so you won't get stuck in a very uncomfortable regulatory box.

There aren’t any flaps?
Nope. The goal of the design of the Ercoupe was to keep things simple. No flaps equals one less thing to worry about. In practice, the short, wide airfoil used by the Coupes, the early Cherokees, the Tri-Pacers and their bretheren and others are efficient airfoils -- but at low airspeeds, they can develop a pretty good sink rate. At low airspeeds, a Coupe can descend like a Cessna 172 with 30 degrees of flaps.

How do I make my approach then?
The common landing approach in an Ercoupe is to first, fly it pretty much like you would any other aircraft.

Choose your own power technique. I start my approaches by reducing power1500 rpm at mid-field on downwind. I leave power at 1500 through the early part of the approach and, when I get to the right spot, I reduce power, eventually to idle.

Fly a rectangular pattern and adjust your glide by adjusting your position and turn locations. During your approaches, if you're too low, make your turns early and gentle so you don't lose so much altitude. If
you're a bit too high, make steeper, squarer turns (reciting "ONLY in an Ercoupe" while you do these steep turns near the ground) to waste energy and altitude.

Pay attention to wind direction and strength and adjust your pattern shape and turn points based on your best estimate of how the wind affects your standard pattern. As you fly lots of approaches, you'll get to be a master at adjusting your pattern. (You'll soon learn approach control skills that will be the envy of pilots who gloss over
their sloppiness with slips and use of flaps. When you fly in planes with those tools, you'll have better approach control than all the sloppy pilots.)

If you lose power during the approach, make an immediate gentle turn toward the touchdown spot. Just like with any plane, you should practice this before you need it.

Slowing down to lower airspeeds will increase the angle of descent when you drop below the best glide angle speed. You should test your own airplane to find out its working speeds -- on your first flight in the plane, assume best glide is 1.3 times the minimum power-off speed you test, at altitude, before making the first approach.

Careful approach management will give you quality approaches.

Low airspeed, high sink-rate approaches
[Pre-warn your passengers (especially if they're pilots) before doing the following maneuvers.] According to the Ercoupe Instruction Manual, if you are a little bit too high, you can lower the nose and land fast, using braking to stop in less distance than would be taken to hold it off to a minimum flying speed touchdown. The book says, "the airplane may be set on the ground at up to twice the minimum speed, and as long as the control wheel is not pulled back will stay on the ground. After contact, the wheel should therefore, either be held still or eased forward gently, preferably the later." [Text color red per Ercoupe Instruction Manual.]

If you need to lose lots of altitude quickly, the factory tested and approved method (it's in the Ercoupe Instruction Manual) is something you should use cautiously and deliberately because it doesn't leave much margin for wind shear or mistake. The book says, "If the approach has been made at too high an altitude, the flight path can be steepended by rolling the airplane from side to side, dipping each wing 20 to 30 degrees. If the altitude is sufficiently high, this can be done satisfactorily with the wheel full back and height is lost quite rapidly, but, because of the high vertical velocity attained, the airspeed reading should be increased to 60 mph or above at an altitude of about 200 feet, and the flight direction should be held staight from about 50 feet altitude to the ground."

Unpracticed people get in trouble with this because you need to push the wheel forward while high enough to regain airspeed (60 to 70 MPH) to flare for landing. This means at about 200 feet above the ground, you push forward and drop the nose. (If you do the "falling leaf maneuver" and say "wheeeee" as you drop the nose, you might get a reputation around the airport, and it may not be favorable to your preferred image.)

If you wait too long there is no time to get the airspeed up and you land very hard. People who don't drop the nose at the right time, the right amount, or who get wind shear at the wrong time, can fold under the landing gear nose wheel and cause major damage -- worse is possible though rare. You can make a very steep approach this way, but there isn't any margin for error. When you push the envelope this way, you'd darn well better not be pushing it in another way, like gross weight or center of gravity. Remember, unless it's a power loss emergency, you can always go around.

Can I install rudder pedals? I like rudder pedals!
Yes, you can. The factory sold Coupes with or without rudder pedals and they are part of the type certificate for all models.

The rudders, when using rudder pedals, have fairly good effectiveness. It is possible to land with the plane axis in line with the runway, wing low, up to about a 15 mph direct crosswind. In crosswinds above 15 mph, you can land wings level in a crab like the other Coupes, or use a hybrid method. It is possible to adjust the rate of descent a fair amount with a good slip, even in the Coupe, and avoid the fun listed in the previous section.

In the air, for good flying practice, you would push the pedals when making big aileron movements to prevent adverse yaw. For cruise, you can leave your feet on the floor just like on virtually all other planes. On climb out, use of the pedals helps keep the plane flying straight. In all situations, since the actual rudder surface is small and the way the pedal cables are rigged, it takes a pretty large amount of pedal displacement to get the ball centered. It takes very little strength. For the same reason, the automatic centering from the wind over the rudders isn't strong and you may have to push the pedals some to center them well.

With any pedal kit, you have less leg room. This bothers people some on cross country flights.

[from Ed Burkhead ( former EOC member ) ]
The Coupes are certified as spin-proof both with and without the rudder pedals. I've tried cross controlled stalls at very high (about 100 rpm less than full throttle) power settings. It was a roller coaster ride, but the plane didn't enter a spin and I could bring the wings almost-level by just adding more aileron while the rudder was still full left (the worst condition). In this condition cross-controlled, very high power, yoke full back condition, I was about staying level or losing a little bit of altitude while slowly turning left. Slightly releasing the back pressure on the yoke immediately brought the plane back to full controllability.

Aerobatics
Personally, I'll be happy to ride along for aerobatics in an Ercoupe as long as Bob Hoover is pilot.  If Chuck Yeager offers to pilot, I'll think about it for a while.  I'll let Bob go practice by himself for a while before I go for that ride with him.

The trouble with aerobatics in the Coupe isn't the rudder linkage.  By its design, the Coupe can't be held in a spin even with crossed controls.  The design is such that it'll fly out of a spin as if you'd made the corrections intentionally.  You would probably have to about do
a hammer-head stall to get into a spin entry.  (Or fly outside the rear CG-limit and then all bets are off!)

The Eroupe is a fairly sleek airplane and the Alon is even sleeker with its bubble canopy.  That's why it flies so well with so little power. The downside is that it can also pick up speed very quickly in botched aerobatics.

It takes very special skill to do aerobatics in a normal or utility category aircraft because you have to have very good control to avoid over stressing the airframe.  And you have to be sure you can do it right every time or you might have pieces depart the aircraft. Flying
aerobatics in any plane not specifically designed for it is a good way to die (or a wasteful way, really).

Fred Weick, when he came to fly-ins, kept emphasizing that these airframes are "almost 50 years old" (and 10 years older, now).  He advised us to slow down on thermally days because the transient g-loads in bumpy air can over stress an aircraft.

Coupes may be tough but they were not designed for aerobatics even when new.  And they sure ain't new, now.
 

What are the different type of rudder pedal kits and why?
There are TWO TYPES of rudder pedal kits. For discussion, I'll call them the ERCO kit and the Alon kit. The differences only affect ground handling.

With the Alon kit, the pedals control the rudders and the nose wheel only. The wheel/yoke only controls the ailerons. You steer on the ground with the pedals.

With the ERCO kit, the pedals control the rudders only. The wheel/yoke controls the ailerons and the nose wheel.

With the Alon kit, after touch down, you can turn the ailerons into the wind and totally eliminate any up-wind wing rise. (Not a significant problem on Coupes with the tail at or near 75 inches high.)

With the ERCO kit, once you are on the ground, you steer with your hands on the yoke. You've practiced this for 10,000 hours in your car, more than 3,600,000 steering wheel control movements. In an emergency, turning the wheel with your hands is your practiced and very well learned (not instinctive) response. (Fred Weick observed this behavior and designed the ERCO kit his way for this reason.) Since the plane steers like a car with the ERCO kit, you have much better control when rolling on the ground. People feel so confident about it, the factory issued a memorandum advising people to taxi more slowly to avoid getting unnecessary fender benders around the airport.

Are the wings metal or fabric?
Originally they were fabric, and then they made them metal. Some older airplanes have been converted to metal wings. The metal wings add weight (about 40 lb.). All Coupes now must have the Swiss-cheese AD's 16 inspection holes on the bottom of each wing so the structure can be inspected annually for corrosion. Fabric wings can be recovered every 20 years or so (whether the new fabrics need it or not) and a really good inspection of the structure can be done. A few owners have converted back to fabric covered wings.

More metal skinned wings have been found with corrosion than have fabric skinned wings. Since these planes are up to 60 years old, being able to inspect the wing spars for corrosion is very important and that's pretty well covered by the 32 inspection holes required by the AD. Consensus seems to be that other old brands of aircraft will have similar inspection requirements coming soon. No Coupes have been lost to corrosion in flight, so far, and we'd like to keep it that way.

What are the different models?
 

What's the difference between them?
The main difference between the 415 series is the size of the engine and the amount of load that can be carried. The 415 D increased the amount of load to 1400 lb., while the 415 E added a notched tail to make performance consistently good from low to high power.

The Forney was basically the same as the 415 series.

The Alon changed the canopy to have more head/shoulder room, and the canopy slides back instead of the windows, which slide up as the 415 series. It also added spring steel landing gear. Most were sold with rudder pedals but no-pedals was a factory option.

The Mooney M-10 added a "normal" tail, rudder pedals, the stall and the spin, thus removing most of what was unique about the Ercoupe.

Who builds the Ercoupe?
Ercoupes aren't built anymore, but Univair is the Type Certificate holder for the Ercoupe series and thus is the "factory" for new Ercoupe, Forney, Alon and M-10 parts. http://www.univair.com

Can I see the type certificate on the web?
Type Certificate Data Sheets for the Erco, Forney, Alon and Mooney M10 (in PDF, you will need Adobe Acrobat) Look under Univair, the STC holder -- http://www.faa.gov/avr/air/tcds/tc/tcds1_pz.htm

What kind of engines do they have?
Various models came with Continental C-65, C-75, C-85, C-90. There is an STC to put a 100 HP O-200 engine as well.

How fast do they go?
It depends on which model, how big you engine is, what pitch prop, etc. Normally it is in the range of 100-120 mph. We'll add more detailed tables later.

How big are the fuel tanks?
The later Coupes have two 9-gallon tanks in the wings, and a header tank, which holds 6 gallons, for a total of 24 gallons of fuel. The header tank is another nice safety feature, in that if for some reason the fuel pump fails, you have a gravity feed tank with enough fuel in it for you to find a place to land. (NOTE: Some early versions of the Ercoupe have 8 gallon wing tanks and a 5 gallon header tank, for a total of only 20 gallons of fuel.)

There is an STC for removing the header tank, and putting two 15-gallon tanks into the wings, but not many people have done this as it is expensive, and that much fuel impacts passenger load.

What kind of fuel economy does it get?
Your mileage may very, but in the 5 gallons per hour realm, up to 6 gph with some engine/power combinations.

Can it run on MOGAS?
Yes, with the proper STC, you can use MOGAS. Make sure that there is no alcohol in it!

How much can you carry?
All models of 415-C and 415-CD carry 1260 lb. gross.

Models 415-D, E, G, Forney F1 carry 1400 lb. gross.

Models Forney F1-A and Alon carry 1450 lb. gross.

Depending on the model and what's installed in it, useful load can be from barely 400 to over 500 lbs.

How much do they normally sell for?
Since Ercoupes are 50 years old, they have fully depreciated! <grin> This means that most Ercoupes are in the range of $10,000 -> $20,000, which is about the cheapest flying you can find. Since they are often flown on the cheap, make sure that the one you buy has been well maintained.

Why doesn't my coupe have a mixture control/wired mixture control?
<Harry Francis> "The C-75/85 engine was supplied with a Stromberg carburetor. It has a mixture control on the top of the carburetor, which is often wired full rich for no particularly good reason. Misinformation saying theStromberg carbs mixture control isn't effective still drifts around. Some people think that leaning is not required below 5000 feet msl and they never go above that, anyway."

In fact, the mixture control on either carb is perfectly effective (given simple maintenance) and can greatly increast range and reduce fouling. It's a good idea to lean using a large-scale EGT gauge -- leaning by sound on a small Continental engine may only give very crude approximation to the correct setting.

What is with the mixture control, or lack thereof? Can the control be reinstalled?
The Stromberg carburetors had a mixture control that consisted of a plate with some cleverly designed holes that slid against another plate with its own hole. By clever design, this varies the vacuum on the fuel in the float chamber (I think) to vary the mixture.

Ed Burkhead ( former EOC member ) said, "When I bought my Coupe, it was wired full rich. It worked pretty well full rich all the way up to 12,500 feet. I later got my mixture control cleaned and reactivated and got an EGT gauge. I get quite good mixture control but I do have to adjust it slowly, watch the gauge, make another slow adjustment, till I get just what I want. I would only get a sensitive EGT with BIG gradations in the 25-degree range. Not the low sensitive type that shows hundreds of degrees in a single sweep of the needle."

Is there an Owners Club?
Yep, The Ercoupe Owners Club. The EOC publishes a monthly newsletter. Dues $25/year (in the U.S.) and $35 outside the U.S.  To join, click here!
EOC
PO Box 7117
Shallotte, NC 28470-7117

Are there any good books about the Ercoupe?
These manuals and documents should be in print from these sources:
Aircoupe/Ercoupe Owners Manual................Skyport Services
Aircoupe Service Manual.......................Skyport Services
Ercoupe Service Manual........................Univair
Ercoupe Service Bulletins & Memorandums.......Skyport Services
Ercoupe Airworthiness Directives, Aircraft
Specifications A-718 & A-787 and Skyport
Service Notes.................................Skyport Services
FAA Approved Airplane Flight Manual for
Ercoupe Model 415-D...........................Skyport Services
The Aircoupe Story............................Skyport Services
Twin Tail Tiger...............................Skyport Services
Specifications, A.D. notes, S.T.Cs ..(ESS)....Univair

The other Coupe specific books are for a pretty specific audience and were not printed in large numbers. They can be hard to find and most are only available from used-book search services.

"The Ercoupe" by Stanley G. Thomas. In second printing as of spring 2000 and there may still be some in print. Aviation Publishing, Inc., PO Box 5674, Destin, FL 32540, phone: 850-654-4696, FAX: 850-654-1542, ISBN 0-9652727-9-6 (pbk).  This is a pretty well done, well researched book about the Ercoupe and its follow-on siblings. It's pleasant to read

"From the ground Up, Autobiography of an Aeronautical Engineer ", by Fred Weick - Autobiography of the designer of the Ercoupe. Has lots of stuff about his other aviation contributions, and a couple of chapters on ERCO and the design of the Ercoupe, as well as his later work on the Piper Cherokee and Pawnee. Printed by the Smithsonian Institution Press, ISBN 0-87474-950-6. This has been sold out.

"THE ERCOUPE, A Touch Of Class" by Frank R. Saletri,esq.  Out of print. If you can find a copy, many people value it highly. It's got some good articles and a lot of cut and past of ads, clippings and other Coupe material. This is a big book that sold for $50, originally.

"Fly-About Adventures and the Ercoupe" and "This & That about the Ercoupe", by Paul Prentice. Tese have lots of Ercoupe photos, and discussion of mods and performance of Ercoupes. Out of print.

"ERCOUPE" by Louis N. Buffardi. This has, among other things, a very good table of Coupe models and serial numbers.  This has been out of print for 20 or so years. It's probably not even available from used book search services but it has some tables of Coupe production history and other information that's good.
 

Does one model of coupe perform substantially better than another
The later the model, the better the performance, more or less. The Forney and Alons have the 90 hp engine with a pretty good prop. The Alon models have the redesigned canopy and get some speed advantage from it. An Alon may sell for $5-$10k more than a 415-C in similar condition. You might want to go more on the condition of the specific machine.

Where can I see some pictures of an Ercoupe?
The "Planes" link here on the EOC page will connect you to ercoupe.net where there's an extensive gallary of Coupe photos arranged by N number. There are some other excellent web pages for Ercoupe enthusiasts. Check out:
Tom Laird-McConnell's page (best viewed with Internet Explorer)
Brian Bailey's Ercoupe Net