Don, Ah, you bring up such interesting issues.
So, you're based at a 5,000' airport? Here's another thought for you - you might want to consider swapping out your engine for an O-200. It won't fly much, if any, faster. But it'll climb a lot better. (Naturally, this depends on the prop you choose and get approved.) Yes, it is possible to mount an O-200 on a 415-C or 415-CD. There is an STC for putting that engine on a 415-D but some people have gotten approval for the engine on a C or CD. In the long run, that may be a very good idea. Until you do that, I'd strongly urge you to fly from the high altitude aiport with a 7146 prop (assuming you have a C-85). And, make sure your mixture control works properly. Some idiots will tell you the Stromberg carb mixture doesn't work. The Stromberg mixture DOES work just fine (albeit slowly) if it is properly cleaned and hooked up. Make a change and wait a moment to see the results. With a high accuracy EGT I was able to tune it to 10° accuracy. If you have the Marvel-Schebler carb, that is OK. As for speed mods, well, there haven't been any. The Coupe is a fairly sleek airframe which explains its cruise speed with a small engine. (It also makes aerobatics extra deadly as the plane gains speed REALLY FAST when the nose is pointed down. Aerobatics of any kind are blamed in most of the very few in flight break-ups we've had.) The Alon canopy is sleeker and accounts for, I think, about a 7-10 mph airspeed gain (though the Alons also have the slightly larger C-90 engine). Alons could out climb me and fly 15 mph faster than my Coupe - but they're not eligible to be flown by Sport Pilots or PPfuSPp. The Kinney wheel pants were designed without benefit of computer aerodynamic design software or even a wind tunnel. They provide virtually no increase in speed, just in weight. But they do look cool. The landing gear mounted landing lights are said to make a lot of drag. First, I'd consider putting the landing lights in the wings or cowl. Moving them to the cowl would be cheaper. Putting one landing light in each wing maintains the bank information other planes get when you are tracking toward them - and it's dramatic as you'll see when a Coupe with gear lights flies toward you. I'd like to maintain that appearance to magnify your flying safety. But, if you are going to fly SP, you might keep the position lights and strobes but lose the landing lights - you are not allowed to fly after the end of civil twilight, anyway. Venturis hanging out the sides also provide significant drag. For speed mods, I'd next recommend you change to instruments you can run without venturis. Getting rid of any nose gear snubber cable (added later and repudiated by the designer) and restoring the nose gear fairing adds speed. Just adding the fairing to the properly extended nose gear adds one (1) mph by careful measurement of the designer. Planes with the snubber cable also have the sissors hanging out in an optimally bad manner. Planes with the snubber cable AND the fairing reflect a substantial error on the part of the owner as the fairing would then scoop air and make for BIG drag. An opportunity for real improvement would be good, aerodynamically efficient wheel pants. This is difficult to design due to the trailing arm of the main gear. But, very light, very efficient wheel pants might add several mph to the plane. No one has yet attempted this. Modifications of the wings may smack up against an FAA wall. You would certainly have to have a really extensive engineering analysis, possibly with an extensive flight test regime to prove the safety of the mod on a plane that is special. As the only plane flying in significant numbers that is certificated as "characteristically incapable of spinning," the Ercoupe is special aerodynamically. Changes to the wing might be prohibitively difficult. Perhaps the wing tip might be possible. Even the fairing between the wing and the fuselage was an integral part of the spinproof certification as was that small ridge at the leading edge of the wing near the fuselage. Perhaps the cowl shape could allow for some speed mods. Don't forget to take engine cooling into account. And, don't lose the engine cant to the right and downward. Well, there are some starter ideas. Please keep us posted on what you get approved and installed and how much difference it makes. We'd all like to be faster if we can afford it. Ed
