The O-290-D2 Yankee FAQ ----------------------------- by Matt Burch (AA1B N6540L) Last updated: 6/23/99 * Introduction This file is my attempt to consolidate all the information and wisdom I've come by during the process of upgrading my AA1B to 140 horsepower. Hopefully it will answer the basic questions that people considering this modification might have. Corrections, clarifications, and additions are most welcome and should be sent to me at . * Why would I want to put an O-290 on my plane? Three words: power, power, power! As someone once said, "there ain't no substitute for cubic inches." Just about everyone agrees that the stock AA1x aircraft are sadly underpowered, with unsatisfactory climb performance in "hot and high" conditions. Changing to a bigger engine has long been a favorite way to extract more performance out of these great airframes, with the Lycoming O-320 engine of 150-160 horsepower being the most frequently chosen powerplant. I personally think that this is too much engine for our airplanes: it will make you go faster, sure, but you may find that you can only carry very lightweight passengers and you're out of fuel rather quickly. The alternatives to the O-320 are to extract more power out of the stock O-235-C2C engine (see Bill Scott's excellent work in this area) or to find an engine that's a happy medium between the O-235 and the O-320. Fortunately this engine exists, in the form of the Lycoming O-290-D2. This 140 horse powerplant (135 continuous hp) is the bigger, older brother of the 108 hp O-235. It is smaller, lighter, and thriftier than the big O-320, but still gives great performance. Best of all, it shares a lot of parts in common with the O-235 and so is fairly easy to install in your Yankee, especially if you have the right bird. * What paperwork is required? You will need to buy a supplemental type certificate (STC) which authorizes the installation of the engine in your particular airplane. The only one I'm aware of that is legal to use with the O-290 is the Collier STC, which is sold by Fletchair (1-800-FA-WINGS). They sell the STC for $350, plus another $150 for another STC which allows you to legally increase the maximum gross weight of your aircraft after you install the new engine. Depending on your airplane, this might be the most useful $150 you ever spent. After your airplane is done having its shiny new engine installed, don't forget to have your mechanic fill out and submit a Form 337 informing the FAA that the modification was "performed in accordance with supplemental type certificate 2477SW" (or somesuch). * What aircraft does this apply to? In theory you could put an O-290 engine into any of the Grumman 2-seaters: AA1, AA1A, AA1B, or AA1C. If you have an AA1C you could technically install an O-290, but as the Lynx already has the newer dynafocal-type engine mount used by more recent engines, you and your wallet would probably be better off just going ahead with an O-320. * How will my airplane perform after this mod? With the 52" pitch prop called for by the STC, I was seeing sea-level climb rates of around 1400 fpm with no passenger and half fuel, and cruise speeds in the 115-120 mph range. Since I've pitched-up the prop to 58" and done some drag-reducing mods, my cruise is up to around 140-145 mph; no numbers on climb performance yet. Your mileage may vary. Fuel burn seems to be in the 7-7.5 gph range. * What should I look for in an engine? First, the engine absolutely has to be an O-290-D2 model; don't buy a -3, -11, -D, or any other kind of O-290. The -D2 has hydraulic valve lifters where the other models have solid tappets, and it is the only model allowed under the Collier STC. Besides that, the standard caveats about engine-buying apply. One good thing to look for in an engine is a fuel pump drive pad. Many of the O-290's on the used engine market have come out of high-winged Piper Pacers and Super Cubs, and so are not equipped with one. Fortunately the accessory housing on your O-235-C2C is easily interchangable with the one on the O-290, thus giving you a fuel pump drive regardless of where your engine came from. * Where can I find the right engine for me? Since the O-290 has been out of production for a while, you won't be finding them at any of the usual engine supply places. Your best bet is to read Trade-A-Plane every couple of weeks and keep looking until you find an engine you like. Another possible source is the Super Cub specialty shops such as Cub Crafters; they sometimes will have an O-290 around that was swapped for an O-360 in some lucky person's Super Cub. Be patient; you may not find the "perfect" engine right away. Don't be afraid to ask questions or ask to have a mechanic you trust evaluate a prospective engine before you lay down your money. * Does it need a different engine mount? Nope. The good news for AA1 through AA1B owners is that you can use your existing engine mount without any modification. While you have the engine off the plane, you might want to bite the bullet and replace the old sagging Lord mounts. Fletchair has them at a pretty respectable price. * Does it need a different prop? Yes. You'll need either a Sensenich 74DM6 or an M74DM. The STC calls for a 52" pitch prop, which is somewhat ridiculous; this is a very low pitch for this engine/airframe combination and will result in a phenomenally short takeoff roll and nosebleed-inducing climb rate, but ho-hum cruise performance. Supposedly they did this to limit the available power to the original 108 horsepower and avoid some legal wrangling with the FAA. Whatever... most people I know with O-290's in their Yankees have pitched their props up to a more useful pitch. 58" seems like a good compromise between climb and cruise. Beware the limitations of your prop before you decide to have it bent; a propeller can only be repitched a certain amount during its lifetime. * Is the spinner different? Maybe. The easiest but most costly thing to do would be to purchase and install a spinner for an AA5x. Your new spinner would fit your new prop perfectly, and you would have your choice of metal or composite construction. However, if you want to save money a slightly more labor-intensive option is to very carefully trim away at your existing spinner until it fits the new propeller. Be careful - you will have to trim almost all the way up to the forward bulkhead. I used a pair of duckbill pliers to give my prop cutouts a somewhat fluted edge, which looks nice and may make the spinner a bit more rigid. * Do you need to install the dorsal fin mod? If you really want to. I don't have a dorsal fin on my AA1B and I do get a case of the "wagging tail syndrome" while flying in turbulence. It is somewhat more pronounced than it was with the smaller engine, but it's certainly not enough to be worrisome. I think that when I can afford it I will eventually install a dorsal fin, but that decision is influenced more by the flight characteristics of the airplane in general rather than a reaction to the performance with the O-290 in particular. * What instrument changes are needed? You can keep all your old instruments - however, the range markings on the airspeed indicator and tachometer need to be changed. If you're really into saving money you can stick colored tape on the face of the instruments... I thought that was kind of ugly, though, so I had my ASI and tach refaced by a local instrument shop. The cost was $50 each to have them calibrated and a beautiful silkscreening job done. * How about the landing gear? You are required in the STC to buy a new, longer nosegear strut to let the bigger prop clear the ground. This is the 507 strut, also used on the Lynx, Cheetah, and Tiger. Used ones are almost impossible to find unless you get lucky. Fletchair sells new ones for $1050 (which seems rather steep for a crooked piece of steel, but you take what you can get). Then there's the maingear. AA1B owners are in luck: your maingear castings are up to snuff and need no changes. Earlier models need to have their maingear brought up to the AA1B standard to handle the increased weight. Of course, you always have the option of not purchasing the gross-weight-increase STC and leaving your maingear as-is, if you want to save a little money. * Does it need an oil cooler? Yes, you are required to install an oil cooler. Of course a cooler is never a bad idea in our hot-running little airplanes. If you are in the pro-filter camp, this would be a nice time to install a spin-on oil filter as well. * Does it need a bigger battery? You are required to install a larger, 35-amp battery. I saved myself a bit of money by enlarging the old battery box with some sheet aluminum instead of shelling out for a new one. * Okay smart guy, is there anything I can keep from my old engine? It may seem like you are replacing everything forward of the instrument panel, but luckily there are many parts you can directly reuse from your old engine. The starter, alternator, magnetos, vacuum pump, exhaust, baffles, plugs, and cowling all bolt right on without any modification. * How much weight will this add? The engine, oil cooler, and prop will add something in the neighborhood of 25 pounds to your airplane and will move the C.G. forward slightly. In my case my airplane actually flew a lot nicer after adding all that weight, as it was fairly tail-heavy to begin with. Interestingly, if you factor in the increased gross weight allowed by the STC, you actually come out ahead with more useful load! If your old Prestolite starter has been acting up, you can junk it and go with a lightweight starter for another 10 pounds or so worth of savings. * The big question: How much will it cost? Obviously every airplane will be different, but I'll use my case as an example. I got my engine with 230 hours since overhaul for $6,000 plus my run-out O-235 in trade. An M74DM prop was $700, plus another $350 to have it overhaulled. The nose strut was $1050, new Lord mounts were around $200, and new plugs were about $200 also. An oil cooler was $350, plus $500 for the two STCs. Add in hoses and other miscallenous parts, and the materials cost was approximately $9500. I helped my mechanic with a lot of the work, and the shop and labor costs worked out to about $1500, for a total installed price of my new engine of $11,000. Interestingly, this is about what I was quoted to have my old engine overhaulled. As you can probably guess, I am quite happy with my decision to ditch the old O-235 and I'm enjoying the feeling of having more horsepower in my pocket when I need it. Comments are welcome - please drop a line to .