Hi Ed and others, Thanks for the replies.
On the speed front, the longish flight I did last Friday was almost no wind, with both out and return legs taking the same time within a minute or two. The GPS indicated ground speed was around 85 kts when my ASI was showing 82 kts. My friend in convoy with a Cessna 150 told me I was flying around 87 kts according to his ASI. So I¹m pretty sure there is no big error here. My prop is a McCauley 1B90 CM 7150. I¹ve no idea what the letters mean, but know that 71 is the diameter and 50 the pitch¹, both in inches. Calculating at 2200 rpm gives a theoretical 104 mph or 90 kts. If the 85 kts is for real then that implies an efficiency of 94%. Maybe in the US the 7153 is standard which with the same efficiency would give 90 kts. I¹m not sure which prop is standard on an Alon A2, but I checked my log last night and it looks like the one before this was also a 7150. My plane was originally used for training and instructors here are typically as heavy as in the US so a reasonable climb makes sense. I get 1,000 fpm no problem solo with full fuel at 70-75 mph IAS. Today on a warm windless day with a heavy friend we only managed 400 fpm. Regarding the tacho the max. rpm I can get in level flight is around 2,400 indicated, which again I think is about right. All the other comments that have been posted are valid but the mixture is fine (just rich side of normal), and I fly it straight although it does need a little right rudder to keep the ball central. I¹ve assumed that the ball is the only instrument that I don¹t have to check! There is no smell of gas anywhere so I don¹t think a static¹ leak is likely. Something in the pressurised lines or the fuel pump diaphragm makes more sense, although I think the pump is quite new. There is a brief smell of gas at take-off, after the engine has been on full power for a short time and before we are airborne. I¹d always taken this to be a little gas weeping out of the fuselage level wire but maybe it is a sign of something else. The weirdest thing of all is that I have been through the tech log for the past 5 years and plotted the fuel consumption during both my own and the previous ownership. The previous owner was pretty careful about keeping records, thankfully. As soon as I bought it the fuel consumption jumps from around 18 lph to 25! He claimed he cruised at 2200 rpm. BR, Mike On 10/4/07 15:38, "Ed Burkhead" <[EMAIL PROTECTED]> wrote: > Mike, > > I think that among the answers you¹ll get will be some useful information. > > I¹ve never owned a C-90 in a Coupe but, from what I¹ve heard, I don¹t thing 6 > gph is out of line (23 lph). > > But I perceive something wrong in that at 2200 rpm, you are only getting 82 > kts , IAS at 2,000¹. My Ercoupe, with a very flat climb prop on a C-85 > engine, would fly 100 mph (87 kts) and an Ercoupe with a ³normal² 7150 prop > (on a C-85) will normally get 108 mph (94 kts). > > Normally, any Alon will just walk away from us in cruise. They are faster > than 94 kts. Many have claimed cruise speeds as high as 115 mph (100 kts.). > I presume that¹s at the C-90 maximum recommended cruise. (One resource says > C-90 max recommended cruise is at 2250 rpm and I¹ve got another source that > says 2350 rpm.) > > Here¹s a chart from Paul Prentice¹s book Fly About Adventures and the Ercoupe: > http://edburkhead.com/Ercoupe/enginepropeller_efficiency.htm > > I¹m wondering what the pitch is on your 2-year-old prop. I¹ve seen a few > planes with ³cruise² props that were so steeply pitched that the engine > couldn¹t turn them effectively at cruise and the plane ended up with a very > slow cruise rather than the desired fast cruise. > > I guess it¹s possible to have a prop pitched so flat that you¹d only get 82 > kts (94 mph) at that rpm. But you¹d have a really fantastic climb if that were > the case. > > Test question: Does it climb really well or very poorly. Great climb would > match a very flat climb prop. Very poor climb would match a very steep > ³cruise² prop or a weak engine. > > Possibly you have a weak engine but I¹d look first at other causes, like prop > pitch. Also, I¹ll agree with John that you should get your tachometer checked > (a model shop digital tester is cheap but many airport mechanics have them). > Also, you should consider doing a test of your airspeed indicator. This > website has a good procedure: http://www.csgnetwork.com/tasgpscalc.html > > Ed Burkhead > http://edburkhead.com > ed -at- edburkhead???.com (change -at- to @ and remove "???") > > > [EMAIL PROTECTED] www.ercoupe.co.uk Alon A2 Aircoupe A-188 G-HARY --
