Hi folks, I'm based in Cambridge UK , not Ireland!
I think I've been through most things about the fuel consumption, and have come to accept it. My Alon/C90 should do 104 mph at 2,350 and I can just about get that but it won't hold it for long. In any case in the UK you need to apply carb heat every 5 minutes to prevent icing and then you have to settle everything down again. Any distance and I average 85 kts (97 mph). Almost all flying is at 2,000 feet due to airspace restrictions, therefore no opportunity to fly higher and lean the mixture. The mixture is not over rich judging by the plugs. All controls are aligned. The prop is around 200 hours and in good condition. Sure there is some more drag since new, with inspection covers everywhere, a few dents and panels that are not as good a fit as they should be. Almost certainly the weight is high, although the radio nav. instruments once fitted have long since gone. The previous owner had his own strip and filled from a can. My guess is he guessed and underestimated the fuel he was adding, or flew slow at 2,200. I use a pump that is certified. So to summarise my performance, C90, 7150, 2,350 rpm, 85-90 kts, 6.6 US gph. Regards, Mike On 16/6/08 00:27, "Ed Burkhead" <[EMAIL PROTECTED]> wrote: > Mike Willis (in, I think, Ireland) wrote: >> Unfortunately I get 25 litres per hour from my Alon >> with a C90. It drops a bit on longer trips, but most >> of my flying is less than one hour so includes a climb. >> 25 litres per hour is 6.6 US gallons per hour. Sure >> I could fly slower and burn less, but to me the >> cruise at 85 kts is as slow as I want to travel. > > ??????????????????? > > 6.6 gph at 97 mph? (85kts.) What¹s wrong, there? > > With my C-85 and a very flat climb prop, I habitually got 5.4 gph at 100 mph > (accurately measured) at 2400 rpm. > > Most Ercoupes get distinctly better speeds with the C-85 engine and a 7148 or > 7150 prop frequently yielding 104 mph (90.4 kt.) and 108 mph (94 kt.) > respectively at 2400 rpm. Forney Aircoupes tend to get a bit higher speed > with the C-90 engine and Alon Aircoupes get 5-15 mph greater speed due to the > better aerodynamics around the canopy. > > If I didn¹t know better, I¹d say it sounds like you have one of these > conditions: > > 1. An over-pitched prop, set too steep, intended for cruise and the engine > just can¹t spin it properly at that power and gross weight. > > 1. An over-weight plane that¹s so heavy, the engine just can¹t get it up to > the normal airspeeds a Coupe should attain with a C-90. This could lead to > flying at a very high throttle setting (even though it might only show a lower > rpm number due to a too-steep prop and a very high fuel burn. (Note that 1 > and 2 can be heavily interrelated though can also occur separately.) > > 1. Engine problems giving low power output at high fuel burn. > > 1. The airframe is mis-rigged or has alignment problems and has low efficiency > due to flying crooked or control surfaces not being correctly aligned. [You > did mention needing some right rudder in cruise?] > > I went looking back through your old messages and saw that you have a 7150 > pitch prop. That means you are getting appropriate airspeeds for your prop > and 2200 rpm. You mentioned that the previous owner¹s meticulous records > indicated 18 lph (4.75gph) @ 2200rpm and that sounds about right to me. So, > your results are not what I¹d expect. > > Do you usually fill up at your field¹s pump? Did the previous owner base the > plane at the same field? Have you cross-tested the pump¹s accuracy? > > Here are numbers from Paul Prentice¹s airplane efficiency chart he allowed me > to post on my website: > http://edburkhead.com/Ercoupe/enginepropeller_efficiency.htm > > ENGINE PROP COUPE AVG CRUISE TIAS TAS MAX IAS TAS > TYPE SIZE MODEL EFFICIENCY RPM SEA LVL 5000' RPM SEA LVL 5000' > > C-75 7351 C-D 97 2275 106 114 2275 106 114 > > C-85 7150 CD-to-G 95 2400 108 116 2575 116 125 > > C-90 7152 F1-F1A 95 2350 110 118 2475 116 125 > > C-90 7153 A2-A2A 97 2350 114 123 2475 120 129 > > O-200 6950 D-G 91 2500 108 116 2750 118 127 > > You¹re already cruising at a conservative airspeed (97 mph) @ 2200 rpm. > > For those who cruise fast and are suffering from high fuel costs, here are > some observations: > I can see high speed cruise for going places, when you¹ve a need to get there. > But, when the purpose is to be in the air and going places is just the excuse, > then slowing down greatly cuts your costs per flying hour. Your miles per > gallon and minutes per gallon go way up at slower airspeeds. > > Paraphrasing ³Stick and Rudder,² the speed we call ³cruise² in airplanes isn¹t > really a good cruising airspeed, it¹s a speed that gets us there fast without > it being too horrendously expensive. > > The cruising speed would be just a bit above best glide speed. > > When flying high with the engine leaned, you are flying in the low indicated > airspeed regime with the engine throttled way back by the thin air of altitude > and the leaning. This is the best angle of attack for maximum efficiency and > range. But, due to the thin air, your true speed is quite a bit faster than > the indicated airspeed that the plane ³feels² so you¹re getting your high > efficiency mushing flight at a fairly fast true airspeed. > > Me, I¹m building (way too slowly) a plane that can soar, engine off, in strong > thermals. If really ridiculous fuel costs make it necessary, I might have to > fly it mostly in the middle of the day, soaring in the thermals with the birds > and just using the engine to get up. > > For your plane, something ³does not compute.² > > (P.S. Your messages are coming through at 6 pt. type and are hard to read. > Is there anything you can do on the sending end to increase the font size?) > > Ed > > Ed Burkhead > http://edburkhead.com/Ercoupe/index.htm East Peoria, Illinois > ed -at- edburk???head.??com (remove the ? marks and change > -at- to @) > > ________________ Alon A2 A-188 G-HARY www.ercoupe.co.uk
