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10 points to Syd. You're right. I should type more slowly so I don't forget my 3rd grade math in the rush. 314.159 square miles it is from a mile high! :) I'd bet I could land a Coupe on a long, skinny acre. It comes out to 201,061 acres. That's a lot of choices of landing area from a mile high. (Some of you people thought I was weird for flying cross-country at high altitude, didn't you? I used to like 11,500' and 12,500' - from 2-miles high, that gives 1,257 square miles or 804,247 acres :) to choose from and that usually includes 1-3 airports in the middle of the U.S.) As to the question of the best speed, each airfoil has a characteristic curve of sink versus forward motion. High aspect ratio wings generally get their best ratios at lower airspeeds. Hershey bar wings like the Coupe and short-wing Pipers get their best glide ratios at a somewhat higher glide speed. In my testing, my Coupe got its best glide ratio at an airspeed of about 75 mph. The top of the curve is somewhat flat and broad so the 5 mph increment just below and the several 5 mph increments just above weren't too much lower of a ratio than the best. The curve DID drop off quickly on the lower airspeed side but it dropped off more slowly on the high airspeed side. Within reason, in a Coupe, I'd say err on the side of slightly higher glide speeds - especially if you want to penetrate into a wind. _____________________________ The testing I did was fun. Here are the steps and I hope SEVERAL of you try it and give us the numbers. 1. Find a confederate to record the data while you fly the plane and watch for traffic. I also wanted the plane to be at gross weight so I picked a confederate who got me right to max gross. 2. Calibrate your airspeed indicator. [This is the step I missed 20 years ago.] The easy way is to fly directly into the wind and get ground speed from your GPS then fly directly downwind and get the ground speed again from the GPS. (Make sure your true course matches the GPS course to be sure you don't have side drift.) Average the two speeds. This give you a correction factor for the error of you airspeed indicator. For really good accuracy, do it at each 5 or 10 mph increment in the range you want to check. 3. Find an abandoned or very low use airport you KNOW you can land on dead-stick. 4. Climb to 4,000' agl over the airport, a ways out and turn toward the airport. 5. Slowly, slowly, slowly, reduce power to avoid shock cooling until you're at idle power and gliding toward the airport at your target airspeed for this run. 6. Start a stopwatch when you pass 3,000' over the airport. You fly the plane as accurately as possible. Don't forget to watch for traffic. 7. At 2,000' over the airport, note the temperature. 8. At 1,000' over the airport, stop the stopwatch and slowly, slowly, slowly apply power to avoid shock heating. 9. Climb back up and do it again at the next 5 mph increment in glide speed. Go back to step 4. Go home and analyze the data. Send the raw data to me if you can't crunch the numbers yourself. Don't forget to figure density altitude because this affects your true airspeed, which affects your forward feet per second. Hint: 60 mph is 88 feet per second. The stopwatch time for the 2,000' vertical drop can be used to get your vertical speed in feet per second. [Side note: the StratoMaster Extreme electronic instrument package I'm going to install in my "ultralight" "experimental light sport aircraft" will give a direct readout of the glide ratio, taking into account density altitude, true airspeed and everything. Sorry you guys can't have modern instrumentation.] Hope some of you can collect the data so we can really pin down the facts on this issue . . . forever. Ed Burkhead http://edburkhead.com/ [EMAIL PROTECTED] -----Original Message----- From: Sydney Cohen [mailto:[EMAIL PROTECTED] Sent: Wednesday, April 23, 2003 9:55 PM To: Ed Burkhead Cc: Coupe-List Subject: Re: [COUPERS-FLYIN] Re Glide ratio ----[Please read http://ercoupers.com/disclaimer.htm before following any advice in this forum.]---- It looks like I finally get a chance to correct Ed. That's really hard to do. The formula for the area of a circle is pi x R squared. If the radius of our gliding circle is 10 miles, we square that, giving us 100, and multiply that by pi, 3.14159, which gives us a circle of 314.159 square miles to land in. We have a fairly good chance of finding a decent spot in that many square miles. Syd Cohen Ed Burkhead wrote: >Allowing for the known airspeed indicator, I'd guess that the true best >ratio was close to 10:1 at an airspeed of about 75 mph. [My exact >measurements gave 12:1 at 80-85mph but I had about an 18% lower airspeed >than was used in the calculations so I'll say about 10:1 at around 75mph.] > >>From 6280 agl, that means you can choose a landing place as much as 10 miles >away and still have altitude to fly a pattern when you get there. That >means you get to pick the best landing field in a 31.4159 square mile zone. > > > > ========================================================================== == == To leave this forum go to: http://ercoupers.com/lists.htm Search the archives on http://escribe.com/aviation/coupers/ ========================================================================== ==== To leave this forum go to: http://ercoupers.com/lists.htm Search the archives on http://escribe.com/aviation/coupers/
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