N1BZRich(at)AOL.COM
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 Posted: Mon Sep 17, 2007 9:38 pm Post subject: Another Flight to Shelbyville |
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Once again I made a nonstop flight from Williamsburg, VA, to Shelbyville, TN, today. It is an early arrival for the first annual Lightning Fly-In which is this Friday through Sunday. I came out a few days early to help a classmate that lives in a town near here to plan a high school reunion (bummer, don't know how I got roped into doing that), but the good thing is I will have a chance to put some more time on the prototype this week before the planned activities this weekend.
As most of you know, when I get the chance to "add some info" for the group, I will write an e-mail so all can share in the knowledge or experience. So here is the latest attempt at that goal. Usually when I make a cross country flight I will post the overall speed and fuel burn so Lightning builders will get some idea of what they can expect with the Lightning/Jabiru 3300 combination. Remember my airplane, N31BZ, is a much modified Esqual with lots of Lightnings parts, the most noticeable being the Lightning cowling and firewall forward, and the Lightning gear leg fairings and wheel pants. Your Lightning, equipped with similar equipment, at a similar weight, and with the other clean up mods, should actually be about 5 mph or so faster. Normally when I make a cross country in N31BZ, I end up cruising somewhere between 8 to 12 thousand feet (I actually came back from Oshkosh this year at 13,500 for most of the flight). The reason for this is to get the higher true airspeeds, the lower fuel flows, and to be above most weather and a "bumpy" ride in the summer. My speeds and fuel flows have usually worked out to be in the 168 to 170 true airspeed mph range burning about 5.8 gallons per hour. As I mentioned above, your "jet" should be faster.
This morning, however, was a very unusual day. No clouds, a smooth ride at a lower altitude, and believe it or not, only about 10 knots on the nose on a flight that is basically on a westerly heading. So I thought I would try something different. I made the flight at 4,500 until I got to the mountains, then climbed to 6,500 until clear of them, then back down to 4,500 for the remainder of the flight into Shelbyville. The speed and fuel flow numbers that I am going to give you are based on the following:
Speed- The clock start for speed calculation started when I added power to takeoff at JGG and stopped when I cleared the runway at SYI. I used an initial cruise climb of 100 mph indicated to 4,500, then used 120 indicated when I climbed from 4,500 to 6,500. Descent from 6,500 to 4,500 was at 150 indicated, then descent to the SYI pattern was also done at 150 until I had to slow down to lower the flaps for a left base to 18. With the 10 knot head wind, my time to climbs, etc. the average tas in mph was 153.4. Add the 10 kt. head wind back in and you get about 165 mph true from start of TO roll to end of landing roll. Not too bad.
Fuel burn- I topped of the tanks late yesterday evening when it was no longer hot in Williamsburg so that I could squeeze in as much fuel as possible. Remember 31BZ's tanks hold about 29 gallons on a cold day and maybe 27 or so on a hot day. I told the EFIS that I had 28 on board. Anyway, the total fuel burn for the flight (start, taxi, engine run up, takeoff, climbs, en-route fuel burn, and taxi in at SYI) was 21.4 gallons with the tanks topped of to the same level as at JGG. Assuming it took 10 minutes to start and let the engine temperatures get up, taxi out and run up at JGG, and two minutes at SYI to taxi in and park at the fuel pump, fuel burn averaged 5,5 gph for the flight. Again, not to bad.
A few quick words on the techniques I normally use on cross country flights in N31BZ. When cruising at the higher altitudes (8 to 12 thousand) I normally set the fuel flow I want (say 6 gph) instead of an rpm. I have made the higher altitude flights enough times that depending on the length of the trip, I find that technique easier than trying to set an rpm. Today, however, at the lower altitude, I wanted to see what fuel burn I would get at a certain rpm, so that is the parameter I sat today - 2900 rpm. No, I did not constantly work the throttle to keep exactly 2900. I had the auto pilot on (altitude hold also) and I accepted the rpm variations as the auto pilot "flew" the airplane to maintain altitude. Much easier on the pilot's work load. Heck, I almost fell asleep several times.
So, did we learn anything from any of the above? Is flying in the 4 to 6 thousand range really almost as economical at flying up at 8 to 12 thousand? Does the Bing carb not lean as efficiently up at 8 to 12 as it does down at 4 to 6? BTSOM, but it does kind of look that way. Let all ask Earl these questions. Now that he has set a world record, he should know.
Blue Skies and hope to see you in SYI this weekend.
Be there, aloha.
Buz
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