lml@lancaironline.net Mailing List Archive

Jim,

Attached is a spreadsheet that I developed for my (naturally aspirated) ES. It calculates takeoff roll from the basic forces - rolling resistance, propeller thrust, efficiency, etc. and it computes the effect of altitude separately on engine power and takeoff speed. It can compensate for altitude, temperature and runway slope, but not humidity. You can change the values in the green cells to match existing conditions. The values in the white cells are the fundamental factors used in the calculations. The blue cells are calculated intermdediate results. The graph shows distance vs the "speed remaining" before liftoff, so when it goes to zero it is liftoff time. I have checked the results for takeoff distance from sea level to 10,000 ft. density altitude and it matches the actual takeoff very closely.

My takeoff procedure is to select about 15 degrees of flap (I don't see much difference from 10 to 20 degrees) and full throttle. Elevations above 5,000 include leaning to pea power. At 60 knots I lift the nosewheel off and wait until it flies off. If I get anxious I can get a brief AOA warning, so I don't get too aggressive. It flies off at probably 80 knots. Like you, I don't see much point in pulling it off early, only to wait in ground effect for it to pick up climb speed. So the calculations are for the distance required to get to a speed that actually allows a reasonable climb rate.

With the numbers shown in the spreadsheet you can see that the predicted takeoff distance is about 1400 ft, longer than the advertising literature would have you believe. I think the ditances calculated are best described as a "reasonable, conservative" prediction of performance.

From Jim:

Guys,

I am trying to tweak my Super ES performance information and would like your input on a couple of things.

I want to put together some charts/tables that let me calculate my plane's performance relative to density altitude. The purpose of this information gathering exercise is to put together a chart that can use realistic numbers to help me calculate performance at higher elevations and density altitudes. I want to do some flying out west and feel my tools are lacking where performance calculations for my plane are concerned.

My gray area is take-off distance. I have never actually done my own tests in this area other than paying attention at my home airport about where down the runway I start flying. If any of you have actual numbers for your ES I would like to see them if you don't mind.

Consensus of information that I found on the internet and in Lancair publications seems to be about a 700 ft ground roll on a standard day at sea level for 3400 pound gw. This number appears unrealistic to me.

The standard procedure that I have seen in a couple of places seems to require lifting the nose wheel around 55 and climbing at 85. Doesn't mention holding brakes till full power. Can't seem to find information that indicates when this method causes the plane to break ground. (Might be the 700 feet that is mentioned). This strikes me as an aggressive method (might not be, just seems so to me given my experience in my plane). I am not a test pilot and have no intention of flying at what might be the edge of the envelope. I prefer a bit of a conservative number, whatever it might be.

I have tried this method on a few occasions and I find it somewhat uncomfortable because the plane tends to settle in a tail low attitude after becoming airborne and seems quite lazy even while still in ground effect. I prefer crisp performance and firm response to control inputs. The 55/85 process doesn't seem to fit these preferences.

My method involves 10 degrees of flaps, deliberate, but not speedy, application of power, slight back pressure on stick beginning about 65, holding that pressure until plane flies off. Usually flying occurs at about 85-90 with no "sag" feeling and very positive control response. Climb out is at 100 till 400 feet then 125-130 to altitude.

On an approximately standard day this results in wheels off the runway at about 900 feet at about 3200 pounds. At gross of 3400 the number is about 1100. Again I have done no actual measurements, just judging by the thousand foot marks on the runway.

So is it possible to put together a chart that can help me figure ground roll and climb rate for various gross weight situations? Is one already available that I just don't know about? The Koch Chart only requires ground roll and climb rate for performance calculations relative to density altitude.

I appreciate any input you might have on this subject. I have not seen this subject on LML so maybe I am not the only one who could use this information.

Just trying to be safe.

Thanks,

Jim Scales (almost 1200 hours and very happy)

Attachment: Takeoff Performance2.xlsx

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