Glass Panel simplified testing

A thread from 2 days ago linked to an EAA video about finding Vx and Vy. However the EAA video seemed to ignore weight and density altitude.

If we have a good EFIS - my remarks are for a Skyview system, but I assume the competitors are similar - data entry is made simple, with more variables collected than you know what to do with.

Nice graphs can be made with a free subscription to savvyanalysis.com. So I was thinking can all of this data be extracted and normalized into a POH for your plane?

After examining the performance data from my certified Tiger POH I have extracted some data constants. I hope simple data analysis and conversion with Excel will do the trick.

Need confirmation from any aerodynamics experts on stuff below.

1. Taking the climb rates from the POH I extracted a straight line that gave a -6.422% drop in climb rate for each 1,000 ft of std day.

Q. I assume that if I convert my flight test altitudes to a Density Altitude this constant will remain the same. Is that correct?

DA has been high during my testing so far, and these individual climb rates were taken at various speeds at DAs ranging from 5,500 to 15,000 with most at 8000-9000. The aircraft weight as not been corrected by are for pilot and about 3/4 fuel.

The curve seems reasonable and sort of shows my 83 inch pitch Sensenich is probably a climb prop.



The confusion I had extracting data from the Tiger POH was that the IAS for max. climb rate changes by std day altitude. The factor was -1.282% per 1000 ft.

Q. Does that make sense? I thought DA would correct for this and IAS remain constant. If not, how do I apply this correction factor to the above data?

More questions to come, but that will do for now. I hope I can get a simplified way of absorbing EFIS data into normalized performance charts and document it for others. When I ask local builders what they did, I found that most never really did any real testing with actual numbers.

* Plane is a RV-6A with gear fairing and wheel pants. Unmodified 180 HP O-360-A1A and 83 inch pitch Sensenich prop.

* Hope the chart comes out OK, it's a Photobucket replacement test.

Raw data for chart - first 3 columns straight out of the EFIS



These are the numbers from my Tiger POH. ROC is divided by 10 just to fit and use one chart scale. Definitely stright lines with std. day altitude. The red line is speed for best ROC -

Your first question is complicated, for the same reasons as the answer to your second question. Q2(lower best rate of climb airspeed as you go up): Your prop (probably a cruise prop, BTW) has its efficiency go up with airspeed (at least in the climb speed range). Also at higher speeds it will turn at higher rpm, so the engine puts out more power. These things add up to give you a best rate of climb airspeed - where you also have maximum excess power (excess over what's needed just to overcome drag) - which is higher than the speed where the power required (just to equal power into drag) is a minimum. However, as you climb, the total power available drops. This shifts the speed where excess power is maximized to the left (lower). As you approach the absolute ceiling the best speed becomes the only speed (to keep from drscending), and that is where power required is a minimum. So as you climb the best roc airspeed decrease. Best angle of climb slowly increases, until it and Vy are the same, at the ceiling.

BobTurner said:

Your first question is complicated, for the same reasons as the answer to your second question. Q2(lower best rate of climb airspeed as you go up): Your prop (probably a cruise prop, BTW) has its efficiency go up with airspeed (at least in the climb speed range). Also at higher speeds it will turn at higher rpm, so the engine puts out more power. These things add up to give you a best rate of climb airspeed - where you also have maximum excess power (excess over what's needed just to overcome drag) - which is higher than the speed where the power required (just to equal power into drag) is a minimum. However, as you climb, the total power available drops. This shifts the speed where excess power is maximized to the left (lower). As you approach the absolute ceiling the best speed becomes the only speed (to keep from descending), and that is where power required is a minimum. So as you climb the best roc airspeed decrease. Best angle of climb slowly increases, until it and Vy are the same, at the ceiling.

Click to expand...

OK, but I'm assuming (sometimes bad, I know) that the engine performance vs. altitude from my Tiger manual with a 180 HP O-360-A4K and a fixed pitch prop would be pretty similar to my RV-6A.

If I go by your notes (which do sound reasonable) then it seems that performance can't be normalized to density altitude and separate ROC charts are needed for selected altitudes. Living at a hot 3000 ft MSL it gets hard to work out/measure SL performance.

I'll do some climb tests on the next smooth day flight, but vary the IAS speeds at a single altitude.

It would be nice to get a standardized test procedure that we all can use extract data from our advanced technology EFIS unit.


As far as 83 inch being a standard prop - Vans only sells the 85 inch pitch for RV-6s while Sensenich calls 85 inch a cruise prop and 83 inch their standard prop. One reference I saw mentioned less drag with the newer wheel pants/fairings allowing more pitch.

Engine performance between the Tiger and RV may be similar; not sure about the prop; and the drag curve, and power required curve, may be significantly different.
As to Vy vs density altitude: Climb at a variety of airspeeds, note rate of climb, find Vy. Do this at 10,000' DA and repeat as low as you can get. Probably pretty close to just use a linear interpolation/extrapolation for other altitudes.
As to actual rate of climb: This is sensitive to weight, be sure to run this test at gross.
Edit: If you can run full throttle at 8000' (DA) without exceeding redline, you don't have a 'climb' prop.

BobTurner said:

.....
Edit: If you can run full throttle at 8000' (DA) without exceeding redline, you don't have a 'climb' prop.

Click to expand...

Full throttle and 2700 rpm occurs at about 15,000 ft DA in my plane with the 83 inch pitch Sensenich prop. Any lower altitude and engine redline would be exceeded.