pivotal altitude

[Ronald Sutton]

I pracise flying all the comercial maneuvers a lot. In the RV4, normally I use 2100 RPM with my fixed pitch aluminum prop as a base for all the high altitude maneuvers, chandels, lazy eights,steep banks, 360, 720 etc I use the formula for pivital altitude which is "airspeed squared divided by 15 MPH or 11.3 for knots". When doing "Eights On", what airspeed do most of you use?:

[BobTurner]

Remember the formula for the pivotal altitude is actually GROUND speed (which is why the altitude changes as you do the maneuver in a wind).

I personally like to stay above 500' agl so I try to choose my into the wind airspeed such that the ground speed is around 75 knots (which puts the pivotal altitude at 500'). The rest of the maneuver will then be higher, as you turn to go with the wind. However, since if you start out too close in to the pivot point the bank angles can get large, I never go faster than Va.

Steep banks, again a bit less than Va.

Chandelles, I usually start at Va and then apply climb power (more than 2100 RPM), ending just above stall speed.

[jcaplins]

I used Va. Which, if i remember correctly, is 98 Knots in a Cessna 172RG.

[Ronald Sutton]

VA speed = stall speed knots X square route of the upper loud limit 3.8
48 X 1.9 = 91.2 knots
pivital altitude is hight = VA squared over 11.3
hight = 91.2 X91.2 =8317.44 over 11.3 = 736.05663 ft agl
I could not come up with a positive VA speed, to get a pivital altitude.
I love the internet, Just type in a question and a formula comes up.Thanks for the help.

[BobTurner]

Is your flaps up stall speed really 48 knots? Remember this should be calibrated airspeed, since the aoa on the pitot tube is non zero at low speeds leading to the IAS being quite a bit less than CAS. Also remember stall speed, and therefore Va, will go down with weight, scaling as the square root of weight.

As I previously mentioned to get the pivotal altitude you need to use the ground speed. So if TAS = 95 knots and the wind is 20 knots, the pivotal altitude will vary between 500' (headwind) to over 1000' (tailwind).

[Ronald Sutton]

I am going to take some instruction first with a local instructor to get the feel again. The only time I am comfortable under a thousand feet is just over the fence on landing.

[pierre smith]

Originally Posted by Ronald Sutton

... The only time I am comfortable under a thousand feet is just over the fence on landing.

Funny...after a season at 10' above the crop, it takes several attempts to get comfortable ABOVE 1,000'

Best,