The 180-degree Turn

[jrs14855]

Prop

Regarding post 350:
Many years ago I had the opportunity to have an in depth discussion with a pilot who had lost the prop of an S2B Pitts. The crank flange failed, the prop departed cleanly, no damage to cowl. The most important take from this discussion is that the pilot extended the downwind to allow for the increased glide. When he turned final he thought that he would land short. As he approached the runway his next thought was that he would overshoot a 4000 ft runway. He made it ok.
On the Pitts there is a huge difference between otherwise identical S1 aircraft, fixed pitch metal vs constant speed. With the fixed pitch 90 percent plus of my landings at home base were idle power abeam the numbers at 800 agl. I rarely had to add power. With the german constant speed, I could be at cruise speed on 1/4 mile final, pull the power to idle and land on the 1000' mark. Downwind abeam the numbers took 1000 to 1200' agl and a very tight pattern to make the runway.
I explain the prop situation by discussing the diameter of the prop in relationship to the wing area directly behind the prop. The larger the percentage of wing area affected by the prop, the more drag with the power at idle/flat pitch.
The fixed pitch wood props typically used on an RV tend to be smaller in diameter than "normal" and except for the RV9 tend to be very high pitch. Because of these two factors the props at idle or windmilling do not provide a substantial amount of drag.

 

[jstamper]

Nice day at the beach

Last weekend I tried a few simulated engine failures at Knott End beach, Lancashire, here in the UK. This followed an article in the UK LAA magazine about turning back after take-off. Here are links to three recordings I made.

Simulating failure at 500 ft. Good lookout on public beach then normal take-off. https://www.dropbox.com/s/ppv1l0w8yderml9/500ft.wmv

Simulating failure at 400?. Normal take-off but not touching down. https://www.dropbox.com/s/uj4fo170sx44w00/400ft 1.wmv

Simulating failure at 400? from flying start. Engine off on final. https://www.dropbox.com/s/uf4cnfh29hfyxxq/400ft 2.wmv

It?s the first time I?ve tried this. Next time I?ll take some cones or streamers to mark the end of the runway to make the exercise more useful. Also if the beach is deserted I?ll fly over dry sand so I won?t be nervous about shutting down the Rotax while over water!

In theory the turns should have been flown at a slower speed but I don?t think turning at a faster speed gives much away. The extra speed, kinetic energy, can be converted to height, potential energy, after the turn when the wings are level and I know the stall speed on the ASI is reasonably accurate. Another reason to install the low cost Angle of Attack parts to get a simple, easily understood indication on the Dynon and get more performance with safety from our aircraft.

John.

 

[RFSchaller]

The 12 is so clean that idle power may make simulated engine loss trials very different from a loss of all power. Just a comment from the peanut gallery with no data to back it up. I would just urge caution about expecting the same glide with an actual power loss.

 

[Snowflake]

A flight instructor told me that a plane such as the RV-12 will glide farther with the prop windmilling. Is that correct?

Only if the engine is producing power. Otherwise, a prop that is turning, when your engine is not running, will create drag that will shorten your gliding distance.

The best case glide scenario after an engine failure is a catastrophic failure where the prop stops turning, and is jammed ("dead stick").

Somewhere in between is any situation where your engine isn't running, but your prop is still turning... the compression strokes slow the prop rotation on each revolution, creating some drag that will depend on prop pitch and whether you have a fixed pitch prop or a constant speed (and whether your constant speed goes coarse, or fine, when it fails).

Worst case is a failure of the crank that allows the prop to truly spin free, ie. massive failures of multiple cylinders, or a shaft failure that disconnects the front of the shaft from the rest of the engine. When the propellor is free to truly "windmill", the drag that results is about equivalent to mounting a disc of plywood the diameter of your prop to the front of your aircraft.

I have done some testing in a 100hp/100mph cruise airplane with both a wooden prop and a metal prop appropriate for that power/cruise speed. I found that the wooden prop would stop within a few turns even at 100mph when the mixture was pulled to idle cut-off. The metal prop would not stop turning until the airplane was slowed to about 70mph, but doing so gained me 300-400 feet of altitude which could be useful in an emergency.

I haven't repeated these tests in my RV with it's metal prop, but others here have reported that it takes about the same speed to get the prop to stop turning, and that getting there requires a rather impressive AOA when you start from cruise flight. It's also been reported that the prop will start turning again if you get over 90mph, so maximizing the benefit of the stopped prop also means having good speed control.

 

[SMO]

Split-S

(Yes I know that a 180 is actually a 210 plus a reverse 30)

Not necessarily, if the engine quits on takeoff push to level, roll inverted and do your 180 vertically, now you are lined up with the runway.......

 

[RFSchaller]

Rob,

All you say is true, but if the idle is high there may be a significant amount of power that won't be there in an actual failure. There have been several posts on the effect of high idle on landing distance.

Rich