I don’t recall the speed and it will be different at every weight anyway. It can’t be done with zero flaps. I’ve tried. The manuals we all have are shown as airspeeds at max gross weight and 1g in level flight. This is how the aircraft is certified.
Today, for example I had a G6 owner and brand new PPL do a high performance blue donut takeoff. We were slightly slower than Vx (and under max gross) and doing almost 1,700fpm. We were at 500’ just past the end of a 3,400’ runway at sea level in a non turbo.
The other day I had another G6 new PPL owner fly a blue donut approach with just the two of us and I think we were under half tanks. I dimmed the PFD so he wouldn’t look at airspeed.
Then, Just on round out I lit it up and noted we were at 63 knots for a greaser. He was shocked.
Blue donut AoA correlates as the minimum sink airspeed and is 30% above stall. Stall speeds change with weight and bank angle. Many new PPL fail to understand it until they actually experience it.
Wally has pointed out something that most people do not understand. That is that a maximum turn rate with minimum turn radius is achieved at a lower speed and higher AOA than L/D max, or best glide speed. This is at the AOA for maximum lift, or CLmax, which the test pilot said happens in the Cirrus with 50% flaps. It is also very close to stalling AOA, and comes with high induced drag. (I learned about max performance turns training in basic fighter maneuvers in the F-4.)
Given that if your engine quits at 500 ft, you likely want to minimize time spent pointing pointing away from the runway, therefore a max rate turn would be theoretically be optimal. It would take a deft hand on the yoke to keep at the edge of the stall horn, kind of like doing slow flight in a steep descending turn. Screw that up though, and you risk a stall/spin fatal crash.
So, just to provide a bit of a safety margin in a time of high stress, flying at the blue donut is a good recommendation in order to get turned around quickly so the runway isn’t too far away.
But what is the altitude loss in the turn with half flaps steep turn at blue donut vs a flaps up shallow bank turn at best glide? I have no idea. This would be a good flight test project.
Now all of this is assuming that you need to minimize altitude loss in the turn. What if you did a steep Vx climb out at half flaps, light weight, into a brisk headwind? It would kind of suck if you completed the turn too high.
Great academic discussion. Just be thankful that you fly a Cirrus and can pull the chute.
What causes the “phughoid” pitch instability that he finds at higher flap settings. I read a little about it in the Airplane Flying Handbook, Chapter 4, dealing with slow flight at speeds below the L/D max on the backside of the power curve.
Great points, and why simply using blue donut for everything isn’t really the best idea. Definitely the easiest, and you won’t stall, so that’s good.
But there are times when you might want max range. Sometimes, max endurance. Sometimes max turn rate or minimum radius. They are all at different AoAs.
Sometimes you might want max SUSTAINABLE rate vs max instantaneous rate. Different again.
We used at least 6 different AoA targets in the T-45, depending on what you were trying to accomplish.
It would take a well calibrated AoA and lots of flight testing to figure them all out accurately, but I would intuitively suspect that half flaps would be the best configuration for any type of “impossible turn” scenario in an SR-xx.
You definitely wouldn’t want to try and figure it out real time.
Scott, I was pondering similar words. Yours are more polite than those I was about to post. It’s a shame when other wise informative posts degrade into such ridiculousness.
Since you just renewed the subject (one I consider important and worthy)…
FWIW I agree wholeheartedly and without reservation that it is a shame when wise informative posts degrade into ridiculousness. Do you think that happened here? If so, please point out where.
I agree that Clmax is higher with flaps 50% than flaps up. But that does not translate into a lower rate of descent with flaps 50% over flaps up.
Please refer to page 370 of Aerodynamics for Naval Aviators, figure 6.6.
You can see rate of descent vs. airspeed in two configurations, clean and landing.
Pick any speed. The rate of descent will be less in the clean configuration than the landing configuration.
Now I am without Cirrus availability at this time or I would do it myself, but a simple flight test would confirm or refute my statement.
Time a 1000 ft. descent clean and one with flaps 50%. Wings level flight, power idle. I predict the difference will be minimal. But theoretically the rate of descent should be greater with flaps 50%.
On a side note for those curious about rate and radius of turn, the difference in stall speed between flaps up and flaps 50% is 3 knots. SR22, 3400 lbs. So not much to be gained by having flaps at 50% in the turn either from a performance or safety standpoint.
Jim, since you asked, I will assume you are seeking constructive criticism. With due respect, you don’t seem to be able to let things go. In this particular thread, the appearance of you needing the last word is strong. FWIW.
I don’t believe that anyone who comes to this forum enjoys this type of interplay; I sure as heck don’t!
I understand. But if you are honest, I think you will have to admit that your core objection is your perception of member doing the posting. In this thread, I made one (and only one) perfectly reasonable safety-related comment which (for an unknown reason) precipitated an aghast response. I then spent some time trying to ascertain the reason for the aghastment. It bugs me to be falsely accused. I imagine you would be bugged too if someone did that to you.
Perhaps the new COPA software will enable us to block posts from members we consider objectionable or unworthy. If so, you can block me. I won’t block you.
Well, you said: “ half flaps is the highest L/D.” As the test pilot said, best L/D is clean, and CLmax is at half flaps.
But when doing the “impossible turn,” the time it takes is not really important. In most cases, what is important is minimum altitude loss in the turn. That is a balance between turn rate and sink rate. I can’t say what AOA and configuration would minimize altitude loss, but would guess that your recommendation to use half flaps and blue donut would be close.