Cirrus down 9A5, south of Chattanooga

[Ed Haywood]

Murphy's Law says the chances of having an engine out on a gusty crosswind day are 100%, ESPECIALLY if you haven't practiced it.

 

[NavAir]

There is a beautiful example of a military Link trainer on display at the Pima Air Museum in Tucson:




It looks like it could be a working model...

 

[wanttaja]

@wanttaja, I would *love* to see that presentation. Does this video get a thumbs up from you?

Oh, yeah, big thumbs up. Excellent detail, reminded me of some of the final technical details that I had forgotten in ~45 years. My own presentation is slanted toward how they flew.

The only error I saw wasn't their fault...they quoted an RCAF Air Marshal who claimed the Link gave the allies an advantage. In reality, both Germany and Japan had lots of Link Trainers. In fact, every German pilot who bombed London in 1940 had 50 hoursof Link time.

The book "The Pilot Maker" says that when the Link company showed up in Japan with a sample, the reprentatives came in one morning to find the Trainer completely disassembled....

Ron Wanttaja

 

[Hengelo]

Great to hear. They didn't dive in (sorry, bad pun) to how the pendulum driven instrument led to pedal-heavy turning but I'm surprised that took so long to surface as a serious issue.

Very funny about the Japanese disassembly!

 

[dtuuri]

Need a tighter turn? Let the nose drop to reduce the load factor, let the airspeed increase a bit, once done level off and re-stabilize things before descending again.

The load factor is a result of the turn rate. If you reduce it, you reduce the turn rate rather than increase it.

 

[Piperonca]

The load factor is a result of the turn rate. If you reduce it, you reduce the turn rate rather than increase it.

Only at a constant altitude, right? What about descents? Might you say load factor is actually a function of bank angle and power?

 

[flyingcheesehead]

Only at a constant altitude, right? What about descents? Might you say load factor is actually a function of bank angle and power?

No, you still need to pull on the yoke to tighten up the turn. If you bank 60 degrees at a load factor of 1, the nose will drop, but you're not gonna turn very tight either... At least, until the accelerating downward vertical speed causes an increase in airspeed and trim starts increasing the load factor for you.

Also, increasing speed *increases* the turn radius.

The two things you need for a tighter turn are lower speed and higher bank angle *and* load factor. All of these things put you closer to a stall. The absolute minimum turn radius you can get on an airplane is if you're banked to the angle that gets you to the maximum load factor and the slowest possible speed you can maintain that bank and load. For a normal category airplane with a 3.8g maximum load factor, that's a 74.7 degree bank and 1.94Vs.

 

[PaulS]

Another sad accident, unless this plane was upgraded it didn't have the bells and whistles of a newer Cirrus. No envelope protection, no airspeed warning, no AOA for FIKI. That said, this accident still shouldn't have happened. Cirrus are docile, easy to fly airplanes, until you do something stupid and they bite you in the ass. You need to stay coordinated and you need to pay close attention to airspeed in the pattern. For a normal pattern, you want to be at 100 knots opposite the numbers, 90 knots on base, 80 knots on final, 77 over the fence. When you add flaps the nose rises, the airplane balloons and airspeed will scrub off if the pilot does nothing. Crosswinds are no big deal for a practiced Cirrus pilot. Demonstrated crosswind is 20 knots for both the 20 and 22, but the 22 will easily handle higher crosswinds. Cirrus recommends full flaps for crosswinds, normal approach speeds unless there is great than a 10 know differential gust. Then use a gust factor.

I did an unusual attitudes recovery course with a Cirrus center, it was a great course. The instructor had a diagram that showed how the wing blocked some of the airflow to the rudder in a spin for a Cirrus. He said you can recover from a spin in the Cirrus, but it will take more altitude than most aircraft. I forget the number he said, but I believe it was over a 1,000 feet. The point was do not get into a spin, especially in the pattern, if you do get into a spin, Cirrus wants you to pull the chute.

Lastly, there is no reason for heroic attempts if you blow through final on the base to final turn, stay coordinated, keep turning, until you get back on final. If you become unstable, add power, climb back to pattern altitude, fly an up wind, try again.

 

[AV8R_87]

The load factor is a result of the turn rate.

No, you still need to pull on the yoke to tighten up the turn. If you bank 60 degrees at a load factor of 1, the nose will drop, but you're not gonna turn very tight either.

Making a level turn at 45* AoB I will have a ground turn radius (at some particular airspeed and no winds, for ease of the conversation) of let's say 2nm. If I change nothing but the bank angle (let's say to 60*), I redirect that lift vector so that more of it gets used to turn the plane and less of it fights gravity. Now my turn radius will decrease because of a couple factors. One, more of my lift is directed towards the turn. Two, my turn is not in a level plane, my turn is now having a vertical component as well. Assuming (again, for ease of math) that my turn now takes a path that has a downward angle of 30*, I have just reduced the ground turn radius by [1-cos(30)], or about 13%. Increase that turning plane angle to 45*, and you've reduced your ground turn radius by 30%.

Yes, my vertical speed will increase and it's not sustainable for a full 360* turn, but we're only talking about the final tightening of the turn that people do when they auger it in base to final. I'm not pulling the 2Gs I would need to in order to hold a level turn at 60*, I'm still pulling the 1.4Gs of the 45* turn. Yes, not ideal choice of words on my side, but I did "lower" the load factor while banking to 60* by not increasing the backpressure on the yoke to maintain level flight. And then got the extra benefits of my turn not being in a horizontal plane anymore.

 

[Piperonca]

I was thinking about @Ed Haywood's successful forced landing with my question. First, the classic bank angle/load factor diagram should include something like Cheesehead's stall discussion with regard to steady state flight. No quarrel there. My interest is in the special case of 'impossible turn' which FAA says is almost certain death, and also the general case of spiral emergency descent through a hole in clouds, etc.

I know one pilot that has survived two impossible turns. Ergo, they're not impossible. Ed did it. Bob Hoover could probably do it while pouring tea. Definitely an aerobatic maneuver, though.

There's a lot of higher math available on the angle of attack and stall related to turns: Aviation Stack Exchange. Fun example to see CFI arguments.

Not being a high time fixed wing guy, all I can compare is keeping extra collective pitch on a teetering rotor system while in a steep turning descent. This loads the rotor so it stays within rpm limits. Very useful maneuver but one must be careful.

Looking for some good rules of thumb if you absolutely, positively have to turn back to a runway, or descend fast over a point. Without looking at instruments.

 

[dtuuri]

Making a level turn at 45* AoB I will have a ground turn radius (at some particular airspeed and no winds, for ease of the conversation) of let's say 2nm. If I change nothing but the bank angle (let's say to 60*), I redirect that lift vector so that more of it gets used to turn the plane and less of it fights gravity. Now my turn radius will decrease because of a couple factors. One, more of my lift is directed towards the turn. Two, my turn is not in a level plane, my turn is now having a vertical component as well. Assuming (again, for ease of math) that my turn now takes a path that has a downward angle of 30*, I have just reduced the ground turn radius by [1-cos(30)], or about 13%. Increase that turning plane angle to 45*, and you've reduced your ground turn radius by 30%.

Yes, my vertical speed will increase and it's not sustainable for a full 360* turn, but we're only talking about the final tightening of the turn that people do when they auger it in base to final. I'm not pulling the 2Gs I would need to in order to hold a level turn at 60*, I'm still pulling the 1.4Gs of the 45* turn. Yes, not ideal choice of words on my side, but I did "lower" the load factor while banking to 60* by not increasing the backpressure on the yoke to maintain level flight. And then got the extra benefits of my turn not being in a horizontal plane anymore.

Sorry, not buying it. Changing the direction of your momentum induces a "g" force. A continuous change gives a continuous load factor. Lessening the rate of change reduces that load. I think you're overthinking it.

 

[AV8R_87]

Try this experiment: trim the plane for a standard rate turn in level flight. Then increase the angle of bank by 15 degrees, without changing anything else. Observe the results. Helps if you also have a g-meter in the panel and if you can record your ground track for later analysis.

 

[dtuuri]

Try this experiment: trim the plane for a standard rate turn in level flight. Then increase the angle of bank by 15 degrees, without changing anything else. Observe the results. Helps if you also have a g-meter in the panel and if you can record your ground track for later analysis.

If you have the results post 'em here. My Citabria is long gone along with the g-meter.

 

[Ed Haywood]

I know one pilot that has survived two impossible turns. Ergo, they're not impossible. Ed did it. Bob Hoover could probably do it while pouring tea. Definitely an aerobatic maneuver, though.

I appreciate the credit, but I can't claim an impossible turn. All I did was a nice tight spiral turn to short final, then put it on the ground. Nothing particularly special except I remembered not to stall, and I got very lucky with my landing site.

Looking for some good rules of thumb if you absolutely, positively have to turn back to a runway, or descend fast over a point. Without looking at instruments.

Don't stall. That's the rule. If you have to maneuver aggressively without power, let your nose drop and trade altitude for airspeed.

 

[Tools]

The number one rule in aviation… stay in the middle of the air.

This can ONLY be done if you remember what Ed Haywood says. DO NOT STALL.

 

[Piperonca]

Don't stall. That's the rule. If you have to maneuver aggressively without power, let your nose drop and trade altitude for airspeed.

Number one rule! That goes on my list for sure. Get the nose down pronto. Others are a quick plan before takeoff (or brief if flying with someone), climb at Vx after takeoff, turn into wind if feasible, etc. Some might say check tanks if flying Pipers. Got to keep the list short though.

My query started with a quibble after a wee hours dribble. Now it's a full stream. Few topics more beaten to death than Impossible Turn it would appear. I am only adding a simple question about optimizing steady descending turns, or getting as close to optimum as time permits. Can't be flying exact angles.

Just an academic exercise for me at this stage but might be useful to somebody. Fastest (maybe safest) way to get on the ground without pulling the wings off. Dive, spiral, or spin? Here comes bank angle and load factor again. I have a hunch there's some commonality.

 

[AV8R_87]

Fastest (maybe safest) way to get on the ground without pulling the wings off.

Tight spiral in a dirty configuration with sideslip.

 

[Ed Haywood]

Fastest (maybe safest) way to get on the ground without pulling the wings off.

The way you practiced it. A mediocre plan well executed is better than a perfect plan executed poorly. IMO it is less important to use the optimal technique than it is to use a technique that you are comfortable and confident with because you have practiced it hundreds of times.

 

[flyingcheesehead]

Making a level turn at 45* AoB I will have a ground turn radius (at some particular airspeed and no winds, for ease of the conversation) of let's say 2nm. If I change nothing but the bank angle (let's say to 60*), I redirect that lift vector so that more of it gets used to turn the plane and less of it fights gravity. Now my turn radius will decrease because of a couple factors. One, more of my lift is directed towards the turn.

Yes, but only on a very transient basis. Since you no longer have the vertical component of lift, you will be *accelerating* downwards, and airspeed increasing, which increases the turn radius.

I put all this stuff into a spreadsheet when I did a mountain flying course. FWIW, a 45º banked turn at 75 knots gives you a 500 foot turn radius. If you increase to 85 knots, it's 642 feet, nearly 30% more.

Keeping the same load factor while increasing bank from 45º to 60º only gives you 22% more horizontal lift component/turn rate, but takes away about 30% of your vertical lift. You'll tighten it up for a couple of seconds, but probably not much more. (Too late in the day for that kind of math.)

Two, my turn is not in a level plane, my turn is now having a vertical component as well. Assuming (again, for ease of math) that my turn now takes a path that has a downward angle of 30*, I have just reduced the ground turn radius by [1-cos(30)], or about 13%.

This... Does not help you. You're trying to carve a path over the ground that gets you to a runway. Vertical component gives you less time to do the turn. If you're high it could be advantageous, but it's a lot easier to fix things when you're high than when you're low.

I'm not at all saying the maneuver is useless, but it's also not magic.

Looking for some good rules of thumb if you absolutely, positively have to turn back to a runway, or descend fast over a point. Without looking at instruments.

Best rule of thumb if you're going to be in a situation where the runway is the only survivable place to put it down: Buy a twin. (And it'll need to be a long runway.)

Try this experiment: trim the plane for a standard rate turn in level flight. Then increase the angle of bank by 15 degrees, without changing anything else. Observe the results. Helps if you also have a g-meter in the panel and if you can record your ground track for later analysis.

If you have the results post 'em here. My Citabria is long gone along with the g-meter.

I am always up for some flight testing. GI275 will record attitude (bank), altitude, airspeed, normal acceleration (g), and ground track.

Just an academic exercise for me at this stage but might be useful to somebody. Fastest (maybe safest) way to get on the ground without pulling the wings off. Dive, spiral, or spin? Here comes bank angle and load factor again. I have a hunch there's some commonality.

I don't know about a general solution, but in spite of being a very slippery bird, my Mooney can fall out of the sky like a rock using the book emergency descent procedure: Pop the speed brakes (which can be done up to Vne) and even pitch up a little to get down to Vloe of 140 KIAS, drop the gear, then push to accelerate to Vle of 165 KIAS. In fact, now that I mention it, I'm gonna do this when I do the turn testing above. I haven't done a good emergency descent since I got the GI275, and the rate of descent was far higher than I could measure previously. I'll even do both the dive and the spiral. No spins though.

One additional thing to consider in the dive, spiral or spin discussion is that, if you're trying to just get on the ground as fast as possible, you probably want to get out of the plane as fast as possible as well because you're probably on fire. That means that the time it takes to get the plane to a stop is also important. A spin might sound like the way to go, but recovering from the spin is going to increase your airspeed again. Can you recover from the spin without exceeding approach speed or entering a secondary stall or hitting the ground? Seems like an added challenge that would be unwelcome during an emergency.

As far as dive vs. spiral, if you're able to make an airport, using the combination of both that puts you in the right spot when you get to the ground is probably the way to go. Dive until you're near the approach end of the runway you want to use, steep spiral down (speaking of commercial maneuvers...). If it's not gonna be a runway, well, it'll still be similar, just a spot on the ground.

 

[flyingcheesehead]

(Too late in the day for that kind of math.)

Oh good, someone did the math in that Aviation Stack Exchange link above. Follow it for all the gory details, but this was the conclusion:

The idea of easing the G-loading by "easing the back pressure" on the stick deserves a little more attention. In the short run, a strong decrease in back pressure on the stick will always ease the G-loading, but the decrease in the wing's lift coefficient and Lift force will then make the flight path curve downward and the airspeed increase, so that the wing is once again making about as much Lift (and therefore Load Factor) as it was before the change. The only long term, sustained effect on Load Factor of a change in amount the back pressure is the pilot exerts on the control stick, lies in resulting change in the L/D ratio. The table above suggests that that will generally allow only an extremely modest long-term change in Load Factor, for flight at any given bank angle.​

​

And finally, to try to address at least one specific question asked in the original post:​

​

For the setup: In a level turn, 30 degrees would equate to 1.15G and increase the stall speed by 7%. What are these values if at the initiation of the turn, the aircraft was in a stable (call it 600 fpm) descent, and the airspeed was kept constant (relaxing back pressure to not decrease or increase the speed)?​

You mention that you were flying a "deadstick" approach, which suggests you were flying a single-engine light airplane. Let's assume your approach was made at 70 mph. If you allowed the plane to descend at 600 fpm, that works out to a descent ratio of 10.27, which gives a descent angle of 5.56 degrees. Keeping that descent angle firmly in mind, look at the second line of the table above. Your decrease in Load Factor, compared to the constant-altitude case, is going to be on the order of 1%. You won't be able to detect any decrease in stall speed due to the fact that you are descending rather than maintaining altitude. The effect you are asking about is completely insignificant.​

 

[FastEddieB]

As an aside, there’s an iPhone app called “Gauges”. Can’t say how accurate it is, but it will record your acceleration in g’s, along with a lot of other info…

 

[tobnpr]

Hence why I was asking earlier about simulator options. An earlier poster mentioned X-Plane, but I was thinking something a bit more immersive with accurate approximations of the physics. The Part 121 guys use sims to train all kinds of emergencies and uncomfortable scenarios that they hope to never encounter in real life. Are there any FFS or FTD options for piston singles? If so, where are they and how much does it cost to get time in them? I'm not talking BATDs. I know Aircraft Simulator Training in TX has pretty realistic Twin Cessna sims.

X-Plane has very accurate aerodynamic modeling. It is used in certified commercial simulators, and can be certified when used with "home-built" sims as well for those that choose to drop the coin.

As someone learning, I find the flexibility to dictate weather conditions as well as in-flight emergencies very valuable.

One can set weather conditions (temp, precip, wind speed/direction including gusts at varying altitudes), time of day, and it can also download existing weather conditions where you're flying and replicate them.

Want to practice engine out procedures at 500 ft AGL on climb out? Or how about random engine out?

Realism gets more advanced by the day. Now, you can set up virtual reality "pass-throughs" that allow you to see your physical sim flight controls- and your own hands/feet in real time- while using a virtual reality headset. Money no object? Add a full-motion platform...

 

[AV8R_87]

If you have the results post 'em here. My Citabria is long gone along with the g-meter.

Got a chance to try this a few days ago with relatively calm winds, and managed to take a pretty poor video, but it was enough to take a couple screenshots.

Exhibit A, entry into the turn, 45 degree AoB, about 500fpm rate of descent - typical of a base to final turn, minus the angle of bank, but that made the G-loads more evident. The plane was trimmed for this turn to ensure there wouldn't be any change in the pitch of the elevator during the maneuver.

Note the 1.3G in the maneuver, pretty typical of a turn at that bank angle. Counting frames in the video, it took about 15 of them (half a second) to turn 5 degrees, or about 10 degrees per second. Theoretical value should be 11 degrees per second, so I'd say we're where we need to be for the entry conditions.

Exhibit B, bank angle increased to 60 degrees, without applying any additional backpressure. This screenshot was taken a few seconds later. Now it only took 5 frames to turn 5 degrees, we're at a turn rate of 30 degrees per second. Note that the G-meter still indicates 1.3G, the same as we had when we were banked at 45 degrees. The pitch dropped from level to 20 or so degrees nose down, and the vertical speed increased to about 1800fpm.


Exhibit C, rolling wings level, and keep in mind that the airplane is still trimmed for almost a level turn at 45 degrees AoB. So it will want to pull up, plus the extra speed increases that tendency. Even so, the G-meter only indicates 1.5G. A couple maneuvers went up to 1.7 if no forward pressure was applied on the yoke. Still, less than the 2Gs of a level turn at 60 degrees AoB.


And now for the conclusion, the actual ground track:

Compare the initial turn radius at 45 degrees AoB with the turn radius of the descending turn at 60 degrees AoB. I'd say there is a pretty significant difference. Yes, it's not sustainable, you can't do it for more than 10-15 seconds or so, but that is more than enough to tighten a turn without potentially stalling the aircraft. We actually get the turn rate (and radius) of a 60 degree AoB turn but without the G-load.
You can argue about how it actually happens, but I think the conclusion is pretty evident - you can safely tighten a turn (albeit for a short time only) by increasing the bank angle but without the increase in elevator backpressure. Enough to salvage a base to final turn that could otherwise result in a stall/spin accident. I completely agree that going around is still the safest way to handle that situation, followed by overshooting final and then correcting, but in a pinch, increasing the bank angle and letting the nose drop will get you in less trouble than trying to tighten that turn in a (mostly) level attitude.

 

[dtuuri]

Got a chance to try this a few days ago with relatively calm winds, and managed to take a pretty poor video, but it was enough to take a couple screenshots.

Exhibit A, entry into the turn, 45 degree AoB, about 500fpm rate of descent - typical of a base to final turn, minus the angle of bank, but that made the G-loads more evident. The plane was trimmed for this turn to ensure there wouldn't be any change in the pitch of the elevator during the maneuver.
View attachment 139964
Note the 1.3G in the maneuver, pretty typical of a turn at that bank angle. Counting frames in the video, it took about 15 of them (half a second) to turn 5 degrees, or about 10 degrees per second. Theoretical value should be 11 degrees per second, so I'd say we're where we need to be for the entry conditions.

Exhibit B, bank angle increased to 60 degrees, without applying any additional backpressure. This screenshot was taken a few seconds later. Now it only took 5 frames to turn 5 degrees, we're at a turn rate of 30 degrees per second. Note that the G-meter still indicates 1.3G, the same as we had when we were banked at 45 degrees. The pitch dropped from level to 20 or so degrees nose down, and the vertical speed increased to about 1800fpm.
View attachment 139966

Exhibit C, rolling wings level, and keep in mind that the airplane is still trimmed for almost a level turn at 45 degrees AoB. So it will want to pull up, plus the extra speed increases that tendency. Even so, the G-meter only indicates 1.5G. A couple maneuvers went up to 1.7 if no forward pressure was applied on the yoke. Still, less than the 2Gs of a level turn at 60 degrees AoB.
View attachment 139967

And now for the conclusion, the actual ground track:
View attachment 139968
Compare the initial turn radius at 45 degrees AoB with the turn radius of the descending turn at 60 degrees AoB. I'd say there is a pretty significant difference. Yes, it's not sustainable, you can't do it for more than 10-15 seconds or so, but that is more than enough to tighten a turn without potentially stalling the aircraft. We actually get the turn rate (and radius) of a 60 degree AoB turn but without the G-load.
You can argue about how it actually happens, but I think the conclusion is pretty evident - you can safely tighten a turn (albeit for a short time only) by increasing the bank angle but without the increase in elevator backpressure. Enough to salvage a base to final turn that could otherwise result in a stall/spin accident. I completely agree that going around is still the safest way to handle that situation, followed by overshooting final and then correcting, but in a pinch, increasing the bank angle and letting the nose drop will get you in less trouble than trying to tighten that turn in a (mostly) level attitude.

You don't think the 22% higher groundspeed in the 45° bank explains this? Btw, I love that you did this no matter who's right.

 

[flyingcheesehead]

Got a chance to try this a few days ago with relatively calm winds, and managed to take a pretty poor video, but it was enough to take a couple screenshots.

Cool! Thanks for sharing your results. Fun stuff!

Exhibit A, entry into the turn, 45 degree AoB, about 500fpm rate of descent - typical of a base to final turn, minus the angle of bank, but that made the G-loads more evident. The plane was trimmed for this turn to ensure there wouldn't be any change in the pitch of the elevator during the maneuver.

Keep in mind that you trim for speed, not pitch. When you lower that vertical lift component, speed will increase and the trim will "pull" to compensate.

Exhibit B, bank angle increased to 60 degrees, without applying any additional backpressure. This screenshot was taken a few seconds later. Now it only took 5 frames to turn 5 degrees, we're at a turn rate of 30 degrees per second. Note that the G-meter still indicates 1.3G, the same as we had when we were banked at 45 degrees. The pitch dropped from level to 20 or so degrees nose down, and the vertical speed increased to about 1800fpm.

Perhaps more importantly, airspeed increased... That will increase your turn radius, and your load factor, unless you re-trim and/or push.

Exhibit C, rolling wings level

I feel like you missed something between B and C - The drastic increase in vertical speed, then airspeed, then turn radius. How long can you hold 60º bank with less than 2 load factor? How does the shape of the curve change?

I'm having trouble remember what on earth we were trying to accomplish when we started down this path... Power off 180? So our point is to get turned around safely with a minimum of energy loss and a minimum turn radius? If so, I think each bank angle should be held for at least 180 degrees to see what the final path looks like.

You don't think the 22% higher groundspeed in the 45° bank explains this?

This.

At 102 knots and 45º, turn radius should be 924'. At 84 knots and 45º, turn radius should be 627'. At 84 knots and 60º, 362'.

If we assume that the red circle above is 924'-ish, it looks like the blue circle has about half the radius of the red one, which would be 462'. The change in speed would have resulted in a 32% reduction while the change in bank angle would have resulted in 18%.

 

[AV8R_87]

You don't think the 22% higher groundspeed in the 45° bank explains this?

The lower groundspeed at the higher angle of bank is because the maneuver became 3-dimensional. The actual airspeed increased as the bank angle increased and the nose dropped.
That's the whole point I was trying to make, a 3D turn will allow you to keep the same load factor while allowing an increase of the the rate of turn and a decrease of the turn radius. I achieved what a 60 degree AoB turn would do with the G-loading of 45 degree turn. And because the airspeed increased (despite the lower ground speed) the aircraft is less likely to stall during this maneuver as well.

Perhaps more importantly, airspeed increased... That will increase your turn radius, and your load factor, unless you re-trim and/or push.

Airspeed did increase, but because of the nose pitching down, the horizontal component (ground speed) of the lift vector was less than the value in level flight (82kt vs 104kt)

I feel like you missed something between B and C - The drastic increase in vertical speed, then airspeed, then turn radius. How long can you hold 60º bank with less than 2 load factor?

Oh, I am well aware that the maneuver isn't sustainable. I'd say you get 10-15 seconds or so before you have to do something about it.

I'm having trouble remember what on earth we were trying to accomplish when we started down this path...

The whole point of this conversation was that if you find yourself overshooting your base to final turn, instead of trying to tighten that turn in level flight (or worse, stomping on the rudder), with the net effect being a base to final stall/spin, you can just let the nose drop and allow the turn to become a 3-dimensional maneuver, which will increase the turn rate and decrease the turn radius, but without the significant increase in load factor.
A few people disagreed with the statement above. Yet we can clearly see that the load factor stayed the same as the bank angle increased, while the rate of turn increased and the turn radius decreased.

The change in speed would have resulted in a 32% reduction while the change in bank angle would have resulted in 18%.

I forgot what my numbers were. But it doesn't really matter, it's like arguing how lift is generated, with all the fun of Newton vs Bernoulli and a sprinkle of equal transit theory.
At the end of the day, the original statement I made stands - if you need to tighten a turn, let the nose drop to keep a lower load factor and avoid a stall. You can't use this to make 360s, all you get is a 10 second get out of jail free card.

 

[flyingcheesehead]

The lower groundspeed at the higher angle of bank is because the maneuver became 3-dimensional. The actual airspeed increased as the bank angle increased and the nose dropped.

Uhhh... I don't think so. If you were going 102 knots and level, for the speed to drop to 84 knots solely because of the descent, your descent rate would be over 5800 feet per minute even without an increase in airspeed.

That's the whole point I was trying to make, a 3D turn will allow you to keep the same load factor while allowing an increase of the the rate of turn and a decrease of the turn radius. I achieved what a 60 degree AoB turn would do with the G-loading of 45 degree turn.

OK. Using the 1.414 load factor of a perfect 45º banked level turn, if we increase to 60º of bank we'll increase the rate of turn by 22.5% but we'll lose enough of our vertical lift to cause a 9.42 ft/s^2 downward acceleration.

Oh, I am well aware that the maneuver isn't sustainable. I'd say you get 10-15 seconds or so before you have to do something about it.

If you started level at 1000 feet, you would hit the ground in 14 seconds. On a base to final turn at 400 AGL that you started at 500 fpm, 8 seconds. At the 1.414 load factor and 60º bank your turn rate would be 13.3º/sec so it would take almost 7 seconds to do a 90º turn. That means you have a bit over a second to recover before you hit the ground.

In reality, of course, you'd be recovering beforehand, but in an engine out scenario this is not a maneuver I'd recommend as you're giving up a lot of altitude pretty quickly.

The whole point of this conversation was that if you find yourself overshooting your base to final turn, instead of trying to tighten that turn in level flight (or worse, stomping on the rudder), with the net effect being a base to final stall/spin, you can just let the nose drop and allow the turn to become a 3-dimensional maneuver, which will increase the turn rate and decrease the turn radius, but without the significant increase in load factor.
A few people disagreed with the statement above. Yet we can clearly see that the load factor stayed the same as the bank angle increased, while the rate of turn increased and the turn radius decreased.

Within reason, and for a very short period of time, maybe.

 

[Hengelo]

Back to link trainers; ran into these guys today at a tiny Dehaviland museum midway between tea Anau and Dunedin.

 

[dtuuri]

The actual airspeed increased as the bank angle increased and the nose dropped.
...a 3D turn will allow you to keep the same load factor while allowing an increase of the the rate of turn and a decrease of the turn radius. I achieved what a 60 degree AoB turn would do with the G-loading of 45 degree turn. And because the airspeed increased (despite the lower ground speed) the aircraft is less likely to stall during this maneuver as well.
...
At the end of the day, the original statement I made stands - if you need to tighten a turn, let the nose drop to keep a lower load factor and avoid a stall. You can't use this to make 360s, all you get is a 10 second get out of jail free card.

I forgot about this thread; had to take a friend to the ER.

I appreciate what you've done here, which is made me think about an old conviction in a new way. Thanks for that. I don't know engineering well enough to comment on @flyingcheesehead 's math, but I revisited my old thought-experiment of "turning off gravity" and then turning the plane to a new heading. So, I concede that fighting the force of gravity accounts for a portion of the load factor generated by the AoA, whether in curving flight or not. If you surrendered to gravity completely, you would be in a vertical diving barrel roll, wouldn't you? Performing any portion of that maneuver approaching to land, I cannot advocate. Still, it was worthwhile to think about. Thanks again.

 

[flyingcheesehead]

I appreciate what you've done here, which is made me think about an old conviction in a new way. Thanks for that. I don't know engineering well enough to comment on @flyingcheesehead 's math, but I revisited my old thought-experiment of "turning off gravity" and then turning the plane to a new heading. So, I concede that fighting the force of gravity accounts for a portion of the load factor generated by the AoA, whether in curving flight or not. If you surrendered to gravity completely, you would be in a vertical diving barrel roll, wouldn't you? Performing any portion of that maneuver approaching to land, I cannot advocate. Still, it was worthwhile to think about. Thanks again.

I'm trying to think about how I want to test this, which will hopefully be Monday. I do want to test more than the 45-60 version and see how it all works out.

You can "turn off gravity" at least in terms of load factor by doing a 90-degree bank. If you then pull the 3.8G normal limit, you'd have quite a turn rate... But you'd also have the vertical acceleration as if your wings had fallen off.

 

[Ed Haywood]

I'm trying to think about how I want to test this, which will hopefully be Monday. I do want to test more than the 45-60 version and see how it all works out.

You can "turn off gravity" at least in terms of load factor by doing a 90-degree bank. If you then pull the 3.8G normal limit, you'd have quite a turn rate... But you'd also have the vertical acceleration as if your wings had fallen off.

You can generate lift with the side of your fuselage in a 90 degree bank. Takes plenty of airspeed and top rudder, but knife edge flight is a staple of the airshow world. Sean Tucker is particularly known for it.

 

[dtuuri]

I'm trying to think about how I want to test this, which will hopefully be Monday. I do want to test more than the 45-60 version and see how it all works out.

You can "turn off gravity" at least in terms of load factor by doing a 90-degree bank. If you then pull the 3.8G normal limit, you'd have quite a turn rate... But you'd also have the vertical acceleration as if your wings had fallen off.

I'll pray for you...

 

[Ed Haywood]

I'll pray for you...

Nah, he'll be ok, as long as he knows what he is doing, or is in an aircraft strong enough to tolerate mistakes.

Whenever I take pilot friends up in the Decathlon, I always let them try steep turns. Usually they start with a tentative roll into a 45 degree bank. After I chide them, they roll into a 60. Then I say "my controls", roll aggressively into an 80ish turn, and pull about 3.5G. Then I give them the controls and let them play with that for a while. As long as you keep an eye on Vne, it's a fairly benign thing to do.

My learning point for them is that you can't hurt the airplane and it doesn't need to be flown like your grandma is flying.

You can sustain that steep a bank for several circles, but you will eventually run out of energy and altitude. In a near knife edge, you can reduce your altitude loss with top rudder, but you will dump a lot of energy.

 

[nauga]

If only there was some way you could tell just how hard you could pull in a turn before stalling. Then you could gauge max performance and make an informed decision on whether or not an oblique turn would make a difference. If only...

Nauga,
and Wolfgang Herbst

 

[flyingcheesehead]

You can generate lift with the side of your fuselage in a 90 degree bank. Takes plenty of airspeed and top rudder, but knife edge flight is a staple of the airshow world. Sean Tucker is particularly known for it.

Yeah, but then there's only a door latch between you and the ground.

Better have the fuel on the high wing's tank too... And preferably an inverted/all attitude oil system.

 

[brcase]

Pure speculation. Looking in the direction of flight, a wingtip hit first, ruptured the tank, the airplane flipped and burned.

That is what I speculated from the photos.

 

[flyingcheesehead]

Got a chance to try this a few days ago with relatively calm winds, and managed to take a pretty poor video, but it was enough to take a couple screenshots.

Exhibit A, entry into the turn, 45 degree AoB, about 500fpm rate of descent - typical of a base to final turn, minus the angle of bank, but that made the G-loads more evident. The plane was trimmed for this turn to ensure there wouldn't be any change in the pitch of the elevator during the maneuver.
View attachment 139964
Note the 1.3G in the maneuver, pretty typical of a turn at that bank angle. Counting frames in the video, it took about 15 of them (half a second) to turn 5 degrees, or about 10 degrees per second. Theoretical value should be 11 degrees per second, so I'd say we're where we need to be for the entry conditions.

Exhibit B, bank angle increased to 60 degrees, without applying any additional backpressure. This screenshot was taken a few seconds later. Now it only took 5 frames to turn 5 degrees, we're at a turn rate of 30 degrees per second. Note that the G-meter still indicates 1.3G, the same as we had when we were banked at 45 degrees. The pitch dropped from level to 20 or so degrees nose down, and the vertical speed increased to about 1800fpm.
View attachment 139966

Exhibit C, rolling wings level, and keep in mind that the airplane is still trimmed for almost a level turn at 45 degrees AoB. So it will want to pull up, plus the extra speed increases that tendency. Even so, the G-meter only indicates 1.5G. A couple maneuvers went up to 1.7 if no forward pressure was applied on the yoke. Still, less than the 2Gs of a level turn at 60 degrees AoB.
View attachment 139967

And now for the conclusion, the actual ground track:
View attachment 139968
Compare the initial turn radius at 45 degrees AoB with the turn radius of the descending turn at 60 degrees AoB. I'd say there is a pretty significant difference. Yes, it's not sustainable, you can't do it for more than 10-15 seconds or so, but that is more than enough to tighten a turn without potentially stalling the aircraft. We actually get the turn rate (and radius) of a 60 degree AoB turn but without the G-load.
You can argue about how it actually happens, but I think the conclusion is pretty evident - you can safely tighten a turn (albeit for a short time only) by increasing the bank angle but without the increase in elevator backpressure. Enough to salvage a base to final turn that could otherwise result in a stall/spin accident. I completely agree that going around is still the safest way to handle that situation, followed by overshooting final and then correcting, but in a pinch, increasing the bank angle and letting the nose drop will get you in less trouble than trying to tighten that turn in a (mostly) level attitude.

OK... I got my turn to test! I didn't take any pretty pictures, but I did download the data off the GI275 and upload it to FlySto. I also didn't get any pretty ground track pictures because I did not have calm winds aloft and since this was about bank angle I wanted to keep a constant bank rather than do turns around a point.

I decided to make a new thread about it rather than further derail this one: https://www.pilotsofamerica.com/com...gency-descent-and-the-impossible-turn.151165/

Long story short, doing this in the first 90 degrees of the turn if you're still climbing at the initiation of the maneuver, and limiting it to about 4 seconds, may have some merit. Further testing to be done...

 

[Mooney Fan]

Short approach, turning base to final and out of altitude, pull then stall. That's my armchair observation.