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We are all taught the correlation between bank angles and g forces in level flight. For a long time now I've wondered what effect a climb or descent has on this. I've looked around for some sort of a formula but come up empty handed.
The reason I ask is that I've been trying to get a better understanding of what's happening on a descending turn to final and the effect on stall speed.
Can anyone provide a formula or something I can work with on this?
If you're maintaining a constant rate of descent, it won't impact stall speed. Same thing for rate of climb, assuming you maintain a steady airspeed.
If one is turning into a bank without changing the pitch to compensate for decreased lift then the rate of descent should be increasing. That's the scenario I'm looking at.
Thinking about it, the in that case the amount of g's shouldn't change in the turn since the wings have 1 g of lift and with no change in pitch the aircraft would accelerate.
Thanks Kyle, that's what needed to get on track. Now to see if I can kill this thread.
Hold on. Physics and common sense seem to offer a different answer. From personal experience, I know that my G-meter says 2G for a level turn at 60 degrees bank, but only about 1.5G for the same angle if I allow the nose to drop in the turn (e.g., top of a wing-over). Since weight (G-load) affects stall speed, the stall speed should be less.
I know that there are more experienced (or just more alert) people on this forum who will be able to provide more precise answers. I may even feel smarter or more alert myself in the morning.
I think it's a fairly pointless exercise to try to think about what the "stall speed" is for all different possible combinations of bank angle, G-load, climb/descent, pitch angles, etc. There are too many variables, plus AOA is all that matters, not airspeed or bank angle. But for a given weight & balance condition of the airplane, and for a given G-load (of at least 1G), there is an airspeed at which the airplane will stall...and that's true only if the airplane is in perfect coordinated flight. The higher the G, the higher the stall speed. Bank angle, climb, descent, pitch angle, etc. is irrelevant.
So if you are in a descending turn, with a constant "G", like any other descending maneuver, your airspeed will increase. With increased airspeed but constant bank angle and "G", the radius of the turn will increase with increasing airspeed. So you will fly a wider and wider spiral until you hit the ground....
Fly safe,
Wes
N78PS
Wes, not sure which post or which point you were responding to, but if it was mine, you may have misunderstood what I was saying. Yes, in your example, airspeed will increase and you will be getting further away from the airspeed that would stall the airplane at whatever G you're pulling. I was simply making the point that for a given G load, under the conditions I mention, that the airplane will stall at a certain airspeed. But of course you won't find that speed unless you're bleeding speed while pulling constant G. I was pointing out that this fact has no bearing on bank angle, pitch, climb, or descent.
In the descent example, it just won't be your bleeding airspeed that will find the stall (your speed may be increasing). But it may be your increasing G pull that finds the stall, assuming you reach it before the wings get pulled off. But if you stall, it'll still be because your airspeed and G coincided at the right point. But like I said in my original post, airspeed is not king. Angle-of-attack is all that matters. Airspeed is an unreliable way to determine AOA due to variable conditions. Airspeed will only "match" AOA in very controlled, known, and specific conditions. I don't think any of this is controversial. Pilots are not robotically precise pilots, nor do they have an accurate running calculator in their head as they're flying. That's why I feel pilots shouldn't think in terms of "what airspeed will I stall at". IMO, pilots should pay attention to AOA cues more so than airspeed.
Eric
I was trying to flip an answer at the original poster. That said, in truth most recreational pilots see AOA as an abstract concept and have no way to observe their instantaneous AOA in their airplanes. They get to derive it from airspeed and the feel of the seat of their pants. Which works for 99% of the recreational pilots. That other 1% we talk about.
The actual answer for the original poster is that the calculation of stall speed during a turn to final or a climbing turn involves more math than can be done by a real human pilot flying the airplane at that moment. Which is why a number of higher performance airplanes do have AOA displays so that they have the direct data that you correctly point out is more precise and valuable.
All of that said, we know that the pilot can make the plots of bank angle, "G", and airspeed converge to a point where the airplane will do something that you generally do not want to see on a landing approach. I guess that sitting at an earth bound desk we can calculate some of the possible graphs, but you and I would rather go fly.
To get right to the point that you were making, the airspeeds that you describe are shown on the V-N diagram. That graph illustrates where "G" and airspeed intersect to potentially surprise a pilot. The original poster might be well served to study that graph in the flight manual. Other folks have done math on our behalf to create that plot.
All of the above is why recreational airplanes like Cessna's and Pipers are required by Part 23 to shake and shudder before they "let go" into an aerodynamic stall. And I will hazard a guess that guys like you and I shake our heads and wonder how a modern pilot can miss all of the cues and complaints that modern airplanes make before they give up on the pilot and go crunch.
Best of luck,
Wes
N78PS
You're unloading the wing by allowing gravity to change your rate of ascent/descent. Just like when you do a push over from level flight, the G-load goes down when you allow the nose to drop through on a wing over...
Thanks to everyone who commented.
We can all agree that there is no way that anyone is going to be able to do the math while flying. The reason I asked was that I noticed a few times when I was turning onto final that I was steepening my bank more than I felt I should. This mostly happens on right patterns. Having the (high) wing block my view of the runway when turning doesn't help. I'm still a relatively new pilot (150 hours) and so when I became aware of that I was starting to do this I thought that I ought to I decided to examine and rethink what I'm doing.
Having been properly indoctrinated into the hazards of cross controls I made sure that the ball was centered during turns, I wasn't feeling any unusual g forces and my speed was somewhere near where it should be (I trim to set my approach speed). I posted trying to get a general understanding of how the physics work when making descending turns without changing pitch. I did some more reading and it turns out that the math is simple and more or less gave me the answer I was looking for.
Part of what led to all this is that I was trained to try to keep a tight pattern in case of a power loss. I need to modify this some when there's a tail wind on base. I've read a several on-line comments recommending doubling the pattern distance when there is a significant a tail wind on base. A friend mentioned that pilots often wait too long before turning to final. Good point. - I flew today and made my turn to base much earlier. I didn't have to turn as steeply and was able to see the runway better. That's a good thing.
Regarding stalls, my old Tripacer was engineered in a period when the manufacturers were trying to idiot proof their products. It has an interconnected ailerons and rudder and was also designed with limited elevator authority so that it will normally just mush and sink on a power off stall rather than breaking. The reason I mention this is that it doesn't have an audible stall warning and also may not exhibit the traits normally associated with a pending stall - at least with the power off. With the power on it's a different story. Essentially when the speed becomes low enough the aircraft just starts to sink at about 600 fpm.
So, that explains why I asked the original question. I was just trying to get my head around what was happening in one particular scenario. I recognized that I was starting to develop a bad habit wanted to work through everything as a part of looking at what I was doing wrong and how to approach things differently. Redbird owes me some simulator time - I think I'll burn some of it playing with landing scenarios.
Thanks to everyone for the input. I would have killed this thread after the first response got me back on the right track but don't seem to be able to find a delete link so as to do so.