Trim all the way up for best glide

172: How much trim is left when at best glide, engine idling, full weight or minimum weight? Will full-up result in a power off stall? Or 10 knots lower than best glide? (I don't know, that's why I'm asking, not trying to be an Internet ass).
 
GrahamC said:
It's not useful; It's careless. Skill in flying, especially emergency procedures is not something to find shortcuts around. Practice, and learn to do it right.
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I've lurked here for a long time but this post (and subsequent ones) enticed me to finally join...

This kind of hubris will kill someone someday (if your advice if followed anyway).

It's well know that a properly rigged strutted, fixed gear, 100 series Cessna will settle in very close to best glide if trimmed full up.

If you want to waste 30 to 45 seconds in an emergency trying to find best glide then knock yourself out, but don't ask others to be stupid and not establish it in about 5 seconds...and then use the rest of the time you're wasting to deal with the emergency at hand.

Have you even flown a strutted, fixed gear Cessna? Have you tried this? I've owned three. Learned how to fly in the first one. My instructor taught me this trick and it works on all three. All three settled in within 3kts of best glide when trimmed full nose up (even taking into consideration the variance for weight). But all my birds have been in great shape (the latest being a 1969 182) and properly rigged.

It's a very useful tool.

With that said, know your airplane, go out and determine if it works on your airplane. If this technique doesn't work then fine...but, if it does, then don't listen to some bloviator on PoA who doesn't think one should save time in an emergency.

Also, do a search here...try something like "trim all the way up for best glide" and you'll find plenty of prior discussion including someone who said he was taught this technique at a seminar at the Cessna plant in Independence.

The bottom line: arguing that something is bogus or false, when it's not, does this whole community a disservice.
 
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GrahamC said:
Knowing to trim for best glide is an imperative skill. I'm saying that fill nose up trim in a 172 will not achieve that. Rather, maintaining altitude while slowing to best glide, and then trimming to relieve control pressure it the best practice. Defaulting to full nose up trim is not useful and is careless.

How do you think an examiner or ASI would react to a Private Pilot applicant responding to a simulated engine failure by running the trim wheel to full nose-up and then going straight to a checklist instead of exercising proper piloting skills and using critical thinking to react to an adverse condition?

Edit: That last question is not meant to imply that DPEs or ASIs are the holy grail of good decision making, but I'd be hard-pressed to find someone to disagree that they are both, overall, representative of good judgement and skill evaluation.
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I did EXACTLY that on my private pilot checkride, twice. Once at altitude and once at an airport. The examiner responded with a temporary airman certificate.
 
TommyTBone said:
I've lurked here for a long time but this post (and subsequent ones) enticed me to finally join...

This kind of hubris will kill someone someday (if your advice if followed anyway).

It's well know that a properly rigged strutted, fixed gear, 100 series Cessna will settle in very close to best glide if trimmed full up.

If you want to waste 30 to 45 seconds in an emergency trying to find best glide then knock yourself out, but don't ask others to be stupid and not establish it in about 5 seconds...and then use the rest of the time you're wasting to deal with the emergency at hand.

Have you even flown a strutted, fixed gear Cessna? Have you tried this? I've owned three. Learned how to fly in the first one. My instructor taught me this trick and it works on all three. All three settled in within 3kts of best glide when trimmed full nose up (even taking into consideration the variance for weight). But all my birds have been in great shape (the latest being a 1969 182) and properly rigged.

It's a very useful tool.

With that said, know your airplane, go out and determine if it works on your airplane. If this technique doesn't work then fine...but, if it does, then don't listen to some bloviator on PoA who doesn't think one should save time in an emergency.

Also, do a search here...try something like "trim all the way up for best glide" and you'll find plenty of prior discussion including someone who said he was taught this technique at a seminar at the Cessna plant in Independence.

The bottom line: arguing that something is bogus or false, when it's not, does this whole community a disservice.
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Welcome!!
 
pigpenracing said:
I don't understand how damn hard it can be just to trim and watch your airspeed???
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Of course it's not hard...it's called "rote". You do it that way because your instructor told you to, because his instructor told him to, for several generations back. It's the lowest level of learning.

The next level of learning is "understanding"...understanding how pitch trim works, understanding the design stability of the airplane, and understanding the way Cessna designed the trim system to behave.

The third level is "application". Being able to take what you know about your 172 and applying it in an engine-out or other situation to allow the airplane to do part of the work, which is good SRM. Maybe if this guy had understood and applied the procedure Beech used to print on Bonanza visors, the outcome might have been different. https://aviation-safety.net/wikibase/wiki.php?id=186933

The highest level is "correlation". Taking what you know and apply to the 172 and/or Bonanza and use it in another airplane. Maybe if this guy had taken his hands off the yoke about the time he declared an emergency, his airplane could've protected him. https://aviation-safety.net/database/record.php?id=20160118-0

Obviously the "solutions" to these accidents are speculation on my part, but if we don't put forth the effort to search out and accept techniques that we weren't directly taught as anything other than "careless" and "not usable", we'll never reach the level of correlation that may save our lives.
 
I literally have the popcorn bag in my lap, reading this thread. Hahahaha.

3e1ee913244106ee09a2f275f5fd98a5.jpg
 
5 or even 10 kts is not going to make much difference in you L/D, Get close and fly the airplane.
This is where pilots screw up and perform the famous stall spin maneuver so a little extra speed is not usually a bad thing.

This link is a theoretical model of a 172 but the L/d chart shows the basic idea that a few knots speed really doesn't make much difference, in fact 10 kts more speed loses less L/D than 10 kts under best l/d does.
https://www.mathworks.com/examples/aerotb/mw/aero_product-astglide-calculating-best-glide-quantities

Brian
CFIIG/ASEL
 
One needs an AOA to know for certain.

I understand the jokes, but this one is a fact.
 
GrahamC said:
In which region are you an examiner? If you're stating that it is not possible to trim a Cessna 172 for best glide, I'd like to steer clear of your part of town.
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Thankfully your profile says you're in Dallas, so we all know to stay the hell out of your part of town. Your methods and arguments are downright scary. 5kts difference doesn't do much for the glide ratio in real world, you will lose the difference in tweaking to find the "perfect" spot (which is out anyway because your ASI won't be 100% accurate), and you end up wasting precious time, altitude, speed and brain power when you live in your hypothetical world and try to hit an exact number.

172 - trim full nose up, and adjust if you have time.
 
Totally confused. If full up trim yields 70 kits, but 65 is desired... how else would you possibly trim it?
Also, 5 it's..?? Really??
 
68 kts in 172 sp, for what it's worth. I will try the full nose up trim next time I fly and report back

Sent from my SM-G935V using Tapatalk
 
WannFly said:
68 kts in 172 sp, for what it's worth. I will try the full nose up trim next time I fly and report back

Sent from my SM-G935V using Tapatalk
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For some reason, 172SP airspeed calibration error at low speeds is much larger than for older 172s. Must be the aerodynamic effect of all those fuel drains....
 
Hmmm, no discussion of whether or not there are at least two trim settings that get you close to best glide. So the follow on discussion of why trimming full nose up would be the least desirable can't happen...or can it?

Anyway, I had a CFI tell me to use the full nose up trim on my last flight review. It worked well enough but it seemed counterintuitive at the time. After thinking about it a bit I realized why it was a poor technique.

While it is true that the wing doesn't care how it is at best glide the aircraft does. We really don't want more load on the tail than we have to have because that additional load induces drag. So at the end of the day if the aircraft will reach best glide at some other trim setting than full nose up that is certainly where you want to be.

Now the question is: will a 172 reach best glide at some trim setting other than full nose up. Frankly I never paid much attention to where the trim ended up when doing engine out practice in a 172. I would have noticed if it would have hit a stop. I could have been close to a stop and not notice that.

Did that do anything for your popcorn Nate?
 
Clark1961 said:
Hmmm, no discussion of whether or not there are at least two trim settings that get you close to best glide. So the follow on discussion of why trimming full nose up would be the least desirable can't happen...or can it?

Anyway, I had a CFI tell me to use the full nose up trim on my last flight review. It worked well enough but it seemed counterintuitive at the time. After thinking about it a bit I realized why it was a poor technique.

While it is true that the wing doesn't care how it is at best glide the aircraft does. We really don't want more load on the tail than we have to have because that additional load induces drag. So at the end of the day if the aircraft will reach best glide at some other trim setting than full nose up that is certainly where you want to be.

Now the question is: will a 172 reach best glide at some trim setting other than full nose up. Frankly I never paid much attention to where the trim ended up when doing engine out practice in a 172. I would have noticed if it would have hit a stop. I could have been close to a stop and not notice that.

Did that do anything for your popcorn Nate?
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Hmm, I guess I don't get it. I can't see how it would be different, if a particular trim setting holds a certain speed, how would a different setting hold the same speed? I can see how rolling it all in at once might give you too much deflection at first, then less as it slows, but once it settles out, doesn't it have to settle on a particular speed? (for that given W&B)

Think about holding best glide with the yoke, then trimming away the control pressure, won't you end up with the same amount of trim in the end?
 
Most pilots tend to overshoot their landing spot, so I question the need to use the perfect "best glide". Best thing to do is to go out and actually land in some fields and on some roads. Its legal if you have private land and safe spots to land. If actual landing is not possible, coming close is next best thing. Also, there are some techniques to coming in so you dont overshoot or undershoot. Actually an engine out offield takes a lot more than just knowing how to get to "best glide".

The other thing a pilot can do is pull the power on downwind and try and power off glide in on the numbers. Spot landings. Get good at them.
 
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GrahamC said:
Knowing to trim for best glide is an imperative skill. I'm saying that fill nose up trim in a 172 will not achieve that. Rather, maintaining altitude while slowing to best glide, and then trimming to relieve control pressure it the best practice. Defaulting to full nose up trim is not useful and is careless.
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Actually, it's been determined that getting to best glide as quickly as possible gives the best range. Holding altitude while you coast down to best guide is NOT the optimal technique.
 
coloradobluesky said:
The other thing a pilot can do is pull the power on downwind and try and power off glide in on the numbers. Spot landings. Get good at them.
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Or places other than downwind. The abeam the numbers isn't the place the engine is always going to fail. I've seen instructors (and I agree with this) close the throttle directly over a grass runway. A student needs to know how to do his energy management to place himself in a position to make a landing on the available field.

In my engine failure, I was pretty much directly over the only available field. I had to make turns to bring myself down to a point where I would make a base to final turn at the end of the field I wanted to land on.
 
flyingron said:
Actually, it's been determined that getting to best glide as quickly as possible gives the best range. Holding altitude while you coast down to best guide is NOT the optimal technique.
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The only faster way in a 172 without making configuration changes (which I think we can all agree would be ill-advised) to achieve best glide would be to climb to bleed of speed. In order to climb, you need excess Power (if you're trying to get a best rate of climb.) How much excess power do you have in a power off scenario? The math doesn't add up. Can you cite your source of that determination?
 
exncsurfer said:
Hmm, I guess I don't get it. I can't see how it would be different, if a particular trim setting holds a certain speed, how would a different setting hold the same speed? I can see how rolling it all in at once might give you too much deflection at first, then less as it slows, but once it settles out, doesn't it have to settle on a particular speed? (for that given W&B)

Think about holding best glide with the yoke, then trimming away the control pressure, won't you end up with the same amount of trim in the end?
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My thought is that maximum nose up trim puts maximum download on the tail for a given airspeed. Maximum download on the tail will give maximum induced drag all other things being equal. Any other trim setting will be better if it yields best glide.

That said we share the same question about trim settings. I never paid attention to where the trim ended up when doing engine out drills in a 172. It could have been close to the stop.

It's sorta funny since I had a conversation once with a tech about the trim indicator. I told him I looked at it when setting it for take off and never looked at it again. He got a little agitated in telling me I should pay attention to it. I think he really had no idea how to fly...trim is to relieve control pressure not to fly the plane. Yes I have seen people use trim to fly the plane. To each their own I guess.
 
GrahamC said:
The only faster way in a 172 without making configuration changes (which I think we can all agree would be ill-advised) to achieve best glide would be to climb to bleed of speed. In order to climb, you need excess Power (if you're trying to get a best rate of climb.) How much excess power do you have in a power off scenario? The math doesn't add up. Can you cite your source of that determination?
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Umm, what?

You do not need engine power to climb if you have excess airspeed. The excess mechanical power is the excess kinetic energy, divided by the time you need for the climb (which can be pretty damn short). No one climbs to bleed off speed at Vy. You would need to bleed off speed to get to Vy.

I think you're trying to minimize total drag over the descent, which (a) is not possible with the back-of-the-envelope estimates you're attempting, and (b) is "polishing a turd." It's going to make no effective difference whether or not you lose a couple of feet of glide range.
 
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Clark1961 said:
My thought is that maximum nose up trim puts maximum download on the tail for a given airspeed. Maximum download on the tail will give maximum induced drag all other things being equal. Any other trim setting will be better if it yields best glide.

That said we share the same question about trim settings. I never paid attention to where the trim ended up when doing engine out drills in a 172. It could have been close to the stop.

It's sorta funny since I had a conversation once with a tech about the trim indicator. I told him I looked at it when setting it for take off and never looked at it again. He got a little agitated in telling me I should pay attention to it. I think he really had no idea how to fly...trim is to relieve control pressure not to fly the plane. Yes I have seen people use trim to fly the plane. To each their own I guess.
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For a given configuration, i.e. Engine-out glide at best glide IAS, there will be one trim setting that will relieve elevator control forces, which will then result in the minimum trim drag. The amount of down force required of the tail is going to be what it is...reducing tail,down force will result in something faster than the best glide,speed, no matter how you do it.

Your tech is right to a certain extent...to the point of this thread, if you know where your trim is for best glide, it will make you more efficient and effective in flying the airplane during an emergency. If you know where your trim is set for your final approach speed and configuration, you'll have a lot more confidence in the event of an airspeed failure than you would using just "feel" or "the seat of your pants".
 
MauleSkinner said:
For a given configuration, i.e. Engine-out glide at best glide IAS, there will be one trim setting that will relieve elevator control forces, which will then result in the minimum trim drag. The amount of down force required of the tail is going to be what it is...reducing tail,down force will result in something faster than the best glide,speed, no matter how you do it.

Your tech is right to a certain extent...to the point of this thread, if you know where your trim is for best glide, it will make you more efficient and effective in flying the airplane during an emergency. If you know where your trim is set for your final approach speed and configuration, you'll have a lot more confidence in the event of an airspeed failure than you would using just "feel" or "the seat of your pants".
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I've got better ways to know my airspeed rather than looking at a trim setting which will vary with weight. Pitch plus power equals performance. It is most definitely not "feel" or "the seat of your pants"
 
GrahamC said:
The only faster way in a 172 without making configuration changes (which I think we can all agree would be ill-advised) to achieve best glide would be to climb to bleed of speed. In order to climb, you need excess Power (if you're trying to get a best rate of climb.) How much excess power do you have in a power off scenario? The math doesn't add up. Can you cite your source of that determination?
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Climbing doesn't require "excess power." Obviously, you couldn't climb at all by your argument. The issue is you've got excess drag for the given lift anytime you're not at Vbg. You need to get there as soon as possible to be efficient. About the only thing that can be said for NOT doing it is that the pilot has other things to worry about than a couple of percent increase in glide distance.

As for references, if you have the book Performance of Light Aircraft by John Lowry, he has a whole chapter on Glide Performance which includes a discussion of this. There's tons of discussions (just google "best guide level vs. zoom" to find tons of online arguments about this.
 
Few days ago I tried this on 180 horse 172P. Basically, same as SP model. Full nose up trim gave me about 63kts. Little too low. About 1/4 turn out of full put it right where it needed to be. Next try i went straight to that point and was instantly on the money. 5 seconds to get there. Tried it from both, S&L and Vy climb.
 
Clark1961 said:
I've got better ways to know my airspeed rather than looking at a trim setting which will vary with weight. Pitch plus power equals performance. It is most definitely not "feel" or "the seat of your pants"
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Pitch & power will have the same general effect.

Remember that the proper airspeed for approach will vary with weight as well...1.3 x a different stall speed is a different approach speed, but the AOA, which is what trim technically controls, will be the same.

Either way is a valid technique...and that's just what they are: techniques. Not mandatory procedures. Do what you prefer, but don't discount the techniques that others use, especially if you don't understand them.
 
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genna said:
Few days ago I tried this on 180 horse 172P. Basically, same as SP model. Full nose up trim gave me about 63kts. Little too low. About 1/4 turn out of full put it right where it needed to be. Next try i went straight to that point and was instantly on the money. 5 seconds to get there. Tried it from both, S&L and Vy climb.
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How far below max weight were you, and what would the reduction in best glide compute to?
 
MauleSkinner said:
Pitch & power will do the same thing.

Remember that the proper airspeed for approach will vary with weight as well...1.3 x a different stall speed is a different approach speed, but the AOA, which is what trim technically controls, will be the same.

Either way is a valid technique...and that's just what they are: techniques. Not mandatory procedures. Do what you prefer, but don't discount the techniques that others use, especially if you don't understand them.
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Attempt to belittle much? it is clear you think trim flies the aircraft which has always been poor technique. I don't use trim that way, I simply use it to relieve control pressure at all times other than setting it for take off.

You should take the same advice you offer. Don't discount me or my methods simply because you do things differently.
 
MauleSkinner said:
How far below max weight were you, and what would the reduction in best glide compute to?
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It's not really the same as an SP. Just the 180 HP engine is. Which doesn't matter if it's failed. For some reason, the ASI calibration is different for SPs at low speed (they read slower than older 172s, at the same CAS), so P's don't compare in IAS.

Max weight is also different, despite the same size engine and same flaps. P's are 2400 lb. SP's are 2550. N's are 2300 lb (but have 40 deg flaps).

With two up front and nothing else with full fuel, I'd be around 2000 lb in an N or P. Of course that will vary for the OP and for installed equipment. But that means a 20% reduction in gross weight, so V speed reduction is around 10%. That makes 63 KIAS fast.
 
MAKG1 said:
It's not really the same as an SP. Just the 180 HP engine is. Which doesn't matter if it's failed. For some reason, the ASI calibration is different for SPs at low speed (they read slower than older 172s, at the same CAS), so P's don't compare in IAS.

Max weight is also different, despite the same size engine and same flaps. P's are 2400 lb. SP's are 2550. N's are 2300 lb (but have 40 deg flaps).

With two up front and nothing else with full fuel, I'd be around 2000 lb in an N or P. Of course that will vary for the OP and for installed equipment. But that means a 20% reduction in gross weight, so V speed reduction is around 10%. That makes 63 KIAS fast.
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MAKG1 said:
For some reason, the ASI calibration is different for SPs at low speed (they read slower than older 172s, at the same CAS), so P's don't compare in IAS.

Max weight is also different, despite the same size engine and same flaps. P's are 2400 lb. SP's are 2550.
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As you said, the max weights are different. The heavier C172 will be at a larger angle of attack at the same airspeed, increasing the position error.
 
Clark1961 said:
Attempt to belittle much? it is clear you think trim flies the aircraft which has always been poor technique. I don't use trim that way, I simply use it to relieve control pressure at all times other than setting it for take off.

You should take the same advice you offer. Don't discount me or my methods simply because you do things differently.
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At what point did I say I fly with trim, or that your way was wrong?
 
dmspilot said:
As you said, the max weights are different. The heavier C172 will be at a larger angle of attack at the same airspeed, increasing the position error.
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That does make sense, but wouldn't you expect a difference between N and P models then, too?

It affects the stall speeds as well (in IAS), which are always at the same angle of attack when clean (as these models have the same wing).
 
MauleSkinner said:
How far below max weight were you, and what would the reduction in best glide compute to?
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I was alone in the plane with 35G fuel. about 500lb under 2550 gross. Not sure on the second part
 
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