Trouble maintaining level flight
dmspilot
Final Approach
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Well the error in such a case is a lack of positive aircraft control, a problem trimming in the right order will mask but not solve.
dmspilot
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Stability is reduced along a steady continuum as the CG is moved aft, it does not suddenly change from getting more stable to getting less stable as you pass the FAA sanctioned limit in the AFM.
Your conclusion does not follow your premise. Your graph showing you have a forward CG with skis (which you say is when it's harder to trim) is not evidence relevant to your argument. The skis have an aerodynamic effect well beyond their effect on CG. And I'm not sure what your argument even is. What do "easier to trim" and "harder to trim" even mean?
Your conclusion does not follow your premise. Your graph showing you have a forward CG with skis (which you say is when it's harder to trim) is not evidence relevant to your argument. The skis have an aerodynamic effect well beyond their effect on CG. And I'm not sure what your argument even is. What do "easier to trim" and "harder to trim" even mean?
Stewartb
Final Approach
My Cub doesn’t have skis. Return to the OP. He had a trim question. I gave him very simple advice. Perhaps you smart guys should address the question rather than gang tackling one response. My answer remains correct whether you agree with it or not. Seriously. I wonder if any of you fly small airplanes. Not Navy jets, not airliners...small SE airplanes. CG near center or aft but inside the envelope provides best speed, best control feel, and best ride. I didn’t know it was a secret.
dmspilot
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Uh you wanted us to look at your Cessna with skis or did you forget? Maybe you should return to the OP because the thread is about trimming, not speed, control feel, or ride. I don't think you know what point you're trying to make.
unsafervguy
En-Route
some of us fly some or all of the above. your answer is still wrong by the physics. by the way, the above statement is also wrong. best speed will be at the aft cg limit,as this is where the down force required by the tail is the least and therefore less drag. ask any reno racer for the data to prove the physics of that.
as to the original poster, he has been given the right information. get a good sight picture, level off, set power for speed and trim on that speed. use the sight picture to get the level flight you need and use control inputs to correct the deviations from the desired altitude and headings.
as to our discussion, at ANY given cg there is a trim speed for it on the curve, under ideal conditions the aircraft will stay on trim. the trim speed,aoa,elevator position will vary but in the envelope the aircraft will stay on trim. now, as to what happens when the aircraft diverted from a stable condition. if trimmed a stable aircraft will go back to 1g flight on its own, at any cg in the envelope. it may not be on altitude, or heading but it will return to stable flight. that is the definition of a stable aircraft. how long it takes to dampen out IS determined by the CG as a aft CG is less stable and therefore will take longer to dampen out, but it will get back to stable flight. now, by moving the CG aft, you increase controllability, and therefore it takes less control input to get aircraft back on heading and altitude. some mistake that for increased stability, it is not, its increased controllability. for a less experienced pilot that my lead to over controlling and making the situation worse.
wilkersk
Pattern Altitude
Level flight isn't a static thing you do, its a continuous process. It involves trim, scan, and feel. Its the OODA loop personified. You're not gonna get good at it until you develop a good scan, and your feel for the airplane and begin to do it without thinking about it. Flying is a lot like playing a musical instrument. To do it well takes a lot of practice.
But, as other posters have said, if you trim then reduce power, you'll have to re-trim if you want to maintain level flight.
Why do I have the feeling the problem is more about looking outside and learning what level flight looks like than anything involving arguments over the specific timing of trim in the first 30-60 seconds after leveling off from a climb? (trim is a process, not an event)
woodchucker
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woodchucker
People, this is a new pilot. Just try to be helpful. Naval aviator references? Tossing ballast in the back? Is that necessary? Maybe part of the problem of asking a bunch of super experienced pilots a beginner question.
In a climb apply full power, and yoke back for 90 kts or whatever your checklist says (or use trim). When reaching climb altitude you pull back the throttle to cruise rpm-ish and then fiddle with throttle to attain cruise speed. At the same time you maintain altitude with yoke inputs. Then use trim to ease those inputs.
Reverse on descent. Pull power and let the plane settle around 500 fpm or whatever. Use yoke input (or trim) as necessary and when reaching desired altitude throttle forward to cruise rpm-ish and same thing as above.
I consider trim as the “afterthought”. It’s important but power and yoke inputs come first. Then use trim to make your life easier.
In a climb apply full power, and yoke back for 90 kts or whatever your checklist says (or use trim). When reaching climb altitude you pull back the throttle to cruise rpm-ish and then fiddle with throttle to attain cruise speed. At the same time you maintain altitude with yoke inputs. Then use trim to ease those inputs.
Reverse on descent. Pull power and let the plane settle around 500 fpm or whatever. Use yoke input (or trim) as necessary and when reaching desired altitude throttle forward to cruise rpm-ish and same thing as above.
I consider trim as the “afterthought”. It’s important but power and yoke inputs come first. Then use trim to make your life easier.
LongRoadBob
Cleared for Takeoff
This isn’t advice, I’m not in a position of experience to give that but observations from another student.
Just add the thought that I’m sayin “it seems to me” before each point here.
My instructor helped a lot when he echoed someone here that posted about “sight picture” being 90% and check with scan of altimeter and VSI, for small adjustments. He first had me level off after climb out, then said “THIS is level flight and how it looks, recreate that when you level off”.
Also I’ve learned to (when going to cruise from climb out) what another mentioned here, level off with yoke first, wait a little bit to build up speed, then adjust power to the target cruise rpm, get that sight picture again, and then trim. Also lean the mixture and that can mean adjust with yoke and retrim.
in general with climb or descent, I read somewhere a memory aid, “look up at the apartment, then down at the dog an pat its head” meaning when leveling off in climb the apartment is APT (attitude power trim) and when leveling off on descent PAT the dog is of course power, attitude, trim. But power and attitude are adjusted pretty close to each other, let it settle then trim.
in all cases I think we students feel we should have total control of the speed and attitude at all times. The thing is there is a lag in the instruments, so we need to again go to sight picture, and it seems to me airplanes in changing speed or attitude need some time to settle. We overreact, and sometimes need to wait a little more.
One other thing my instructor showed me which helped, he mentioned (this might be be not totally true and an idea that just helps a student get there, I’m not sure but) that in climb or descent adjustment of rpm is pretty close to 100 rpm one way or the other equals about 100 fpm whether climb or descend.
one thing I need to work on, we’ve done slow flight, but to adjust airspeed (say to 70 in downwind) without any zoom, or climb. Seems like I would adjust power a little down, then raise the nose and repeat until I hit target airspeed?
A big revelation for me was when my instructor first had me trim, then climb at 80 kias, descend at 80 kias, and level off at 80 KIAS. That was a good while back, but it blew my mind as I had the wrong idea about speed vs. Altitude. Also him talking me through demonstrating to myself that when trimmed the airplane will want to keep that airspeed no matter what, but...that it (just like a pilot) will first over then undershoot cyclically and then get to target solidly.
This article also was a huge help to me in thinking about the factors
https://www.aopa.org/news-and-media...-training-magazine/a-pilots-guide-to-airspeed
Just add the thought that I’m sayin “it seems to me” before each point here.
My instructor helped a lot when he echoed someone here that posted about “sight picture” being 90% and check with scan of altimeter and VSI, for small adjustments. He first had me level off after climb out, then said “THIS is level flight and how it looks, recreate that when you level off”.
Also I’ve learned to (when going to cruise from climb out) what another mentioned here, level off with yoke first, wait a little bit to build up speed, then adjust power to the target cruise rpm, get that sight picture again, and then trim. Also lean the mixture and that can mean adjust with yoke and retrim.
in general with climb or descent, I read somewhere a memory aid, “look up at the apartment, then down at the dog an pat its head” meaning when leveling off in climb the apartment is APT (attitude power trim) and when leveling off on descent PAT the dog is of course power, attitude, trim. But power and attitude are adjusted pretty close to each other, let it settle then trim.
in all cases I think we students feel we should have total control of the speed and attitude at all times. The thing is there is a lag in the instruments, so we need to again go to sight picture, and it seems to me airplanes in changing speed or attitude need some time to settle. We overreact, and sometimes need to wait a little more.
One other thing my instructor showed me which helped, he mentioned (this might be be not totally true and an idea that just helps a student get there, I’m not sure but) that in climb or descent adjustment of rpm is pretty close to 100 rpm one way or the other equals about 100 fpm whether climb or descend.
one thing I need to work on, we’ve done slow flight, but to adjust airspeed (say to 70 in downwind) without any zoom, or climb. Seems like I would adjust power a little down, then raise the nose and repeat until I hit target airspeed?
A big revelation for me was when my instructor first had me trim, then climb at 80 kias, descend at 80 kias, and level off at 80 KIAS. That was a good while back, but it blew my mind as I had the wrong idea about speed vs. Altitude. Also him talking me through demonstrating to myself that when trimmed the airplane will want to keep that airspeed no matter what, but...that it (just like a pilot) will first over then undershoot cyclically and then get to target solidly.
This article also was a huge help to me in thinking about the factors
https://www.aopa.org/news-and-media...-training-magazine/a-pilots-guide-to-airspeed
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luvflyin
Touchdown! Greaser!
My ballast is 50 lbs of survival gear, not a lot but seems t help a bit...
Some of my ballast was survival gear. Water @ 8 lbs a gallon back yonder a moment or two. I wouldn’t necessarily do that routinely with any airplane but mine was a notoriously nose heavy plane that was nearly impossible to get aft CG
luvflyin
Touchdown! Greaser!
Good point and I mean that sincerely. The counter point is,
exploring the ‘details’ can be valuable
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No need to be humble. As another student, you are probably closer to the answer that is actually needed than detailed explanations. Your instructor was absolutely right.
AKBill
En-Route
The Sport also has a 20 pound ballast weight in the tail.
EdFred
Taxi to Parking
For the most part it is. But there are a few (very few) instances where it may be necessary.
sardonux
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Mr Smith
If you’d like text references to the lengthy commentary contained within this thread of responses, I’d highly recommend spending some time in chapter 5 of the Pilot’s Handbook (free from the FAA). There is a section called “Aircraft Design Characteristics” which goes in-depth on topics like Longitudinal Stability. That will give you context to help you improve your workflow in flight.
PaulS
Touchdown! Greaser!
I love trim.
luvflyin
Touchdown! Greaser!
Reggie
Stewartb
Final Approach
My point was made in my first post. If an airplane is difficult to trim for level flight? Add some weight aft for balance and it usually calms the up and down hunting that most planes do when flown light of baggage and cargo, which is how trainers are flown. In the CG graph I posted? If I didn't have 35# of tools and gear stowed in back the airplane wouldn't be within CG. Even as shown it's not much fun to fly. Mid CG is better. Mid CG trim control is better.
To the book thing about "stability". The reason I bought that book was to read about a comment a guy made on the Supercub site about stability increasing as the CG went forward. I had several discussions about that with one of my best friends, a professor of Aerospace Engineering at a major University, because my Cub was such a handful to fly unless I added weight in the back, which I discovered the first time I took my dog with me. The statement made on the other site referred to forward CG being characterized by "excess stability". That made no sense to me. Well, in the context of the Navy book stability is the opposite of control-ability, right? So as the CG moves forward our control response diminishes. That doesn't mean it flies arrow straight. The Navy book describes the forward CG limit as where the plane has minimum control-ability while the aft limit is where it has minimum stability. The important point to consider is that in the airplanes 99% of us fly those limits have been explored and the safe margins established. Most of us appreciate a nice mid-CG equilibrium that allows us to relax. But as the CG moves fore and aft we find different characteristics, some of them beneficial some of the time. Bottom line, in my experience if the airplane has a forward CG, even inside the envelope, it'll be more difficult to trim for maintained level than if the CG is neutral or a little aft.
My personal observations after having flown my airplanes with forward and aft CG including outside the envelope? With Aft CG speed is your friend. The forward CG speed is the enemy.
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My primary instructor taught me to end a climb by reducing power first, and to end a descent by raising the nose first. I never asked why, but I later figured that doing it that way avoiding overspeeding the prop. (This was with a fixed-pitch prop.)
An airframe in flight is stable when the CG is forward of the CP ("Center of Pressure"). Visualize it this way. Imagine yourself throwing a dart. What happens if you try to throw it with the feathers forward and the weighted point rearward?
Control inputs (including trim!) are more effective when the plane is less stable (not unstable). Make the plane too stable (CG too far forward) and your elevator will have almost no effect. That's why the plane seems easier to trim if the CG is moved aft (but still within the envelope). The elevator and the trim tab are more effective ("have greater control authority" in aero-speak) in that condition.
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Domenick
I think there is a difference between aerodynamic instability and pilot instability.
It may be easier for a human pilot to control a plane with the lesser stick force imparted by a somewhat aft CG.
It may be easier for a human pilot to control a plane with the lesser stick force imparted by a somewhat aft CG.
Tantalum
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San_Diego_Pilot
@Wingingit here's my process, assuming I was trimmed in climb so I'm not keeping constant pressure on the stick
-start leveling off, give the trim a few turns to "ease" the plane into cruise
-wait for plane to stop accelerating
-reduce power to cruise settings
-keep trimming until the stick forces are gone and the plane maintains level flight
^all that takes about 3-15 seconds
Like the other said, it's a fluid and dynamic process. Speed is really the big thing that impacts trim, and flap settings.. if you trim the plane for 120 knots.. and pull the throttle out, you'll notice the plane (usually, assume a typical plane) pitch down and accelerate to 120.. etc. These are planes with natural stability
for @Stewartb I got what he meant.. when you have two dudes in the front and nothing in the back landing the plane, with flaps in, etc., (at least in the low wings I fly) you'll find you need a tremendous amount of up elevator and the plane gets a little more "touchy" or "wiggly" with pitch. This makes sense, with all the weight in the front you need a lot of downforce on the elevator and small elevator pitch changes will have a magnified effect on pitch.. (like balancing a heavy block on your finger tip).. I do find that when my CG is in the middle, or even near the rear limits.. the plane is "easier" and "sportier" to fly.. this also makes sense.. the "relaxed stability" does increase an aircraft's controllability.. in the extreme cases where FBW is required. For what it's worth my best landings (IE, smoothest, most stable), are with a near-rear-limit CG
Cheers.
-start leveling off, give the trim a few turns to "ease" the plane into cruise
-wait for plane to stop accelerating
-reduce power to cruise settings
-keep trimming until the stick forces are gone and the plane maintains level flight
^all that takes about 3-15 seconds
Like the other said, it's a fluid and dynamic process. Speed is really the big thing that impacts trim, and flap settings.. if you trim the plane for 120 knots.. and pull the throttle out, you'll notice the plane (usually, assume a typical plane) pitch down and accelerate to 120.. etc. These are planes with natural stability
for @Stewartb I got what he meant.. when you have two dudes in the front and nothing in the back landing the plane, with flaps in, etc., (at least in the low wings I fly) you'll find you need a tremendous amount of up elevator and the plane gets a little more "touchy" or "wiggly" with pitch. This makes sense, with all the weight in the front you need a lot of downforce on the elevator and small elevator pitch changes will have a magnified effect on pitch.. (like balancing a heavy block on your finger tip).. I do find that when my CG is in the middle, or even near the rear limits.. the plane is "easier" and "sportier" to fly.. this also makes sense.. the "relaxed stability" does increase an aircraft's controllability.. in the extreme cases where FBW is required. For what it's worth my best landings (IE, smoothest, most stable), are with a near-rear-limit CG
Cheers.
Tantalum
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^but yes, the way we were taught "stability" the more forward the CG the more "stable" the plane, IE, it will pitch forward, harder to stall, etc.. but I don't find flying a forward limit CG plane particularly pleasant.
When I taught primary, I taught the exact opposite.
Attitude then power then trim for climbs and level offs from climbs.
Power then attitude then trim for descents and level offs from descents.
But... like the age old argument about pitch for airspeed/power for altitude and the reverse, we are merely describing techniques for accomplishing two goals, a major one being simply transitioning a student from the world of two dimensions to the world of three. We choose the one which seems to work best to accomplish that goal. They are not religious dogmas.
Reading your post made me realize that I only told half the story, i.e., the ending of climbs and descents. He taught the same as you for beginning them.
LongRoadBob
Cleared for Takeoff
this is what I learned too. As I mention “look up at the APT, look down and PAT the dog”
So when climbing and when leveling off APT (attitude, power, then trim) when descending and leveling off from descent PAT (power, attitude, trim)
like you describe it it better to wait til airspeed comes up, before adjusting power, but I think all the rest it is very close together with power/attitude adjustments, then wait a little to settle and trim.
Also, students tend to think they have to force the airplane to their will at all times (in the back of their mind anyway) but we have to learn finesse and patience, when to wait a little, let the plane settle in.
while it might seem like wasting a lesson, I have toyed with the idea of a lesson where the instructor does all the flying, I think it would be a good idea to see what the goal is and how to get to it. Watching an instructor take off and level out to cruise, while relaxed and not flying, and keeping an eye on sight picture and instruments, see what is possible could have some benefit! Seeing to that it isn’t instantaneous, when they wait a little, etc.
As the CG moves aft all aircraft become less stable. It’s basic aerodynamics. Aircraft handling may appear to be better because control force's are reduced with a aft CG. At some point however as the CG moves aft pitch control gets difficult as very small control surface movements can produce large pitch changes. All the tandem seat aircraft I have flown land better with the CG forward.
As far as trim you should trim all the time to keep stick forces neutral. It should become so automatic you are unaware you are even trimming. In military flight training instructors often asked to see your hands held up. If when they called hands the aircraft deviated from its flight path because it was not in trim you could expect a grade reduction. If well flown a aircraft should always be in trim or trimming.
As far as trim you should trim all the time to keep stick forces neutral. It should become so automatic you are unaware you are even trimming. In military flight training instructors often asked to see your hands held up. If when they called hands the aircraft deviated from its flight path because it was not in trim you could expect a grade reduction. If well flown a aircraft should always be in trim or trimming.
EdFred
Taxi to Parking
Some people claimed that if you flew above your target altitude, and then descended back to it you could cruise at a higher airspeed. Called it getting on the step like with watercraft or seaplanes. What you were talking about is slightly different.
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jsstevens
And here's a writeup of one attempt to prove or disprove the On The Step concept: On the step...
Read the rest of the Thread to see the full discussion.
John
Read the rest of the Thread to see the full discussion.
John
wilkersk
Pattern Altitude
I don't know about "on-step" (as it applies to a boat hull or aircraft floats) is a thing for airplanes moving through the air. But, I do know that my little Sonerai will struggle to get up to best cruise speed unless I hold the throttle up, allow the speed to build, then trim throttle and pitch for cruise. A slight descent for 100' or so will make it happen even faster.
And, to get it to slow down to pattern speed, I have to pull the throttle way back and keep feeding in pitch to get it to pattern speed, then quickly add power to level off at pattern altitude. If I just pull the throttle and level off at pattern altitude, it'll never slow down to pattern speed until I pull the throttle back. And then I have to use pitch to control descent rate.
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jsstevens
It sounds like your Sonerai matched my results in the 172 in that the climb above, descend to accelerate is the fastest way to get stable cruise. As for "struggle" to get to cruise speed, it does take longer to get there on cruise power alone, for sure.
And slowing down to pattern speeds is NOT a problem with the 172. It's draggy enough... Although if I left cruise power in I would be going faster than I like in the pattern anyway.
John
Cogito
Pre-takeoff checklist
POA is the right place for a single reasoned answer to your question.~
Clip4
Touchdown! Greaser!
Holding altitude as a student is usually one of two issues.
1. During level off from climb the student doesn’t understand it takes time for the aircraft to accelerate to cruise speed and the tail down force is changing during that process.
2. During level flight they don’t understand they must determine small changes in pitch visually and not chase the altimeter.
1. During level off from climb the student doesn’t understand it takes time for the aircraft to accelerate to cruise speed and the tail down force is changing during that process.
2. During level flight they don’t understand they must determine small changes in pitch visually and not chase the altimeter.
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jsstevens
Yes, waiting for speed changes to take effect is a big part of it. Also, once on speed, the aircraft will often make small perturbations around the altitude/speed which will damp out if left alone. If you try to correct all those with trim, you'll chase it forever. Fix small stuff with the yoke and then feel if you have to keep pressure on it. If so, trim the pressure away.
Dan Thomas
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That's not to make trimming easier. It's to get the airplane's empty CG to a spot where the various loading scenarios aren't likely to put it out of CG range. Plenty of aircraft designs come out nose-heavy or tail-heavy when things like engines are changed to make a different model, or a CS prop is installed, and so on. The usual fix for nose-heaviness is to shorten the engine mount, but if there's no more room between the engine and firewall, you're left with adding ballast in the tail in order to save the model series.
chemgeek
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In most phases of flight it is normal to trim to neutral control pressure to maintain the desired flight attitude. When changing attitudes it will be an iterative process of adjusting power and trim. For example, when leveling off to cruise after climb you will have to change attitude and adjust power. Both of these changes will require retrimming, and the attitude change will in turn require additional slight adjustment of power, which will require slight adjustment of trim, etc. Once the plane settles down in the new attitude, you can hone in on both the desired cruise power setting and trim. Up and down drafts will have you adjusting yoke pressure or trim as needed. In smooth air you may be able to trim for level flight for miles and miles, but in more turbulent air you will be making continuous adjustments in attitude, trim, and possibly power to maintain level flight.
In practice, when transitioning from climb to cruise I like to start with attitude first, allow the plane to accelerate to cruise speed, then reduce the power to the desired setting while dialing in trim to neutralize control forces. Then a series of little adjustments follow to get it just right. You can adjust power first then change attitude, but in a low power aircraft it could take a while to accelerate to the final cruise speed and you will normally have to make additional power additions to accelerate. I find the attitude first approach quicker, just pay attention to power during acceleration to ensure you don't overspeed the engine. Neither way is "wrong" in a light single. But you should normally fly at neutral control pressure.
Dan Thomas
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Dan Thomas
Fixed-pitch props are pitched so that the engine is at redline at full throttle in level flight. That will give an airspeed well beyond normal cruise. If an engine overspeeds while levelling off, that airplane has the wrong prop on it. Some owners used to intall a lower-pitch prop to get better takeoff and climb, but that's rare these days.
A constant-speed prop's governor will prevent overspeed.