poppy2

I have not been flying for about three years or so and have decided to get active again. Back in the beginning, three years or so ago, I trained with a great professional person that really knew how to fly. After I got my wings, I flew myself about 25 flights or so and brought the plane home safely each time. I have 3 trainer planes and that is all that I fly. All this information is to let you know who I am and what my skill level might be. I am in a club, pay my yearly dues, but have not been active there also.

My question is this. I know that power is what takes you up or down and elevator is speed, faster or slower. With that said, what is the correct power to trim the plan for straight and level flight? My intuition tells me that half throttle would be the place. This way giving more throttle would cause you to go up, less throttle would allow you to decline. If you were trimmed out for straight and level flight at full throttle, you would have "no more" power to go up if you wanted to.

Having been away for some time, it is fun getting the planes out and going over them. Reviewing aerodynamics, battery charging, and engine adjusting skills has got me reeved up.

Thank you in advance.

Poppy2

scale only 4 me

My Feedback: (158)

It depends on the plane and the speed you'll be flying it at.. Obviously a Q500 race plane will be trimmed at full throttle, I had a Royal Stearman that I trimmed at just over 1/4 throttle,, because that's where I flew it at. Had a midwest AT-6 trimmed at 1/2 throttle.

good luck

jetmech05

IMHO and the way I do it is trim for thumbs off at around 1/2 throttle. I'm flying IMAC now so when I go to full throttle I'm on an up line when I'm back to 1/2 throttle I'm setting up for the next maneuver or I'm out of the box.
This is the way I like to set my aircraft. You might like yours differently

speedracerntrixie

My Feedback: (29)

What you describe from my understanding is common practice for full scale. I do not fly full scale so Ican only assume this is done for safety reasons. My guess is that it gives the airplane some self righting abilities and more tollerant of CG changes due to passengers and/or cargo. However setting up or models in this fashon is not nesessary and IMO not wanted. All of my models are set up so that there is no elevator trim change from 1/2 to full throttle. This is done by setting wing incidence, tail incidence, thrust angle and CG to a neutral setting so that no elevator trim is carried. The end result is that the airplane has minimal elevator trim change while at slower speeds, has no trim change from cruise speed to max speed and will react less to wind gusts and throttle changes. For those flying aerobatics it greatly reduces the pilot workload and makes manuevers much easier to fly in a precise manner.

Ed_Moorman

My Feedback: (1)

If you are flying a trainer with a flat bottom airfoil, the trimming is a little different. Planes with a symmetrical airfoil will trim easily for level flight at virtually any airspeed. A plane with a flat bottom airfoil is very power sensitive in pitch. Add power and it will nose up and climb. This is due to 2 things. First, the engine is below the area of highest drag, the wing, which tends to slow the upper part of the plane. The engine mounted below the wing then "turns" the nose upward. Second, the lifting airfoil generates a lot more lift with greater speed causing the plane to climb.

What you are looking for is the natural cruise speed of the plane. Fly at the power setting you like, trim for level flight, then land without re-trimming. Leave the radio on and check the position of the elevator. If it is slightly down, you are flying faster than cruise and having to compensate by adding down trim. By the way, most of our trainers will fly perfectly well with a .20 or .25 instead of the usual .40-.46. We tend to over power a lot.

If you use less power to slow down until your elevator is level, you'll be at the natural cruise speed.

Now then if you want to go faster with the same plane without re-trimming-actually resetting the cruise speed, you need to change the wing incidence. I use what I have called "Popsicle Stick Aerodynamics." The next time you put your wing on, add a popsicle stick under the trailing edge. After flying, re-trimming and landing, if you still have down elevator, add a second popsicle stick. Two is usually the right number to get the elevator close to level. If you don't like the wing gap, CA the popsicle sticks in place, squirt some silicone seal on the wing saddle area, cover it with Handy-Wrap and rubber band the wing back on. Let it cure over night, remove the Handy-Wrap, trim the edges and you're good-to-go.

jester_s1

The proper trim speed on a trainer is the lowest throttle setting that the plane will fly smoothly with. If it's getting tossed around in the wind or is on the verge of a stall, then that's too low. If it's carrying its tail high and zipping along, that's too high. Get a comfortable flying speed where the plane has enough reserve speed to handle the occasional wind gust on its nose and to get through turns smoothly, and that's the speed you should trim for. If you are using the recommended engine for your plane that setting will probably be between 50% and 70% throttle. If you're overpowered, it may be lower. When you move to sport planes and aerobats the advice will change, but this will give you a smooth trainer that retains its tendency to pull its nose up when you throttle up. That's a nice feature for panic go arounds.

poppy2

I would like to thank everyone for all the information and insights that have been shared in these post. Again I want to let you know that all I fly is trainers and at age 71 that will probably be my limit. I am beyond grateful that I have gone this far. Again, my understanding is that power takes you up or down, and elevator is for speed, faster or slower.

I have also come across some other information, not sure where, possibly from this forum years ago, that states, "During a flight, a pilot will alter the speed and angle of attack of the aircraft. These two factors are often balanced against each other. If the pilot wishes to increase speed and maintain level flight, the angle of attact must be decreased to offset the extra lift that is provided by the increase in the speed of the aircraft. The faster the plane moves through the air, the more lift the wing developes at a given angle of attack. Within limits, the greater the angle of attack, the greater the lift at a given speed. If the angle of attack becomes to great, the wing suddenly loses lift and is said to stall." This information is for a trainer with dihedral wing. How is differs from other planes, I am not sure.

Which brought me back to my orignal question, "At what speed do you trim the trainer?" Now with all this information, input and intuition, I believe that the sweet spot is between 50 to 70 % of the max power of the engine. And the engine that I am using is an OS Max 46 AX.

Again I want to thank everyone who took the time to respond to my post.

Poppy2/WD4LNK

jester_s1

I'm glad you figured it out. I'll add that the final test is your perception for how the plane flies. Also, don't be scared of sport planes. Unless you are frequently losing orientation and needing the plane to self right, an Ugly Stick is actually an easier flyer that is much less affected by the wind.

speedracerntrixie

My Feedback: (29)

Poppy, the quick answer to your question is trim at a speed you are comfortable with. The problem with that is you must fly at a constant airspeed. Easy with a full scale not so much with a model. That is the basis for my previous answer. I will agree that with a flat bottomed airfoil my trimming method will not work. It will work on most any other airfoil sections as I have used it on semi-symmetrical airfoils, symmetrical airfoils and even sailplanes. My perspective and one that has been proven several times is that it is actually easier to fly an airplane that holds pitch trim regardless of airspeed. I beleive in this to the point that if it were not for the fragile nature of the airplane I could easily train someone to fly with my giant scale aerobatic airplanes.


With all that said, the main focus is having fun and you appear to be doing just that. I applaud you sir.

HighPlains

My Feedback: (1)

Six blind elephants were discussing what men were like. After arguing they decided to find one and determine what it was like by direct experience. The first blind elephant felt the man and declared, 'Men are flat.' After the other blind elephants felt the man, they agreed.

jester_s1

And a little squishy...

jaka

Hi!
You are right speed... All R/C model airplanes should be trimmed out at full speed! The reason is like you describe.
You trim a modelplane so that it flies without any trim changes from let's say 30% of full speed up to 100%. This is easily done by changing the Cof G as far rearward as possible and at the same time reduce elevator throw, trim the plane in axial plane and checking the wings for wash-out.
This process adheres to all model airplanes!

KW_Counter

I strongly disagree!
You trim it at the speed you normally fly.
This trim still will not remain constant because wind speed will never be the same.
There are many other factors involved in the plane being able to be flown hands-off,
and they are constantly changing.
Trim it so you are comfortable flying the plane.
You will be adjusting the plane's inputs on a regular basis,
the trim is to make these adjustments smaller and a little less frequent.
If you adjust at full speed and never fly at full speed you will be adjusting your
planes control surfaces more often.

Keep it Simple, it's a Hobby,
KW_Counter

speedracerntrixie

My Feedback: (29)

I sat and looked at my monitor and tryed to come up with an explanation on how so much of this post is just wrong. I came to the conclusion that not everyone wants to learn so I'm just going to leave it alone.

jester_s1

I'll have to disagree with one of Jaka's recommendations, and that is that the CG has to be rearward to get a wide speed envelope. Having a plane that maintains trim over a broad speed range is a combination of wing and tail incidence, down thrust, and CG. A moderate CG can still give you a plane that maintains good pitch trim over a reasonable flight envelope if the incidence and downthrust are right.

jaka

Hi!
From my 38 year experience both competing in pylonracing and scale and constructing R/C planes I can only say that if you want to have a good flying R/C plane you trim it at full speed! This is regardless of what typ of plane it is, be it a racer, pattern or scale doesn't matter.

There is a general rule that says that to have a good flying R/C airplane you must try to obtain the most rearward Cof G as possible ,and still have the plane behaving good. This triming takes a little time but is necessary if you want to have a perfect trimmed airplane. All people that has been competing knows this is true.

For a newbie trimming at medium speed could be disastrous because when he/she comes in a situation when he/she needs to have full power the planes reacts in a diffrent way than he/she is used to.

jester_s1

It's a trainer he's talking about Jaka. If we were talking about pattern planes or racers or even sport planes like a 4 star I would agree with you. But unless you've forgotten how trainers fly in those 38 years, you may recall that they are purpose built to be pitch sensitive in relation to speed. They aren't designed to be flown at full throttle all the time unless the pilot wants the nose to drop every time he tries to cruise around at a reduced speed. Trainers are supposed to fly at 60-70% throttle and automatically gain altitude when you gun them in order to save the pilot from a botched landing or a stall.

scale only 4 me

My Feedback: (158)

Got to agree fully, you trim a plane at the speed you intend to fly it at, simple as that, It amazes me a how such a simple concept is even debated.

JohnBuckner

My Feedback: (1)

INDEED!

It also amazes me how so many flyers who have been active even for years cannot even trim their own airplanes in flight because of this failure in attitudes.

John

jaka

Hi!
Been teaching newcomers for 35 years or more.
Even a trainer,properly trimmed out, can maintain the same altitude at nearly all power settings! The slight descent that takes place when you throttle down is easily compensated for by giving slight up elevator.

The problem for newbies when trimming their plane like you say (at slightly under full power) is what happens when they try to land and have to go around an make another try....then they give full power! what could happen then is that their plane goes upward more than the pilot intended and this could be disastrous and I have never seen a newbie pilot that hasn't given full power when making another try at landing! -Have you?

scale only 4 me

My Feedback: (158)

Unless the plane is inverted on finial approach, I've never seen pitching up slightly to be a problem

poppy2

I have been reading these posts with great interest. At this point is seems that there are several opinions and I suspect that is the way it will be. Seems like that is the way we are wired up. Let me say that I am far from an expert in this hobby. I have only about 25 successful flights under my belt since I "got my wings" and I suspect the people that have responded here have way, way more then that. Also, I might add that the flights that I have had were with my trainer. And as one poster has commented, "It a trainer that I am wanting information about." There seems to be a little information that just doesn't apply to a trainer. So with that in mind let me say this about my trainer. There seems to be some absolutes about this kind of plane.

MORE THRUST-more lift / LESS THRUST-less lift

LEFT RUDDER-left yaw, left roll, pitch down / RIGHT RUDDER-right yaw, right roll, pitch down

LEFT AILERONS-left yaw, left roll, pitch down / RIGHT AILERONS-right yaw, right roll, pitch down

UP ELEVATOR-more lift less speed / DOWN ELEVATOR- less lift more speed

LIFT-Some lift is directed rearward. This is induced drag that occurs when lift is being produced

SPEED-As the speed of the airplane increases, the volume of air that flows across the wing per unit of time also increases. This results in more lift because of the pressure difference above and below the wing.

Lift depends on the shape, area, and tilt of the wing and on the speed of the aircraft.

If the angle of attack is increased while the speed remains constant, the plane will rise. If the angle of attack is decreased, the plane will descend.

An airplane will climb from level flight if its speed is increased, and will dive if its speed is decreased.

During a flight, a pilot will alter the speed and angle of attack of the aircraft. These two factors are often balanced against each other. If the pilot wishes to increase speed and yet maintain level flight, the angle of attack must be decreased to offset the extra lift that is provided by the increase in the speed of the aircraft.

The faster the plane moves through the air, the more lift the wing develops at a given angle of attack.

Within limits, the greater the angle of attack, the greater the lift at a given speed.

A trainer will have the bulk of it mass below the wing, the wing will be a flat bottom, and the wing will be a dihedral, at least mine is, all three things giving it great stability.

Now with that all said, I have to think that since this plane is not for racing, I am not going to get it up and keep it at wide open throttle. It would seem to me flying at mid range would be where most of my flying would be, given my current level of skill and interest. That for me would seem like the place to trim it for hands off, level flight. At mid range. Then if I wanted to go faster, there would be that extra thrust needed to get the job done. If I wanted to go slower, just reduce the throttle. There would be some reserve power there if needed. Plus someone I think mentioned or implied that if the plane was trimmed at mid throttle, the added inputs either up or down from mid range would not be drastic. That makes a lot of sense to me. Maybe someone with many hours of skill would like to try and race it and see how fast they could get it flying. Perhaps the place to trim the plane for that person might be way off the mid range. Perhaps the place to trim the plane is in the eye of the beholder. Perhaps there are certain absolutes, as mentioned above, that can not be changed or ignored but perhaps there is also a "gray" area for trimming which would take into account the reason why the pilot wants to fly the plane.

Again, I am far from an expert in this hobby but I am one that asks a lot of questions. The idea of perception was brought up and that makes sense to me also. If something does not look or feel right, maybe you need to question it.

I see that the opinions have gone from one side to the other but that does not surprise me. That's just the way we are wired up. Even the elephant was introduced into these posts and believe it or not there is some wisdom there or at least there was for me. "Don't just follow the crowd." Give some thought to what's going on and after discerning the information, decide for yourself what is best and seems to be the wise thing to do. In school we are taught the lessons than given the test. In the real world we are tested and then hopefully learn the lesson. I hope this post has helped others as well as it has helped me. I am still willing to read what others have to say. And as one poster has said, it about having fun. I agree. It's also about passing your information along to others. We really don't have enough time to make all the mistakes it takes to learn. Passing on that information, you that have many miles under your flying belt, speeds up the learning process for us newbies. When I was young, I had all the answers. Now that I am 71, I realize that I really only have a few answers. Thanks again for all your help.

Poppy2/WD4LNK

jaka

Hi!
But what happens at take off??? Then you use fullpower! don't you!?

If you trim your plane att less than full power you have to reduce power imidiately after take off to have the plane fly level and not climb too much(no good for a newbie as his brain is fully ocuppied with just controlling the plane).
Belive me...I have been teaching newcommers for more than 30 years and there is only one way to go if you want to be a good fliers and that is to trim all your planes att full power.

Top_Gunn

My Feedback: (6)

One more thing to consider: some people are very comfortable flying while holding some back pressure on the stick. This is not a bad way to fly, because it's hard for many of us to hold the stick forward while flying. If you are one of those people, by all means trim your trainer for level flight (or even some loss of altitude) at full throttle and compensate with back pressure while flying more slowly. That way, you'll never have to hold the stick forward (except when inverted). I wouldn't recommend it to a beginner, though. Hands off flying at normal flying speed is easiest for training.

poppy2

Thank you again for your patience and input. First let me assure you that I am not writing these posts to convince you that I am right and you are wrong. I do have a listening ear or two. I have to say that with all information I have learned in the few years that I have been flying still leads me to the conclusion that the plane would be best trimmed at or slightly above mid throttle.

Let me try this interpretation. Let's assume that my trainer has been trimmed at mid throttle. I feel pretty comfortable while flying there that I could take my hands off the controls and it would still do fine. (just for a moment or so) Now if I had more throttle power left and I just decided to give it full throttle, I should go up some. Great. I would have to surely keep my hands on the controls and maintain what ever attitude I wanted at full throttle. No problem. Back to mid throttle and again at a comfortable speed. Now when I want to land, I circle around, line myself up on the runway. Once lined up, I am at idle speed and I just let the plane come down on its own. My object is to come in over the beginning of the runway, give some up elevator to level the plane out at about five feet , then at about three feet off the runway, flare, and just let the plane come down on it own. If I see I should go around for whatever reason, give it full throttle and I should go up and reduce throttle after I am up. Back on the ground, now when I want to take off, I give it full throttle, when it is up to speed, give some up elevator, and it is gone.

Now some questions.....

I do agree with you that once off the ground I do have to throttle back, but what is the problem with that?

Having trimmed the plane at mid throttle, when I take off again, would the elevator be in a position that would allow me to take off full throttle and allow me to put in some up elevator for rotation? Would I have to make some correction to the elevator before take off? Make sure it is in neutral position?

When I am coming in to land, having the trim set at mid throttle, is there still enough movement with the elevator to give it up elevator for leveling and flare?

Hope these questions are not too confusing. Perhaps they can give some fuel for answers.

Poppy2/WD4LNK