cfircav8r

My Feedback: (1)

There are compromises that have to be made, no matter how a plane is set up. To say it is foolish to have an airplane that requires retrimming with throttle changes is as bad as saying it is foolish to build a scale plane underpowered, by model standards, just so you can keep it in the cowl. We all have different tastes and expectations from our aircraft and to discount my method as foolish is a tad bit elitist. I personally want a plane that, no matter what the power setting, I know it will not stall as long as I keep my elevator below a certain position. I want a plane that will maintain speed on final and increase or decrease descent rate with power changes. I do not have any trouble compensating for a tendancy to climb with power changes and what some see as bad tendancies, I see as realism.

Speed you say that a "plane that holds constant trim is easier to fly." On that we agree, we don't agree on what that means. To me trim is for airspeed, for you trim is for attitude. Which do you think is safer for a less experienced flier? I believe trimming for airspeed is safer.

speedracerntrixie

My Feedback: (29)

We are not flying full scale.

speedracerntrixie

My Feedback: (29)

Cfircav8r. I would tend to agree with you on most points. As far as what is safer for a new pilot, I would have to leave it as whatever works best for that particular pilot. As for the average sport pilot I would encourage them to give it a try. Everyone has different tastes so what works for me may not work for everyone. I suppose I came out a bit strong on this one due to the response I recieved initially. Your right about the two means of trimming, I do beleive that trimming for attitude is a better way to go as airspeed is not a constant, Drop the nose just a few degrees and now your speed is higher and out of trim. A new pilot is not going to be able to re establish the speed at what the trim was set to. End result is he is chasing the trim around instead of concentrating on flying. At least that is the issue my kids were having while I was teaching them.

cfircav8r

My Feedback: (1)

Sorry you posted while I was typing.

cfircav8r

My Feedback: (1)

The thing about trimming is if you set it up right and trim for airspeed it is now a constant. It will, within reason, maintain a fairly constant airspeed. My way if you want to maintain speed but want to descend just reduce power and it will drop the nose to maintain speed. If you want to fly that way it works great, if you want to fly as you do it would be frustrating as all get out. That is the great part about flying. I don't have a bone to pick with you and I agree your way is great for high performance style flying, but for lazy day flying it is just not that good. With my style if while flying you encounter turbulence and the planes attitude is disturbed give it a sec and it will smooth out, with yours you have to right it. I do have planes set up like yours, I just don't enjoy them as often as I used to, but then I am not 20 anymore, or 30 for that matter, Aw man! Im not even 40 anymore. Now you got me all depressed. Thanks a lot![:@]

cfircav8r

My Feedback: (1)

As with your set up it takes practice and a specific technique, but you don't fly that way so you should teach how you fly. Again neither way is wrong, just different.

flycatch

My Feedback: (26)

This is my set-up for trimming any model. C/G set at 27%
Throttle setting 3/4

Any throttle setting above or below this point you fly the airplane.

jaka

Hi!
So you mean you don't try to establish the "best" Cof G you can obtain? You just settle for a certain percentage??

To comment of what some of you have said. I find it very hard to belive that some of you constanly retrim your planes depending on what speed you fly?!
Yeah! I trim and retrim many times when I have a new plane (be it trainer, scale or racer doesn't matter) but I only do so to obtain the "perfect" trim setting on that particular plane. This process can take days, weeks or months depending on the amount of labour involved, like moving the battery, servos changing elevator throw, axial and latteral balancing etc. And for each change ...test fly! But finnaly all my planes flies straight at full speed and when I throttle down slightly the plane just flies forward with just a slight altitude desendent and this is easily adjusted with just a bit of elevator

flycatch

My Feedback: (26)

All airplanes, model or full scale, have an aft and forward C/G range. I gained my knowledge from books written on aerodynamics not from word of mouth. The number I used is standard through out the aviation industry and so is the power setting. We modelers normally fly at a power setting that suits the model we are flying. I know that when I apply full throttle the model will climb and when I reduce throttle it will descend. The elevator goes along for the ride. If you don't believe me than that a ride in a civilian aircraft. When you come in for a landing it is throttle management that establishes a glide path not elevator.

perreback

You lost me there - care to elaborate? I'm not questioning your method, I simply don't understand what 27% refers to.

flycatch

My Feedback: (26)

In order to explain this number you most understand what the average chord of the wing is. I'm not an engineer but I use a book written by "Gordon Whitehead". The book is entitled "Radio Control Scale Aircraft Models For Everyday Flying" and will become your bible. It was first published in 1980 and released by RM Books Ltd., Guildford, Surrey England. Do a goggle search and you may still find it for sale.

perreback

OK, thanks.

flycatch

My Feedback: (26)

I did a goggle search and the book is still available in the UK and on Amazon.

jaka

Hi!
Flycatch! All my planes fly straight forward when I give full power from near stand still.They do not go up or down! I have not read anything in books , just learned from personal experience. Cof G is something that could be altered to obtain better flight performance/more easily flown plane, it's not something that is fixed.

When it comes to newbies they have no time trimming all the time depending at what speed they fly. They have all focus on just flying! Being training people to fly for decades. That's why it's best to trime a plane at full power because at that position the model plane flies straight. In all other throttle setting it will descend slightly, but just slightly, but that is easily compensated for by just adding a tad of up elevator. Please! Do not mix full scale plane flight with R/C models, they are a different bread!

flycatch

My Feedback: (26)

So all your planes fly straight and level at full power. Well imagine that and that puts you in the minority. There are only three wings platforms to choose from; symmetrical, semi-symmetrical and flat bottom. Your answer comes from a person who knows it all and will argue the point until the cows come home. I fly fingers and the vast majority of flyers in the USA fly thumbs. Why is this? The answer is simple because that is how they were taught. From what you have expressed your opinion is biased and remains inflexible. You sir are doing more harm than good and take your comments to the "pattern" forum.

cfircav8r

My Feedback: (1)

Look at the highlighted sentence. You state that if you are flying below full throttle you just have to hold a tad up elevator to maintain level. You could just re-trim, gee that is what we have been saying. You seem to of the belief that it must be done as you do or it is wrong. We experience the same changes as you, yes with some aircraft the amount of elevator is more due to the desired characteristic of more stability, but the physics are the same. As far as full scale goes we also can do as you, but if we cut it too close we don't just loose an aircraft we loose a life. The only difference between full scale and models is models are stronger and therefore can handle our higher expectations and there are no lives at stake if it fails. The physics are the same. Models are not magically different just more forgiving of our pushing the envelope.

HighPlains

My Feedback: (1)

Well it looks like enough descriptions of the elephant have been made, so with one eye open here goes………

To address poppy2’s original question, is there a correct speed to trim out an airplane. No is the simple answer. It really depends on how you want to fly the airplane. Trainers are generally set up very close to way general aviation aircraft are set up. They are generally nose-heavy so that once trimmed they will just motor along without much pilot input at all. If the pilot should pull back on the elevator for a brief time and then let go, the airplane will slow down slightly to a point where the down force from the tail no longer generates enough force to continue to hold the nose up. Since the forces acting on the airplane are no longer in balance, the airplane’s nose will drop until it is slightly downhill and the airplane picks up speed. Unfortunately, without pilot intervention the airplane will overshoot it’s trim speed and due to the excess speed start climbing again. If the airplane is well designed and trimmed out, this excessive climb and dive will eventually die out, but will still continue at a reduced level. This is a long period response called “phugoid”, and it is a constant exchange of speed and altitude. For most GA airplanes it takes about a minute to go through one cycle, so most pilots are mostly unaware of it. There is also a short period response that aircraft have to quick inputs of elevator control, but they dampen out in just a cycle or two if the airplane is well designed. For models due to the smaller size it is thought that the phugoid and the short period are nearly the same, but I have my doubts. For one thing RC models are turned so often that you almost never fly for more than a few seconds without a change in direction. Which is also why I am somewhat skeptical about claims of speed insensitivity due to having a low static margin (ie., flying tail heavy). While I do tend to set most of my models up very tail heavy, I don’t think that it completely divorces the pilot from making minor pressure changes on the elevator control to maintain altitude with different throttle settings.

As far as not being able to climb if the nose heavy airplane is trimmed out at full throttle, why not? You have the forces all balanced out, the airplane would be flying as fast as possible with the available power, and if you just pull back on the stick it trades kinetic energy for potential energy. The exchange of KE and PE shows up as changes in speed and altitude.

You mentioned your experience and goals, so here is mine. I’ve flown RC for 43 years, also have a private pilot’s license and have a degree in engineering. Much of my RC flying was in pylon racing, and nearly every current pylon design incorporate features that I developed years ago. Monkeys see, monkeys do. Don’t worry, I stole all the good ideas that others developed too.

Quite often people blame the airfoils models use for how they fly. Well, that is not the entire story. The decalage of the airplane along with the balance matter more than the airfoil. Decalage is the variation in angles between the wing and tail. Most trainer types with a flat bottom airfoil, or better yet a “Clark Y” or flat bottom with a bit of “Phillips entry” (where the bottom is mostly flat except towards the leading edge where it raises slightly) will generate lift until the wing is at some negative angle of attack. For some of these airfoils, they will generate lift until about -4 degrees. So throw in a couple degrees of positive incidence, and you have lots of lift. While most “advanced” RC airplanes are set up pretty much 0-0-0 with regards to the wing, stab, and thrust line, most full size GA airplanes have a couple of degrees positive incidence in the wing or lots of camber in the airfoil. Both do about the same thing in terms of creating lift at flying speed, but have slight differences in pitching moments which the tail has to overcome by pulling down to maintain balance in un-accelerated flight.

There is a limit to how nose heavy you can fly an airplane. At some point you run out of elevator, or speed, or you stall the tail. You could increase the size of the horizontal tail and keep landing speeds short of full throttle speeds, but generally moving the CG back does make most airplanes land easier. Years ago when most RC flying was done with just rudder control, the models were set up with loads of decalage and were quit nose heavy. They didn’t have very much speed in flight with the engine running and the landing speeds were almost as fast as the flying speed. But even with just rudder control, they could do loops and rolls by going into a turn until a bit of excess speed was generated then KE and PE did their thing. Kicking in the rudder at the right time then got you where you wanted to go. With your basic trainer, you can still do the same thing today with just rudder and throttle. Though some of the available ARF’s have wings of suspect strength. An RC pilot should learn how to control a model with a failed servo, as if you fly enough it will happen sooner or later. I have managed to land multiple times without the elevator servo working or ailerons working. Unfortunately a perfectly set up advanced model with no roll coupling from the rudder will not lift a low wing no matter how you try, but two wing servos overcome that slight problem. Losing the rudder or motor control is pretty much a non-event. Hell, I even landed one airplane after losing the entire tail due to a mid-air. The semi-symmetrical airfoil had a slight pitching moment, so I rolled the airplane inverted and negative pitching moment was now a positive pitching moment.

As far as the ongoing discussion on racing and trim, it is quite different than most RC flying. Elevator controls direction and ailerons control altitude. The airplane is trimmed so that it does not gain or lose altitude when the wing is banked about 40 degrees to the left….

Paul_BB

My airplane is normally trimmed at 70% of throttle. I also have programmed one switch to add a few % of up elevator. When I toggle the switch, the airplane is trimmed for a level flight at 30% of throttle. This corresponds to a slow but secure speed. This way, when I want to slow down for a landing, I set the throttle to 30% and toggle the switch. I let the speed settle down, head for the runway and then throttle down. The airplane comes down. Thus, If I am a little short I just set the throttle back to 30%. I don't care about the ground speed, I know the plane will not stall.

Jetdesign

My Feedback: (8)

This is a worthless thread. There is no 'right answer' and most people don't fully 'trim' an airplane, so generally people fiddle as much as they feel like and settle on something that feels good to them.

poppy2

If this is a worthless thread gaRCfield, are you suggesting that I just ignore what you just posted? Everyone has their opinion and that is their right. You can listen and ponder all you want. Does not mean you have to agree or even do what they say, but you can listen and you might even learn some thing. People who have all the answers have nothing to learn. I don't have all the answers and I am sure willing to listen. I respect your opinion and appreciate your response.

Poppy2/WD4LNK

ncsky

Congrats Poppy on getting back into flying. As jester suggested you might want to look into a stick as one of your next planes, great sport and easy flying plane. It is available in all sizes and power setups. We have several at our club of all sizes.

Good luck and Happy Flying!