kdheath

Every airplane can be trimmed to fly at a variety of throttle settings and speeds. Set the throttle and then adjust trim for level flight. When you increase power, the plane will settle into a climb, but at the same speed as before. Reduce power and the plane will settle into a dive or glide, again at the same speed as before.

Now change the trim while in level cruise flight. With back trim, the plane will settle into level flight at a new, lower speed. Roll the trim forward, and the speed will increase because you are now allowing gravity to take over and "pull" the plane down at a new, higher speed.

The trim tab/elevator are wherever they need to be to get the job done. Whether they are up or down or whatever isn't really relevant. What matters is getting the desired performance.

Here's an illustration of the forces that work on a airplane in flight. Here's NASA's basic flight forces page. http://www.grc.nasa.gov/WWW/K-12/airplane/forces.html

Hope some of this helps. It's not real intuitive. It may be that the best thing you can do is forget that you ever saw a car. Planes and cars don't act much alike. But once you understand the forces involved, you'll understand better why your plane does the things it does.
Kelvin

Oops, the labels didn't come with sketch. They are Lift, Gravity, Thrust, and Drag.

BWooster

Poppy2,

If the stab incidence is set correctly, then the elevator and stab will be straight at cruise, because this setup has the least drag. But it is not necessary, and frankly, is probably overkill in sport models.

Just after I posted the previous message, I read another post elsewhere that explained how downthrust will cancel out the effects I have described. I should have thought about that . [:@] When an aircraft has downthrust an increase in throttle will lead to a greater amount of lift, but the downward component of the thrust counteracts the excess lift. The example cited was the Ercoupe, a famous 'everyman's' airplane of the '40's.

Like kdheath says, an aircraft can be trimmed in many, many ways. The lesson is that the elevator controls angle of attack, and thus controls lift and drag. Throttle controls thrust and therefore lift. So both acting together have an impact on lift.

Go to the local library and see if you can get a copy of the classic "Stick and Rudder". It will explain these things much better than I can.

L

feep

One thing that I have noticed at our field is that most pilots have a tough time with their approach because they are wary of the trees at the far end of the field. Most pilots are far too high on their base leg because of this and either do not throttle back until final or throttle back and when they make their turn for final, they lose too much altitude and overcorrect with elevator,flair the aircraft and follow it with a dive for the runway. One way to correct this is to get a sense for the distance and the best way I have found to do this is to have someone out at the edge of the tree line. When you fly over their head they will wave. After I had done this, I had the confidence to fly around the entire field at waist height, and it allowed me to make my final from a much lower altitude and control my desent with trottlle.

RevGQ

Trimming the airplane: this is a personal preference thing, but I like the author of the statement above like my trainers trimmed for level flight at 3/4 throttle and my low-winged warbirds at 1/2 throttle. I think it is a comfort zone thing when one finds himself in trouble. We back off of the throttle and attempt to get the plane to settle into a stable flight.

The landing using throttle vs elevator, well I think if I were flying the full scale puppy I would defer to my full scale pilot friend, since I have never had the pleasure of flying full scale, but fully understand the wisdom of accepting instruction, particularly when my *&& is on the line. However, I think the model airplane is a different beast to tame as one is not sitting inside the cockpit. Outside of the cockpit I rely heavily on the sound of the engine and prop and the visuals of perception of the planes altitude. As I set the plane in a landing pattern, I attempt to get the plane to fly several click of throttle beyond stall holding it altitude untill I decrease throttle momentarily to set a decent rate that will bring me in at the proper glide-slope. The way I describe it here is not technically correct, for I am not a pilot, but it works. Another way to describe my approach is like flying a plane in on flaps. On flaps, you can maintain an altitude by utilizing the throttle. When you decrease throttle in small increments, you set the rate of decent. If you need to lengthen the touch down at this point, you simply add throttle enough to maintain altitude without climbing.

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poppy2

As a novice, I think that understanding what an airplane will do will help you in take offs, flying, and landings. I have taken some notes over time, mostly from the book by Robert T. Motazedi, "Beginner's Guide To Safe and Easy RC Flying", and a few other places. I have got to keep it as simple as I can get it. I have read some information that gets way over my head and I get nothing from it. These are the notes that I have and if it can help any one else, amen. If any one can clear some things up for me, amen.

THRUST--Force generated by spinning propeller, which propels the airplane forward.
DRAG--Property that results in slowing down an airplane. There are two types of drag: parasitic and induced.
LIFT--Force that is generated by a wing as it moves through the air, resulting in the airplane raising against gravity.
WEIGHT--Downward force of an airplane resulting from the pull of gravity.
YAW--Effect of rudder control, resulting in turning the nose of the airplane to the left or the right.
ROLL--Effect of ailerons which cause the airplane to rotate around its longitudinal axis.
PITCH--Degree of nose up or nose down from level to the horizon.

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 the 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 increased 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 the angle of attack is decreased, the plane will decend.

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

If the angle of attack becomes to great, the wing suddeny loses lift and is said to stall.

This information is for a trainer with a dihedral wing. How it may differ for other planes, someone my comment on that. I am far from an expert. I am a novice learning to fly. These are notes that I have taken that seem be true. Again, if it can help someone, great. If someone has some corrections, great. I just need to keep things as simple as I can get them.


Poppy2

RC_Fanatic

My Feedback: (1)

Hmmm. I think left aileron gives right yaw because if the induced drag. That's why you use differential.

BWooster

Poppy2, you've got it. Actually, you've got a lot more than your typical beginner, so good on you. My comments, (for what they are worth!)

Rudders will only bank an airplane with dihedral. Otherwise it is close to pure yaw control. The more dihedral, the more roll control.

Ailerons give rise to 'adverse yaw', that is left aileron will have a tendency to produce right yaw. In a big airplane you would look at the ball below the artificial horizon, and give left rudder until the yaw is cancelled. In a our aircraft, we just do it by sight. This effect is particularly noticeable at high angles of attack, and is probably the leading cause for RC crashes, in my opinion. It is caused because, all things being equal, the aileron that drops produces more drag than the one that lifts. So the high wing has a tendency to yaw out of the turn.

You can see that at high angles of attack, adverse yaw will drag the high wing below stall speed, the plane snaps in the opposite direction of the intended turn, and the airplane crashes. That is why you always make a co-ordinated turn in a final approach.

Adverse yaw can be designed out of an airplane in a couple of ways: differential throw - more up than down (originally used on the Tiger Moth) or ailerons that when deflected up, protrude slightly into the airstream on the underside of the wing.

L

poppy2

Snitch-

Thanks for the comments.

I am aware that the rudder will only bank a plane with dihedral. At the end of my post I tried to make it clear that the information I was giving was for a plane with dihedral wings. Your information is right on. OK on the averse yaw. On my Superstar 40, one aileron goes up more than the other one goes down. In the manual, it states that the reason for that differential is to prevent the adverse yaw. It must work, because my plane does make a nice smooth turn with no adverse yaw.

Now if I can just take some of this knowledge from my head and transfer it to my thumbs, I would be very happy. The nerves seem to be my biggest problem. Some day it will all come together I hope.

Thanks again for your help. I can use all that I can get.


Poppy2

aerospot

The above stated method made learning landings much, much easier for me. It took the thought process away from the control reversal and made it automatic. I still use it to some degree today even if I only turn my body slightly in the direction of flight. Thumbs automatically move the sticks the right way...
This was the biggest obsticle that I had to overcome in learning to fly RC. And the old timer who taught me was constantly yankin my shoulders around to put me facing the direction of flight.
Dave

MajorTomski

OK Poppy, you ARE following what he said exactly!

ALL airplanes can be trimmed to fly level at only ONE particular airspeed or power setting. In the case above trimming for level flight at 3/4 throttle will result in the airplane flying at one trimmed airspeed, just for example let's say 40 MPH. In the trimmed state all of the forces are balanced. If we add a little more power, the airspeed will increas slightly, the wing will create more lift because it is moving faster, the tail will create more down force because it is moving faster, and the combination of these new forces will cause the airplane to nose up into a climb. It will continue to rise until power and drag balance out again and the airplane will be climbing at the trimmed 40 MPH. Now reduce the power to idle, the plane will nose down and accellerat untill the trimmed airspeed of 40 MPH is reached again.

This is a series of confidence building flights done by 1:1 scale pilots in the commercial course. Learning that a trimmed airplane will hold a given trimmed airspeed.

To slow down from a given trimmed airspeed, add up elevator. To speed up add down elevator.

t

poppy2

Major Tomski-

Thanks for the comments. Excellent explanation. To maintain level flight and speed up or slow down, you have to offset one action with another, or one force with another.


Poppy2

Semi Retired Aviator

It may have been said already, but if not, practise on simulator until you can land 20+ times without difficulty or mishap.

Using a simulator, try taking off, climbing not too steeply for about ten seconds, closing the throttle, roll inverted, pull through and you'll be lined up on the opposite runway. This saves time and really sharpens your skills.

I have a friend who practised on a simulator before actually flying an aircraft, and his progress was much faster than mine in the learning stage.

wtb3886

Greetings Poppy 2 :-)

There are a few things that need to be in place before you can have a good landing.

Proper trim of elevator for desired speed, Attitude of airplane (slight nose down), control of air speed, crosswind (your input to counter act).

This is the advice that a great friend of mine taught me when I was learning how to land and I have passed it on to the ones that I have taught.

Take your airplane up about 3 mistakes high and reduce throttle to 1/2, level your airplane and see if it will maintain altitude at this power setting.

If you have to adjust elevator (trim) so that it flys level.

Now come down a little lower flying the landing pattern and check to see that at 1/2 throttle you can maintain level flight throughout all 4 turns of the landing pattern.

If you have to adjust elevator (TRIM).

Now drop a little lower and in turn 3 (Final Approach) set your throttle to 1/2 and watch the attitude of your airplane on final approach, you want to see slight nose down attitude and coming down towards the end of your runway, if you are falling short of the runway add throttle (just a few clicks), if you are too high reduce a few clicks of throttle. Pratice this until you feel comfortable with your approaches.

The object here is to find out how much power it takes to maintain level flight and maintain attitude towards the landing area.

Once your airplane is over the end of your runway you want the attitude of your airplane to be SLIGHT nose down and wings level. Be prepared if the wind kicksup to level your wings or if your airplane slows down too much just add a few clicks of power.

Once your airplane is over the desired landing spot reduce power and start adding elevator back pressure, bring the nose level, watch your airplane and control it with elevator and or power until it touches down, don't forget that you have to control it until it stops rolling.

DJJ

Years ago, I was taught how to fly on a Goldberg Eagle 2. The instructor would coach me on to final and then kill my engine from the transmitter. I was forced to land and believe it or not, really helped me.

As far as I'm concerned, landing is still the most difficult for me. Because we stand about 8' from the runway when we fly, I try to align the plane towards me when on final. It's much easier for me to set it down where I want to when I do this.

As said by other posts, all planes are different. I have a warbird now that is a real handful compared to the Tiger 2 that I had 6 months ago.

Just takes alot of practice.

-DJJ