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Trimming For Landing

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Trimming For Landing

Old 09-03-2005, 09:28 AM
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chuck l
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Default Trimming For Landing

How many of you readust your elevator trim for landing an plane? I have a Sig Sun Dancer that is giving me some problems landing. It won't slow down and if I use the elevator to slow it down, the plane moves around too much, nervous thumbs. Last time out, I slowed the plane and retrimmed the elevator for level flight. This resulted in a much better landing. I'm thinking about putting an elevator offset on a switch for the slower flight.

Any comments or suggestions?
Old 09-03-2005, 12:49 PM
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BMatthews
 
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Default RE: Trimming For Landing

On my sailplanes the elevator trim function is a major flight control and sees almost as much use as the main sticks. I brought that habit over to my power flying as well. To help out you need to add a longer arm to the elevator trim lever. On a couple of my Tx's I drilled a hole for a snug fit on a 2-56 screw about 3/16 into the end of the lever and added a 1 inch long screw. Just be sure to choose a screw length that won't interfere with the main stick movement. Go for a 3/4 inch screw if it is an issue.

In use the screw makes it a LOT easier for the fingers to find the elevator trim instantly among the front panel "Brail clutter" common on today's molded plastic Tx's with their copious amount of bumps and widgets. Once you get used to using a couple of clicks here and a few there it'll become easy to manage.

BUT!.... just be aware that an aborted landing and power up to go around again will likely require you to hold some forward stick pressure if you let the model speed up too much. You can get around this during an aborted landing approach by only powering up to max for a split second and then back to about 1/3 or 1/2. The idea being to accelerate quickly from near stall to a safe low speed cruise but then cut the throttle back to just hold that low speed cruise for the new approach until it's time to cut to idle. The nose up effect is speed related so if you don't make the model go FAST it won't want to nose up as hard. You don't want a lot of speed in the approach pattern anyway, just enough to be comfortably over the stall speed.

My latest Tx uses click type computer trims. That means I can't tell where the trim is at any particular point without looking down at the display. Time will tell if that works out for me and my elevator trim lever mod. I certainly means I need to double check the trim position before each flight while my eyes are still free to look down at the display.
Old 09-03-2005, 05:27 PM
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Geistware
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Default RE: Trimming For Landing

I am not sure how you use the elevator to slow the plane down. Are you flaring early? I attempt to land without flairing. Set up a gentle slope and adjust the decent with the throttle.
ORIGINAL: chuck l

How many of you readust your elevator trim for landing an plane? I have a Sig Sun Dancer that is giving me some problems landing. It won't slow down and if I use the elevator to slow it down, the plane moves around too much, nervous thumbs. Last time out, I slowed the plane and retrimmed the elevator for level flight. This resulted in a much better landing. I'm thinking about putting an elevator offset on a switch for the slower flight.

Any comments or suggestions?
Old 09-03-2005, 09:54 PM
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chuck l
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Default RE: Trimming For Landing

Geistware,

Sounds like I wasn't real clear in my original post. I'm slowing down by reducing the throttle, but as that is done, the plane loses altitude unless up elevator is held. Thus my question, does anybody mix in some up elevator on a switch so you don't have to hold as much up elevator with your thumb? Again, I have somewhat nervous thumbs, although I'm working on relaxing them more, along with using exponential. I do adjust altitude with throttle.

I'm trying to avoid trimming the elevator with the elevator trimming slide. I can see forgetting to reset the trim before taking off again and having a steeper climb out than expected. Not a big deal, but just trying to make better landings.

Chuck
Old 09-03-2005, 11:33 PM
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WS
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Default RE: Trimming For Landing

I have attempted to teach this method to new pilots with mixed results. On one hand, it does give much better control over airspeed and more solid, consistent approaches. On the other hand, to go around, you have to be VERY careful as the plane will have a tendency to climb very steeply and possibly even stall upon adding power. In order to prevent that, your thumb has to come off the right stick to retrim. Or, you can reach over with your left thumb, but that means loss of rudder control, which is not good at slow speed/high power either.

While full size pilots use that technique, they can keep their hands on the controls as they trim whereas our transmitters don't make it easy. I find that just holding the elevator during the approach works well, but takes some practice to keep it in place as you manipulate the ailerons.
Old 09-04-2005, 05:42 AM
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65 Chevy
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Default RE: Trimming For Landing

Hello Chuck,
I have two models set up with a !QUOT!landing!QUOT! set up. I use a switch to turn on flaperons and have positive elevator mixed in with the flaperons. It does take a few flights to get the flaperon setting and elevator mix programed, but the results are well worth the trouble.

The plane that got me into doing this is an Aeroworks Edge 540 T. With the dual tapered wings, it could easily turn into a racer for landing. It is a great flying plane but really needed some speed for landing. By applying small amount of flaperons and mixing in elevator, I was able to make this plane into a kitty-cat for landings. It really floats in nice and gentle like a big trainer.

Start with maybe 10 or 12 degrees of flap and 6 or 7 degrees of elevator. This will allow you to adjust the ratio of flaperon to elevator to control sink rate and landing speed. I try to adjust the flaperon and elevator to a point to keep the plane level or slightly nose down at three to five clicks above idle. Then you can add more or less flaperon and or elevator to get a speed you like for landing. By doing it this way, you can either just power up when you abort a landing and the plane is still very controllable, or you can just hit the switch and turn everything back off for the go around.

This way, you don't have to readjust trim for power out.
Old 09-04-2005, 07:02 AM
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Geistware
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Default RE: Trimming For Landing

I would again, recommend that you set a good glidepath and adjust the decent rate before touchdown with throttle. It is very easy and to me looks cool.
Old 09-04-2005, 07:26 AM
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65 Chevy
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Default RE: Trimming For Landing

Geistware ,
Are you completely against the notion that there are alternatives to simply using the throttle?
If so, I know of many aircraft that would be difficult to land gracefully. Many scale type models and other models that have above average wing loading, thin and / or symmetrical wing profiles, do not just glide in with a shallow sink rate. I though the reason for a forum was to be able to offer several possibilities to solve a problem or address an issue.
Just my opinion
Old 09-04-2005, 08:02 AM
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Johng
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Default RE: Trimming For Landing

There is nothing wrong with adding an elevator offset to a switch for a landing mode. In my case, a Funtana, it gets too slow with power off, so I add a bit of down elevator to create a "landing mode" along with a little spoileron.

If you do add upp elevaor, you do need to remember to swich it off when adding power, or you can have problems with pitching up or stalling.
Old 09-04-2005, 10:28 AM
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khodges
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Default RE: Trimming For Landing

For my nickel's worth, I agree with Geistware-- learn to land with the sticks, instead of depending on a setup with the radio. All it takes is practice, and eventually you'll be a much better pilot for it. It gets too easy to depend on the special mixes, however much it makes the plane easier to fly. I used to mix rudder with aileron to make turns smoother, but found I didn't know how to use the rudder control as well as I should for other circumstances, so I took it out and just learned to use the rudder.

But if you insist, try making a custom mix that changes your elevator trim with throttle input. Not sure it's possible with all radios.
Old 09-04-2005, 11:12 AM
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AlexF
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Default RE: Trimming For Landing

Could it be that the plane would fly better with a little more downthrust or tailweight? I'd expect either to reduce your trim change -- worth a shot if you haven't tried it yet, maybe.
Old 09-04-2005, 02:22 PM
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rmh
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Default RE: Trimming For Landing

I can understand the original question-- the business of computing a glide path is simply very hard for newer flyers to grasp-- Anymore , when someone runs out of fuel in the air - I can usually direct them to a proper descent path -for a proper runway landing -Instantly--- It did not happen overnight.
The usual errors are:
A trying to park it in the air
or B- dive to the runway then pray for good brakes.
Downthrust/tailweight -whatever you try---- each model is a case by case setup and there is no "perfect landing' trim setup.
The best setup is very old -- treat each landing as a go around - and practice till the go around is a relaxed event. It will soon become automatic as to what the best approach speed will be . also the best rate of descent.
Forget trim setups - they will bite you.
A dual rate elevator setup is handy if you use either extemely low or high flying rates (speed setup or aerobatic setup). select a moderate not really low - elevator ATV
A s a general rule - learn to carry solid, controllable flying speed to threshhold of field -at a low altitude- then by slowly reducing power , allow model to settle - NO FLARE! then apply power and fly away with little or no change in elevator.
Once this all seems familiar, change the approach rate (descent ) slowly at first -till the power control become automatic.
Trying to control the touchdown with elevator is really hard to learn.
First learn to control that descent rate. (sink)
Old 09-04-2005, 03:08 PM
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BWooster
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Default RE: Trimming For Landing


ORIGINAL: chuck l

How many of you readust your elevator trim for landing an plane? ....
For what it's worth, I do. If I change the throttle, I change the trim.

Once you get used to it, it becomes automatic, like using the rudder.

(I don't own a programmable radio either!)

Old 09-05-2005, 10:15 AM
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Johng
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Default RE: Trimming For Landing


There are other ways to make landing easier as well. You might try a flatter pitch prop. Flatter pitch creates more thrust power on, and more drag power off, with a possible downgrade of top-end speed. I always use as flat a pitch as I can and still have speed and climb balanced. I have made some pretty slippery landers much better behaved with just a different prop and tuning the low end mixture to allow lower idle speed.
Old 09-05-2005, 11:24 AM
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Default RE: Trimming For Landing

Just hold some back tension (pull!) on the elevator stick to hold the nose of the plane above the horizon (maybe 5-10 degrees). The plane will not climb, it will sink at idle. Add a little more power to slow the descent. The key is holding the tension on the elevator stick. Most pilots I coach are afraid to hold the elevator, they pull tension and then quickly let go back to neutral. You need to keep holding the tension!
Old 09-06-2005, 08:40 PM
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Default RE: Trimming For Landing

The biggest thing to realize on these rockets that scream down the glide path is that they can be landed with several methods. Some people dive them down early and hope that a more level attitude near the ground way out there will bleed off the airspeed in time. Sometimes it does. Most of the time, it seems that turning final and holding a level attitude until the plane slows down to settle into a nice glide is the best method. If I dive my pattern plane it won't lose airspeed. I've had the engine quit a bit close to the ground when vertical for a stall turn and all I had to do was put the nose down and it took off fast. But, if I hold the nose up level on final it will lose airspeed and settle into a very nice glide on its own. I just stay off of the sticks until time to flare at the bottom if there is no wind.
Old 09-06-2005, 09:17 PM
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chuck l
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Default RE: Trimming For Landing

Thanks for all the responses, they have been quite helpful. I was out practicing approaches and landings tonight and am getting a better feel for holding up elevator to slow the plane and maintaining altitude with the throttle. I still need more practice, but you convinced to not mess with putting up elevator trim on a switch or adjusting the elevator trim slider.
Old 09-06-2005, 09:36 PM
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rmh
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Default RE: Trimming For Landing

Good idea - patches are just that -patches -
Fix the real issue - recognition of rate and descent.
Flying models is exactly like larning a musical instrument - you must learn the basics and then practice. short cuts and band aids can't really do the job.
Old 09-06-2005, 09:52 PM
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Default RE: Trimming For Landing

Chuck,

I think the biggest thing that improved my landings was practicing flying around the pattern at the same speed and angle of attack as the plane will fly on the approach. The key is to do this without loosing altitude. The plane kind of mushes through the air this way and you can really get a feel for the way the control surfaces become less effective at the slower airspeed. Flying inside and outside horizontal eights at this AOA and power setting is very good practice. This is really a left stick (mode two) exercise. If the plane starts to lose altitude, add a click or two of throttle. Mind your rudder when doing this.
Old 09-07-2005, 05:06 PM
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Default RE: Trimming For Landing

Hmmm. I like to fly a model the same way I fly a full-size plane. I like to have a "stabilized" approach with a certain amount of power and trim. Of course, it takes a bit of flying around and doing takeoffs and landings to the point that I find the appropriate power and trim setting for the model. But once I find that setting, then I gradually reduce power to that point where I want to start the descent from pattern altitude. Descent rate can be adjusted with power. Yes, you'll have to use the elevator stick a bit, but once you have the trim and power levels found for a stabilized approach for that model, landings become much simpler because you can concentrate on directing the model to the runway and not worry about pitch and power.

Please realize that when it comes down to making good landings, your landing will only be as good as your approach. You want the model stabilized in power, pitch, roll, and yaw as it comes down the glidepath. Some people like to use the trims to help them reach that end, others just hold the stick where they want them. The main key, as stated above, is PRACTICE! PRACTICE! PRACTICE!

Shoot a lot of landings, and you'll either discover you'll never be able to land worth a hoot, or you'll get better. Because the former is super, super rare, you'll eventually become great at making landings.
Old 09-07-2005, 08:23 PM
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Default RE: Trimming For Landing

Bax,

I was a helicopter pilot in the service. When doing autorotations you looked for 'steady state' on the way down. The aircraft would settle into a nice glide based upon airspeed and it was extremely stable at that point. I carried this over to rc planes. It seems that all of the models that I've flown have a certain profile on approach which is just like a steady state once you find it.
Old 09-07-2005, 10:20 PM
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Default RE: Trimming For Landing

A bigger prop with a low idle sometimes helps slow the heavy ones down. To get a nice approach angle it sometimes helps to use the split ailerons as spoilers and kill some lift. Set the mix to bring them up, increasing the approach angle. Most modelers assume they want flaps for a landing, when, in fact, the spoiler option works better. I use the back right slider switch on my 9C so I can raise or lower the ailerons in unison. Gives all sorts of options for lift and glide angle.

I also have the idle down set so that the engines just about burble (for spins and landing).

Otherwise, I don't trim for landing. I trim for level flight into the wind and then fly the plane "by the thumbs" thereafter. The less temptation I have to take my eyes off the plane while landing the better it works out for me. I still have the bad habit of looking down when working the trims.

Add some flying wires. That slows 'em down.
Old 09-09-2005, 11:38 AM
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Default RE: Trimming For Landing

Personally, I LIKE to set the trim for approach. Kind of like the Piper Cherokee I used to fly. When in the pattern, I'd set the RPM to 1500, add a notch of flaps and two turns of the elevator trim crank. Use the yoke to prevent the pitchdown with flap application and then let the airplane "have its head" as it stabilzed to the new configuration. No pressure needed on the yoke to hold the trimmed airspeed, just to take care of osciallations caused by gusts.

With a transmitter like the 9C, you can set an offset mix that will give you just the right amount of elevator trim you need for the landing approach you prefer. When you get on downwind, retard the throttle, flip the switch, and use the stick to keep the model from pitching until it stabilizes at the new airspeed. Use throttle to help control the descent rate, and you're golden...just one thing less to worry about.

I set up switches so that all forward is for takeoff or go-around.

Just one man's opinion.
Old 09-09-2005, 09:32 PM
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Default RE: Trimming For Landing

I have a 9C too and it looks easy, like you said. However, I'm surprised you aren't flying with the 14MZ, Bax.
Old 09-10-2005, 12:00 AM
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Default RE: Trimming For Landing

There is no substitute for practice. I like shooting touch and go landings. My oldest airplane has 445 flights and no doubt more than 5K (more likely closer to 10k) touch and go landings over that time.

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