Trimming an Aircraft With Flaps

[Dallas Moore]

Sorry, I'm sure this question has been asked more than a few times.
Today I was flying a new airplane with flaps.  On the second flight I really started looking hard at its attitude and control surfaces.  I couldn't tell much about the flaps, but in level flight, the plane appeared level, but there seemed to be a slight amount of up elevator.  Does this mean I need to adjust the elevator down a slight amount in relation to the flaps?
Thanks,
Dallas

[Paul Taylor]

Start here.

http://flyinglines.org/pw.trimflow1.html

[John Carrodus]

Hiya Dallas
    Have you checked that your flaps and elevator wre perfectly aligned in nuetral, ie both are running parallel with the centreline/datum line/thrustline?

[Dan McEntee]

Start here.

http://flyinglines.org/pw.trimflow1.html

   What Paul said, plus ad in that a helper outside the circle watching the airplane can see things you can't because you are so focused just on the airplane flight path. Several passes at shoulder level looking at it as it is coming at them and then going away will tell a lot. What happens when it runs out of fuel? How does it transition into the glide? If you have to give an elevator input one way or the other then someting is off a bit.
   Type at you later,
    Dan McEntee

[Mike Scholtes]

A wing with a symmetrical airfoil needs to fly with a slight positive angle of attack in order to generate lift opposite to gravity. I would guess that this model needs to fly slightly nose-up whether inverted or upright in level flight.

[Motorman]

If the flaps are neutral or slightly up with a neutral elevator then the plane will have to fly nose up to stay in level flight and it will need up elevator to do that. If you want it to fly straight and level, adjust your flaps to be slightly down when the elevator is neutral so the wing has more lift. Or, could be your plane is just dang nose heavy.

MM

[Dave_Trible]

I'd guess (all you can do without seeing it) these last two responses are pretty close.   If the airplane is flying steadily upright and inverted "in a groove" without hunting up and down or needing much correction then I'd just ignore how the elevator appears to you from the middle of the circle.   If the flap and elevator neutrals are not aligned the airplane will fight staying in a level groove and readjusting those neutrals will improve the flying.   Indeed if the airplane is extra nose heavy a touch of elevator may be required to hold the nose up.  Also if there is any down thrust in the engine it might need a little up elevator when upright but not so when inverted.  I'd be more interested in how the airplane is flying rather than anything else.

Dave

[Ken Culbertson]

What Dave Said.

Ken

[Dallas Moore]

Start here.

http://flyinglines.org/pw.trimflow1.html

Thank you.  I've read this several times trying to get a good understanding.  For a newbie there's a lot to it. 
Things were so much simpler more than 50 years ago when I was 14.

[Howard Rush]

You are getting some misinformation.  A symmetrical airfoil needs to have the leading edge higher than the trailing edge to have lift in level flight, but flaps bias the relationship between lift and level-flight pitch angle so the wing could be level or pointing up or down in level flight. Which way the wing points is also a function of speed, air density, and airplane weight.  Don’t worry about it.  In Paul Walker’s Criterion 5, if I interpret it correctly, you fiddle with the elevator deflection relative to flap defection until the level-flight pitch angle is the same upright and inverted.  For most flapped stunt planes, this angle will come out close to zero.  For sure, don’t worry about what elevator angle it takes to get there.  When my airplane's flaps are centered, the elevator is 4.5 degrees down.

[Mike Scholtes]

Not to be argumentative, but the OP was trying to understand the seeming conundrum of why a model in steady level flight would need to have some up elevator in order to maintain altitude. The answer is always going to be "a symmetrical wing needs to have a slight positive angle of attack  in order to produce lift in a direction opposite to gravity." Certainly the chord line from leading edge of wing to TE of the flap with the flap deflected can produce that positive AOA even with the wing not "level" (i.e. chord line of wing ahead of hinge line parallel to horizontal), but that may be too much theory when trying to understand the basic principle. As Howard notes, the best thing is always to go to Paul Walker's trim articles. I think I learned from Ted Fancher that in a traditional stunt ship the TE of elevator will normally end up with slight down with flaps at neutral.

[Howard Rush]

The line between the wing leading edge and the flap trailing edge has no physical significance.  It is not the line that, when parallel to the horizon, gives zero lift.  One could use it as a line from which to measure angle of attack, but we don't, because using the line between the leading edge and trailing edge of the part that's fixed to the fuselage as a reference is more convenient. 

To answer the original question regarding what to do about the elevator deflection, I would look at elevator deflection as a dependent variable.  It takes whatever it takes to make the airplane hold still.  Elevator deflection needed for level flight is whatever it takes to make the sum of pitching moments (torques) equal zero. Usually, it mostly balances the moment caused by the airplane's weight pushing down farther forward than the airplane's lift pushes up, hence Dave's comment about forward CG needing more up elevator, but there are other moments in the mix.  It gets even more fun in maneuvers.

[Dallas Moore]

Thanks everyone; I appreciate your input.
This question was probably better suited in the Handle section.  Let me try to answer some of the questions/comments.

This plane is precisely balanced at the recommended CG.  I don't believe it's nose heavy.  I don't remember having to make any significant control inputs when going into the power off glide.  It seems to glide well, and lands well. 
I don't have anyone to help me; just the wife to release.  She has no idea what she's looking at.  She's made videos and some snaps.  I haven't looked at them yet.
Last week I took it up for the first time with a partially filled tank.  It took off nicely, stable, but responsive with good line tension.  I only made 3 to 4 laps before it ran out of gas and glided to a decent landing.  I was thrilled, but it was getting dark and didn't get anymore time with it.  Yesterday I got two full flights out of it.  I think it flies nicely, but.....

Now something about me.  I flew C/L when I was about 14, but never got to inverted, loops, etc.  Last year I had my first C/L flight in more than 50 years with a Sterling Beginners Mustang I built.  It was fun and brought back some good memories.  I'm a good builder, and am amazed how I threw these things together, with almost no thought about CG, leadout rake, or tip weight, and then flew the heck out of them.  Sometimes I wonder if I now overthink, but then read these forums.
I became an Army helicopter pilot.  I have about 1200 hours in Blackhawks and about 200 hours in Chinooks.  At the risk of sounding  arrogant, I could fly the rotors off a helicopter, and have been known to fly better than others with much more experience. With that said, I have a thorough understanding of aerodynamics.  However, there's a huge difference between being strapped into the machine, and being on the outside.

Sooo, this plane I'm asking about, is not only the first plane I've ever flown with flaps, is slightly larger than anything I've ever flown, and  (other than the little Mustang I've flow 3 time in the last year) the first flights I've had in more than 50+ years.

Dallas

[John Miller]

Dallas, First, thanks for your service. There are a lot of Veterans on this site, me also being one.

I'm offering something that I use to refine the task of determining the correct trim and CG for my stunt planes. Some may disagree with me, and that's fine, but it has worked for me.

Many of the things described below are designed in or built in when I design and build my planes.

I begin with bench-top trimming my plane. I'm an advocate for 1-2% downthrust. I believe it helps reduce "hunting" in level flight.

My initial trimming "on the bench," I strive for, after checking the downthrust, wings, stab, flaps, and elevators are level in span, and parallel to each other, with no warps or twists in them is.

0-degree wing incidence and a slight positive stab incidence. Not much, usually a degree or slightly less.

I verify my flap, and elevator throws, and make adjustments, if necessary. What I'm interested in is the flap to elevator ratio, so if the plane is not a heavy PIG (1 to1 ratio), I prefer 24-26 degrees flap to 33-36 degrees elevator. Next, I want to adjust things so that I have equal up and down throws at the beginning. I try to design and-or build this in with the Bell crank centered.

I'll install about 1 ounce of tip weight, seal the control surfaces, make sure the controls are smooth, and easy, "slippery" as I can make them. Make sure the gear is aligned to keep the plane out on the lines, Taking off, and landing.

Check for any in-thrust, or rudder. If so, correct to slight out-thrust, or no in-thrust at all. I'm of the school that wants rudder at 0-0 straight ahead.

At this point, I'll begin flight tests. As has been suggested, have Paul Walkers trimming guide at hand during the flight trimming. When you are ready to start inside and outside loops with equal turn rates up and down, Look for the following happenings.

During the inside loop you should notice one of the following conditions.

1. The best one is that the plane tracks around the loop without trying to open up, or close up.  Congrats, your Cg is located correctly.

2. If it acts like it wants to open up, tries to throw the nose out, it is likely nose heavy.

3. Tightening up, throwing its tail out, then it's likely tail heavy.

This can help establish the best CG for your particular airplane.

Check with outside loops, they should react the same way.

I believe the CG indicated on the plan is a starting point as every plane built, seems to have its own point that needs to be determined.

Anyway, it works for me with most designs I've done this to, flew great with few trim changes, from the building board.

John M





 

[Dan Berry]

Where are you? Help might be close

[Jim Svitko]

He is in Seguin, a bit east of San Antonio.  There should be someone near him who can help.

[Dallas Moore]

Dallas, First, thanks for your service. There are a lot of Veterans on this site, me also being one.

I'm offering something that I use to refine the task of determining the correct trim and CG for my stunt planes. Some may disagree with me, and that's fine, but it has worked for me.

Many of the things described below are designed in or built in when I design and build my planes.

I begin with bench-top trimming my plane. I'm an advocate for 1-2% downthrust. I believe it helps reduce "hunting" in level flight.

My initial trimming "on the bench," I strive for, after checking the downthrust, wings, stab, flaps, and elevators are level in span, and parallel to each other, with no warps or twists in them is.

0-degree wing incidence and a slight positive stab incidence. Not much, usually a degree or slightly less.

I verify my flap, and elevator throws, and make adjustments, if necessary. What I'm interested in is the flap to elevator ratio, so if the plane is not a heavy PIG (1 to1 ratio), I prefer 24-26 degrees flap to 33-36 degrees elevator. Next, I want to adjust things so that I have equal up and down throws at the beginning. I try to design and-or build this in with the Bell crank centered.

I'll install about 1 ounce of tip weight, seal the control surfaces, make sure the controls are smooth, and easy, "slippery" as I can make them. Make sure the gear is aligned to keep the plane out on the lines, Taking off, and landing.

Check for any in-thrust, or rudder. If so, correct to slight out-thrust, or no in-thrust at all. I'm of the school that wants rudder at 0-0 straight ahead.

At this point, I'll begin flight tests. As has been suggested, have Paul Walkers trimming guide at hand during the flight trimming. When you are ready to start inside and outside loops with equal turn rates up and down, Look for the following happenings.

During the inside loop you should notice one of the following conditions.

1. The best one is that the plane tracks around the loop without trying to open up, or close up.  Congrats, your Cg is located correctly.

2. If it acts like it wants to open up, tries to throw the nose out, it is likely nose heavy.

3. Tightening up, throwing its tail out, then it's likely tail heavy.

This can help establish the best CG for your particular airplane.

Check with outside loops, they should react the same way.

I believe the CG indicated on the plan is a starting point as every plane built, seems to have its own point that needs to be determined.

Anyway, it works for me with most designs I've done this to, flew great with few trim changes, from the building board.

John M

Thanks John, I appreciate your insight. 

[Dallas Moore]

He is in Seguin, a bit east of San Antonio.  There should be someone near him who can help.

👍

[Dallas Moore]

Again, I amazed at how, as I 13/14 year old kid I managed to throw these planes together, and fly the crap out of them.  Ignorance is bliss?
Of course the art and science with C/L has come a heck of a long ways since 1973.

[Jim Svitko]

You are not alone there.  When we gathered to fly on a Sunday afternoon, many years ago, the planes were mostly kits, built just as shown, with no measuring for proper placement or alignment of components.  After all, we figured it was a kit, it should be right, all the positions are marked.  Yeah, right!  It is a wonder we got them to fly more than a lap without crashing.

[Dan McEntee]

Again, I amazed at how, as I 13/14 year old kid I managed to throw these planes together, and fly the crap out of them.  Ignorance is bliss?
Of course the art and science with C/L has come a heck of a long ways since 1973.

    Well, if you did follow the instructions, they would fly!! Most kits seemed to be engineered and designed with a slant towards safety and almost guaranteed success. As you progressed, at that time, think what you could have done if you had what beginners have now with the internet?? A lot was in the magazines but not everyone bought those or could sit still long enough to really read what Bill Netzeband, Larry Scarinzi, or Jack Sheeks and many others had written. The rest of us just went through the school of hard knocks!!  I think this is to our advantage, though. If you have any memory of what things were like in your younger days and how planes and engines flew and performed, you are already a leg up on anyone else just discovering now you get to start splitting the air a little finer and find out things that you didn't even know back then!! And still have a lot of fun along the way!!
   Type at you later,
   Dan  McEntee

[Steve Helmick]

My advice is to keep trimming, which means tweeking everything between the control handle and the outboard wingtip ...everything! Certainly be able to return to the previous setting, but keep adjusting one thing at a time. What doesn't work will still be a valuable lesson. If/when you can fly the full pattern, DO THAT on every flight if/when it's safe to do so.

1) If the model doesn't want to glide most of a full circle, the CG is likely too far aft, OR the flaps are UP at neutral elevator. Observe when the engine quits...if the nose pitches up or down. 
2) Propellers can be magic or paint stirring sticks.
3) Handle type and neutral setting is HUGE, so a dedicated set of lines and handle for each airplane is a basic requirement, if you want to get better. Though some guys apparently don't care to get better? What I do know is that the better the model flies, the longer it will last. 

And thanks for your service! Any chance you knew Pete Bergstrom from your Army heli days?  Steve

 

[Dan Berry]

Make a trip to Katy Texas and get first hand help.
An expert outside the circle is the best thing you can get