wagen017

I think it would make sense if within one thread we could collect all trimming tips, charts and other information. For newbie's, sort of newbies and all others, that could be really helpful.
Also everybody can then ask their trimming questions in this thread.

Then maybe if the collected information really makes sense, this thread could become a "sticky" in the pattern forum.

A good idea?

Volkert

wagen017

This would be my first link to post. I personally would read first the midpart by Buddy, then the chart and then the comments by Chip Hyde. Very helpful!

http://www.rcaerobats.net/trim_chart.htm

wagen017

Next could be this by Peter Goldsmith:

http://www.mini-iac.com/Portals/57ad...20trimming.pdf

wagen017

This is a bit more basic article, but might work as well:

http://www.modelflying.co.uk/news/ar...82933320374342

wagen017

Then this short but also very helpful article by Don Szczur

http://www.horizonhobby.com/Articles...ArticleID=1194

mjfrederick

Bryan Hebert's trimming guide, edited by me for publication in the K-Factor. A little caveat (pronounced cav-ee-ott for those who aren't aware) to all who want to learn from the guys who post here: don't trust anything you read unless you can reproduce the results, and if someone tells you to add mix in their trim guide it's an indication that they gave up on perfection... or the designer did.

[link=http://www.hebertcompetitiondesigns.com/Triangulation.html]Triangulation Trimming[/link]

apereira

Good thread idea Wagen017!

Regards

dhal22

whatever would we do if we were only allowed to use a 4 channel radio. no mixes, no expo. we might have to concentrate on flying.

david

Giln

This thread is a great idea Volkert. Thank you!
I am just starting to build aerobatic planes for IMAC and Pattern, so it's very timely for me.

Also thanks to mjfrederick. I hadn’t come across Bryan Hebert's trimming guide.

Very good material and I’m sure I have months if not years of practical application in order to become proficient at this.
I love this hobby, so I’ll enjoy every build, trim and flight however long it takes.

Regards
Gil

mjfrederick

Novel idea, huh?

MHester

My Feedback: (1)

In today's ARF world, that'd be um....interesting. back in the old days it was common to cut a wing in half to change dihedral, cut or move the stab, etc etc.

When most people today have heartburn at the idea of installing a servo, or heaven forbid gluing something, yeah this would be interesting LOL

-Mike

wagen017

Great! Thanks for the responses. I always try to tinker as long as possible to fly without mixes. I am not that intelligent I guess, so I always try to keep my flying as simple as possible (and therefore the way I programmed my transmitter as simple as possible). I am struggling with one of my models now so if by Saturday I still haven't figured out my problem, I will post my question.

I think it would be great once we have the basics covered thru the various trimming guides (which in my opinion are aides for each person individually to try to figure out what your plane is doing) people start posting their questions in this thread. This will be a big help for all that are struggling to get their planes flying.

MJFrederick, thanks for posting this great trimming info! I will read it in detail because I now find myself with an ARF with 0-0 incidence and I am struggling with it.

wagen017

Mike Hester's comment on mixes yes/no which I found in another thread. Sums it up greatly and to me a big help. Thanks Mike!

Here we go:

Welp...first of all, if you have a decent design, you're usually able to get it to darned near zero mix, depending on a number of factors, such as whether or not you have snaps and spins, how "hot" you like your set up, how much expo you can handle, etc.

Trying to answer this question is like painting with a VERY broad brush, but there are some similarites in most designs with most set ups. I may get poo-pooed for posting this, but what the heck.

First of all most people run thier CG too far back and don't have enough positive incidence. This was the trend a few years back as we transitioned from the ballistic style of flying to the more slowly constant speed larger planes. As with everything when you make a large change in total overall concept, there is a steep learning curve. A leading pilot/designer/builder made common a set up that used darned near zero on the wing, negative on the stab and the CG pretty far back. it worked, but with strange effects. Some of the problems associated with this carried over into modern day, but due to the work and guys like Bryan Hebert and myself to a much smaller extent, we're running somewhere around 1/2 degree positive on the wing, stab at zero or very close, and a much more forward CG.

This does a number of things, most good, but everything has a trade off. First it darned near nullifies mix, all lines track better, the plane is much more stable, and has a very locked in feel around neutral. This is a good thing! but we deal in balance, so here is the down side.

You usually end up running a good deal more throw for snaps and spins, but they do land much cleaner with a LOT less displacement. And since the planes are flying slower to begin with, this "problem" is compounded by a more forward CG. So if you're able to handle a hotter set up, with more expo, there is no "problem" to speak of. Most guys that fly masters and FAI have become accustomed to this hotter set up because that's what it takes to get through the patterns with snaps, spins, etc. you can use a condition switch to alleviate some of his but it's troublesome and slightly more work.

Rolls require a little more rudder input at slower speeds with a more forward CG so this is something else to get used to.

But I will say that this general set up theory is the best I have ever personally used and is well worth getting used to. I now fly my whole pattern with no need for throwing any switches, and that is also a plus. The other is in severe wind. if you run a lot of expo, you much more likely to hit that banzai curve in the throw that sticks an unexpected and very high rate of throw at you making it very hard to correct smoothly in the wind. The less expo you can run, the easier it is to fly consistently in high wind. Generally speaking that is....

Now with all that being said, and understanding that you CAN get most modern planes to zero mix if it is a good design, some people are very uncomfortable with the "feel" of this set up and seem to need to work into it. This approach is debatable, some will tell you just jump in and learn NOW. Easy to say at this time of year, much more difficult in say, June

So...what most people do is a bit of a compromise. They use the more forward CG, but not to the fullest extent. They run higher wing incidence, but not to the fullest extent. They run higher throws, but again....not to the fullest extent. What they end up with is a fairly nuetral plane that requires very little mix for thier set up. It's not perfect but most people live with it. The more "common" mixes end up being:

1 Rudder to elevator: usually the plane being tail heavy pitches to the gear on KE. This is easily fixed for KE flight, but at hard over extremes such as a KE loop, a lot of planes need the mix removed at the ends. So they use a curve or they don't fly FAI LOL

2 Rudder to aileron mix: Less common and dpepends on design, CG, Incidences of the wing. Roll coupling. You can get this out usually by adjusting your incidence, CG and retrimming from scratch. This may affect #1 though....since this is normally offset by dihedral, a good design needs little to none of this.\

3 Aileron differential. This will depend mostly on the design of the plane and the incidence. In order to get the plane to roll axially (and not wallow), it is sometimes necessary to move one aileron more than the other. This is fairly common but not always. A good design and careful attention to linkage gemoetry and symmetry and usually this is minimal or non existant with modern planes.

4. Throttle to elevator. A lot of people experience a pull to the canopy on the downlines. usually 1-2% down E at idle takes care of this, but be warned: this is one you need to fix without mix. because it will bite you all over the place in the upper classes especially. You hit idle, inverted, the plane doesn't need as much down to hold level...speed up and it changes...go into a 45 and it changes again...get the picture? It ain't good but you can get away with a very small amount with enough practice.

5. Throttle to rudder: a plane that has a wider speed envelope and a rearward CG will experience this fairly dramatically. You trim the rudder for level cruise speed, but a downline the plane yaws right. So people mix in L rudder to idle. Again not a good deal.

6. Down elevator to left rudder: This is a rare mix but depending on the design, prop, engine, set up and everything else, the plane might yaw hard in a push such as the double immelman. Some people mix in rudder to the elevator to "fix" this. Depending on the plane and set up, I have seen it work flawlessly, and I have seen it spell unpredictable disaster. Proceed with caution.

Now here's the rub: Most very good designs end up with a very minimal amount of 1-2, and occasionally 3-4. Some have mixes numbering in the teens and more...and some are unmixable/untrimmable due to inherent flaws in the design. if you're not flying the FAI finals sequence, you can get away with a lot more mix and a much less "perfect" airplane, but if you ever intend to fly on that level, you're not doing yourself any favors. 5-6 are usually sign that you have pretty severe problems elsewhere, and might be due to set up but more likely design.

So if I have any "advice" it would be the same as you're likely to hear from many others.

1. Take the time to properly trim the CG, incidences and engine thrust. if you do this your mixes will be minimal to non existant.
2. If you still have a few strange characteristics, go back and repeat step one.
3. Repeat step one again for good measure.
4. Add mix as necessary...but it needs to be VERY minumal and you need to fly your plane through everything imaginable to look for unintended consequences.
5. If after doing this you find the plane just "feels" too nose heavy or hot on the sticks, back off and compromise SOME for the time being until you get used to it...then at a slightly later date, ease back into it and "retrain" yourself.

Now anyone who wants to paint a broad brush and say "if a plane isn't perfect you gave up" or "there's no such thing as perfect", I'll go ahead and concede that you're both right. But I believe the best set up is the one you can fly and make it look good doing it....and the more "true" your plane flies, the easier that becomes. Start down the road to perfection and never give up and never get lazy or complacent. You don't HAVE to do it all in one swift stroke, but it's easier on you if you take as many steps on that journey as you're capable of. if some of this sounds contradictory, it's because it is. We're dealing with balance, and a changing balance at that. As your skill improves so will your "feel". What feels great to you today may not feel so great after a couple hundred flights. Do what is necessary to fly that elusive perfect sequence. And remember, the fun and reward is in the journey, the destination is it's own reward.

-Mike

_____________________________

Owner Custom Airframes of America, Team YS, Mercury Adhesives

EDIT: here is the link to the original post: http://www.rcuniverse.com/forum/fb.asp?m=8077510

wagen017

I must say for me the trimming info of MJFrederick was an eye-opener. And also the other threads currently running about mixes and downlines.


So this was the question why I came up with the idea of this thread.

Today I applied the lessons on 0-0 incidence setup and as a consequence had to dial in some mixes to get this right.
I first set the CG back forward again.
As a consequence my KE on left rudder pulls to the belly and my KE on right rudder pulls to the canopy. I guess then I am at optimum what I can reach (without changing incidence) and put in a rudder to aileron mix to compensate. I set it up so I can switch on/off this mix.
I had to dial in aileron differential to get more straight rolls.
I had to trim the rudder a bit right to get a straight upline and mixed in some left rudder for straight downlines at idle. For this I assume I can fix this by putting in some more right thrust.
I already have some Gator Incidence adjusters, so when I have some time I will put this in so I can adjust the wing incidence. As a start I will put it at 0,5 degrees positive.

Thank you all for all info, now I can go ahead.

One thing is maybe an interesting question. I measured this plane in every way I can imagine and am pretty sure it is straight. The feedback I have sofar it "tracks like on rails" etc. Now we all know this is internet and you never know for sure until you have seen it yourself.
However, this plane claims to be a hybrid electro/glow. In my opinion it is setup as an electric. Hence these guys fly with 17 or 18'' props. How will this effect the plane's behaviour? Can this explain why I am having trouble? I fly with an APC 14x10.

Volkert

Jetdesign

My Feedback: (8)

In relation to trimming, what are some recommended tools for measuring throw and incidence? I'm looking for my first set - want something pretty decent without breaking the bank, and was thinking of the AnglePro - good choice?

rcpattern

My Feedback: (45)

I've heard good things about that. The old Robart Incidence meter is still hard to beat also. The biggest thing is get it really close. You'll dial things by following the trimming charts. The throw meter from central hobbies works well also,

Arch

Giln

I have been a little dissapointed with the Anglepro.
Two issues:
- For throws - the meter itself is quite heavy and is only useful for large models, the larger the better. For smaller models the weight of the meter distorts the measures when clipped to the control surface.
- For incidenence of surfaces it works well eccept where one needs to use the bar and clamps these are not easy to set up accurately. Again, weight on the aileron / elevator can distort the picture somewhat (a couple of degrees) when really one is looking for fine accuracy.

On a positive note, this is useful as a precision level tool wher the surfaces one is measuring are stable - thrust angles etc.

If anyone has found a good way/technique to use this tool to set throws on smaller models please let me know.

Regards
Gil

wagen017

Gil, don't know about the AnglePro, I am using a Robart Incidence meter.

So, finally made my first step and changed the incidence on the wing to +0,5 degrees. When flying had to adjust the elevator trim only slightly. Downline is now perfect, upline seems OK as well. Problem with Knife edge still exists. So next step is to get the CG more forward.

Volkert

wagen017

The weather has not been really helpful here [:@]. Anyway, I still had one servo in the tail. I moved this forward and installed pull pull for both elevators and rudder. Today went flying.

Results: zero pull on left rudder knife edge; some pull at right rudder knife edge to the canopy. So this is already much better then before! For now I dialled in 3 "degrees" down elevator to compensate.

I dialed in 20% aileron differential for axial rolls.

So, all in all I am happy with this progress. Have to reread some stuff to see if I can do some more progress then this.

Volkert

Jetdesign

My Feedback: (8)

So how does CG actually affect KE flight? Is it because we have the plane trimmed for level flight, and in KE we're feeling the effects of the trim? Another way of asking this is, if we moved the CG around but kept everything else (trim) the same, would the plane exhibit the same KE behaviors?

In my head, I can't see how moving the plane's CG fore or aft, during KE flight, would cause it to pull or push.

MTK

Arch,

Get yourself a Height Gauge from Harbor Freight. Simple and inexpensive tool that will get you unprecedented set-up precision.

Once you have the fuselage prepared, just set the fuse on the flat surface and reference from there.

Soon you will find more uses for a HG. Example- wing, stab or control surface flatness. The precision is limited only by the thickness of the reference line you draw on the various parts. I use a drafting pencil with a 0.25 mm tip, producing a line that is around 0.010" thick. The HG scribe will split that line for a precision of .005".

If one builds a model with 5 thou precision, many weird trim issues go away.

The caveat in all this set-up stuff is and always has been this: an average trimmed model with mixes galore in the hands of great pilot, will still look great. Great ploting will always trump mediocre trim and vice versa

mjfrederick

The short answer is yes, it is because of all the other things an aft CG causes to change in the force arrangements that make CG impact knife edge flight. For example, take an airframe that is trimmed for straight and level flight. Change nothing else but move the CG back a few inches. When you try and fly staight and level now, the plane will want to climb because the tail is being forced down (just like with up elevator application). So you put in down elevator trim to bring the tail back up and have plane fly level. Now that the airplane is flying level, roll to knife edge. Now what that aft CG is doing is making you require less rudder to hold the knife-edge. Sounds like a good thing except the down elevator trim you put in to fly level is no longer having to counter-act the CG shift, so what is it doing? Making the airplane tuck to the belly on the knife-edge. Me, I'd rather have to use more rudder than mix-out the tuck.

Jetdesign

My Feedback: (8)

I'm glad it's that 'simple' - I thought I was missing something, of course I haven't taken any aero classes, yet...

Thanks.

guille2006

Here is a valid copy of the triangulation method. A very nice reading for this winter!!!!
Hope it's usefull for everyone


Cheers
Guille

lablover

Great thread for newbies like me...Lots of good info here so far.