bench trimming galaxy

[scott matthews]

Hello everyone , the galaxy is finished and I was wondering how to bench trim it.It is very nose heavy when using the CG on the plans.I started stacking weights on the stabilizer to balance it and I'm quickly up to 1 oz. Is this abnormal or am I just getting freaked out because I would be making the plane heavier? I would really like some guidance on a straight forward article for bench trimming to help me.The current set up I have is a OS 25 LA,9x6 apc prop ,Factory muffler,3 oz tank and plastic spinner from Brodak. The plans also call out a 1/2 of weight in the wing tip, When the plane is up side down and you push down on the in board tipand release it falls pretty quick to the out board side.One last question how do you post pictures, when I go to additional options and click browse, I open my picture in Windows Media Player and click open and it attaches to the browse area then when I click post I get an error message that says the post times out.Any help is appreciated , thanks Scott

[RC Storick]

You are doing it right but the pictures are too big or the wrong format.

[Tim Wescott]

Hello everyone , the galaxy is finished and I was wondering how to bench trim it.It is very nose heavy when using the CG on the plans.I started stacking weights on the stabilizer to balance it and I'm quickly up to 1 oz. Is this abnormal or am I just getting freaked out because I would be making the plane heavier? I would really like some guidance on a straight forward article for bench trimming to help me.

Trim to the plans.  I've got an own-design plane that's got 4oz in the nose, in a 20 sized plane, if that's any consolation.

The current set up I have is a OS 25 LA,9x6 apc prop ,Factory muffler,3 oz tank and plastic spinner from Brodak. The plans also call out a 1/2 of weight in the wing tip, When the plane is up side down and you push down on the in board tipand release it falls pretty quick to the out board side.

The tip weight needs to balance out the weight of the flying lines---so it should unbalance the plane on the bench.

One last question how do you post pictures, when I go to additional options and click browse, I open my picture in Windows Media Player and click open and it attaches to the browse area then when I click post I get an error message that says the post times out.Any help is appreciated , thanks Scott

Media player?!?  Oi.

It's probably too big, but you could try just finding it with "browse", and leave as many Microsoft products out of the mix as you possibly can.

[scott matthews]

How do I change the size or format and were do I do it.

[Tim Wescott]

How do I change the size or format and were do I do it.

You need a picture editing program that will let you rescale the image, or save it at a lower quality.

When you look at the picture in your file browser, what does it say about size?  (If you're looking in "thumbnail" mode then you should be able to right click on the thumbnail, then click on "properties").

[scott matthews]

I went to paint and tried a resize so here we go.

[Tim Wescott]

Looks good.  With that short of a tail, I'm not surprised at the balance issue.  If it's an older design it's made for no muffler, and those things do weigh a ton.

[scott matthews]

Hey it worked!Now back to some more guestions. Is there a basic procedure or article for bench trimming? And what size do you resize photos, mine had the pixles set at 4000 horizontal.I am going to attach a few more pictures so you can see the set up I have.I would like to take this time to thank everyone with the great advise with helping me build this plane and a special thanks to Bob Burch for the informative article about ultracoat covering in the building the T-Rex article.

[Steve Helmick]

Mr. Brett Buck did a bench trimming article...you might try the search function here, or SSW, or even Google.

Lose the 9-6 and get a 9-4 APC (for break-in and early flights), then change to a 9.5 x 4.5 APC or 10 x 4 APC as the engine loosens up and can deal with increased load.  Steve

[scott matthews]

Thanks Tim, when you add weight to the tail do you locate it on the body of the aircraft< and do you use something like 2 sided tape to attach the weights or something else?Also  is there a prefered side say in board or out board? Do you balance the plane at the CG to where its perfectly balanced or do you get it close as long as its still a little nose heavy like some articles here say is better than tail heavy?

[Brett Buck]

Mr. Brett Buck did a bench trimming article...you might try the search function here, or SSW, or even Google.

Lose the 9-6 and get a 9-4 APC (for break-in and early flights), then change to a 9.5 x 4.5 APC or 10 x 4 APC as the engine loosens up and can deal with increased load.  Steve

   The quick answer in this case is set the CG at 15% of the mean chord, put in about 3/4 oz of tipweight, leadouts about 3/4"-1" behind the CG and select-in-test for everything else. One nice thing about elevator-only models, they are dead simple to trim - get the wings level, adjust the handle spacing or elevator horn to get the response you like.

     Brett

[Chris Edinger]

A big help for the nose heavyness is to get a tongue muffler... you might be suprised how heavy the stock muffler is... as Tim said..
personally I would try to balance it by getting rid of nose weight.. before I start adding weight somewhere else..

[Brett Buck]

A big help for the nose heavyness is to get a tongue muffler... you might be suprised how heavy the stock muffler is... as Tim said..
personally I would try to balance it by getting rid of nose weight.. before I start adding weight somewhere else..

  Except they tend to run much better on the stock muffler. If it comes down to better running VS 2 oz, go with the 2 oz.

    Brett

[Ted Fancher]

Tim,

As usual, Brett is pretty much on the money.  The only quibble I would have is the suggestion for 3/4oz of tip weight on a light weight profile with the tank and engine already outboard of the fuselage centerline.  The added weight can't do any harm for initial flights but you might find it excessive.  If the outboard wing seems to "flail" around during hard maneuvers (dropping low at the bottom of maneuvers both inside and outside is the most obvious clue) you might want to back off the tip weight a quarter oz or so at a time until it stops doing that.

The single most important thing to understand is that proper trim is "more" important than lightest possible weight.  If it takes an ounce (or even more) to get the CG in that 15% of the average (another word for "mean") chord throw it on and forget it.  The difference in "wing loading" (how much it weighs for a given amount of wing area) is next to meaningless.  If you don't add the tail weight your airplane requires it will likely be unresponsive to inputs and more difficult to fly in winds, for instance.  If the CG is much farther aft than that 15% number you will find it very difficult to fly it smoothly and, if it's real far aft of that location you will probably crash it...no kidding.

As Brett suggests, absolute optimum trim (in the pitch axis) is much less important for an elevator only design.  Get the CG in the ballpark of 15% and then adjust the control response with either the length of the elevator horn or the line spacing at the handle.  Even though Brett's a "rokit sientist" the flapless sport stunt model is about as basic a machine as there is.  Your Galaxy appears to have quite a short tail so it's not at all surprising that it ends up a little nose heavy if built light to start with and has a modern engine, muffler, spinner and tank on the nose.

Any remotely "normal" flapless design from a competent modeler can be bench trimmed within a fraction of optimum by insuring the wings are straight, the wing, stab and thrustline are pretty much parallel, the CG (using whatever weight addition or subtraction is necessary) is located roughly 15% aft of the leading edge at the average chord, the leadouts are located as Brett suggested ~one inch aft of the CG at the wingtip and the outboard wing is enough heavier than the inboard that it will fall to the table briskly but without breaking anything when the model is held at the nose and tail at the centerline.

It really is just that simple.  Fine tuning of such a sound airplane will require only modest adjustments from that basic set up and most things the pilot doesn't like about it can be fine tuned almost as well by adjusting the handle, line length, prop, fuel etc.

Now, put flaps on that thing and it starts to get more complicated.

Good luck.  The airplane looks terrific!

Ted Fancher

[Tim Wescott]

Thanks Tim, when you add weight to the tail do you locate it on the body of the aircraft< and do you use something like 2 sided tape to attach the weights or something else?Also  is there a prefered side say in board or out board? Do you balance the plane at the CG to where its perfectly balanced or do you get it close as long as its still a little nose heavy like some articles here say is better than tail heavy?

Tape that's aggressive enough to trust isn't going to let go easily enough for adjustment.  I'd either build a weight box in the tail end of the plane, or I'd just bolt weights onto the side.  You want to be able to dink with the weight a bit, to find out what works best for you.  Unfortunately you've already put on that nice finish -- but some weights tucked up underneath the horizontal stab won't show that badly.  On the outside is probably better -- it reduces your need for tip weight.

[Dennis Moritz]

Don't add tail weight. 3/4 ounce tip weight makes sense. You can adjust these weights later, if needed. If you're not using a weight box, glue the weight on the bottom of the wing tip. Easier to hide the patch where you slit the covering to adjust. I built one of these a while back, early on into me retread (present) phase. Very nice flying plane. Versatile. Still fly this plane five(?) years later. I flew the complete pattern for the first time using this Galaxy. Competed with it at the NATs in Classic. Finished third. Third from last place. Have finished mid pack in Intermediate at Brodak with it. Nice transition stunt/trainer. More distinctive looking than the Streaks. I actually like it's flying qualities better than the Streaks. Mine is powered by an FP40 with a tongue muffler. Which matches the weight of your LA25 with muffler, or at least is close. Never checked the CG, but the resulting configuration points well. Quick responding but smooth. A slight nose weight bias will slow the responsiveness of this bird. A good way to get to know the flying qualities of this Sport/Stunt trainer. Judging from your questions, you are not an Expert flier. Slower handling is better. There's a big flapper back there, even tho the tail moment is short. The big flapper can came things happen quickly.

I'd use .015x58' eyelet to eyelet. A bit on the short side. This way if you've got any aerodynamic weirdness (misalignment, warp and so forth) you'll be able to keep line tension more easily. Hard to trim a bird that has splattered in pieces.

[Ted Fancher]

Tape that's aggressive enough to trust isn't going to let go easily enough for adjustment.  I'd either build a weight box in the tail end of the plane, or I'd just bolt weights onto the side.  You want to be able to dink with the weight a bit, to find out what works best for you.  Unfortunately you've already put on that nice finish -- but some weights tucked up underneath the horizontal stab won't show that badly.  On the outside is probably better -- it reduces your need for tip weight.

The problem with the stick on weights with the foam double sided adhesive strips (Prather's were my choice but unsure if he still markets them) is how aggressive the adhesive is...which is great if you want it to stick forever but makes it hard to remove while doing CG testing. 

Here's a technique that will allow you to use the stick on weights without concern about the finish.  It's what I do.

Take an appropriately sized piece of "crystal clear" tape (it's a more flexible version of Scotch tape that peels off cleanly...I also use it for hinge line seals) and stick it on where you want to put the weights.  I always double a corner of the tape back on itself before doing so so there will something get hold of when you want to take it off without digging at it with your fingernails.  Stick your weights to the piece of tape and you'll find that, with care, you can peel the tape off, taking the weights with it.

One caution, don't put a long single strip of weight on and expect to peel it off easily.  The long strip's rigidity forces you to pull it off the model rather than "peel" it off.  Pulling it directly up off the finish exposes you to the finish problems you're trying to avoid.  I never put more than 1/2oz of weight on as a single unit and 1/4oz segments are even safer.  Remember, you're trimming the airplane so the trim weights don't have to look pretty while doing so.

Once you're happy with the state of trim determine the amount of weight and its location and then decide on a way to install an equivalent amount in a hidden or less obtrusive manner.

Ted Fancher

[Brett Buck]

The only quibble I would have is the suggestion for 3/4oz of tip weight on a light weight profile with the tank and engine already outboard of the fuselage centerline.  The added weight can't do any harm for initial flights but you might find it excessive.

    That's what I was shooting for. It is almost certainly overkill but will overcome a pretty good warp, too, so it lasts long enough to discover it. And truth be told, it's not going to be turning all that tight, and if it's not turning tight, the excess tip weight doesn't really hurt anything.

    Brett


p.s. Ted posted while I was, but note well the point about the servo tape. After a while, that stuff *is not* going to peel up, period. It's really tough. But put it on in a spot you can easily cut foam part (I usually use a #11 blade without the handle) and that allows you to remove it. Then the residue can be removed with SIG Airplane Cleaner.

p.p.s.  Dennis - huh?  If it needs tail weight, it needs tail weight, period, there's no trim trick to get around it. And making the engine run differently to save a few ounces is *always* a mistake. The engine run is *much, much* more important than the wing loading.  If the tongue muffler works better than the stocker (very unlikely) then, yes, you get a double bonus, but otherwise, set the engine up the way it runs best and trim the airplane however it needs to be trimmed. Even a minor improvement in the engine run is worth almost any reasonable weight, even on a little no-flap jobbie.

     A rather stubborn buddy of Ted and ours once built a Barnstormer, and it had DAU75 car paint put on with the consistency of Jello - and was exceptionally heavy. He put the engine in, and it was *grotesquely* tail heavy. We went out and flew it anyway, and it survived (due to his exceptional natural skills) but was hopeless. I suggested he put in  enough lead in the nose to balance it. He added *6 oz* to get it where it needed to be. Flew much better, perfectly acceptable. But he took it all back out because it "made the airplane too heavy*. And in pretty short order he quit flying it. That's the degree of "weight insanity" that people sometimes have - it's better to have a light but unflyable airplane that hangs on a wall, than one that is heavier than you expected, but flies fine. Makes you wonder what the point of this event was. 

[Dennis Moritz]

No. No. No. I am saying let the plane start off a bit nose heavy. It'll slow things down. New fliers or less accomplished fliers are more likely to get into trouble over controlling a sensitive plane. My thought is that the FP40 with a tongue was similar in weight to an LA25 with a stock muffler. If the airplane has a slower turn than the fellow likes, it's easy enough to add weight to the tail. My FP15 (tongue muffler) powered jr. Streak was definitely on the nose heavy side. It was slow turning that way, but easier to control without getting into trouble. I wound up with a quarter ounce plus in the tail. Decent amount for a an old fashioned .15 bird, which is in actuality half-a sized. Definitely fun flown rung out. To summarize, I've found birds on the nose heavy side to be slower on the controls than birds with a further back cg. Useful when getting to know a new plane.

[Bob Whitely]

Something no one has mentioned that I would do is first get rid of the APC
prop cause  they are really heavy.  Second use the lightest spinner or no
spinner at all. Third lose the metal tank and use a plastic uni-flo.  For sure
you will reduce the noseweight probably by three plus ounces.  The plane
will love you for it and be much more user friendly. I for sure would use a
slow handle to start with and speed it up as necessary down the road.  RJ

[scott matthews]

Thanks guys for all the info.I did a little checking yesterday after reading some of the replies,I went down stairs and picked up my 20 year old ringmaster and I did no math for cord or trying to find CG.Placed the plane on my fingers approximately the same place as the galaxy and it s nose heavy also,No surprise I built it 20 years ago I was young.Point is I have been having fun with it for the last year not knowing any better and flying it out of whack.I am defiantly going to add the tail weight like everyone suggest, Who knows I will probably be very surprised to find out what these planes are suppose to handle like.I also found Bret's article on Tulsa Glue Dobbers web site that had alot of good info on building , flying, trimmingand judging how much wind is to much.Now that I learned yesterday how to post pictures I will post one of my ringmaster that you guys gave me info on setting up an OS 40 FP engine, and how to grow a pair and go flying in some wind. Which I now realizes is better than no wind for doing some basic stunts.Thanks

[scott matthews]

Sorry posted before attaching picture.

[john e. holliday]

That Ringmaster looks nice.   Bob has some good advice.   Now you get one plane to fly the way you like.  Then get the other one to fly the same.   But, with the first plane once set, let an expert fly it to see if there are problems.  Anyway keep having fun and don't get discouraged.

[Ted Fancher]

Something no one has mentioned that I would do is first get rid of the APC
prop cause  they are really heavy.  Second use the lightest spinner or no
spinner at all. Third lose the metal tank and use a plastic uni-flo.  For sure
you will reduce the noseweight probably by three plus ounces.  The plane
will love you for it and be much more user friendly. I for sure would use a
slow handle to start with and speed it up as necessary down the road.  RJ

Shucks, Bob.  Who cares how much the prop weighs.  Half of it is always going up anyhow, right?

Re the spinner.  Would you take the spinner off the Miss Kell (my favorite Whittley ship) instead of adding a 1/3 of an oz to the tail?  I expect the "look" is just as important to Scott...right Scott?  The lighter tank I can live with for a sport ship.

I'm in absolute agreement about the slow rate handle especially if he takes either of our suggestions to move the CG aft.  It would be of interest to me to know what bellcrank and elevator horn drive arms are.  All too often these older ships used the classic Veco horns with a max of 1/2" arm coupled to a three inch crank with a longer driving arm.  Remember all our old Ringmasters back in "the day" with 80 degrees of elevator so they would "turn quick"?

Ditto the suggestion to increase the line spacing at the handle as necessary rather than moving the CG forward.

Ted

[scott matthews]

Hello Ted ,I just read your response so I went down stairs to check.I the kit was supplied with a 3.0" bellcrank and the control horn measures 1.0" tall.The stabilizer movement is 45 degrees either direction. My daughter wants to make a Galaxy should I get a 4.0" belcrank instead she is a total novice and has not completed here first flight unattended. So did pancake the ringmaster shown in the photo and broke the nose clean off, then yesterday she broke the stabilizer loading it into the car (kids).I also found your articles on design flying and trimming on egomaniacs web site. Boy theres a lot to digest but its raining here so I'm getting an education.

[Tim Wescott]

Hello Ted ,I just read your response so I went down stairs to check.I the kit was supplied with a 3.0" bellcrank and the control horn measures 1.0" tall.The stabilizer movement is 45 degrees either direction. My daughter wants to make a Galaxy should I get a 4.0" belcrank instead she is a total novice and has not completed here first flight unattended. So did pancake the ringmaster shown in the photo and broke the nose clean off, then yesterday she broke the stabilizer loading it into the car (kids).I also found your articles on design flying and trimming on egomaniacs web site. Boy theres a lot to digest but its raining here so I'm getting an education.

Keep in mind that if you just break something off on a profile, you can often slather things with CA glue, put it back together, and be in the air in minutes.  As long as the wood isn't crunched (or sanded off) you can often carefully fit all the fibers back together again -- this gives you a tremendous amount of area for re-gluing.  You can either get the thing fit back together and apply a generous amount of thin CA to the crack, or you can apply gap-filling CA to the parts and put them together.  Doing a dry test-fit will tell you which is the wisest course of action.

[scott matthews]

Flew the maiden flight today.Had 1.25 oz of weight on tail which still left the plane a little nose heavy, 1/2 oz weight in wing tip and 9x6 prop on 25 engine.The results were engine started fine then as soon as I get airborne went sluggish for 3 laps I'm thinking this is not good.Plane seems to have very light pull on lines and is squirrelly compared to ringmaster.Engine did settle in after 3 laps then ran forever(12 min).This was the OS 25 first flight too,I know I got alot of variables going on for a first flight.I think I need to add 1/4 oz more weight to the wing tip,add 1 more washer to cant the engine out a little more and now I wonder if I should take a 1/4 oz of weight off the tail to make it less sensitive.What does everyone think?

[Ted Fancher]

Flew the maiden flight today.Had 1.25 oz of weight on tail which still left the plane a little nose heavy, 1/2 oz weight in wing tip and 9x6 prop on 25 engine.The results were engine started fine then as soon as I get airborne went sluggish for 3 laps I'm thinking this is not good.Plane seems to have very light pull on lines and is squirrelly compared to ringmaster.Engine did settle in after 3 laps then ran forever(12 min).This was the OS 25 first flight too,I know I got alot of variables going on for a first flight.I think I need to add 1/4 oz more weight to the wing tip,add 1 more washer to cant the engine out a little more and now I wonder if I should take a 1/4 oz of weight off the tail to make it less sensitive.What does everyone think?

HI Scott,

I'd only reiterate that the "weight in oz" info you gave us is not very meaningful.  Where the CG ends up is the important thing.  As far as sensitivity is concerned there are a ton of variables involved the most important being the line spacing at the handle (huge factor) and, again, the CG location.

I grew up using three inch bellcranks and 1/2 inch control horns because that was what was available.  I think the defining datum is the size of the human hand.  They're all pretty much ~four inches wide at the grip.  I think the now very available four inch bellcrank is a perfect match.  A MOL one to one relationships between handle deflection and bellcrank rotation.  To enable us to use an aerodynamically optimum CG (the singe biggest factor to an airplane competitive in all conditions) we  then need to optimize the output from the bellcrank to the input to the elevator so that the response isn't so quick you can't control it or so slow that you can't turn it.  today's modern "slider" adjustable elevator horns are the cat's meow for doing so.  Start out so that the BC output arm = the elevator input arm and then adjust the slider to suit your taste.

The best way I know of to tell if the CG is in the right place is to carefully observe the airplane's reaction when the engine quits.  If you can whip it more or less forever it's probably a little to a lot nose heavy.  If it gets floaty on the lines and is hard to land in the wind it is probably tail heavy.

The easiest way to get a flapless ship in the right ballpark is like Bob Whitely suggested.  Start with the CG at around 15% of the average chord (or slightly forward but not aft) and with the controls pretty slow...so the BC output is less than the elevator input.  If the glide after the engine quits is either too easy to whip or too floaty, change the CG a little at a time until it can be whipped if necessary but takes some effort to do so...and, when it comes around into a headwind, it doesn't balloon and get floaty to the point that you can't control the touchdown point.  Once the airplane does that it will be pretty much "happy".  If the controls feel too sensitive either lengthen the elevator input at the horn or narrow the spacing of the handle (or vice versa if response seems sluggish) until you, the pilot, is happy with your ability to point it where you want it to go.

One last thing.  The 9X6 is almost certainly more prop than the little .25 is happy with.  Bolt on a 9X4 and rev the engine up to 11.4 to 12K and see if the run isn't more consistent and the speed and line tension better. (Speaking of line tension, be sure that your leadouts exit the wingtip about one inch aft of where it balances on your fingers when held by the wingtips).

Enuff for now.

Ted Fancher

[jim ivey]

I wouldn't add all that weight. nearly all the profiles I ever knew, were way nose heavy, the flite streak being the worst and it flys very well. I moved the engine back far enough to balance one once, and it wouldn't fly level! hunted like a hound dog. I filled the back cover full of serabin and that helped, but didn't fix it.     jim

[scott matthews]

Went flying today for the second time.Much better results after using the formula for finding MGC and taking weight of the tail to rebalance.Took evryones advise and installed a 9 x 4 prop,and ran the 25 LA using Brodak's 10% fuel with 11% synthetic and 11% castor.Plane new has good line tension and feels like it can really sharp corners.My engine run was a little hit and miss though.I starte the engine and adjusted the need valve till it broke from a 4 cycle run into a 2 cycle run then went a little more and it would try to stall, so I backed it down to where it was in a constant 2 cycle on the ground.When flying it would cycle on and off between 2 and 4 in level flight what am I doing wrong?Should I lean it out and then back it up to a 4 cycle hoping it leans out in flight? Also bought a fuel syringe and only put 2 oz of fuel in tank and its still plenty of time to fly for me.Thanks Bret and Ted for your great advise today made me feel like the Galaxy does have quite a bit of potental as a stunter, were as the first flight I thought I had Wasted a Bit of time building a plane that felt out of control.

[john e. holliday]

Well I got out last Tuesday evening and flew my version of John Lowrey's Stuka.   LA .25 on muffler pressure.  10-4 APC and Excaliber 10% fuel with 22% oil,50/50.  First flight was a little on rich side of 2 stroke.   Took needle in about 4 clicks and it was an enjoyable flight.  Hadn't flown the combination since last year early summer.  Now why the APC instead of my usual Top Flite Power Point 10-4?  It was just enough more to make the plane handle nice.