forestroke

avr8r - I think the 52 is golden for this plane. the 70 will be fine as well since bipes tend to be tail heavy. but it's 6 ozs heavier for a measly 0.2hp. it's no wonder everyone chooses a 91, which is 2oz heavier but give you 0.5hp in return!

as for flying brick, my old ultimate was wicked fast and really didn't slow down as quickly as i was lead to believe. i think the very thin airfoil makes this ultimate much more aerodynamic than say other bipes.

lee101

stick the 50sx into it as this little bipe is head heavy... i'm still wondering how to move the battery to the back to balance the CG ...... i think a 4 stroker would be too heavy for it unless its a YS63

forestroke

lee - really? i'm shocked! i would think that it would be tail heavy. for my ultimate, i had a 6V AAA pack foam-taped and zip tied to front of the firewall to get it to balance so it flew nicely. but then that was because i was using a 32SX with a slimline pitts muffler.

lee101

yupz head heavy on my 50sx . i got to move the rx batt to the rear. which i have to figure out how to go about it.

da Rock

My WM.46 Ultimate balanced on the CG location the mfg suggested without too much fiddling. I have an OS46AX in the nose with a Slimline Pitts muffler. I just weighed a 46AXwPittsMuffler and the combination is about 16.5oz. The published specs for that motor with the stock muffler is 17.2oz. With that up front, I moved the battery around to see where I wanted to install it and it wound up just at the back of the equipment bay.

I built a box against the wall of the fuselage for the 800mAh flat pack I used. The box's bottom is the servo tray. The box is open at the top which is just under the wing. When I button on the wing, it also acts to close the box. I have a 1/2" piece of foam rubber fitted at the top of the box to cushion the pack against the wing. The box is sized so that the battery pack fits exactly when it's surrounded by 1/4" foam.

The model seems to fly very well with that CG location. I hold just a slight amount of down when inverted. And here is how much rudder I need to hold once I've established the knife edge.

da Rock

Just the other night I went back and revisited the control setups. I needed to put sort out the carb connections. I'd chosen the wrong holes both the arms. And I wanted to bring the servos centers closer, get rid of the radio's centering for pure mechanical centering. So when I flew yesterday it was like I was flying without setup trim. But it flew now with no trims and being somewhat used to it's reactions, I got a better feel for the WorldModels' suggested trims.

The little guy really knows it's got a rudder back there. About the only thing I did was give the TX more exponential for the rudder. I'm up to about +40 (I fly a JR8103) to give the plane a lot more steering accuracy on takeoffs and for torque on takeoffs and for crabbing into the wind on landings.

I'm going back into the insides tonight and up the aileron deflection some more. The suggested 10mm throws just might be conservative because whoever designed the sucker with the aileron connectors that screwed up the top wing aileron deflections just might have detuned to ailerons just to keep the snapping tendency down. Mine doesn't show any tendency to snap with equal moving ailerons. And I have brought the sucker into landings in almost dead calm at a VERY slow approach speed. I gotta admit that I wasn't just trying to see how slow she'd go, I was showing her off. Dumb, but fun. And anyway, she has only a fairly fast roll and I want a blinding fast roll. And I"ve backed down the exponential on the ailerons some. They're nowhere as sensitive around neutral as I expected.

I've already given the elevator connector a jump, one hole in, to increase the deflection. I was expecting a dangerously fast elevator from that short coupled planform and had visions of tearing off the top wing when doing fast snaprolls. But with a decent amount of exponential, the elevators have proven to be just about right for me at the mfg's throws to be low rate. My increase throw, little as it was, seems good right now. And the exponential really helps when you go to bigger throws. I'm completely amazed at how accurately the elevator tracks the model. It's flying like a long#ss pattern ship.

I really thought you had to fly BIG birds to get this steady a flyer. I can't imagine how good the 25% and larger ones fly.

lee101

do you have any pics of the insides of the belly?

wollins

Man! I just gotta do your aileron mods! Your Ultimate's flying characteristics sound SWEET! Wild when you want it (doin' "stuff" ) ) and gentle when you NEED it. (Landing! ) Hopefully I'll get your mods right without the close up pics to guide me.

Hey ... by the way ... I read in another thread that the manufacturer's CG suggestion was somewhat off ... supposedly it should be 2 7/8 inches for the CG measurement at the CL of the fuselage, not the 3 3/4 given in the documentation.

Where is yours at?

da Rock

BTW, I've tried a couple of props so far.

I mostly fly wood. I like most of the "plastic" props good enough, but simply like wood for a couple of silly reasons.

I started out with a 12-6 and didn't like it. Don't actually remember why because I immediately swapped on an old 11.75"x5 that I'd cut out of either a 13-5 or a 12-5 (don't remember that either) and that sucker was so good it wiped my memory.

Just to prove what I thought would happen..... I stuck on a 10-6 and sure enough, with that little airframe and that little fan, the 46AX acted like it was running too cool. I really embrace the belief that you gotta make the engine actually work up some effort or it won't run right. But you know what.... whenever you think you know the answer before you test it, you're probably not going to see the results at all clearly. I was trying a stock 10-6. I bet if I took one of my low aspect ratio BOARDS off my Hots (which has NO ground clearance and really needs prop blade area) the wider blade would make the 10-6 work better with this plane/engine combination.

I've run a stock 12-6 and 13-5 and didn't like the engine speed in the air. I was a bit surprised that the 13-5 was so limp. I figured it's extra fan area would pull stumps.

Anytime you overpower an airframe you ought to expect that propping the thing will get very selective. I think I was lucky to have had an already carved up 11.75x5. It seems to have enough blade area to be a wide-rpm prop on this little bird. And the pitch is flat enough to give amazingly slow speeds. And the combination keeps the prop working at those slow speeds. And it'll accelerate great, something the splinters don't always do.

Somebody asked what the little sucker would do for vertical the other day. We had a beautiful sky going at the time. It was about 30% very high cumulus and the rest was BLUE blue. I'm used to spec'ing out big gliders so have little worry about altitude and have this silly notion that altitude is somehow a wonderful thing to have. So I stuck 'er nose up and firewalled 'er. I had to hold a touch of rudder at first but once she came up on the step, she was gone. It dawned on me that it's one thing to spec out a glider that's trimmed to take care of itself and quite another to send a short span, short coupled, almost brand new HONKER out of sight. .... so I quit that foolishness when she was a BIG dot.....

I just stuck some nose art on her that I think is almost appropriate.........

da Rock

I think I'm going to have to name this little plane. And the nose art is almost perfect in a couple of ways, but it suggests a name.......

DaMouse

desmobob

darock,

When I had a .46 on my SIG Ultimate Fun Fly, it wouldn't quite "come up on the pipe" with an 11x5 APC prop mounted. I think the drag from the extra wing was a just a little too much. When I switched to a Master Airscrew 11x5, it would spin up nicely and performed noticeably better than with the APC. (I think this was the one and only time I got better performance with a MA prop)
Like your WM Ultimate, it would go vertical farther than I cared to let it....

I have some .46-size engines around, but I also had three Super Tigre .40s that weren't busy, so the .40 is what I put in my generic Ultimate. I'm dying to fly the little bugger.... It's the off-season here in upstate NY but there's a small chance I'll get the opportunity to put her up before the winter is over.

I'm still looking for some appropriate aluminum to add the "missing" braces to my cabane. I may use some flattened aluminum tubing (or maybe ovalled and just flattened at the ends) if I don't find any flat stock that fills the bill.

I enjoyed the photo of your Ultimate (Da Mouse) in knife-edge flight; I always love to see in-flight shots.

Good flying,
desmobob

da Rock

My local home improvement store has a big rack of aluminum stock right beside the big rack of steel rods/bars/etc. I was looking at some of the aluminum stuff to use for landing gear blanks and noticed some fairly light aluminum. I thought it might be light enough to be of use to me if I ever bend up the cabanes on DaMouse.

Actually, both Lowe's Home Improvement and Home Depot have racks of aluminum "stuff". You might give your local stores a look. I know I'll look closer next time I'm in there. (Which will undoubtedly be very soon because something in this house breaks down about every week. And of course, next to the LHS the home improvement stores are my favorite places.)

And come to think about the brace, there isn't any rule that says it's gotta be aluminum. I'd bet a piece of ply would work great.

Matter of fact, I've got a 2nd WM Ultimate (the yellow one) that's calling to me from it's box............ And I'd already made up a list of things I was going to do up front to improve "her". And I was trying to figure a better, stronger, lighter, less drag method of doing that framework and had about come to building it from wood. Cheaper, easier to find the materials, more rigid.....

desmobob

I'm 25 miles from both Lowe's and Home Depot. My Dodge 4x4 gets 11 MPG, so I don't make the trip unless I REALLY need something badly, or need a whole bunch of stuff.

I think I'll just add some aluminum tubing to my next Tower Hobbies order and use it to fab some additional left and right side aft-to-front cabane braces. If I was to redesign the whole deal, I'd probably use birch plywood. I think that's the way the old WM Ultimate 30 was done, right?

If I like the way this airplane flies, I'll probably get a back-up for it. Of course, I also want to get a back-up for my Hobbico TwinStar (a screaming deal at $119) and a back-up for my CMP P-40E (the retracts are worth more than the airplane... if I crash it I'll need another one to put the retracts in. ) etc., etc..

Funny... the only model I ever bought a back-up for so far was a Tower Hobbies Fun-51. I had one, liked it, and the model was being discontinued. I bought another one. Shortly after, I crashed the one I was flying. That was a few years ago and I still haven't built the back-up....

Good flying,
desmobob

lee101

all most done

lee101

just 1 more

lee101

took it up for its first flight.. all over the runway as the rudder is way to much and too fast! punch it on a apc 11x7 30% nitro and it just leap off the ground!! nail it full bore till its fully up and safe and trimed. on full throttle it wants to fly up? or is just the wind.? it flew fast and tiny.
rolls are nice on high rates and the rudderhas alot of control!! stall truns are fun and the turning radius of this little bipe is sharp and small.

let let it fly too high and too far. its gets tiny in the air. landing is pretty fast ....maybe too much pitch on the prop..

will fly it again soon.. how very exciting!!!

da Rock

desmobob,
You know, I was just looking at the closeup pictures of the cabane structure and an idea came to mind.

That diagonal brace is actually just stiffening the front cross brace. The rear brace is not being helped much at all. I think I'm going to add a light brace (it wouldn't have to be very strong at all) between the two bolts that're through the top wing. Those bolts go through the strongest part of the wing and that ought to provide all the front-to-back bracing necessary. Only need is to use that strength to help the rear cabane crossbrace with the help the front one gets with the WM design.

If I run a piece of thin ply just under the wing, on the other side of the two aluminum cross braces, from the front wing bolt to the rear wing bolt, that ought to stiffen up the rear cross brace for front-to-back forces. That cabane structure ought to get about twice as rigid. I'd guess the ply would be 3/32 thick and as wide as the flat-bottom V it'll be sitting in.

I would suggest that it's about the simplest solution to stiffening the cabanes when the top wing isn't on the plane and you're handling it in the shop. I'd still figure that the diagonal adds enough strength that it'd be definitely be necessary, but this addition ought to be the perfect finishing touch.

Right now, with the diagonal bracing all the front-back stresses on the top wing, with only the front crossbrace resisting, all the stress has to be handled by the front wing bolt. The back one is worthless for this because the brace it goes into has almost no front-back strength. Since the diagonal gives the front crossbrace more than enough stiffness, it can easily share that with the rear crossbrace and the ply connector will do the "sharing". And now both bolts would be holding the wing against front-back forces, not just the front one.

(edited to clear up a badly written point)

forestroke

darock - i don't think the diagonal is to reinforce the front cabane strut per se. but rather it is there so that both cabane struts stay upright rather than moving the wing forward and backward. only a diagonal piece that has both tensile and compressive strength can be used. a piece of wood to tie the front and back together would not help the situation, the structure would still collapse.

the only easy way you can ensure they stay upright is to tighten the bolts or epoxy them. another way is to glue a peice of ply between the fuse and the top of the cabane so it doesn't allow the structure to collapse.

da Rock

forestroke,
Actually, the WM diagonal really doesn't do any good at all to help the rear bracel on my WM Ultimate. The reason I figured to add the top brace was what I experienced with the WM design in use. You're spot on about diagonals and what they do, but the WM design only "braces" the front, not the rear. And the rear will move on it's own quite a bit. It's only aluminum after all and has no diagonal support at all.

The front crossbrace is so solid with the diagonal support, that it'll easily support the rear diagonal too. And a strip of ply from the front to the back would work like gangbusters. Just run the wing bolts through the crossbraces and then through the ply and tighten the bolts. Dead simple and easy. No extra drag from additional diagonals and almost no weight.

Truth is, with the front braced as well as it is, additional bracing for the rear is probably overkill. But the added weight is so insignificant, and the effort so small, that it's worth doing just for the fun of it. And of course, having two wing bolts holding against front-back forces instead of one is worth something.

forestroke, I think if the diagonal was supposed to keep both cabane crossbraces upright, it'd have to be connected to the rear one somewhere that'd help it stay upright. Really, since that diagonal is only really connected to the fuselage at the rear and then to the front crossbrace, it's got to be there only to reinforce the front cabane.

wollins

If you do decide to do it ... it'd be cool if you could show it in a pic.

da Rock

wollins,
I'm thinking that I'll take some pictures as I build my yellow Ultimate.

wollins

EXCELLENT! Remember to take "detailed" close ups of your aileron setup and that rear bracing mod. Any idea as to when we could expect such a build to commence? I've got mine waiting for all the final details of all these mods.

Colin.





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desmobob

I figure the diagonal brace keeps all the parts where they were supposed to be....

I imagine a square formed by the front and rear cabanes the the sections of wing and fuselage between them. Rearward pressure on the top wing allows the square's sides to pivot on the mounting screws --the corners--, turning the square into a rhombus. A diagonal brace from the bottom of the rear cabanes to the top of the front cabanes should effectively eliminate this.

That is the bracing arrangement used on most Ultimate models, including my Dave Patrick 1.20 Ultimate, considered by many to be the best ARF ever.

My aluminum is on the way, but if I get a chance to put the little Ultimate up in the air tomorrow, I'll try it out with the "incomplete" bracing.

Good flying,
desmobob

da Rock

Well, it certainly will keep the front crossmember from collapsing back, or forward for that matter. But if you look at where it's connected to the rear crossmember, you'll notice that it's not actually connected to it.

The WM setup with one diagonal going up to the front crossmember, one on each side, obviously is perfectly adequate. The front support for the wing is going to be rigid in all directions. And the bolt that runs through the wing up front there has obviously proven to be sufficient to keep the wing from moving to the rear. While the rear crossmember and it's bolt won't really contribute much to support the wing from moving backward or forward, because that crossmember can resist those movements only insofar as it's two screws hold it to the fuselage sides, nothing says that it can't be improved.

The better design would be to have two additional braces going from the front screws that hold the front crossmember on, back to the back crossmember, very much like the present two diagonals. But that'd look awful, and it's obviously not worth it to any kit mfg to go to that trouble.

But if the rear crossmember were braced against front-rear movement, it would also contribute to holding the wing against that movement. As it is, only the front wing hold-down screw does that job. By bracing the rear crossmember from the front, the rear hold-down screw will now contribute.

Is it necessary? naahhhh Obviously not. But it'll be insurance and fun to show off. And it will help the model last longer. But that's moot too, ain't it.....

forestroke

you would only need to double brace it if the material of both braces is either only compressive or only tensile. given that the aluminum has both tensile and compressive strength, only one diagonal is necessary. this is provided that the rectangle sides are rigid.

this is because of the amazing qualities of the triangle. even if the joints are loose on a triangle, as long as they are held together, the triangle is still rigid and cannot change shapes. this is unlike any other polygons. by putting in a cross brace, you effectively create two triangles.

the addition of another diagonal brace would improve the overall rigidity of the structure but is not necessary. desmo, good luck, though on yours the only thing keeping it upright is the flatness of the cabane struts, the friction of the bolts and the compression of the struts that are on the outside of the wings!