does anyone have experience with a 16x4 on a ys 91. I'm thinking about getting one because it spins a 15X6 like nothing and I want more power

Coo, now this was before I set the valves. With the 16/4 I was pulling around 8700, so with the adjustments maybe you could see 9000. As far as the rocker clearance its just enough to touch the supplied feeler guage, still able to pull it out and insert it, but its touching. I'd say it was three times the thickness of the guage before adjustment. On that 16/5 I'm going to trim it to a 15/5 and see. Hasn't been fuel burning weather untill today and I'm useing up this 4 stroke fuel before I purchase the 30%, but will let you know when I do. Joe

16x4W for ys 91 is the right choice. Something about 9000~9500 RPM.

Rain here in its 12th consecutive hour. Got a little squirrely today and decided to take on a long anticipated project. Take a little off the top please.........3" to be exact. Inspired by a pic here way back in early 2003 and reinforced by Contempo's success with this mod. First pic is stock, second is mono peeled back, with the new ridge installed, before chopping the top, last is the new look. If the weather breaks I'll see if this helps the NASTY bad habits in knife edge. I'll post on the results. Joe

Joe, this is something I had wanted to try. Let me know if works..........

Will do Raj, going to check the weather site now, keeping my fingers crossed. It took about a half hour of actual work. Had to run out for an hour while the epoxy set up. Very simple. Did put myself in a possible situation though, removed the covering without looking to see if I had any balsa on hand. Luckily there was a piece. You have to be prepared for mods on a Saturday night. I would have been out of luck for tomorrow. With a little good weather I'll post tomorrow. Joe

this post is huge! and i thank everyone for their input on the ucd 60. i put everybodys own thought about the plane and put it all together for mine! so far i'm running a saito 100 w/ cline reg. a 16*4w apc 15% wildcat fuel, xp8103 with hitec 605's on the ailerons, 537's on the elev. and a hitec high speed high torque on the rud. w a hitec hs55 on the throttle! fuel tank located near the cg which is balanced a 6 1/4" form the LE.

next upgrades will be digital servos! i wonder if the ds811 will work?strong enough?
and the rudder mod. just waiting to see how others turn out!

also tuning my saito with the cline reg. seems not right! i cant get the high speed neddle to richen, theirs no leaks in the fuel system. its not running lean-exhuast oil seems normal, not burnt! any input on this? thanks rod!

What kind of RPM numbers are you getting?

The ds811's suck for this plane (My opinion here). I had them on every surface before I knew much about servos. First the rudder would shake when just sitting there.. later after about 20 flights the rudder would shake all over the place in flight too.. replaced it... then after a few more flights the elevators started to shake (a lot) and the ailerons would give a little shake too. Basically i think I wore out the pots b/c I had max deflection and the ds811's only have 47oz of torque at 4.8v (If you run 6 it will have enough torque, but, wear your servos out faster I have been told). I think the 50+ that the directions call for on the elevator and ailerons (90+ on rudder)... I believe really increases if you are trying to get all the throw you can out of the surface.

Some people were telling me to move in on the horn and in on the servo arm.. but.. I want full deflection.. then they say to increase the deflection to 150% up an down on the 8103... talk about something that wears the servo out and.. you take a possibly fast servo and make it slow.. or a slow servo slower... if you think about it.. you increase the servo arm throw 50% and it will make it 50% slower. It was noticably slow.

The ds811's got so bad that I flew by at a medium speed and could see the elevator servos shaking up and down about 3" up and 3" down. I really didn't think it was going to stay in the air. I landed it.. went to the hobby store.. replaced the servos and all is well. Everyone kept telling me that was normal for digital.. and I even tried all the tricks everyone else did to stop the shake.. did not work. After replacing my servos with other servos.. no more probs. It was just the ds811's.. and.. now after thinking about it.. I think they just weren't strong enough for the plane.

I stayed with digital for the rudder.. hs 5925MG ($90). That thing is FAST!! About 30 flights with absolutely 0 shake. The ds811 was shaking before I even took it up.

I ran out of money when the others went out.. got some hs 625MG's for the aileron and elevator ($35-40). I wanted digital, but, think that dual BB, high torque, and decent speed are more important right now.

I have been SO frustrated with the ds811's. I tried everything and I think they just couldn't hold up under the weight of the large surfaces.

Also.. might want to keep and eye on the 537's.. they only have 40 oz of torque. Especially on elevator (I tend to give that a good yank from time to time) if you do aggressive throws.. it is asking for 50+ on the low end of things.

I may sound a little frustrated.. ha.. b/c I am. I am sending the ds811's in for service and am going to use them on a smaller plane. I am a pretty good troubleshooter from years of computer experience and it has proved to help me in this hobby. I have read everything I can get my hands on too.. but.. I have only been in the hobby 1 year so I don't think I know it all... If someone disagrees.. they might be right.. I just know how it was for me. Getting good servos has made it easier if nothing else.

Just got back from the field. The results are in. After removing 19 sq. in.(3") from the top of the rudder, there is no more opposite wing drop when rudder is applied. Still wants to dive to the deck but not as bad. That part is now contollable. Here is my take on the rudder. At 85 sq. in. it is considerable in size. I don't think the large size is as much a problem as is the shape of it, or the distribution. This is how it breaks down in relation to the horizontal thrust line of the fuse. At 14 1/4" tall, 25 sq. in. is below the thrust line, 60 sq. in is above the thrust line and of that 60 sq. in. 31 sq. in. is on the top in the counter balanced area. With that unevenly distributed volume at the top of this tall rudder, when applied, it twists the plane, causing the the opposite wing to drop. Right rudder, left wing drops and vice versa. Having taken care of the wing drop, now to deal with the dive to the wheels. Its almost as if it stalls the plane when rudder is applied in level flight, therefore the nose over. Yet, if it was a stall then in knife edge it would drop out all together. May need a different rudder and I think the right direction is now to add more volume to the area below the thrust line and remove more above. We will see. Joe

When you say dive to the deck.. i guess you mean to the left or right... like.. to the wheels?

Yes, to the wheels. In stock form, in level flight, when rudder was applied, it dove to the wheels big time. It still goes to the wheels, but now, its not as drastic. In knife edge, without applying up elevator, it would circle in about a 20 foot radius. For now, untill I decide which way to go, I've been making all my observations from level flight. If it can't do a rudder turn easily then it can't knife edge easily. Joe

Joe,

I think your results concur with mine. Add some area below the thrust line and your knife-edge performance will improve. I am now able to do long extended knife-edge passes with ease. I have not programmed a mix, I am just adding a slight amount of "up" elevator control. No roll coupling present. A buddy in the club maidened his stock UCD this weekend. I noticed when he attempted rudder turns, it wanted to snap out of the turn. This is not present in my modified UCD. Congrats on your mod!

Matt, how did you add area below the thrust line ? Pics will be great. Thx..........

I don't have a side by side comparison to show, but I will try and explain.


The stock rudder angles up from the bottom of the fuselage. I made the bottom of my rudder level with the bottom of the fuse. I also extended the trailing edge of the rudder out about 3/4" at the bottom and tapered to the top.

Matt, did you cut off 3" from the top of the rudder as per Joe ?

I designed a whole new rudder from scratch. Here is an aproximate comparison of the two rudders. If you (or anyone else) want a copy of the plans of my rudder I can email them to you. I have it as a .pdf file. Unless there is a way to attach a .pdf file to this post?

Matt, just emailed you. Thx !

Contempo,
I got your .pdf about a week ago, thanks again. I haven't gotten a chance to get started on it yet, but I wanted to ask, did you modify the fin as well or just the rudder?

Matt, where do you have your cg now ? Is your fuel tank in the stock location ?

How did you arrive at this rudder design, by trial and error or calculation ?

Thx !

Contempo, my initial thoughts on increaseing the area below the thrust line aside from lengthening the width and squareing up the bottom, I plan on adding on to the heel of the fuse, on the bottom where your tail wheel is mounted, resulting in the ability to lengthen the rudder downward as well. Joe

Im curious to see your results as you progress through this Joe.

It appears( with most planes) GP did not test this plane properly and just put it out there. Such a shame.


matt

Did you modify the fin as well or just the rudder?

Both fin and rudder were redesigned. No modification is required to the fuselage. The new fin is designed to mount in the existing slot.


Matt, where do you have your cg now ? Is your fuel tank in the stock location ?

CG is at 5 3/8" . It has great 3D performance without being too sensitive on the elevator for landing.
Fuel tank is on the CG. (I am running a YS 1.10)


How did you arrive at this rudder design, by trial and error or calculation ?

It was really a "that looks about right" method. I really don't like the look of the stock rudder and I wanted to make one that both performed better and was more visually appealing. So, I got improved function through improved form.!

cumn thru, on your rudder mod all you did was chop 3" from the top! or did you also redistribute the 3" cut and added that to the aft part of the rudder?

also what are you using to hold your fuel line to its fittings and cline controller? and does your engine richenup to the point of it sputtering, mine will not.


whats a good digital servo thats not hitec and that its not overkill for the ucd .60 on the elev and ail.

The cline regulates the fuel flow, only giving the engine what it demands. In effect it becomes the limiting device once the high speed needle is backed out to a very rich setting. Using a cline requires that you adjust your thinking appropriately and then it all becomes clear...

I'm biased towards Hitec digi's so I can't help out in that department, they ALL have worked flawlessly and give great control and performance on my airplanes.