I have a magnum 91 4-stroke that will pull out of hover for a 8-lbe plane, using 15x4W APC, peaking 9800 rpm. So a Surpass 91 on this prop will defilitely hover UCD (if it's around 7 lb) and pull out.

Tower is selling the OS 91 SX-H for $215, which should be a good choice for UCD. The airplane version with its remote needle valve is just not worth it. The stock muffler is heavy and power-robbing , so you'll want a Jett or Ultra-thrust muffler anyway. This helicopter engine has 3 needles valves, and should have better midrange and transition than the 91 FX. Y-NOT is using the 50 SX-H on his Flip with great luck. So this SX-H should work well for the UCD.

Wow... won't hover with the .91 Surpass, eh? The only UCD I've actually seen in person uses this engine and seems to hover fine but I don't know how easily it pulls out. I've not flown it or seen what throttle level it takes to do it but have seen it happen at our field. Which prop are you using and what rpms are you getting? Maybe someone else here can offer a comparison with their same set up.

-s

One of my friend is putting a rc gas engine on his rcs 140 gas. Not finished yet has been having trouble. The covering that came on the wing was upside down. The replacement wing was crushed in transit both times .so still waiting for one more try......

One of my friend is putting a rc gas engine on his rcs 140 gas


HUM?

What happens when you try to hover?

Wouldn't want any less power for 3D, altho it could fly on less than half of what a Saito 100 supplies.

It would be very difficult, if not impossible to alter tank level. Most of the comments about loading up have been focused on two fixes: fuel regulators, and fine-tuning the idle screw.

mt

Yea , he has already installed everything , but he's still waiting on the wing to come in.The gas engine is only 32oz which should be close to a Saito 150 or 180 .But alot cheaper to operate . His name is supertiger .He will post everything when he's finished and test flown.

As for the UCD wing,.. I didn't really know there is a top and bottom! (as symmetric as it looks, and as good as it flies upside down.. you'd never know!). Only problem I guess is that the aileron servos would be mounted on the top of the wing vice the bottom... Oh well...

As for the idea of installing an RCS 140... I thought about this. After looking at the specs, and comparing them to the specs of an OS91FX, you will quickly determine the following:

Even though the RCS 140 is "2lbs w/ ignition" as the webpage says,... you still have to add the weight of the muffler (~another 1/2+ lb, depending on what you install). This doesn't even take into account the required ignition battery!

The OS91FX is under 25oz, w/ muffler.. with the RCS140, you would be adding another 1-lb up front ! Yikes! Imagine how much lead you will have to add to the tail to get the CG at 6" (for good 3D)

The RCS140 with muffler costs over $200 more as compared to that of the OS91FX!! Ouch!

Both have similar HP (2.6-2.8).

Obviously, the RCS140 will not easily fit under the UCD cowl, regardless what way you mount it (that is assuming you are installing a mulffer !

Nice engine nevertheless. I have to say that because I just purchased a ZDZ40 for my new Giles!

I've tried a number of different props from a 14x6W to a 15x6W and standatd 15x6 etc. My elevation is 2200ft. When I pull into a hover it will hold for a second but just seems to fall out left/right/or back. I'm sure I have the CG far enough back at 6" to at least get a bit of a hover, I just can't seem to hold it there for more than say 5 seconds....

Frustrated!

Davey_Flyer
www.blue-ether.com

Check your lateral balance and very important, have you check the engine incidence because in hover this can make it more difficult to perform well, and usually it is more set up than airplane problem and some people in the thread already talked about the engine incidence, good luck

The RCS 140 might actually be a hot engine for this plane. ALL UP with all mufflers, switches, extra battery etc it weighs 3 lbs. It swings a 16" prop and can deliver up to 14 lbs thrust.
It will hover and slow pull out an 11lb 1/4 scale sukhoi, just like my OS91 FS does with the UCD. So yes, it is a pound heavier and has a similar listed HP but the trust is much higher.
You would have balance issues but you could get 30 plus minute flights on the same fuel tank. LOL!!!!

I just noticed that there is a link to the RCU review that Marc did on the UCD listed on the Great Planes website. It is right at the top of the UCD page. Way to go Marc!

http://www.greatplanes.com/airplanes/gpma1270.html

Eric

I'm FINALLY in the process of getting all the upgrade goodies together to assemble mine. Through all the reading of the various threads, I've even read where some have already unfortunately lost their UCD's, so.... as I was looking at reversing Y's like the Miracle Y I thought I would inquire if anyone had one left from an "unfortunate landing".

I've decided to go with Hitech 425BB's all around and a 605 on the rudder after reading everything from standards to digitals. Putting the 6v on these should put them in the recommended range.

Thanks!

-s

I am running 605's on everything except the rudder which has a 645mg. (of course the throttle also had a standard servo) Had a supertigre 91 on it until an unfortunate throttle linkage breakage caused the throttle to stick wide open..... Talk about a handful.........About 2 minutes in to this wild ride the prop broke sending the engine into an unlimited rpm meltdown.......

The plane was landed safe and sound dead and is now the recipient of an OS91 4 stroke transplant

I did think about smaller servos at 6 volts, but the higher current draw equals much less flight time..........

Just some thoughts to ponder............

Thanks for the info, Vanman and sorry to hear about such a wicked time for your UCD! Yep, I thought and thought and thought about the servo choice. Reliability of servos, weight of servos, cost, and weight of battery. I finally decided to go this route and hope all will work fine. I read some 6v flight times somewhere around here that didn't seem too bad. Hope that's the case. If not, assuming all is in tact, maybe there will be some changin' going on.

-s

Smartwork,
I had the Saito91, on my UCD. would barely pull it out of a hover.

I now have a ST90. I like the performance of the ST90 better than the Saito91. The ST90 has more power.

m-

Barely pull out, eh? After all the raves, I'm going with the Saito 100. I'll keep those fingers crossed that it's a winner. I'm now going through looking at all the mods to do before getting started.

I saw where one guy replaced hinges to get more travel than the CAs allowed (due to close mounting). Also, I think I'm going with the pull/pull rudder and upgraded linkages - not to mention that reversing Y for the elevators. Had to use one on my 1/4 Sig Extra too!

Oh, and I think that silver canopy is in my sights too. Black or silver but I think silver is winning out.

-s

upgrading to the 4-40 rods is a must, the 2-56 crap they included will simply bend up like a wet noodle.

Any other "must dos" that you can think of that haven't been listed?

-s

I also had one comment about the tank. A lot of people have been asking about putting the tank at the CG. In order to do this you need to either buy a tank that will fit, or do a little cutting on one of the fuse supports.

One other option, although not quite at the CG, is to simply not push the tank all of the way toward the engine. You can push it rearward all of the way until it touchs the support that the servo tray glues to. That is much closer to CG than the stock installation and you do not need to do any cutting. You'll need to secure it in some fashion, but there would not be any cutting involved.

Are you talking about with a pumped engine? Oh, by the way, what is the "rule" regarding how long the feed hoses can be with a non-pumped engine?

-s

Yes. I'm talking about either a pumper like a YS, or any other engine that is using either a Perry pump or a Cline regulator.

As far as length I couldn't tell you a sure fire number. Iedally you want a non pumped engine to be as close to the tank as possible. Putting atank at the CG without a pump would not work.

While I think the UCD is a terrific plane I have noticed the rudder seems to couple badly to both elev. and the ail. with 45 deg. of rudder it takes about 3/4 inch. of up elev. and 1/2 inch of ail. at the fuse to keep the plane stable. Don't think I am to tail heavy, the plane does not flat spin well and requires quite a bit of throttle to harrier nose hi. Is it just this one or do they all act this way.
mike,

I've read about it not flat spinning that easily and that amazed me as I would have thought this plane had "flat spin" written all over it. I'm assembling mine now in hopes that it does better than I've read. What exactly does yours want to do when you attempt flat spin?

-s