HFrank

Hello. I have always wanted to build a classic pattern plane, and the UFO looks like a very good choice, I know it is fast, accurate and smooth, but its fuse side area seems a bit "small" to me, specialy because I like to practice 4 and 8 point rolls, slow rolls, etc. My questions are : is it capable of sustained KE flight ? does it have some adverse roll or pitch coupling ? is a ASP .91 2 stroke overkill for this airframe ?

Thanks in advance.

KLXMASTER14

The UFO will do all that you are looking to do. The .91 would be a bad choice for the UFO, I would choose a good strong modern .61 engine like the OS .65 AX or the NovaRossi.

Best regards,
Robert

Jim Johns

I agree with Robert on all counts. A .91 2-stroke would be gross overkill, especially due to balance issues from the engine's weight. If you decide to go with vintage power, an OS 61 FSR would be a nice choice IMHO. Of course, I'm partial to OS engines.

The UFO doesn't have a lot of side area, but it does have that HUGE vertical fin and rudder to help hold knife edge. The photo is of a UFO (front) and a Dirty Birdy at a Kansas contest back in the '80s. Notice the major differences in the fin and rudder.

HFrank

Thanks for your replies, guys. I was considering a .91 2 stroke for one reason : Tuned pipes used in .60 engines are intended (as far as I know) to increase power, and with the .91 I have the extra power with a very little weight penalty. But I must admit I have never used tuned pipes, and I have no idea how to tune them, so I'll try to keep things simple and use an engine with standard muffle , It's a shame the TH .75 is no longer produced.
Now, please help me to understand. While in knife edge flight, lifting is produced by the fuse side area, or the vertical fin, or both ...

Thanks again

Skylane

My Feedback: (3)

The rudder deflection controls the angle of attack of the fuselage in knife edge flight. A larger rudder can cause a greater angle of attack and this makes up for the smaller side area.

Jeff

doxilia

My Feedback: (3)

Further to what Jeff mentioned above, putting the model in KE effectively inverts the roles of the the rudder and elevator. The rudder becomes an elevator and vice versa. The difference of course compared to wing level flight is that there no longer is a wing to produce lift. The shape of the fuselage including its side area, airfoil and center of lift take on the role of a wing albeit not as well as a wing proper. For this reason, sustained KE flight usually requires a much higher AOA compared to wing level flight. The increased fuse "incidence" of course also results in the engine producing upward thrust.

David

stuntflyr

Tuned pipes are easy to set up, once they're set they don't have to be changed except for gross elevation changes. 61's on pipes have the power with no weight change from original design. The new OS 65 is a real powerhouse, KLXMaster knows them well, he put them on the pipe and showed the YS boys where it's at. The 65 is extra discplacement with 61 case size.
Chris...

HFrank

Hi David. During KE the rudder becomes a elevator, and Fuse becomes a "wing", and beeing the UFO side area relatively "small" I had some concerns about its ability to perform that maneuver, this is why I started this thread. But according Robert (a few posts above) it is capable.

HFrank

OK Chris, I will reconsider the idea of a tuned pipe.
Thanks

KLXMASTER14

This is Dick Belden's UFO. It is powered by an OS .55 AX using the stock muffler. Dick flies this model in Master's classic and AMA pattern. The .55 is "adequate" power to fly the airplane in both pattern disciplines. It is definitely not in the blistering hot ballistic category by any means, yet it performs KE, 4 & 8 point rolls, etc as required. The aircraft has retractable landing gear and is scratch built. The secret to it's performance is light weight construction, and not relying upon brute power for it's performance. Watching Dick fly his UFO is a real treat, it tracks and presents with unique authority.

Follow Dick's method, build a light airframe, and it will be more airplane than you would have imagined.

And yes, power it with a piped .61-.65 engine and you will be that much more rewarded.

Robert

HFrank

Thanks Robert for exposing this example. BTW that UFO is a real beauty.

jetmech43

My Feedback: (9)

He must have built it with out the anhedral, the UFO had that

MTK

Jim, Huge Vertical fins and even huge-r rudder to compensate for the fin (For KE flight) was a common misconception of the era. Dave Patrick's Conquest series models comes immediately to mind.

The huge fin/rudder does one great thing for the classic pattern models....makes them incredibly directionally stable so they groove like no other. The small fuse side area works in favor of directional or yaw stability. It's similar to huge stab/smaller wing regarding high pitch stability.

The small fuse side area however requires much greater deflection of rudder (plus a heck of alot of power) just to sustain KE flight (continuous slip in yaw). We made it work reasonably well for the patterns of the day, but it wasn't the ideal design feature.

To me, the best KE model was the Arrow. Lots of fuse side area about the CG producing a significant increase in lift compared to other typical models of the day and requiring minimal rudder deflection to hold KE. Great at rolls and point rolls as you would expect.

stuntflyr

HFrank,
Interesting ly, Robert has added the philosophy of Dick Belden and his lightweight, moderately powered UFO. Robert is a hardcore proponent of hard pounding power from the likes of his pipe equipped Magnum .61, OS .65 AX, Nova Rossi Speed 13, and will be using a YS .61 Classic very soon. His ability to get top power from these engines is well known on the west coast. He is a great builder, flyer and leader in the Classic Pattern group in California along with Tony F too.

Matt, I think the large canopy shouldn't be forgotten here on the UFO, it is large and far forward and provides a useful keel depth making the model not poor in regard to early KE aerodynamics. I agree the with your assessment of the Arrow, and I add the Tipo to that list as well, their forward side area starts father forward and extends full length.

Chris...

KLXMASTER14

Chris, you hit it spot on regarding the canopy. A UFO or Dirty Birdy without that canopy is little more that a Kaos. IIRC, the original Dirty Birdy article described the undercut in the canopy cross section (similar to the "tuck" or groove in the Tipo fuse) as being there to "channel" the air so to speak, assisting in holding the aircraft in KE. I do not know if the same feature was included in the original UFO canopy, or if it was effective.

Mike, you are correct about the flat stab. This is what Dick calls the "UFO II". The obvious mods were the flat stab and the different canopy. See a pic of this model and his standard UFO side by side below.
Robert

FLAPSDOWN

HFrank,

I built several Dirty Birdies and UFOs back in the 70's and early 80's. All with Proline radios, Enya 60X engines, pipes, and Rhom retracts. There's a ton of praise for both models all for good reasons and all true. The UFO flew better but I had a soft spot for the Dirty Birdy because it was my first plane I competed with when I was 13. You can still pick up Enya and OS engines and occasionally see Rhom retracts on that auction site. Macs pipes and Spring Air retracts are readily available. I wouldn't build either plane without retracts and a pipe. You can take a pass on the Proline and Kraft radios though.

There are a couple of awesome UFO builds on RCU you may have already seen. if not.........

Here's a great ground up build to a beautifully finished flying model.
http://www.rcuniverse.com/forum/clas...ufo-build.html

And an all wood build to paint. An awesome build but wasn't finished for flight at least in this thread.
http://www.rcuniverse.com/forum/clas...-all-wood.html

You of course can purchase a UFO kit which is still in production.
http://www.bridiairplanes.com/hangar/ufo.html

Hope you take the plunge and decide to do a build thread as well. It's always fun to follow along. It may compel me to crack open my hoard of Rhom gear, Enya engines, and fiberglass kits I have stashed away. I've been sitting on 2 Dirty Birdies and 2 UFO kits for decades.

Best of Luck.

tomclark

I scratch built two UFOs from the magazine size plan in RCM back in the early 80s. The first was slightly smaller and had a 45 in it. The second was slightly larger with a piped 60. Sorry, don't remember either of them holding a sustained knife edge. They were great flying smooth planes.