OK Models 3D Cap -- What Engine???
 

:confused: Ok, I followed the instructions and mounted an OS .46FX on my OK Models EZ Cap. It took an additional 8 ozs of lead inside the cowl to correct for the recommended CG. Guess what, it barely had enough power to get off the ground.

I've read the RC Mag review on this airplane and took note of the fact that they thought a 45-size engine was not enough -- they used a piped 49.

Well, I found that my MDS 68 crank case was pretty close to the OS FX .46 and weighed in about 8 ozs more so I mounted it. CG was pretty good without any extra weight. I mounted an 11x8 prop and flew it with that configuration for several flights. Nothing to write home about except after about the 6th or 7th flight the wing split in 2, the 2 wings halves stayed with the fuselage until I got it on the ground thanks to the mounting screws and the lip the leading edge fits under -- it was flapping like a bird though. I boxed it up and sent it to the importer and they reluctantly replaced the wing (they took exception to me running a 68 in a 45-size airplane) -- OK Models left out a lot of glue in the wing root area.

I finally got it back together this past week -- after more than 6 months in the shop. The MDS 68 is running pretty good -- 11000 with the 11x8 prop. Unfortunately that configuration does not give this plane much authority in the air -- certainly not even close to trying any 3D maneuvers. I switched out the 11x8 prop for a 12.25x3.75. That didn't improve it much. An attempt at hovering almost succeeded but I was unable to fully control throttle because it required almost full to bring the airplane to a virtical stop. Unlimited virtical -- NOT EVEN!!! This is a 68 size engine in a 45-size airplane.

What am I doing wrong? Did I mentioned that this plane tops out at 7.5lbs? Do I need to go to a 90 to get this airplane to fly as designed?

EZ CAP 3D
 

You should have read the review in RCM.

First of all. the CG is WAY off. :angry: The instructions call for 100mm. It should be 30 to 33 % of the wing chord (I don't have mine anymore or I'd tell you exactly). Mine balanced without added lead with an MVVS 49 or HP 61.

As far as engine, you will need either an HP Gold Cup .61, a Saito 72 or a YS .63 for passable 3D or a 91 four stroke for awesome acceleration out of a hover. The 91 will be heavy though, and will make some of the other 3D maneuvers harder to do.

Jim

OK Models 3D Cap -- What Engine???
 

dear jim,
Though they recommend a 46 size engine, its way underpowered with it. I am planning to put a 91FX two stroke!!
Buddy of mine has tried out 3 engines on it..
46 FX..really sux
YS 63 ..pretty ok, but not enough to pull out from hovers
91 FX..great! amazing torque rolls!!
Since a 91 is a little more for that size, u will have to use a low pitch prop to keep the speed slow. You could try out the APC 16x4 W ! it should be perfect with a 90 two stroke!
I shal be using the same setup soon!
cheers,
mayur

Wrong prop to boot
 

hilleja,
The apc12.25x3.75 is really a .45-.50 size prop, your MDS68 must have swung that thing fast. Try a Zinger14x4, I ran that on a Magnum61 on a pipe, and it had alot of vertical.
DKjens

Clarification
 

JRF -- Wrong assumption on your part. Actually, I did read that review, in detail. There is also a review on RC FLIGHT Unlimited by Anders Hoberg that is pretty detailed.

After posting this I called MRC and based on their recommendation and reviewing Anders Hoberg's review, I've decided to try the MVVS .49. According to both reviews this seams to be the engine for this plane. It is both low weight (13ozs) and high powered and according to Hoberg will hover this airplane at 1/2-3/4 throttle. With the new CG recommendation this engine should mount with virtually no adjustment for CG other than RX and battery placements. I'm also going to dual-servo the elevator and replace the pushrods with carbon fiber shafts.

I had considered the 72 4-stroke but after the dismal response with an OS FX .46 decided that that is too much money for an engine that was probably not going to fit the mold. The larger 4-strokes looks promising but you start to get into weight that would be hard to balance.

BTW, the current recommended CG by MRC is 125mm. That is 25mm further back than OK's original recommendation.

DKJens -- , actually the MDS 68 only swung the 11x8 just over 11,000rpm. I didn't tach the 12.25x13.75 but assume it was slower than the 11x8. According to reviews the MVVS .49 swings the 12.25x3.75 prop in excess of 15,000 rpm.

EX CAP 3D
 

The MVVS didn't work for me. I couldn't get it to accellerate cleanly in the midrange with the big carb, and it didn't have enough power to pull out of a hover with the small carb. (If you buy one, find out which carb you are getting. It makes a big difference!)

OBTW, that's 13 ounces without the manifold, connector and pipe. With the mni-pipe it weights about 18 ounces. And yes, with the MVVS, the CAP should balance at 125mm with no lead.

Jim

MVVS Large vs Small Carb???
 

jrf,

You had me going there for a while because I just ordered that MVVS .49 this morning, and at $140.00 it isn't cheap. I called Morris and talked to one of their engine gurus.

What you failed to say was the small carburetor was taken from a 40-size MVVS. Pilots looking to get more instantaneous speed out of small props have been making the carburetor swap. The standard size carburetor that comes with the MVVS .49 is designed to give the engine greater control with a larger prop, e.g., the 12.25x3.75. Instantaneous transitions/high acceleration is not important here. This is a 3D airplane and I'm looking for torque power, not speed power. If you overspeed this airplane you are guaranteed to be picking up the pieces from the flutter.

How old is your MVVS .49.? Morris tells me the engines being shipped today have a new-style carburetor that is optimize for the engine to swing a large prop.

EZ CAP 3D
 

My 49 was brand new about 6 months ago. At that time, the 49 was available with either the 60 size carb or the 40 size carb. I tried them both, with the results stated above.

If MVVS has now designed a carb specifically for the 49, that may well solve the problem. Good luck, and please let us know how it works out for you.

Jim

MVVS 49
 

Hello,

I did the review on the Cap, using the MVVS . 49. I forgot to mention that Kozak gave me the new carb for acceleration. On a 12.25-3.75 APC fun-fly you don't necessarily need all that power, but linearity, and acceleration are musts. According to various hrust calculators you'll get 12-14 pounds of thrust with this setup. If they are only 70% correct, you will have enough thrust to get out of a TR....

Best Regards,

Anders

OK Models 3D Cap -- What Engine???
 

I had forgotten about this thread.

Here's a little history since my original input:

After waiting for over 6 weeks for the MVVS .49 I finally cancelled the order and ended up putting an OS SX .50 on my EZ Cap. It took almost 6oz of lead on the firewall to balance at 125mm.

The SX .50 is still breaking in (ringed engine) and has yet to give me the power I need for any kind of 3D, if it ever will. Right now I have just enough power to do simple aerobics. I've tried the 3D throws on the airplane and they are very very sensitive. For now I'll leave it on low-rates until I get enough engine power for 3D.

This has been a strange airplane. OK Models is emphatic that it is a 45-size 3D airplane. It weighs over 7lbs. My Ultra Stick 60 is a 60-sized airplane with a Saito FA-100 on it and it weighs 6.3lbs.

3d cap
 

That sounds very heavy. I wonder if there are production variations or something. I believe that the intended design of the machine with that wing should be flown below 6 pounds... Anything around 7 pounds is way too heavy for a .45 size airplane...

EZ CAP 3D
 

Mine weighed 6 3/4# with no lead. It would hover and pull out vertically (gradually) with the HP 61. I sold it (cheap) and the new owner put an OS .91 Surpass II in it. It works reasonably well with that engine.

What would make a manufacturer produce an airplane that is supposedly optimized for 3D, weighs 7 pounds, with the recommended CG an inch too far forward and then sell it as a 45 size airplane? With a warning not to use a bigger engine or the warrentee is void. :confused:

And on top of that, it costs more than a Lanier Edge 540T 1.20 ARF (to name just one alternative).

Jim