beigemonkey

Hello All,
New to the site and to the hobby. Picked up what seems to be an older arf kit. A beautiful Cessna Skywagon 185. Seems to have come out in the early 2000's. Builld going well and having fun with it. Lot's to learn obviously.
I'm now at the point where it's time to install an engine and wondering about size. Any guidance would be appreciated.
The Skywagon is a Kondor product and has a wingspan of 87". Also has floats and I believe the flying weight is going to be about 18 lbs give or take. I picked up a Zenoah G23 twp stroke gas that I think might work. Trouble is I saw an old thread on this site dating back to 2002 and noticed a bunch of chat where guys were putting 30cc engines in theirs. So now I'm in doubt and don't want to do the wrong thing.
My other conundrum is that I bought the kit from an older guy that had it hanging around his garage for years. The directions that came with the plane indicates that a 120 engine is recommended. I thought that would be a good guide to find a comparable gas 2 stroke but the trouble is that the directions (which appear to be for the 185) erroneously indicates that the model wing span is 73" when it's actually 87". So another reason to question what engine I'd be safe with using. Just want to eventually fly the plane. Not looking to be the guy with the bigger engine or do fancy tricks. This is my first plane and I still haven't flown yet.
Thanks for any insight you can provide.
Norm

init4fun

Norm , your gonna hate me for saying this , but what you have is not a good choice of a first RC model plane . I would suggest you continue on building it , equip it with the best gear you can afford since you seem to like it well enough , and then plan on it being your 3rd RC plane or so , while you get the learning curve accomplished on a couple of inexpensive RC trainers first . Look into such planes as the "Sensi" and the "Apprentice" and also a good RC flight sim as well . Of course finding a local club and having their instructor teach you is the least costly , plane wise , but plenty of determined folks have self taught in the days before computer stabilized trainers or club instructors , with of course the associated model mortality of having no one experienced at the sticks .

I wish you well on your journey ....

beigemonkey

Thanks for the reply init. Actually don't plan on taking this one up till I know what I'm doing. Got the kit at a good price and thought the build would not only be fun but also a good learning experience that might help when I do take a trainer up. Especially helping with the lingo associated with the Hobby. Have been practicing on "Realflight" simulator that came recomended highly by local RC folks as a good start. Much to learn.
Anyway, did you have a thought as to the engine size question? Installation of the engine is my next step but don't want to start the mounting process if the feedback I get from seasoned builders suggests I should go higher than a 23cc.
Thanks

JohnBuckner

My Feedback: (1)

Hey Beigemonkey first off welcome to the forum and especially Kudos to you for wanting to learn building. So few these days actually want to learn what is the basic core of this wonderful hobby and that is building.

Next thing, init4fun has given you an excellent brief and there is no way this airplane should be used for a first or second airplane and you seem to have a good attitude about that and that is a big plus in your favor.

OK having cleared the air a bit there lets move on to your question. While I cannot say I recognize exactly which kit you are building however I have flight tested several kit built large Cessnas and the common thread of all have been that they all came out quite heavy. Your airplane is likely to be far too heavy and big for a little G-23. Will it fly? Sure but it will require far to much from the pilot and pilot skills to fly and its likely the airplane will become a hanger queen.

It would be slightly better with the latter G-26 but only slightly... Now I am going to suggest two more modern choices and relative costs between the two has nothing to do with the choice as far as I am concerned and I do have examples of both flying and I do love them both.

First is the OS 33GT it has been a long serving and successful for me and this one is worth considering especially because it is a front carb engine making mounting a piece of cake. This is a bigger consideration when one is dealing with scale cowl.

The second one I am going to suggest is a DLE 30 cc . This one I do not have but I do have two of the 20cc units these have proven to be excellent. But you really do need at least 30cc I feel a G-23 or 26 would be a huge mistake.

Enjoy the adventure

John

beigemonkey

Thanks for the insight John. My instincts, however limited in RC were telling me I might not have the right size. Too bad. The Zenoah is a nice engine and I'm hearing good remarks overall about it. Sadly, it was a person at the hobby shop that I was relying on to guide me. He indicated a 20cc would cut it ... so I went to 23cc thinking I might need more to make up for potential novice builder issues I might incur. Also disappointing cause with it temporarily mounted and most of the other components in place, the center of gravity thing is working out beautifully.
Oh well... would have been worse to get it done and find the mistake on first takeoff. Thanks again for your insight.
Norm (aka...beigemonkey)

TomCrump

I fly similar sized models on G-38s. At 18#, your G-23 may do the job, but if it were mine, I'd be more comfortable with the 38cc Zenoah.

init4fun

Hi Norm ,

Sorry I forgot to answer the most important part of your question , and both John and Tom have filled in the details nicely . As to engine size , you can follow the well established figures of power to weight if you want an exact and scientific answer . The figures are as follows ;

mild ROG flight = 50 watts per pound

Mild aerobatics = 75 watts per pound

Aggressive aerobatics = 100 watts per pound

3D or high speed = 125 to 150 watts per pound

Competition = 300+ watts per pound

So , looking at those numbers , if your all up flying weight will be 18 pounds and you are looking for somewhat spirited performance you'd be looking at 18 pounds times 100 watts per pound equals 1800 watts . So what's up with the watts ? Well , 746 of them equals one horsepower and so you will need 2.41 horsepower to fly the aircraft at 18 pounds with "aggressive aerobatic" performance .

Now remember , these figures are recommended minimums to reach the desired performance and a bit more power is always preferable to a bit less .

For fun , in the full scale world the Piper Cub , at 1220 pounds with a 65 HP engine is right around 40 watts per pound , VS the Spitfire IV at 5000 pounds with it's 1440 HP engine was flying at 215 watts per pound .

In our model plane world , the accuracy of these figures will be entirely dependent on the engine manufacturer's honesty . If they say a given engine is for example 2.5 HP when in reality it puts out only 1.75 HP , well there are gonna be problems with not enough power .

In closing I'll say that the 30cc engine will be plenty of power , and I posted the figures above just to illustrate how the actual engineering of power to weight works for the intended level of performance .

beigemonkey

Thanks again init. Very helpful, and nice to see somewhat of a formula... however variable it may be due to the manufacturing peculiarities and characteristics of individual models. Will be tucking my G23 away for a future model. Already have a Zenoah G38 coming. I know it weighs more but am hoping the extra pound won't be that much of a hassle. Also concerned about how much cowel I'll have to hack away since I'd prefer to keep the plane looking like a replica and not a tricked out street rod. We'll see. if too big physically, I may try the dle or evolution as has been suggested. They are physically smaller from what I have seen on the spec info.
Appreciate the help from you and all. The term, "it takes a village" has always been true, but even more so in the RC world. So much to learn but very exciting. Feel like a kid again.
All the best,
Norm