Size Motor for size of airplane

[Gary Anderson]

Hi guys, I don't remember, what the rule of thumb about engine size to plane size? There was a lot of kits that showed what size motor to use. I have noticed that the newer type planes seem to be using smaller engine for weigh, wing size, fuse length and of coarse line size. Different planes like the score, strega, tutor and many more have been using motor smaller than what we used to use. Years ago when someone said his plane weighed around 60 ounces you automatically would use a 60 size motor. Now it seems a lot of people are using a 46 OS and it seems to work for them. (not me) I tried the 46 in a score and it flew great until I started doing several square loop and she would fall out the sky. (just me) I only crashed two of them doing this, yes, I did put them back together. The engine offset is so great on the score it will pull your arm out. (Maybe thats why they stay out so well, until something else happens.) The engine doesn't set out 90 degrees, just feels like it does. I guess question is what is the formula used to figure engine size versus plane size?

[Wynn Robins]

Cant help you on the formula - but the OS LA 46 is more than enough engine for the score - falling out of the sky is an interesting happening - when you say "several" square loops - it tends to make me think you are bleeding too much speed off.

I have a friend that flys a score with a 46 in it and it goes like a champion.

[Joe Yau]

I have a friend that flys a score with a 46 in it and it goes like a champion.

Would you know what Prop and RPM he is running in the SCORE?

[Bob Reeves]

LA 46 on a Score... Not unless all you want to do is fly level, you will never see this combination in competition except maybe beginner or an Intermediate that doesn't know any better.

[Joe Yau]

LA 46 on a Score... Not unless all you want to do is fly level, you will never see this combination in competition except maybe beginner or an Intermediate that doesn't know any better.

Is it really that bad?  ("fly level")   I know on my other plane when I get a slow run, it has problem pulling up on a wing-over in the wind, but loops, sq eights, etc and most of the maneuver still could be done.. sometimes with a bit of stepping back a few steps..   but the overhead stuff  (45 degree +) are mainly the issues though.

[Ray]

Compared to 50 years ago, when "Glow" engines were only a decade old, and every model engine had an iron piston, a steel cylinder, and loop-scavenged porting, there is a much wider range of power packages for the various displacement sizes -- for instance, OS Max made "VF" engines in .20, .25, .40, and .46 sizes that had huge power output ratings compared to more ordinary engines.  Matched to tuned pipe exhaust systems, the VF 40 had/ has equal or superior stunt performance to a Tigre 60. 

A modern Schneurle ported ABC or ABN 25 may easily have as much raw power as an iron 40 of 30 years ago, so it's not quite as easy to break out planes and engines in particular size classes as it once was, but one very neat possibility does exist that is well appreciated.  The mounting bolt pattern of a medium case OS Max is now a virtual drop-in for a Fox 35's mounts, so an FP 20, or LA 25, can swap with a stunt Fox. 

What I cannot point you toward is any chart anywhere that ranks the engines we now have access to, in order of their performance capability. 

[Andrew Borgogna]

I watched a guy fly the pattern several times with a Score powered by an LA46.  I was supprised after everything I had heard but I saw it with my own eyes.  I was very interested because I too have a Score and plan to power it with a ST-51. 
Andy

[RandySmith]

Hi guys, I don't remember, what the rule of thumb about engine size to plane size? There was a lot of kits that showed what size motor to use. I have noticed that the newer type planes seem to be using smaller engine for weigh, wing size, fuse length and of coarse line size. Different planes like the score, strega, tutor and many more have been using motor smaller than what we used to use. Years ago when someone said his plane weighed around 60 ounces you automatically would use a 60 size motor. Now it seems a lot of people are using a 46 OS and it seems to work for them. (not me) I tried the 46 in a score and it flew great until I started doing several square loop and she would fall out the sky. (just me) I only crashed two of them doing this, yes, I did put them back together. The engine offset is so great on the score it will pull your arm out. (Maybe thats why they stay out so well, until something else happens.) The engine doesn't set out 90 degrees, just feels like it does. I guess question is what is the formula used to figure engine size versus plane size?

HI Gary

YOu would be better off  just asking about a specific plane you built or are building, how much you think it will weigh, what your going to do with it and anything else special...like you live and fly in Denver..or  at sea level

It is very hard to make a catch all list

Randy

[Randy Powell]

I have a plane I have flown with both an OS40VF and a RO-Jett .65. Only real difference in flying is in the wind, the RO-jett has more juice. But overall, the flying characteristics are pretty similar. The RO-Jett allows a bit wider adjustment band and is somewhat more forgiving of a bad run or a missed needle setting. The OS has to be spot on. When it is, it's great.

[Bob Reeves]

Is it really that bad?  ("fly level")   I know on my other plane when I get a slow run, it has problem pulling up on a wing-over in the wind, but loops, sq eights, etc and most of the maneuver still could be done.. sometimes with a bit of stepping back a few steps..   but the overhead stuff  (45 degree +) are mainly the issues though.

Probably not that bad but the LA 46 isn't a VF, it's great on a 48-50 ouncer but on a 62+ ounce Score not my idea of near enough, ST 51 would be marginal. Please realize my engine choices are based on being able to take the airplane to a contest and be competitive in most any conditions flying advanced. If all you want/need to do is fly a few loops or only fly in perfect conditions at sea level with the temprature in the 70's then ya you might be able to get away with an LA 46 on a Score.

[Bill Little]

Probably not that bad but the LA 46 isn't a VF, it's great on a 48-50 ouncer but on a 62+ ounce Score not my idea of near enough, ST 51 would be marginal. Please realize my engine choices are based on being able to take the airplane to a contest and be competitive in most any conditions flying advanced. If all you want/need to do is fly a few loops or only fly in perfect conditions at sea level with the temprature in the 70's then ya you might be able to get away with an LA 46 on a Score.

I have not been sold on a LA 46 in a decent size model.  A flying buddy lost a good airplane to the lack of power.  He flies Expert, and worked like crazy to get it right.  Finally lost the plane.

For serious contest work I would only put one in a Profile or Classic plane.  I have flown a truly World Class engine set up, and the LA 46 isn't really close.  BUT, they are fine for certain applications.  My own, personal, not so humble, opinion.

Now, I know that there are some here who will take exception to what I said, they already have.  But they have the "Perfect Right to be Perfectly Wrong!" 

Bill Little

[Ray]

I know on my other plane when I get a slow run, it has problem pulling up on a wing-over in the wind, but loops, sq eights, etc and most of the maneuver still could be done.. sometimes with a bit of stepping back a few steps..   but the overhead stuff  (45 degree +) are mainly the issues though.

If/ when you still have good line tension below 45 degrees with a marginally slower than usual engine run, but fall out of maneuvers above 45 degrees, I blame it on an excessive amount of line rake causing too much speed to be scrubbed off overhead.  What Bob is referring to, though, is just not having an adequate power reserve for varying weather conditions, different altitudes away from the home field, etc. 

[Bill Little]

Hi Ray,

Most everyone it seems, in the beginning, uses to much offset in all regards.  Lead outs, engine, rudder, tip weight, etc., etc.........  you only *need* enough line tension to have adequate control of the plane, as you well know.  If it is excessive, something is wrong.

[Randy Powell]

Mike Haverly is using an OS46LA in his new classic plane. About 660 square inches, but pretty heavy at close to 53 ounces (before he put 3 ounces of lead in the tail. The OS seem to do fine. But that's just observation. I have an OS 46LA that I've been using on a porky profile. Works OK. But would not be my first choice if the engine hadn't been given to me.

I'm all for using way more power than you could possibly need and throttling back. A V8 in a Nobler is fine with me.

[john e. holliday]

I wonder how you can just say such and such engine will work on such and such airplane and no other engine will work?  The engine isn't the only equation the mix.  You have to take into consideration the prop used, weight of the airplane, type fuel,  length line and all the other stuff that has been mentioned.  I am with Bill in that I want enough tension so that my arm isn't pulled out of the socket.  Did forget to mention about where in this great country of ours do you fly?  Just going to Denver from KC calls for fuel change and maybe a prop on a plane that flies great at home.  Later, DOC Holliday

[Leo Mehl]

I usually don't listen to any of this. I use what works for me an I have been around long enough to know what works. In other words I have nothing to offer to this post so why am I writing this?