Since I've been exposed to a lot of RC flying and my friends have been exposed to CL flying, we've been exchanging knowledge and questions about each subject of model aviation. One question I keep getting asked is why our fuselages are so thin and I can't answer that. My guess is its because there's less drag.

Is that the reason or is it just for the simplicity of building?

Matt I think you should ask why theirs is so wide and drag producing.  (They have to get all the junk inside). Our fuse width is historically based on engine crankcase plus motor mounts plus doublers plus fuse sides equal width.  Anything more is power robbing in terms of penetration, and sure it's just easier to build that way. There have been a few like Al Rabe who did something different and proved it could be done.  It would be easier now with all the power we can have. As long as the fuselage/cowling isn't too close and blanking out too much prop disc and a big open cowl doesn't hook too much wind you could go a little bigger.

Dave

Most RC models have a far more scale look than CL ones but if you look back in time more of the early sport CL models did indeed have scale wide fuselages as well as high wings and other recognizable stuff from full sized flight.

Look back in time to the late 1970's, early 1980's, and RC pattern planes were pretty thin, too.  It wasn't until turnaround, and then IMAC, that they started looking like actual planes again -- before that they tended to be skinny and tall, probably to optimize knife-edge flying without being obvious about it.

Wider fuselages can be stiffer for a given weight.  They are also easier to get electrickery into and bend that fat wire around. 

I'm not so sure how "real" those RC pattern ships look, but like all competitive models, form follows function - and rules. Recently FM magazine ran a series of columns covering the history of pattern model design. I'm sorry that I don't remember the specifics, but I do think that the fuselage size reflects rules and their relation to things like knife-edge flying and other maneuvers they do at the speeds they fly and the radii of their turns. I have just some limited time now, but I'll try to find those issues when I'm done with a couple pressing things here now.

SK

Skinnier is lighter all things being equal. But I think a lot of it comes from progression from Fox .35s to the big block ships of today. If you look at a Nobler or a Skylark the fuselage looks right. Of course, I may just be programmed to think that now.

Just before power started going up ships like the Genesis and Stiletto were in vouge with the trim sleek look. I remember looking at Al Rabe's Mustang and Sea Fury at the NATs and thinking how HUGE they looked.

The thing with a stunt ship isn't that it's so thin, it's that it's so long. The long nose of a stunt ship ( in my humble opinion) contirbutes to the overall thin look. If you look at homebuilt single seat arcraft, they generally ARE thin, but the nose is only long enough for a motor mount and a 4 cylinder Lycoming or Continental. Since they are air-cooled opposed engines, you have the cowling bumps which makes them appear wider.

I'm 6',165 pounds soaking wet, yet I've flown some acro aircraft where my shoulders were rubbing the chrome-moly tubes.

in a simple view of most aircraft from the second world war. You might notice that the fuselages was a continuation for whatever powered the aircraft. Look at early models of the spitfire and the engine is wrapped by the fuse. and tapers and narrows to the back of the plane. Same with the 190 folkewulf and the hawker seafuries.
design was to figure out what was to power it and draw lines back from their.

If I remember right, the Owl Racer had a huge cowl but had less drag than some of the smaller cowled planes. I think it depends alot on the shape of the cowl more than the area. And to a point I think you can build a wider fuse just as light as a narrow one and it will probably be stiffer.

Would there really be significant drag reduction with a thin fuselage?  And if there was, would it matter much? I'm just thinking that with our high-thrust, thick-winged, slow-flying models, a bit of extra parasite drag from a wider fuselage isn't going to be much of an issue.

Just for reference, I've been contemplating building a semi-scale something for my next project.

If I made an airplane that's got a 50-inch wingspan, make all the "numbers" match current stunters, and retain the fuselage aspect ratio, then a Beech Bonanza would end up being just about six inches wide through the cabin, while an Extra 230 would be over six inches wide in the cowl (although it would taper nicely to a point in the back).  I think a Spit or a Mustang would be narrower, but they'd still be honkin' big.  It'd be much more of a challenge to build a light airplane if it's six inches wide than if it is two.

Planes can never be too skinny or too rich.

I have experimented with wider fuses over the years.

Here is what I have found. Yes they can be made stiffer than their skinny counter parts. The trade off is weight.  The wider fuse has more surface area and will require more finish to complete.  Thus making it heavier.  I know it isn't much but it adds up.  If you can make the thinner fuse stiff enough to handle flight loads then going wider is actually only adding weight and drag.

That drag makes a difference.  Any added drag in our situation is compounded by the plane being tethered.  And we cant just give it a little throttle to compensate for it.  We have to adjust our whole run.  

From what I have learned thin and tall seems to give the best performance.  Tall for side area and tracking, tall is a relative term of course.  Thin for less drag.  

The less drag you have the more open you are when it comes to the type of engine run you can chose.  When I had a very thin tall fuse I could run extremely flat pitched props at high rpms, 10500-10750 on a PA 65 at take off, 12" four bladed prop. It was a very steady run with minimal on and off cycling. The prop essentially became the brake along with the pipe.  It was a slick setup for sure.

As I ventured into a more wider fuse phase I was having to run much more on and off type runs to pull the plane out of hard corners.  The added drag was was cornering me into a certain type of run along with a slightly fater lap time. It is for sure that both styles will work, and work well.  Its a matter of which one you find easier to work with and more pleasing to your peronsal liking.  

 
Detail of  my Boeing retirement cartoons of a retiring GEEBEEEE LOVIN' modelmaker manager Dick Minard who loved THOSE GEEBEEEFATTY'ZZZZZZZ. Yes, Fat fuselages used to rule the early full scale designs....Seems like Boeing was also into FATTY FUSELAGES in the early dazedays of flight. 

Something to do with those single-row radials, perhaps?

YES! THOSE RADIALS...NOT ONLY WERE MASSIVE...BUT ALSO WEIGHTEEEEEEEEEEEEEEEEEEEEEEE!

There are some advantages to going slightly wider... 

I know one of the great advantages for those of us who use plastic clunk tanks is you can slant the rear of the tank towards the outboard side of the plane and get a killer 1/2 lap shutoff!!!  None of this 6 laps of beeping nonsense to fight through.  It helps a great deal in FAI with the 7 minute limit.

There are many reasons to have a thin or thick fuse, but I think a lot of it
just comes from personal taste and aesthetics. Or, it's just what the builder's
eye prefers.

Personally, I prefer my fuselages to just a bit wider than the 'norm'. On my own
designs my planes usually have a 2.75" wide fuse. I do this because I like the way
it looks and it also makes it easier to package the power train. Also, as Doug
said previously a wider fuse allows for a canted tank which will aid in the shutoff.

Later, Steve

As for fat bodies, I refer you to Willie Dixon:

'Cause I'm built for comfort
I ain't built for speed
But I got everything
That a good girl need

A fat fuselage doesn't seem to slow my planes down any.

A6M2 Zero stunter with RO-Jett 76

Floyd

I assume that the exit for the airflow is under the radial cowl?

Nice model too!

. . . Also, with carefull selection of materials, structures, internal design, and dimensions of those materials, a "fatter" fuselage can be built stronger and for no more weight than a fuselage considered to be "thin". 
Keith

Keith's many-years-old Rabe Bearcat is proof of that!  Always a top contender in Classic and Expert PA, with many wins to its credit.

Of course, much of that has to do with the guy on the handle.

I had this wide body in the 80s. It was about 4 1/2 wide and flew great. The airplane was based on the CP-90 design by Claude Piel. It is closely related to the Emauraude and CAP 10. ST .60 for power.

My CP-90 was painted like the French Connection airplanes, got 18 points at the Nats... even had an Aresti card in the cockpit.

Met its demise to Circle Burner turbulance.  From the 45 on top of the square 8 it got hit from 2 directions and went Flat from the 45 to the ground. It felt like I was hit by a Mack Truck!

Steve,
That is the only picture that I have found. There are probably more, but I don't know where. I still have the rough drawing (on shelf paper), templates for the foam wing, and the canopy plug. That's it.

The airplane might be worth revisiting, possibly for electric. There are only a few minor changes that I would make.

Heres one for the masochists .  
need retracts , for the vertical C. G. , Id think . like a Widgeon , maybe .

got one on paper , 40ish size . played with a bit as theres no decent scale drgs ,
but captures the lines o.k. . ( a 12 in. prop .40 ! )

Matt,

Retracts like those are possible. Guys smarter than me have done it. 

I'm working on a set for a F3F-1. I put in the time eons ago and made drawings.

I'm also doing a set for a Widgeon. Same but different.

These drawings are what I did in CAD, photo of the monitor actually. I can draw them any size.

What have you got for drawings for that model?

 Charles

Reducing drag on a stunt ship is really not a governing design parameter.  The difference between the total frontal area of two "typical" 60" wing span stunt ships, one with a fuselage diameter of say 6", the other with a fuselage cross section of say 2.5" x 6 " is something in the neighborhood of 5% or less......

Also, with carefull selection of materials, structures, internal design, and dimensions of those materials, a "fatter" fuselage can be built stronger and for no more weight than a fuselage considered to be "thin". 

Hurrah for Al Rabe and his Super Semi-Scale Stunt Ships, otherwise known as SSSSS's.

Keith

Double hurrah for what Al has done

The frontal area to me isn't as much concern as the wetted area.  Added wetted area adds drag for every square inch.  Frontal area is muted by streamlining.  I suspect the typical stunt fuselage, because of the corners and edges, has about the same drag as a much larger, more streamlined fuselage.  But the differences are relatively small compared to the lines.

Phil C

Jim,

Actually, in the WWII era if you look down on a fuselage you will find it is an NACA 00XX with the required modifications for power.  The P40 is a perfect example as is the Spitfire, P39 and many others once you know what to look for. For radials they still based it the same way and then just stuck the engine out there.

Are you referring to the shape of the fuselage when looking from the side ?
When looking from the top down or the bottom up the fuse is rarely much wider than the nacelle/engine mount.
Same goes for the geebee or or even most modern rotary aircraft. Only when they went to the supersonic aircraft did the fuselage seem to become a coke bottle to try and move the point where the pressure wave was a problem.
unless i'm missing something...maybe the drawing I am looking at are inaccurate
Then again maybe maybe a NACA 00xx just follows the taper or any flexible yardsticl when held in place at both ends