Why don't they stick to a scale?

[Boots Whirlygig]

Why do manufacturers stick with a common wingspan rather than a common scale? I used to build plastic kits and liked the 1/48 scale, and would love to have a livery of WW2 R/C planes with a common scale. It bothers me that the ME109 and FW190 has the same wingspan as a P-51 and P-47, when they come from the same company.
Also, why don't manufacturers, or MRC, display the scale a model of theirs represents?:Confused:

[Beeg]

Yes, if it was just about scale models I would agree. But these are flying models.

In my reasoning the short simple answer is that it's about wing "area" rather than span to get a decent flying model with a given power system and weight. I'm sure there are many other factors but this one seems like the primary reason.

Example:
A 1/10th true scale P-47 has a wing area of 4320 sq.in.
A 1/10th true scale Bf-109 would have a wing area of 2491sq.in. Without fudging on dimensional proportions an equivalent wing area with a 1/10th scale P-47 would put the 109 at around 1/6th scale.

If I'm way off base here maybe Alpha could offer his expertise into the production of Scale RC models.


As for existing scales, it's easy enough to calculate if you're using wingspan and you do a simple search for the full scale aircrafts wingspan.

[Alpha]

It's a fair question, Boots. Beeg is correct in that RC manufacturers often fudge on certain scale aspects in order to deliver a well flying RC model. Wing area and empenage area are the most frequently deviant, and his example of the 1/10 Bf-109 and 1/10 Corsair is insightful.

In many of the FlightLineRC descriptions on the product page, we include a statement of approximate "scale". As to why it isn't more common practice, I cannot say, but I would speculate it is because a standard wingspan category (1200mm, 1600mm etc) or EDF size (80mm, 90mm, etc) is more helpful to most customers than a scale factor would be. For those wanting to know the approximate scale factor, as Beeg said, it's easy enough to divide the full size's wingspan by the model's wingspan (using the same units of measurement). I've attached an Excel in the past about Freewing and FlightLineRC approximate scales, and I've updated that Excel here. These "scale" figures, however, do not tell the entire story.

Strictly speaking, we should remember that "Scale" is not just a matter of wingspan-of-fullsize compared to wingspan-of-model. "Scale" is technically a matter of ALL proportions of an aircraft. And here is where RC models, especially in foam in this size, begin to fall off that narrow road. The most visually obvious, to my eye, is that wing thickness and stabilizer thickness is often far out of scale. In addition, wingspan is sometimes enlarged, or propeller diameter or wheel sizes or wheel stance is changed. Sometimes, even, the ratio of a model's length to its wingspan does not match the ratio of the full size aircraft's length to its wingspan, so, depending on which measurement someone was comparing, they'd actually arrive at DIFFERENT "SCALES"! For my larger composite/balsa aircraft that can execute more accurately scale proportions all around, due to their larger size (and material choice and price point), it makes sense that Skymaster or BalsaUSA for example specify their actual scale factor. But for foam electric... it's less of an Instructive number than it is a Referential one.

Another factor in standardization to a wingspan measurement instead of a strict scale factor is box size and common parts. It is also perhaps a reflection of the history of RC modeling that many manufacturers sized an aircraft to its powerplant (.15, .25, .40, etc). That rating equivalent carried over into electric power (Power 15, Power 25, etc) when ARFs were prevalent, but as the foam electric PNP market grew, manufacturers designed for a standard wingspan and standard airfoil instead of rating by a powerplant. That standard wingspan template made things easier for design/development/production, but also, and perhaps most importantly, it made things simpler for the mass consumer, who more readily could digest what "1200mm wingspan" meant rather than what "1/12 scale" meant. Again, in this example, "1200mm wingspan" is an Instructive number, and for a mass market, this kind of clarity is important.

This gets deeper when we look at EDF jets. These aircraft are standardized to the powerplant because in that case it's much easier to control for performance, wing loading, cost.

As a plastic modeler, I like scale factors, and can relate to them. But, I would think that, if our website listed our FlightLineRC products as, for example, "FlightLineRC 1/10 scale P-38", the first thing most customers would ask is "but how big is that?". Listing the product as "FlightLineRC 1600mm P-38" answers that question before it's even answered, without getting too long of a title.

[Boots Whirlygig]

I realize all the parameters involved with the manufacturers. I see a LOT of ingenuity in these epo birds. The scale details and scale outlines and flight performance is phenomenal! Such a huge leap in technology! Alpha, I have not been active in the hobby for 30 years and i want a hanger of WW2 fighters. Today my first one from MRC will be delivered, the FMS 1400mm Zero. Next will probably be the FMS 1400 P-40B, P-51B, and Spitfire, the wing span of those being within a foot on the full scale icons, 36 to 37 ft. But the span difference of a F4U and BF109 is just a bummer. I believe FMS could/should do a Corsair V4 1500mm and the ME109F at 1300mm. If I ruled the World that's what I'd do! Easy cheesy lemon squeezy!!:Cool:

[TSHobbies]

Not being an aerodynamics engineer myself, why do some dimensions have to be changed when scaling down from the real aircraft? just curious is all..most of the time you dont really notice it unless you compare it to drawings or photos anyway.

[Beeg]

Most of it has to do with "Cube Loading".

http://www.theampeer.org/CWL/reynolds.htm

This is my understanding of scale model airplane design. As simply as I know how to put it.

If you scale down a scale drawing of say a WWII fighter, they would have a very small vertical stab and rudder and horizontal stab and elevator. This would be okay if you were moving at really high speeds but proportionally they would be very ineffective when you slow down. Particularly for landing and takeoff. Therefore, most "scale" models in the typical sizes of RC aircraft have at least a 10-20% larger stab and/or elevator to bring it's cube loading more inline to be effective. The size of the wing may be enlarged as well from scale to also bring the cube loading into an acceptable range based on the size of the model.
Another factor is the thickness of the airfoil to produce a reynolds number that will work for a small scale aircraft.
You also have the finess ratio of the given model. For instance, if you look at the top drawing of a Bf-109 compared to say either a P-51 or an A6M Zero you will notice the wing of the 109 appears smaller and the distance from the trailing edge to the elevator greater than of the other two. This is the main reason you have a comparatively proportional difference in the wing size of a flying scale model of a 109 as compared to a P-47 or A6M.

Anyway, I think most of this is correct.

[wvrailfan]

I am scale sensitive also. I guess it comes from 50 years of scale model railroading. When I choose what to take to the field on any given day, I try to take planes that are somewhat close in scale, so they look good together when sitting on the ground. I understand manufacturers have to take liberties when designing our models, and I can live with that. You can scale size all you want, but you can't scale mass or the atmosphere, so something has to give.

Motion does a pretty good job of letting us know "about" what scale a plane is, though I can do the math and get pretty close, and that plays into my purchase decision making process.

Also, I am finding that as time goes by, I am a little less OCD about scale, when it comes to my RC planes. I don't have any problem parking my approximately 1/8 scale FMS 1500mm Thunderbolt next to my about 1/10 scale Freewing 1700mm Thunderbolt II.

[Boots Whirlygig]

I'm happy with the FMS 1400 A6M and P-40 as they're pretty close to 1/8.5 ish for the fuselage and 1/8 for the wings on both. I would to stay this scale on future purchases, but it won't keep me from buying a plane that falls outside if it's one I've GOT to have! :Silly:

[OV10]

I would LUV to have a fleet of 1/6 scale sized warbirds but as it is now the mix of 1/8 and 1/10 has me jammed for hangar space @ 30 birds.
I would only be able to have half the amount of variation that I have now if doing the 1/6 routine.
Besides, FL is the first one to encroach upon a sub 1/7 scale foam bird with the Spitty so I would be SOL for a foamy in 1/6
I totally get what you mean Boots about the vendor sticking with the same general scale scheme like FL has done with the 1/10th.
Most of the larger FMS stuff is approx. 1/8 but I had to go with a Dynam FW-190(1270mm) in order to have the same scale appearance side by side with the Mustang and others cause the FMS version certainly didn't.
My last observation, I have to agree with Alpha's analogy that it is all about the marketing of a standard span category.
Oh well..................:P

[PappaBear]

To keep it simple as to why when you scale an aircraft down in size things are often changed to improve the flying and handling characteristics.It's the following.

The full size has been designed for a specific purpose in mind. Wheather it is a fighter, a bomber or a civilian aircraft. The said aircraft will have been designed to give a certain performance at various altitudes and airspeeds.

Bearing in mind all the above, when you then scale down to a model size, the one thing you cannot scale down is the environment in which it has been designed to operate. The AIR. The full size has been designed to operate in the air around us. Now you are scaling down to operate in the same air pressure and as such many things do not compute the same as they do for the full size.

I hope this helps just a little.

Martin.