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Apr 12, 2006, 01:42 AM
Registered User

1:72 scale micro RC biplane

I have been reading about these little micro sized RC planes people are constructing. I have never put together a micro sized RC plane thus far. The Butterfly and such is neat, but I am more of a scale person and thought I'd test the waters to see what some of your opinions would be on trying to RC something like this:

It's a little 1:72 Sopwith Camel that is made of photo-etched brass framing and a few plastic parts. I was thinking it could be covered much like a balsa wood frame model with the shrink wrap covering. This plane should have about a 4" wingspan and 3" long fuselage. Maybe use a Plantraco RC reciever and transmitter....micro electric motor and battery and hinged magnetic actuators for the control surfaces.

Hmmm wonder if the model would be lighter than an 100% injection molded plastic kit of the same size...I am thinking it would be...but I could be wrong. Could probably replace the brass sheeting around the cockpit with just covering, to make it even lighter. Seems like it would be pretty cool looking all covered up and flying thru the air...

As a side question, has anyone gotten a 1:72 or 1:48 scale injection molded plastic model to successfully fly under RC power?

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Apr 12, 2006, 10:27 AM
I'm not exactly super good at micro scale models, but I'm gonna venture a guess here and say that any solid frame made of plastic will be too heavy. For a 4" wingspan on a 3" fuse you're probably looking at 2-2.5grams maximum weight, including all electronics.. Just a guess.
Apr 12, 2006, 10:40 AM
Nem Jr.
Nemesis_49788's Avatar

One small Bird

One small bird only requires one small obsticle to obstruct it's flight......

I salute you for your ambitious nature,your vision and your bringing this question to a thread where you will surely get some answers to your proposal.

I have to say that these models are minute pieces of art,as I have this one and the wright flyer. They are wonderful display models that represent fine craftmanship and attention to detail. They should however, not be used for anything other than a mantlepiece. If you have a connection to this type model or even this particular model, my suggestion would be to try thin balsa sheet or a thin sliced foam alternative like depron. And yes, keep the weight to no more than a few grams....2.0-2.75 grams total flying weight. Perhaps a SS direct drive. Carve your own prop.

Nem Jr.
Last edited by Nemesis_49788; Apr 12, 2006 at 01:46 PM.
Apr 12, 2006, 01:40 PM
why wont it fly
after working on my micro, micro pitts (work still in progress) iv discovered that you have to keep weight to the absolute minimum around 2g aufw should be good. i dont mean to discourage you but i agree with Nem. rather keep it for display
Apr 12, 2006, 10:47 PM
Registered User
I figured someone would most likely say it would be too heavy to fly..

Perhaps someone could explain why a full size Camel that has an emtpy weight of 420kg and loaded weight of 660kg can fly, yet a 1:72 scale version of the same plane cannot exceed 2-3grams in weight? I know I may sound stupid asking that, but oh well.

Scaling the planes down size to weight would make the 1:72 Camel weight in empty at 5.83kgrams. Obviously there is a BIG difference in weight to size, and maybe this has to do with air density over wing load space. Smaller a plane is in size, the less proportional weight it can carry.. The little Camel's propeller thrust wouldn't be anywhere near 1/72 of the real plane's thrust, perhaps that is another reason?

I guess I just don't understand why the small planes need to be soooo lightweight. If you designed a small plane to fly TWICE as fast as a typical plane of the same size, couldn't that plane afford to be TWICE the weight of the slower plane?

I know a hummingbird weighs more than any of the palm sized micro planes, and flys much better too. Course they fly kinda like a bumble bee (which technically is suppose to be too heavy to fly..I read that somewhere). Guess nobody told the little bees that, as they continue to fly every day.

Apr 12, 2006, 11:32 PM
why wont it fly
Steve, when scaling down from fullsize your wing area does not scale at the same proportions . a half scale sopwith camel will have four times less wing area than the fullsize, so a half scale aeroplane at half the weight of the fullsize would have twice the wingloading!

hope this helps
Apr 13, 2006, 12:07 AM
Registered User

According to what you said, then a 1:2 scale Camel would have the same wing
loading at a weight of 165kgrams and 1:32 scale Camel would have the same wing
loading at a weight of 644grams..... and a 1:64 Camel would be 161grams.. Still much too heavy according to how you guys build your planes.

Is there a formula that can be used to figure this out?
Apr 13, 2006, 12:49 AM
Plantraco's Avatar
Wing loading is important. How many oz/ft2 of wing area?

Thrust is important

Mass is important.

You need to make thrust of about 60% of the flying weight of the aircraft to have a hope (anywhere from 50% up, yes, there are exceptions too).

If the "injection plastic" model is heavy, you will have a tough time finding the propulsion unit that puts out enough thrust! Even if you find it, the high wing loading of an injection plastic model will make your flight speed really really fast! It can fly, but it's going to need to go really fast to get the lift to maintain level flight.
Apr 13, 2006, 03:08 AM
Registered User

You hit the nail on the head! I played around with the FoilSim II program at the NASA website and I am understanding all this much better now.

In the case of the little Camel, one would have to know the finished flying weight of the model and it's wing loading (for both wings combined in this case). The FoilSim program will help to figure out how fast the plane needs to fly to generate a given amount of lift based upon it's wing dimensions along with angle and camber of them. Angle and camber increases in an upward direction increase lift dramatically too, at a price of increased drag resistance though.

Anyway this is all interesting...

What you said about injection plastic models is probably true..about faster flight speeds...which may be a good thing if your plastic model was based on a rocket powered airplane....hehe
Apr 13, 2006, 04:54 AM
Sticky Shepherd
Graham Stabler's Avatar
Unless 1/72nd means 1/72nd of the volume then you can't just divide by 72.

In the same way 1/2 scale model of a cube weighing 1kg would weigh 0.125kg as the volume is 0.5X0.5X0.5.

Apr 13, 2006, 05:23 AM
Beware of the cabbage
MeGrimm's Avatar
Also Steve, even if you do scale the model itself down, you can't scale the air particles around it, making the atmosphere very dense. So the model's perfomance is actually more like swimming than flying!

I haven't seen that 'FoilSim II programme', but does it have anything about 'Reynolds Numbers'? These are very interesting and make a HUGE differnce to the model's flying ability too!

But the great news is that there are other models flying very nicely at this scale, so it CAN be done!

Good luck!

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