I’m looking for some help on a 1/5 scale RC P51 D project that I would like to start on. While I’ve always enjoyed building static models, my true passion is RC scale. In the RC community we have many rc kits for the P51D but most are terribly inaccurate.
Most have problems with the cowling profile, fuselage sides, fuselage spine behind the canopy, spinner, landing gear position, wing airfoil and the list goes on and on. Everyone says we have enough Mustangs all ready but how about one that looks right! The Aerotech kit was probably the best but they are out of business. There kits were all carbon fiber, very expensive, came out of the moulds fully detailed with rivits and fasteners.
I would like to draw my own plans and scratch build my own P51 D in 1/5 scale by scaling up an accurate plastic kit. The question is which one to choose. I have the Tamiya kit but is there something better. I’m going to slice the fuselage at each station matching the the NA drawings to ensure I get the correct cross sections.
John, I don’t believe any 1/48 or 1/32 model can be scaled to 1/5 and look right. Somewhere around here I have a pretty good set of Mustang drawings, they are the best I have found but I’ll have to find and scan them. The old Monogram 1/32 kit looks the best to my eye, especially with regard to the airfoil. But I wouldn’t start with it, the measuring and translating introduces too many inaccuracies. It would be nice to have a structural repair manual, some of them yield pretty good cross sections and station diagrams.
It’s all in the weight, Bill. I used to have a mid size Mustang that flew extremely well. Sure didn’t like me landing in the weeds, though. landing gear retracts peeled right out and stayed in the weeds. I do have a 1/5 scale Mustang now, but it’s a bit portly. Got it used, the lazy way.
I found the drawings I like, they are by A A P Lloyd, one of the English perfectionists, like Cox. I think they would be an excellent basis for a large scale Mustang. The drawings are in 1/24 scale with lots of cross sections and details including what looks like a pretty good rendition of the airfoil, and the standard markings. Details for the B, C, D, and K.
Now all I need to do is scan them in. Where’s that gonna fit the schedule? Oh well, I’ve always planned to do it…
Actually, at 1/5 size scale can fly quite nicely. Even the Mustang’s laminar-flow wing works at that scale. A common airfoil used in RC is the Clark Y, which is also commonly used in full scale aircraft of all types (even WW2 fighters).
And I wouldn’t trust squadron’s 3-views. They are a good reference point, but they are far from perfect. There are better 3-views out there. Here is a link to some that I use frequently:
I speak from ignorance, but a 7,300 pound a/c scaled to 20% in dimension, weighing about ?50lbs? which is about 0.75 % takeoff weight, and flying at 10% or so the speed of the original must throw the performance curves down the potty. Big ailerons?
R/C is obviously black magic to us mere physics students. I’ve got a 1/350 Liberty ship that floats in the tub when I take my bath. But she doesn’t displace forty tons. Must be the bubbles.
I’ve looked at the photos of the TopFlight and the resemblance is ok, but it’s not scale.
Years ago my dad worked with a guy, whose name I can’t recall he had a garage business building rc models of jet transports with ducted prop engines. The big one was the early 747. These were NC machine shaped out of styrofoam. It sort of worked because they didn’t weigh anything, but they didn’t have any takeoff power either. There was a surgical tube launch system (big slingshot). And once they got in the air they didn’t have a mass to rotate against.
Not Dad’s fault though; he was too busy recruiting young aero engineers to the Concorde program, although they really were stuck computing runway loading of DC-7s for foreign airports as UAL plotted to expand…
Certainly, and again I aver that I know nothing about scale flight but am eager to learn,; sucking sound at my wallet; but isn’t an improbably light model a kite in the wind, and if so how do you control it?
They usually end up plenty heavy, especially the scale warbirds. They actually fly quite like real warbirds. Sluggish at slow speeds, crisp at high speeds. Similar climb / dive performance. Watching a good RC warbird, the way it accelerates and turns, it’s quite easy to start imagining that it’s the real thing. Not all of them, mind you; but the ones that are setup correctly.
To explain the weight difference:
Everything on the model can be scaled down in size, but the air density cannot. At 1/5 size it’s almost like the viscosity of the air has been reduced: the air doesn’t get trapped underneath the smaller wings as easily. It can slip over/around the wings if the pressure is high enough. So you have to compensate by reducing the weight to reduce the wingloading to reduce the pressure. Once you do that, it’s almost like you’ve scaled down the air too.
A 1/5 mustang will only weigh ~25 lbs, which as you pointed out is far less than 1/5 of a real mustang’s weight. It all goes back to fluid dynamics equations that have alot of variables raised to the 2nd & 3rd powers. It’s those squared figures that causes the weight requirements to be so drastically reduced.
I never thought about inducing accuracy issues from scaling up a plastic kit. I would love to see the drawings mentioned at the beginning of this thread. The help and comments are greatly appreciated. If you compete in scale RC modeling your project must be presented with the three views it was built from. Even if they inaccurate the model must match the drawings. This project for me is more about seeing if I can design a Mustang that looks correct and flies well. So the more information and opinions I can get the better off I’ll be at this point in my project.
I’ve been flying scale RC warbirds for many years including Mustangs. At 1/5 the typical weight is in the mid twenties range with about an 85" wingspan. At that size they fly very scale like if they are not grossly over powered. They can be stable and quite smooth, landing requires flaps and good throttle control to keep the power on until you touch down on the mains. So if you can control the weight they behave pretty well and are really fun to fly.
One thing about the Mustangs wing is that you have to be carefull with elevator input at high speed. The Aerotech kit I mentioned was totally scale and prone to high speed stalls in a loop if pull to much elevator at the top. The plane would snap and roll on its back and into a spin. In many cases it was unrecoverable since RC models tend to be flown close in. That’s an expensive object lesson with a scale model. The full scale 51 acts the same way and they train pilots on how to survive a high speed stall in a Mustang. In this case altitude is life. Bottom line if you build scale they fly scale as well but you have to manage the power to weight carefully.
I have both the parts and structures manual for the Mustang. The elevator, horizontal, vertical and rudder rib half bredths are provided and so are wings leading edge airfoil ordinates from the front spar forward. Some of the fuselage cross sections are provided but stop at the engine bearer. That probably explains why most RC Mustangs look pretty good until you get to the cowling. So those books are a big help but not the complete answer. I guess its back to looking at drawings and picking one that looks good. I’ve been trying to get in touch with Charles Neely on the Mustang forums. He has a set of drawings he did at 1/16 using the 900 rolls of micro film that the North Amercian drawings are on. So far no luck but I’ll keep trying. I would love the Loyde drawings if you could scan them.
Not trying to hijack the thread, but for bondoman’s info…
RC has come a long way in recent years. Properly powered, the flying speed of a 1/5 scale P-51 would be real close to 20% of the speed of full scale. Its not uncommon at all to see 1/5 scale planes flying at scale speeds. In this case 20% of the cruise speed (depending on who’s spec sheet you read) of a P-51D would be ~64-72 MPH… easy to do. Max speed ~86 MPH… again easy to do. Its nothing to see 100 MPH scale prop planes these days.
As far as jets, they have also come a long way. They are using “real” miniature jet engines. 200+ MPH is VERY common.
Take a look on YouTube and do some searches. You’ll be amazed.
I started with plastic kits and love to build them but there is something special about doing a low pass with the gear sucked up on a nice 51 that gets in your blood. For me is was a natural extension of building static but moving into the dynamics of flight.
Yes its expensive and I can tell you it hurts pretty bad when you lose a nice plane. That happens from time to time, but with the high quality of radio’s and power systems the biggest issue becomes pilot error. Dumb Thumbs.
If you enjoy detailing a nice plastic kit, RC can bring it to life. RCuniverse is a great website to learn all about different aspects of RC for all types of aircraft.
This guy sells original production documents for many aircraft (including the p-51). You can buy a DVD set of the ORIGINAL North American P-51 drawings (about $100). I bought this set to do ‘long term, detailed research’ for a similar project. The seller is from New Zealand. I had no problem with the transaction, and in fact have exchanged several emails with him.
I wouldn’t necessarily recommend it if you are just looking for a few GAs, but if you are a real Mustang fan, this is for you. There is actually so much information, it’s hard to figure out where to start (to be honest, the files aren’t organized in a real well). The problem I have, is getting sucked into spending hours just reading through the 17,000 pages of stuff (including some 3-D CAD models, that if you are proficient, could pull section cuts from).
I am still debating 1/5, 1/4. If you stick to 1/5, there are several suppliers out there that sell very scale parts for things that would be difficult to make yourself (like retracts).
Other options for 1/5 scale plans would from Bud Nosen or Ziroli, but I am with you “scratch” means “scratch”, meaning starting with a clean sheet of vellum.
When I go the minature airport in Sacramento and watch the RC planes fly, whenever there’s a P-51D (they’re always “Ds”), The visual clue that destroys the look is the wing root. Almost always the angled step on the leading edge of the wing root is missing. That is the area where the landing gear folds into. P-51s don’t have a straight leading edge on their wing. (except the P-51H and that type is dang obscure)