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Model Forum / Radio Controlled / Air Models / July 2008Good books on designing model airplanes
I want to design model airplanes. I want a good book that will introduce me to aerodynamics and other details such as how to pick a good speed control that can be used for both brushed and brushless motors, and how to go about sizing a motor and power system given an airframe. I probably want to focus on scratch-built electrics. Probably the best way to do what you propose is to build a few existing designs from kits or plans, then build some modified versions of them and see if they do what you expect them to do. After you do this a few times you'll be able to design your own. > I want to design model airplanes. I want a good book that > will introduce me to aerodynamics and other details such as > how to pick a good speed control that can be used for both > brushed and brushless motors, and how to go about sizing a > motor and power system given an airframe. I probably want to > focus on scratch-built electrics. (top posting fixed) >> I want to design model airplanes. I want a good book that will >> introduce me to aerodynamics and other details such as how to pick a [quoted text clipped - 6 lines] > and see if they do what you expect them to do. After you do this a few > times you'll be able to design your own. There are books on RC model airplane design, there are also occasional articles in Flying Models and similar magazines on various design aspects. Build a lot. Fly a lot. Modify a lot. Tossing parts from different airframes together and seeing how it flies can be educational.  SignatureTim Wescott Wescott Design Services http://www.wescottdesign.com Do you need to implement control loops in software? "Applied Control Theory for Embedded Systems" gives you just what it says. See details at http://www.wescottdesign.com/actfes/actfes.html > Probably the best way to do what you propose is to build a > few existing designs from kits or plans, then build some > modified versions of them and see if they do what you > expect them to do. After you do this a few times you'll > be able to design your own. The main thing that I want to do is know how to size an engine for an airframe, I am guessing that this mostly depends upon total weight. I also want to know how much torque that the servos will need. Also is there such a thing as an ESC (speed control ) that works on both brushed and brushless motors? How do I know which ones these are? >> I want to design model airplanes. I want a good book that >> will introduce me to aerodynamics and other details such >> as how to pick a good speed control that can be used for >> both brushed and brushless motors, and how to go about >> sizing a motor and power system given an airframe. I >> probably want to focus on scratch-built electrics. >> Probably the best way to do what you propose is to build a few existing >> designs from kits or plans, then build some modified versions of them and [quoted text clipped - 3 lines] > The main thing that I want to do is know how to size an engine for an > airframe, I am guessing that this mostly depends upon total weight. I'd ask TNP about that. I also want to know how much > torque that the servos will need. Also is there such a thing as an ESC > (speed control ) that works on both brushed and brushless motors? How do I > know which ones these are? I've never heard of anything like that. They are controlled differently. mk >>> I want to design model airplanes. I want a good book that will introduce >>> me to aerodynamics and other details such as how to pick a good speed >>> control that can be used for both brushed and brushless motors, and how >>> to go about sizing a motor and power system given an airframe. I >>> probably want to focus on scratch-built electrics. > Probably the best way to do what you propose is to build a > few existing designs from kits or plans, then build some > modified versions of them and see if they do what you > expect them to do. After you do this a few times you'll > be able to design your own. I want to minimize the total cost, thus minimizing the number of false starts. >> I want to design model airplanes. I want a good book that >> will introduce me to aerodynamics and other details such >> as how to pick a good speed control that can be used for >> both brushed and brushless motors, and how to go about >> sizing a motor and power system given an airframe. I >> probably want to focus on scratch-built electrics. >> Probably the best way to do what you propose is to build a >> few existing designs from kits or plans, then build some [quoted text clipped - 4 lines] > I want to minimize the total cost, thus minimizing the > number of false starts. Sounds like you want to do everything right the first time, which is a good way to live, but usually with model planes you'll change your mind several times before you even know you're doing it, and there really isn't any such thing as "right" when it comes to designing a plane. There's only "good design", and good design depends on what your goals are. To design a plane you have to know what kind of plane you want. Your options include everything from thermal soaring to 3D aerobatics, and just making one little change (power loading, wingspan, weight, aspect ratio, etc) will create a different airplane. If you haven't flown a plane one way, you won't have the insight to want to try it another way for comparison. I'm not trying to rain on your parade. All I'm saying is that until you start flying something you won't really know where to go next. It's definitely a good idea to have a book that describes what each design factor of an airplane does. That will help a lot in your design-test-redesign process. If you need a book about power ratios for electric planes, I'm not sure you'll have a lot of success finding one. It's a lot harder to publish a book on specialized hobby topics now that the internet is out there. You're likely to have the best luck asking specific questions on a public forum, once you figure out what kind of plane you're designing. Then a few guys will throw a bunch of bewildering info at you about battery type and size, motor size, gear ratios, and propeller sizes. Sooner or later you'll have to buy some equipment and try it out, and I think you'll have the greatest chance of success if you ask other electric pilots what powerplant they would put in their plane. As mentioned, there are many different types of planes and each one is designed diferently. But assuming you want to do typical RC planes, check out the article at "http://www.uoguelph.ca/~antoon/hobby/ pmdesign.htm". It's a place to start. There are many other links to design information such as sizing motors, engines, propellors, including many for books and software - do a little googling. You'll be overloaded with the suggestions. Richard One of the best, R/C Model Airplane Design by A.G. "Andy" Lennon ISBN 0-87938-238-4 Then check Amazon.com http://www.amazon.com/s/ref=nb_ss_b?url=search-alias%3Dstripbooks&field-keywords =R%2FC+Model+Airplane+Design+&x=18&y=17 Great that is one of two that I already ordered. From the Look Inside table of contents it looked like a really good one. Here is the other one that I ordered: Radio Control Foam Modelling by David Thomas and Sid King (Paperback - Mar 2000). http://www.amazon.com/Radio-Control-Modelling-David-Thomas/dp/1854861794/ref=sr_ 1_1?ie=UTF8&s=books&qid=1215965631&sr=1-1 > One of the best, R/C Model Airplane Design by A.G. "Andy" > Lennon ISBN 0-87938-238-4 > > Then check Amazon.com > http://www.amazon.com/s/ref=nb_ss_b?url=search-alias%3Dstripbooks&field-keywords =R%2FC+Model+Airplane+Design+&x=18&y=17 >>> Probably the best way to do what you propose is to build >>> a few existing designs from kits or plans, then build [quoted text clipped - 12 lines] > There's only "good design", and good design depends on > what your goals are. OK, fine. I want a scratch-built double (or possibly triple) sized firebird phantom that can handle 15+ MPH wind. The cost of all of the airframe, (excluding the electronic components) must be very low, and comprised entirely of cheap things that you can buy from the hardware store. I want to start with the lowest cost components that will work, brushed motor and NiMH, and later upgrade to more powerful brushless and LiPoly. The one airframe piece that I may simply purchase from a hobby store may be the wing, because making a good wing with the proper aero dynamic properties looks too tricky. The body will probably be a solid piece of heat treated pink foam. (melting the outside layer of foam with a heat gun adds a lot of strength if done properly). The stick part of the body will probably be 1/2 inch PVC, this is very strong and weighs 1.3 OZ per foot. All of the body pieces will be attached together using epoxy. From what I understand greater weight adds wind stability, thus I am shooting for a total weight between 16 - 32 oz. Like the Firebird Phantom, this will be a push prop, this saves props and prevent direct motor impact. The motor, receiver and ESC will be encased in the foam to reduce impact shock. The servos will probably be directly attached to the PVC, using screws so that they can be reused after a total wrecking crash. The V-tail will probably be constructed separately and attached with screws so that either the body or the V-tail can be re-used in the event of a serous crash. The wing will be attached to the body using the conventional rubber-band method. > To design a plane you have to know what kind of plane you > want. Your options include everything from thermal [quoted text clipped - 22 lines] > chance of success if you ask other electric pilots what > powerplant they would put in their plane. With the above mentioned specific design parameters, someone out there should be able to provide very specific advice. I want a scratch build double (or possibly triple) sized firebird phantom, since its weight is likely going to be disproportionally higher, (Firebirds weigh 8.5 oz) and I want to keep the cost low, I need to know exactly the size, of the motor, and the specs for the prop. To provide a precise basis for further discussion, lets say that the total weight of a double sized firebird phantom will be exactly 34 oz, making my design exactly twice as heavy. Can I simply buy a quad sized motor with a double sized prop? What parameters specify the size of the motor? I just realized that I was ambiguous in my specs by double or triple sized, I am referring to wing area, not wing span. >>>> Probably the best way to do what you propose is to >>>> build a few existing designs from kits or plans, then [quoted text clipped - 87 lines] > Can I simply buy a quad sized motor with a double sized > prop? What parameters specify the size of the motor? > OK, fine. I want a scratch-built double (or possibly triple) sized > firebird phantom that can handle 15+ MPH wind. So you want to build a trainer able to handle some wind and front impact. > Like the Firebird Phantom, this will be a push prop, this saves props and > prevent direct motor impact. That's the advantage of the Firebird's prop location. The main disadvantage is that you are limited in the propeller size. You can't put a large propeller for higher thrust, and high thrust is a good feature in trainer airplanes, because it allows you to prevent a bad landing by climbing quickly. That is good in case of a sudden change of mind, or a sudden change of wind. Also, larger propellers allow you to slow the airplane down easily. In that case, I would use an inexpensive brushless motor mounted on an easily-replaceable stick. The stick acts as a fuse in case of a crash, preventing more damage on the more expensive motor or airframe. A prop saver can save the prop. If the motor is inrunner and it crashes pretty bad, you probably have to fix or replace just the gearbox. If it is an outrunner, you probably replace the shaft and then you are ready to fly again. In my humble opinion, it is better to prevent crashes rather than being able to survive crashes, and a larger propeller can make a difference. Another disadvantage of the rear mounted motor is the CG location, which can be tricky if the motor is behind the wing. By the way, if it is your own design, you might want to try different motors, and having a stick-mounted motor makes it easier. > The V-tail will probably be constructed separately and attached with > screws so that either the body or the V-tail can be re-used in the event > of a serous crash. Why a V-tail instead of a conventional tail? A conventional tail does not require mixing. > Can I simply buy a quad sized motor with a double sized prop? What > parameters specify the size of the motor? Some ideas taken from a previous post, maybe not all are applicable here: + You must consider at least 50W per pound for a slow trainer; ideally, 80W or 100W. If you want a sporty airplane, 130W per pound is OK; for 3D, 150W or more per pound. + Watts is roughly motor voltage times current (assuming high efficiency). Typical setup for small trainers is 2- or 3-cell LiPo (7.4V or 11.1V). If you go with 3-cell, 100W (1-pound trainer) require about 9A, usually a bit more considering that motors are roughly 70% - 90% efficient. Then you need an ESC, motor and battery rated at at least 9A. + ESC, motor and battery have two current ratings: continuous and burst (example: 10A continuous, 14A burst during 30 seconds). If you don't know your flying style (how long on full throttle), start with some margin, or do short flights and then check whether any component is hot (warm is usually ok). + ESC must match motor type (brushless ESC for brushless motor, brushed ESC for brushed motor) and battery chemistry (LiPo, Ni-MH, Ni-Cd). + Typical motor ratings are: KV and max current. KV is roughly number of thousands rpm per volt, no load. Example: KV=1000 -> with 11.1V, you get 11,100 rpm. In practice, when you attach the propeller you get 8000 rpm or so. + High KV motors (~3000 or 5000) require a gearbox to reduce KV and increase torque. Those are inrunner motors. Outrunner motors have lower KV (<2500 or so) and a propeller can be directly attached to the shaft. Outrunners are quieter and usually require less maintenance. However, if you crash, there is more chance that you'll damage an outrunner motor. Typical damage is a bent or broken shaft, and shafts are inexpensive and easy to replace. + Motors come with charts with suggested propeller size, current and power consumption depending on number of cells, thrust and pitch speed. + 2-blade propellers have two numbers: diameter and pitch, in inches. More diameter -> more thrust. More pitch -> more speed. Both relations are pretty nonlinear (again, a watt-meter is much better than guesstimations). For a trainer airplane, use a big propeller. Not very fast, but allows you to control the airplane speed without much delay. + Depending on the current draw and ratings, cooling may be necessary for motor, esc and/or battery. A good airflow is usually sufficient. + When you test a motor on a bench (static test), it draws more current than when the airplane is moving. + Go brushless. More power, less weight, more durable, more efficiency -> more flight time for the same battery. + Go LiPo. They are reasonably safe if you handle them properly (again, a watt-meter and GOOD charger and balancer are a must), and have much more energy per ounce than Ni-Cd or Ni-MH. + Batteries have three main ratings: voltage (given by number of cells in series), max current, and capacity, in mAh. a 2000mAh battery can give you 2000mA (or 2A) during one hour before going empty. If your airplane draws 10A continuously, the battery is depleted in 1/5th of an hour, this is, 12 minutes. + Another important rating in batteries is the charge/discharge rate, expressed in C (example: 1C, 10C, etc.). 1C means a current so that charge/discharge takes 1 hour. Example: for a 2000mAh battery, 1C means 2000mA or 2A. LiPos must be charged at 1C maximum. Discharge rate varies (10C to 25C or more, depending on the battery). A 10C, 2000mAh battery can be discharged at 20A, etc. + A good way to get a feel on the numbers is by using an electric flight power system software (like http://www.motocalc.com/ or some other free alternatives). Some numbers I like for a trainer (personal preference): + Motor: KV around 1000, maybe less. + 3-cell LiPo. + propeller pitch around 4.7 + propeller diameter as large as ground clearance or amp draw allows. + Outrunner brushless motor. Hope this helps. Best regards! >> OK, fine. I want a scratch-built double (or possibly >> triple) sized firebird phantom that can handle 15+ MPH [quoted text clipped - 35 lines] > try different motors, and having a stick-mounted motor > makes it easier. I took your suggestions and those of others and got a GWS Slow Stick, I will use both a prop save and a stick. I don't know exactly what you mean by the stick. The advantage of this plane is that it flies very well, (thus preventing crashes) and the entire airframe (everything that breaks if electronic parts are properly protected with foam rubber padding) can be completely replaced for $21.00. >> The V-tail will probably be constructed separately and >> attached with screws so that either the body or the [quoted text clipped - 91 lines] > > Hope this helps. Best regards! Peter Olcott Wrote: > I want to design model airplanes. I want a good book that > will introduce me to aerodynamics and other details such as > how to pick a good speed control that can be used for both > brushed and brushless motors, and how to go about sizing a > motor and power system given an airframe. I probably want to > focus on scratch-built electrics. Wow, a lot of questions in this post. There are a ton of books o aerodynamics and a lot of design articles here on then internet. A for designing a model your first consideration is how you expect the model to preform. Then everything else has a place such as wing span wing area, total weight and of course engine or motor size. As for the best speed control I don't think there is just one that wil handle both brushed and brushless motors as they operate differently. Guy Fuller +++ STARCAD PLANS +++ Your site on the Internet for FREE Model Airplane Plans Bookmark this site for the fantastic resource it is. http://www.starcadplans.ne -- starca Some of the major vendors ( Tower, etc.) have great explanations of r/c items on their own websites. It's all free and there to help you buy the right material in the first place. Plus, RCGroups and RCUniverse ( and many other) sites have tons of Q & A, on every topic imaginable, going on, every single day. It takes lots of reading to cover the gamut of choices in this hobby. I doubt that "all of the answers" exist in any one place...and...if they did, a lot of people would disagree with their conclusions. regards, Rich |
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