Hello....my first post here.I am asking if there is a weight,wing span and engine power ratio for designing a ultralight.
Hello....my first post here.I am asking if there is a weight,wing span and engine power ratio for designing a ultralight.
In the US, applicable rules for wt. speed and other parameters are under Part 103 of the regulations. https://www.eaa.org/en/eaa/aviation-...or-ultralights
Include AC 103-7 in addition to FAR 103 in your study material. Hope I remember the dash number correctly. It is old and has never been revised.
Hi Kibet,
To answer your question directly, I'm not aware of any design ratios that are specific to Part 103 ultralights. The combination of 254 lb empty weight and 28mph max stall speed (from the Part 103 regulation) tend to force most designs to some similar design values. I would say that the most common design value that you will find is a main wing surface area S = b x c ~= 115 ft^2 where b is wing span and c is wing chord. This value can vary based on flap type/size or flaperon usage.
Engine power can vary widely. Common values range from 27HP to 50HP. Generally designers will put the largest engine they can on the ultralight but still remain below the 254 lb empty weight limit.
Hope this helps.
Hi--- I'm new to the whole forum world, but am very interested in ultralight aircraft. I have a private pilot's license, but since retirement, I can't afford rental rates. Seems my only option to get back in the air is to build and fly an ultralight plane. I was a product engineer before retiring, and have been a model builder/designer since third grade or so. I use my TurboCAD 3-D program now primarily for designing ultralights. I have many designs developed to various degrees of completion, but two of them to the point that I could start building. One is a very utilitarian design and would be the obvious choice with minimal build time in mind. The other design was developed with a bit of cuteness in mind and has an enclosed (pretty much) cockpit. I guess what I would primarily like from the forum is an exchange of ideas on ultralight design in general, keeping designs simple and light, structural options, and some general encouragement to keep working at it. I live a hundred miles from the nearest EAA chapter, and communication with them indicates very little action and no ultralights, so I'm pretty much on my own. I'll try to figure out how to include pictures with these messages.
EDIT: Added picture
Last edited by luftbuggy; 08-24-2018 at 06:45 PM. Reason: Added picture
Welcome to the forum luftbuggy. May want to start another thread with your thoughts and a few specific questions to get started.
Always fun to discuss design. Sadly, only 20 Ultralight Chapters left now.
Nice drawing.Originally Posted by luftbuggy
Looks like wood construction. First order of business is likely to decide on building materials. All airplane type ULs struggle with the 254 # limit. The newer engine options help that to some degree.
To make the weight limit you will likely need a fabric cover over wood or metal tubular frame. Oratex is the lightest fabric cover http://www.betteraircraftfabric.com/. Aluminum or 4130 steel tube are durable structure. Woodworking is the choice for many and is light and strong. There are several UL plans of wooden aircraft similar to your drawing. They would be useful for comparison.
Belite sells kits of a very similar metal design that would more or less assure success.
Let us follow your thought process.
The used market can be an economical way to get started if you are careful and seek advice from others. Most are somewhat of a project or work in progress so you will still get some building experience.
Would you consider simply buying a proven design ultralight kit or plans for same? A whole lot of options going that route.
Last edited by CHICAGORANDY; 08-29-2018 at 05:10 PM.
The extension FAR 103-7 mentioned by Jedi include the exemptions for a seaplane version this pushes the empty weight up as far as 314 lbs . I chose this because I wanted a sturdy airplane and a softer environment, apparently to crash into since I did it twice. I am alive to prove that as well my choice of materials bare this. All aluminum air frame with Stuarts covering system UL fabric. The Air frame is undamaged from the 2 hard nose in crashes The foam and glass hulls did not come off unscathed, but they were and are repairable. I got to small cuts from the last and very wet.
I don't expect a ground crash would have been the same outcome. Consider this also when you make choices.
Crashing is not a design option but they can and do happen.
After you design ,make sure its balanced that is not an option. This also where your design makes deviations. As a UL your pilot weight is a strong factor unless its directly below the CG A pusher is more susceptible to this, as mine was and is a struggle to get things right.
Last edited by Norman Langlois; 11-09-2018 at 02:56 PM.
The HomeBuiltAirplaneS.com web site is much more active and will have many good comments and suggestions.
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