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Thread: New to forum

  1. #1

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    New to forum

    Greetings,

    I am a new to the forum and new to ultralight aviation.

    I am an aerospace engineer and have decided to design and build my own ultralight. I got into engineering late in the game and have an extensive history in machining and mechanics (mostly automotive amd heavy equipment). So, I have, at least, the basic skills to take this project from start to finish.

    I plan on a full metal craft with a semi monocoque fuselage and a rib and stringer wing.

    I have been working from my Senior design class text by Raymer and have mostly completed the rough sizing calculations. I have stared into the conceptual stage where I need to start generating basic lay out drawings (read: the fun part).

    I am sure I will have many many questions and would be quite interested in finding someone local(ish) who has been down the same road. I am in Wichita KS, and would love to chew the fat at my design firm office (Starbucks) and learn some insider tricks.

    Also, if anyone has a 5 axis mill and a CNC lathe with live tooling just sitting in their garage waiting on something to do....


    First serious questions:

    Do I pick a reasonable gross takeoff weight (W0) considering my own size ( working on reducing that...) Or do I set a gross​ weight based on an average pilot to set wing area for minimum stall speed requirements? If I design it for a 170lb pilot and consider the spare tire I carry as "crash protection" and live with the higher stall speed, is that reasonable?

    Next question:
    Are there any power plant considerations which will be about 30-35 hp without breaking the bank? I have seen a Yamaha engine showing up on ebay, but cant find any info on it. Also a reasonable Cayuna on ebay, but that seems to be an antiquated engine and parts may be hard to find.

    I appreciate any help and would love to find some new friends of like mind to share enthusiasm.

    Thanks.

    Sent from my XT1585 using Tapatalk

  2. #2
    rwanttaja's Avatar
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    Quote Originally Posted by Ivanstein View Post
    First serious questions:

    Do I pick a reasonable gross takeoff weight (W0) considering my own size ( working on reducing that...) Or do I set a gross​ weight based on an average pilot to set wing area for minimum stall speed requirements? If I design it for a 170lb pilot and consider the spare tire I carry as "crash protection" and live with the higher stall speed, is that reasonable?
    Design it for the weight at which you expect it will be operated, and add a 25% margin on top of that. So if you weigh 200 lbs, design it for 250 lbs. It'll thus be happier a lighter weight.

    Ron Wanttaja

  3. #3

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    I agree with Ron on the weight issue as there is always an issue with going over gross, helmets, clothing, a little carry on kit, etc., etc. As far as engines are concerned no matter what you start out with in 10 yrs. if not sooner it will be way behind in the new designs and technology. I have an old 447, and a rebuilt 40 yr. old Cayuna I went thru for a back-up, doing a couple updates in the process. These older engines are tried and true, and parts are readily available.

  4. #4

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    Gross weight is your choice, depends on if just one for you or if selling plans to others.
    AC103-7 (online) has much info about the weight rules.

  5. #5

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    Quote Originally Posted by Bill Berson View Post
    Gross weight is your choice, depends on if just one for you or if selling plans to others.
    AC103-7 (online) has much info about the weight rules.
    Thanks for that. I am currently running calculations for my altitude +1000' which is right at 2300' msl. So, if I am reading the description correctly, the airspeeds can be corrected for a standard atmospheric day at sea level. This will help a bit on the wing area required to meet stall speed requirements, as with the somewhat thinner air here, the q (dynamic pressure) value is lower requiring more wing area to produce the same lift at sea level.

    So, apparently I can suffer the higher stall speed due to thinner air. However, that doesn't help with performance at altitude either. I think, with everything engineered, there will be a trade off.

    Sent from my XT1585 using Tapatalk

  6. #6
    Dana's Avatar
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    If you're designing for Part 103 you will want to use the AC103-7 appendix calculations for speeds. Not as actual design values, but as a sizing guide. The calculations in the appendix are very conservative, and accepted as proof of 103 compliance without actual demonstration. So you can have a legal ultralight with somewhat higher performance than the regulations would suggest.

    As for engines, the Cuyuna is not a bad choice. Lots of them still around, parts readily available and far cheaper than Rotax.

  7. #7

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    Bear in mind that the required stalling speed is at the flying weight. Many ultralights have the gross weight set by determining the maximum weight that the required stall speed can be achieved. As Dana said AC103-7 will be of great help in this pursuit.

  8. #8
    Dana's Avatar
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    Quote Originally Posted by Greg Wilson View Post
    Bear in mind that the required stalling speed is at the flying weight. Many ultralights have the gross weight set by determining the maximum weight that the required stall speed can be achieved. As Dana said AC103-7 will be of great help in this pursuit.
    I think AC103-7 has you do the calculations with the "standard" 170# pilot and full fuel. But then I never worried about it because I happen to weigh 170.

  9. #9

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    The FAA isn't concerned about some overweight, according to an article in Sport Aviation, August 2017.

  10. #10

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    I am the Crazy one that designed and built, then learned to fly the thing all from scratch without any aeronautical knowledge or engineering . I had the skills you mention an industrial fabricator machinist. The first thing you need is to be aware the normal structure is going to be lighter than you would like it to be. You also will be flying with very little around you [ hang cage structure ] therefore Ultra light is harder to get there than you can imagine. The usual tube structure is proven . The usual ladder tube wing design also . If you plan to build an efficient ultra light they do not exist they fly slow not far, they do not glide well . Mostly because weight limits the wing area. To over come area shortage you need speed, that's not allowed ether. The solution is thicker air foils higher drag. Then there is the power plant. I have a new Kawasaki 440 they are around. The lightest power to weight package I could find. I just made the weight with all my considerations.I wanted amphibious I had to give up land base and opted for water only because of extra flotation weight allowance. My base flying design weight was 296 lb the final was 303 lb
    I do not have a normal wing structure and I would not give it up . So what are you willing to give up in the venture I assure you there will be comprise. Be careful and be safe I was just LUCKY

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