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Thread: 103 Ultralight concept - thinking outside the box

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    Registered User Rienk's Avatar
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    103 Ultralight concept - thinking outside the box

    As many of you know, I've been toying around with designing a legal ultralight for a while. I've been noodling all sorts of ways to improve on the performance while still staying legal. Here are the pertinent thoughts that led me to a potential "eureka" moment.
    .
    • Most people do not like how UL's get blown around in even light winds, due to the typical wing loading.
    • Most people don't like having such a limited top speed that most UL's have, due to high drag.
    • The FAA allows a designer (though it is actually the responsibility of the pilot to prove) to choose to demonstrate max speed and/or stall speed using a published formula.
    • If one was creative, they could use the formula for max speed to use a small wing with other drag inducing elements (eg struts) to keep the "calculated" speed below the threshhold.
    • A UL with more complex high lift devices could possibly exchange the weight of such by reducing the overall size of the wing - and thus meet the "actual" stall speed requirement by actual demonstration (calculated with a 170 lb pilot with 5 gallons of fuel and no "removable equipment" on the aircraft (seat cushions, instrument panel, parachute, etc?)
    .
    SO... here is my "outside the box" idea for building a legal UL.
    .
    • .Have only an 80 square foot wing (wing loading would then be about 6-7psf, instead of 4-5).
    • The pilot can be in a sleek and aerodynamic fuselage (formula calls such 'pilot drag factor' "totally enclosed, streamlined").
    • With a smaller wing, the fuselage can be shorter, but if still fairly long, a much smaller tail group can be used.
    • Overall, the airframe could be lighter than a typical size UL, while still using beefier structure.
    • According to the max speed formula, a streamlined fuselage with an 80sf wing, using a 32hp engine, would require 10 struts (at least 4' long, 45-90 degrees into the air) to meet the calculated legal max speed - even if the aircraft can in fact actually go faster.
    • Struts can be streamlined - and be included simply for inducing drag (do not have to have a structural purpose). Two struts on each wing, maybe four 'jury' struts, and or a number of struts on the tail group).
    • Engine power must be based on the Manufacturer's label/designation.
    • I want to use the Generac industrial engine, which is labelled as a 32hp engine, even though they show an 'alternate' power curve that shows the engine putting out 38hp (with 40-50 claimed on the Backyard Flyer).
    • With a good airfoil (not laminar) and slotted flaps (maybe even double slotted) it should be possible to still get the aircraft to stall at the required speed.
    .
    THUS, if the 'actual' stall speed can be met, it would be possible to have a legal UL that can cruise faster (maybe 75 mph), while it looks and handles more like a "real" airplane.
    .
    • I envision a wing of about 27.5 feet long with a 3' chord (aspect ratio of over 9).
    • Might possibly build a tapered wing, with a 30" tip chord and a 42" root chord.
    • A heavier version could still be a motorglider.
    • Wings would be two piece, with overlapping spars inside the cabin, typical of many sailplanes. It would have automatic control hook-ups. Each panel would be 15' long, and manageable for one person to easily install.
    • Fuselage would be about 18' long, from tip of spinner to back edge of elevator.
    • Engine would have a 1.9:1 redrive, allowing for 2100 rpm at max power. It would swing a 72-84" prop, and put out about 250-300 pounds of static thrust. That is almost a two-to-one ratio, and should allow the aircraft to have an incredible climb and very short takeoff.
    • As mentioned, 'actual' top speed could be much higher, since it legally meets the requirements of the FAA.
    • The airplane would have lots of removable equipment: canopy or doors (depending on low or high wing), plug and play instrument panel (full moving map, radio, etc), seat cushions, and anything else. Even the fuel tank might be easily removable (simply for the convenience of filling or swapping tanks).
    .
    Its styling will be inspired by the BMW 'Gina' (which is a "rag-and tube" automobile, pictured below).
    .

    103 Ultralight concept - thinking outside the box-bmw_gina_concept_car.jpg103 Ultralight concept - thinking outside the box-bmw_gina_museum.jpg103 Ultralight concept - thinking outside the box-bmw-gina.jpg103 Ultralight concept - thinking outside the box-bmw-gina-dark.jpg



    NOW - what do you think?

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    Registered User BBerson's Avatar
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    Re: 103 Ultralight concept - thinking outside the box

    AC 103-7 is an advisory circular that has guidelines for compliance but is not the law, and apparently the FAA doesn't use this AC.
    And according to Dan Grunloh (in a forum at Oshkosh two weeks ago), the FAA is not using any formal method to evaluate compliance. He said: " the FAA only checks for one seat and no more than 5 gallons fuel capacity maximum"
    They don't check for weight, speed or wing area size (as long as it mostly "looks" like an ultralight)

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    Registered User Vipor_GG's Avatar
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    Re: 103 Ultralight concept - thinking outside the box

    You may run into trouble if you sell it as a complete plane and someone crashes in a way that attracts attention. Selling as a kit that could be built UL with a lower power engine or LSA with the Generac would probably be safer legally for you.
    BTW I like outside the box.

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    Registered User Tiger Tim's Avatar
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    Re: 103 Ultralight concept - thinking outside the box

    I thought the whole idea of Pt103 was to keep them impractical and rare. Beating the rules could ruin a lot of people's fun.

    -Tim

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    TFF
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    Re: 103 Ultralight concept - thinking outside the box

    254 lbs is the real problem. Plenty of people who have porky, fast stalling ,fast flying ULs. Does not make them legal but close enough to not raise suspicion.

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    Re: 103 Ultralight concept - thinking outside the box

    Tim, i think you may be right, the orginal rules we set about to keep the general public out of the air, however, what Rienk is after is an ultralight that can go faster than the Legal Limit, but still meets the 103 requirements. Rienk that is completely possible, i have been building a plans plane for a while, but at the same time i have combined 4 different aircraft to come up with my ideal aircraft, the goals are as follows, 103 legal or dang close to it, but my main goals are go faster, fly farther and cheaper than the next guy using a 40 HP engine.

    so far my fuselage is coming in about 15 pounds lighter than a Preceptor pup, i am currently writing my own software for weight and balance, so far from what i have completed, if i place the fuel in the correct location and move the pilot back 2 inches, i can run 5 to 10 gallons of fuel and i can fluctuate the pilot from 150 to 250 pounds, and at any fuel usage level my version stays within the CG limits.

    so my box is a clean sheet drawing, taking the best ideas i can find from existing aircraft and drawings to meet my goal.

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    Registered User Hot Wings's Avatar
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    Re: 103 Ultralight concept - thinking outside the box

    Quote Originally Posted by Rienk View Post
    As many of you know, I've been toying around with designing a legal ultralight for a while. I've been noodling all sorts of ways to improve on the performance while still staying legal. Here are the pertinent thoughts that led me to a potential "eureka" moment.
    .
    You are thinking along the same lines as I have been working. 2 old ultralights, the Mitchell U-2 and the Saddler Vampire have proven that a part 103 legal ultralight can fly on as little as 15 Hp. Any more power and they tend to break the speed and weight limit. Climb rate, especially at altitude is poor. That puts them on line 5 on the AC appendix graph for speed. Extrapolating using the same graph does indicate a possible speed of around 75 on 30-ish Hp.

    Actually building a slick plane with enough "paper" drag using lift augmenting wing devices for legal stall speed and stay under 454 gross test weight might be a real trick.

    As Tiger Tim pointed out if these kind of "legal" ultralights become common the FAA just might find the time to change things. The same kind of thing happened to cheap rifle ammunition when someone decided to build an AR-15 based pistol in 223 caliber. This meant that cheap import "armor piercing" steel core ammunition was no longer legal to import because it was now classified as pistol ammo. A few people got to buy a unique pistol. The rest of us had to pay more for our ammunition.

    IMHO the first batch of clean high performance part 103 ultralights had better be 100% legal and within the spirit of the regulation. Bending the rules too much at one time is likely to draw unwanted scrutiny. Kramer's Lazair may not have been technically legal using a strict and conservative interpretation of the rules but it looked like an ultralight. If it actually had the same overall performance that an internal combustion version had I'm betting the FAA would not have been as tolerant of it being overweight.
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    Registered User Rienk's Avatar
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    Re: 103 Ultralight concept - thinking outside the box

    Quote Originally Posted by BBerson View Post
    AC 103-7 is an advisory circular that has guidelines for compliance but is not the law, and apparently the FAA doesn't use this AC.
    And according to Dan Grunloh (in a forum at Oshkosh two weeks ago), the FAA is not using any formal method to evaluate compliance. He said: " the FAA only checks for one seat and no more than 5 gallons fuel capacity maximum"
    They don't check for weight, speed or wing area size (as long as it mostly "looks" like an ultralight)
    Well of course, to BE a legal ultralight, it will tend to look like one.
    On the other hand, if I can make a legal ultralight that looks and performs more like a "real" airplane, then all the better.
    I believe the "intent" of the law is to allow for safe, fun flying. Thousands of them were flying in the 80's, and there is no major reason why tens of thousands of them can't be flying now. As I see it, the current main obstacles are price, performance, and sex appeal.

    The only way that sport aviation is going to take off is if it becomes more affordable and available.
    Ultralights will need to be sold RTF (ready to fly), and there has to be enough of them to create some momentum - among the (currently) non-flying population. There also has to be an easy way to finance them, but that's another thread.

    I want to sell these as RTF, and know that I am also meeting the "letter" of the law, so that I'm not leaving customers in the lurch if they DO get ramp checked - especially if there is a ground swell in popularity - leading to the inevitable stupid pilots and subsequent accidents.

    So, ignoring for now that the FAA doesn't currently check all aspects of a "legal" ultralight, what do you think of my method of building a Super UL?
    jedi likes this.

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    Registered User Brian Clayton's Avatar
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    Re: 103 Ultralight concept - thinking outside the box

    Hahaha.....what you are describing is a way to "cheat". I imagine the FAA looks at it this way..... If it looks legal (big wings, looks light, looks slow, little engine, 5 gallon tank, one seat) then they will not bother you on the ramp. IF you have a accident or a problem, either you are dead or they can bust you then with flying a unregistered plane/no license. Talking to other UL guys, I am at the same understanding, 5 gal of fuel, one seat, looks "right" for a ultralight, means the FAA doesn't bother you. Unless you have a problem. If a UL crashes, the FAA shows up and says "its a ultralight" and leaves. But.... if you cause a accident with a registered plane, or hurt someone else......I imagine they would dig much deeper. When I first started on mine, I was interested in "bending the rules". At this point, I am considering registering mine anyway, so I don't have to worry about weight, stall, top speed, etc. Plus, getting a sport pilots license is pretty cheap, and you wouldn't have to be looking over your shoulder.....just fly and have a good time. But then again, you do hear horror stories.... and some airport managers and other pilots might have a hard time "minding their own business".

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    Registered User Rienk's Avatar
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    Re: 103 Ultralight concept - thinking outside the box

    Quote Originally Posted by Hot Wings View Post
    You are thinking along the same lines as I have been working. 2 old ultralights, the Mitchell U-2 and the Saddler Vampire have proven that a part 103 legal ultralight can fly on as little as 15 Hp. Any more power and they tend to break the speed and weight limit. Climb rate, especially at altitude is poor. That puts them on line 5 on the AC appendix graph for speed. Extrapolating using the same graph does indicate a possible speed of around 75 on 30-ish Hp.

    Actually building a slick plane with enough "paper" drag using lift augmenting wing devices for legal stall speed and stay under 454 gross test weight might be a real trick.

    As Tiger Tim pointed out if these kind of "legal" ultralights become common the FAA just might find the time to change things.

    IMHO the first batch of clean high performance part 103 ultralights had better be 100% legal and within the spirit of the regulation. Bending the rules too much at one time is likely to draw unwanted scrutiny.
    Good points, but here are my counters.
    With a clean plane, 30hp should give about 75mph at cruise. However, with the necessary drag inducements allowed for, the aircraft can still meet the letter of the law.

    As you say, the real trick is still meeting the actual stall speed; at least 117 square feet is virtually required to meet the 'formula' for the stall. But I want as fast a UL as possible.

    However, if this plane does become popular (common), I don't think there will be unwanted scrutiny - although it wouldn't surprise me that they check whether it meets the letter of the law.
    I liken it to the LSA Carbon Cub using a 150 hp engine, but rated at that power level only for 5-10 minutes (I forget the exact wording), but then derating it to 100 hp for calculating Max "continuous" power.

    Similarly, what I am trying to do is use the letter of the law to my advantage - without breaking the law. I happen to be one of those people who tends to drive the speed limit... but do I drive well below the speed limit to make sure I don't get pulled over? No, but I do stay right on it as best I can (if you get pulled over and admit you were driving even 1mph over the limit, you'll get a ticket).

    But I think we'll be fine if we meet the letter of the law, just like the Carbon Cub - which by the way, is kind of a "certified" plane, with much more scrutiny than an ultralight. Bend, but don't break.

  11. #11
    Registered User Rienk's Avatar
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    Re: 103 Ultralight concept - thinking outside the box

    Quote Originally Posted by Brian Clayton View Post
    Hahaha.....what you are describing is a way to "cheat". I imagine the FAA looks at it this way..... If it looks legal (big wings, looks light, looks slow, little engine, 5 gallon tank, one seat) then they will not bother you on the ramp. IF you have a accident or a problem, either you are dead or they can bust you then with flying a unregistered plane/no license. Talking to other UL guys, I am at the same understanding, 5 gal of fuel, one seat, looks "right" for a ultralight, means the FAA doesn't bother you. Unless you have a problem. If a UL crashes, the FAA shows up and says "its a ultralight" and leaves. But.... if you cause a accident with a registered plane, or hurt someone else......I imagine they would dig much deeper. When I first started on mine, I was interested in "bending the rules". At this point, I am considering registering mine anyway, so I don't have to worry about weight, stall, top speed, etc. Plus, getting a sport pilots license is pretty cheap, and you wouldn't have to be looking over your shoulder.....just fly and have a good time. But then again, you do hear horror stories.... and some airport managers and other pilots might have a hard time "minding their own business".
    Some of you seem to be missing the point.
    This will be a LEGAL ultralight, according to the regulations set out by the FAA (assuming we can meet the stall speed).
    It will "legally" meet the max speed, the stall, speed, empty weight, seat and fuel limit.
    Frankly, even 80 sq.ft. of wing will "look" like an ultralight. This will just be kind of a hybrid between "typical" ultralights and LSA types. There is nothing I am proposing that others haven't done, I'm just trying to do it in a unique way.
    Let's say a pilot gets ramp checked, and shows that the "base" aircraft comes in at 254 pounds (actually, it will be 278 pounds with a parachute). After that, all they have to do is show the part 103 chart, show all the blanks filled in, point to the legitimate Generac sticker on the engine (32 hp) and they have proven they are in compliance.

    That's not to say that someone can't register the plane and soup it up, change the prop pitch, etc - and maybe get 90-100 mph, but then it does need to be registered.


    Not cheating, not breaking the law.
    Again, just like the Carbon Cub.

  12. #12
    Registered User Hot Wings's Avatar
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    Re: 103 Ultralight concept - thinking outside the box

    Quote Originally Posted by Rienk View Post
    Some of you seem to be missing the point.
    This will be a LEGAL ultralight, according to the regulations set out by the FAA (assuming we can meet the stall speed).
    It will "legally" meet the max speed, the stall, speed, empty weight, seat and fuel limit.
    Going by a strict interpretation the only fully legal ultralight is one that meets the requirements of the part 103 regulation.

    The AC was put out to make things easier for the field personnel to determine if the plane was an ultralight without having to actually test the plane in question. Meeting the terms of the AC lets the FAA presume that the plane in question does meet the letter of the regulation and gives individuals a practical way to show compliance for a one of a kind plane. When it was originally drafted the state of the art in the ultralight world was such that if the plane was built to the AC specifications there was an overwhelming probability that it met the letter of the part 103 regulation.

    The fact that we can now probably build a plane that meets the specifications of the AC but does in fact vary significantly from the letter of the regulation doesn't automatically mean that it is a legal ultralight. If we go about this incrementally and can show a good safety record for these ultra part 103 planes then the FAA will probably have better things to do with their time. If we get too assertive and shove the AC in the face of the FAA they might not be too happy.

    Another problem is the marketing of a super part 103. You certainly can't advertise the fact that the plane will cruise at 75+ mph and call it a legal part 103. That would be just begging the FAA or some anti airplane group to call out the lawyers.

    I think that part 103 is the only way we have in the US of cracking this chicken and egg thing of getting more pilots so we have a market that can justify the needed investment to build cheaper planes which theoretically will attract more pilots. We need to be very careful that we don't soil our own nest.
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    Registered User Rienk's Avatar
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    Re: 103 Ultralight concept - thinking outside the box

    Quote Originally Posted by Hot Wings View Post
    Going by a strict interpretation the only fully legal ultralight is one that meets the requirements of the part 103 regulation.

    The AC was put out to make things easier for the field personnel to determine if the plane was an ultralight without having to actually test the plane in question. Meeting the terms of the AC lets the FAA presume that the plane in question does meet the letter of the regulation and gives individuals a practical way to show compliance for a one of a kind plane. When it was originally drafted the state of the art in the ultralight world was such that if the plane was built to the AC specifications there was an overwhelming probability that it met the letter of the part 103 regulation.

    The fact that we can now probably build a plane that meets the specifications of the AC but does in fact vary significantly from the letter of the regulation doesn't automatically mean that it is a legal ultralight. If we go about this incrementally and can show a good safety record for these ultra part 103 planes then the FAA will probably have better things to do with their time. If we get too assertive and shove the AC in the face of the FAA they might not be too happy.

    Another problem is the marketing of a super part 103. You certainly can't advertise the fact that the plane will cruise at 75+ mph and call it a legal part 103. That would be just begging the FAA or some anti airplane group to call out the lawyers.

    I think that part 103 is the only way we have in the US of cracking this chicken and egg thing of getting more pilots so we have a market that can justify the needed investment to build cheaper planes which theoretically will attract more pilots. We need to be very careful that we don't soil our own nest.
    That is a good pointl
    Of course, if I even attempt to build such a plane, let alone succeed, then the marketing will obviously not flaunt the top speed capabilities of the aircraft. Like any other plane, a certain pitch prop can be provided with the RTF plane, though someone can always elect to install one designed more for cruise than for climb.

    Again, this is a concept, not a project I am yet pursuing; as mentioned - just trying to think outside the box.

    Like many others, I think the physical limitations on part 103 aircraft are absurd, and borderline unsafe. I wish the industry wasn't so afraid to push for a realistic increase, given the relative success of LSA. Be that as it may, we have to try to work with the limitations we have at present. As we all know, there are many UL's that are obviously over the weight limit and may not meet the stall requirement. In my estimation, the least important requirement to enforce is maximum speed; as long as the UL meets the weight and stall requirements, that should be the important thing.

    I don't even know if this plane is possible. But if it is, I assume that a fair number of people would fly it as a registered plane anyway. And if we actually start building it RTF as an ultralight, it would be fairly straightforward to certify is as a S-LSA later.

    Just wondering if this idea is worth pursuing (someday).

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    Registered User PTAirco's Avatar
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    Re: 103 Ultralight concept - thinking outside the box

    Quote Originally Posted by Rienk View Post

    Like many others, I think the physical limitations on part 103 aircraft are absurd, and borderline unsafe. I wish the industry wasn't so afraid to push for a realistic increase, given the relative success of LSA. Be that as it may, we have to try to work with the limitations we have at present. As we all know, there are many UL's that are obviously over the weight limit and may not meet the stall requirement. In my estimation, the least important requirement to enforce is maximum speed; as long as the UL meets the weight and stall requirements, that should be the important thing.
    I have to agree totally - no aeronautical engineer who was given a task of designing a low speed, safe ultralight type of airplane would set an empty weight limit of 254 and a wing loading so ridiculously low. Low wing loading can create as many hazardous situation as they try eliminate.

    If one were to plot the weights of "normal" aircraft structures in relation to payload over the last century, one would realize that 254 lbs for an aircraft to lift a pilot and some fuel is only possible by making a LOT of compromises somewhere and safety is certainly one of them.

    It's like being asked to design an aircraft like a Cub for example, but with half the weight allowance - something has to give somewhere. It's simply unreasonable from a basic engineering perspective. And don't tell me that many designers have achieved it - of course they have. But only at the expense of something else. Either they are delicate beyond belief or so limited in performance that anything but short hops around a field in perfect conditions is about all you can do with them or they have other sever shortcomings or end up simply being overweight and technically illegal.

    A practical ultralight class would go a long way to re-kindling an interest in aviation. Look what it did in the 80s before the whole thing collapsed. The impractical rules had a lot to do with it, not just bad press.
    Last edited by Topaz; August 19th, 2013 at 11:35 AM. Reason: Fixed the quote code.
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    Re: 103 Ultralight concept - thinking outside the box

    i believe the key thing here is no one is making any money off of us UL guys, so there is no incentive to do anything that assists us in our pursuits.
    maybe if enough UL's are built that meet the letter of the law and we have a proven track record of safety we will have the amunition to change the law in our favor for a little more weight and breath much needed life back into aviaiton.

    i dont know about you all, but i am sick of gettin tailgated on the way to work just beacause i follow the legal speed limits.


    robert
    depot level helo mechanic, and ground up drag car builder.

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