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Thread: ul and lsa performance

  1. #11

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    Back to the original question, I have to agree with Dana that it depends on the specific aircraft design. I'm not personally aware of 503 powered planes at higher altitude airports but do know of many 912ULS powered LSAs based at elevations up to 7500 feet. My particular LSA has a service ceiling above most 180hp fixed gear GA aircraft (16000 ft).

  2. #12

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    Steve,
    At sea level, most pilots takeoff at 100% and cruise at 75% power. But 75% is all you get at 7000-8000 feet and that is enough for cruise. If you want to cruise at 100% power than get the bigger engine.
    Electric boost is an option now. Not just my idea, Burt Rutan suggested the same last year. Of course it is experimental.

  3. #13

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    Back to the original question:
    High altitude limits the performance. The solution is usually to reduce the gross weight. Floatplanes are forced to fly with reduced payload. For example, a Cessna 172 on wheels is a four seat airplane, but on floats is usually limited to two seats to get off the water.

    High altitude flight conditions is a bit different than float plane issues, of course, but buying a four seater and using it as a two-seater might work. Or a two-seater flown as a one-seater... or use a loooong runway.
    Bill
    Last edited by Bill Berson; 12-13-2011 at 12:09 PM.

  4. #14
    WyoDan you said 700fpm was minimal in 150. You probably also talking about climb angle. For an ultralight or trike, 700fpm at that altitude would be plenty. It would need to do at least 1300 (or probably more) at seal level. Simply pick a craft like an STOL that does 1300+ fpm at seal level loaded the you want to load it.

    And by the way, Bill is ahead of his time but only a little.

    Hybrid gas/electrics are coming soon and maybe sooner than pure electrics. You should hear Jeron Smith (Raven redrives) talk about it. Probably building right now. Electric and gas for takeoff and climb but then gas only for cruise. Batteries much smaller. Better range. Engine charges batteries in flight.

  5. #15
    steveinindy's Avatar
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    And by the way, Bill is ahead of his time but only a little.

    Hybrid gas/electrics are coming soon and maybe sooner than pure electrics. You should hear Jeron Smith (Raven redrives) talk about it. Probably building right now. Electric and gas for takeoff and climb but then gas only for cruise. Batteries much smaller. Better range. Engine charges batteries in flight.
    I still think you guys are being overly optimistic about how fast the electric motor technology is going to advance. Of course, it also might just be a difference in what you all seem to consider useful and what I consider to be so.

  6. #16

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    Steve- electric motor technology is advanced. Current motors are very light and up to 95% efficient. Batteries are limiting technology.
    That's why short boost with a small battery is better than trying to go pure electric. The range is limited on pure electric vehicles and the huge battery would cost too much for the limited battery life.

    The Chevy Volt is a plug-in hybrid.
    Read about this in the book: Car Guys vs. Bean Counters by Bob Lutz, 2011

  7. #17
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    Steve- electric motor technology is advanced. Current motors are very light and up to 95% efficient. Batteries are limiting technology.
    That's why short boost with a small battery is better than trying to go pure electric. The range is limited on pure electric vehicles and the huge battery would cost too much for the limited battery life.
    To me, especially on aircraft where there is a definite upper weight limit by regulation, the idea of lugging around extra weight for an "extra boost" seems a bit odd. I was speaking about the battery weight issue not the motors themselves. If you have such marginal performance with a design that a second motor is a consideration, the design in terms of the primary engine, wing aerodynamics and drag needs to be reassessed. I am a big believer in the KISS method of aircraft design: the fewest systems and parts able to do the job means the fewest systems and parts to break and cause problems which is usually a very good thing. Put a bigger engine on the plane instead of trying to figure out how to have one you have to rely upon for takeoff and then shut down.

    Think about it this way: what happens to your "hybrid" design if you need to go around in one of these high DA airports and you can't get the little motor started because of some mechanical issues that has gone unrecognized because it has been shut down until just before you need it? That would be my big concern. It's not just necessary to have it running for takeoff but for any activity that involves what would be more or less the standard performance of said aircraft. Simplicity of systems design in such situations is going to be your best bet. Adding 25-100 lbs of extra weight just to get the "gee whiz" factor of a marginally performing but technically advanced aircraft is simply an extra 25-100 lbs of extra mass to add to the F=ma equation that will likely determine the severity of your injuries in the event of a crash.

    It's not like you have to be so concerned with fuel consumption in this class of aircraft that you need to move towards an hybrid system since even the high end of UL and LSA engines sip gas like a man missing his upper lip compared to your "average" GA engine. I would think developing a Rotax or something like that which doesn't freak the hell out if it comes in contact with ethanol would be a much more productive gambit. It's not that I don't think electric aircraft or hybrid aircraft are an inherently bad idea, I just think it has an almost Rube Goldberg-esque quality to it when it comes to solving a problem that can be solved much simpler and more effectively with better established technology for the same or, in some cases, less of a weight and drag penalty.

    The Chevy Volt is a plug-in hybrid.
    Read about this in the book: Car Guys vs. Bean Counters by Bob Lutz, 2011
    Yeah, it works in cars because they don't have to be (as) concerned with weight as those of us in the aviation side of things have to be. You have a few extra pounds on the vehicle- even if poorly placed- it is highly unlikely to be an issue to anything beyond the life of the brakes and suspension.

  8. #18

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    Steve- I am suggesting that an electric boost system might be lighter than getting a larger Rotax for the brief power. Also, dividing the power between two sources, engine and electric booster gives the option of twin engine safety. The electric could allow for an extra minute of controlled flight after engine failure at takeoff. Burt Rutan suggested this at Osh last year.

    The only reason I will wait a bit longer is battery cost. Cost should improve somewhat every year.

  9. #19
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    Burt Rutan suggested this at Osh last year.
    I recall him making an offhand comment during one of his presentations that I attended but based on the multiple times I have heard him speak, he seems to like to theorize out loud.


    gives the option of twin engine safety
    Are we talking driving this thing through the same propeller as the engine or are we talking about a second setup? I don't see a second engine as being an added positive aspect of safety unless it's properly designed and properly used by people who know what they are doing.

    The electric could allow for an extra minute of controlled flight after engine failure at takeoff.
    The question from an engineering standpoint is would the minimal added thrust you're counting on for "an extra minute of controlled flight" be sufficient to truly give that and would it be sufficient to actually counteract the added weight?

    Cost should improve somewhat every year.
    Given how much Fox News is crowing about the Volt and other electric vehicles, I think if the Republicans win we can kiss a lot of the federal funding that is driving the battery research goodbye shortly after the inauguration. It might not be directly affecting the electric aviation but I am willing to bet that the real progress in terms of this isn't coming out of the handful of guys working on electric or hybrid planes.

    I am suggesting that an electric boost system might be lighter than getting a larger Rotax for the brief power.
    Well, let's look at then the numbers:
    Rotax 447 39.6 hp 61.3 lbs (with carb)
    Rotax 503 45.6 hp 71.2 lbs " "
    Rotax 582 64.4 hp 64.4 lbs "
    Rotax 618 73.8 hp 76.5 lbs
    Rotax 912 81.0 hp 127 lbs
    Rotax 914 115.0 hp 137.1 lbs
    (SOURCE:http://www.theultralightplace.com/in...ionweights.htm )

    I don't think you're going to find an electric motor and battery system that would effectively double your horsepower for a weight gain of less than 15-20 lbs (assuming you went from a Rotax 447 to a Rotax 618 with their respective exhaust systems). This is especially the case when you start figuring in a drive mechanism to hook it into the engine's propeller (or the weight of adding in an entire new propeller, it's attachments, etc), the mountings for the motor and batteries, etc. Even figuring in an extra 2.1 gallons of gas to allow for equal flight time with a 447 and 618, it likely would at most break even in terms of power and weight benefit. In a situation like that, it's probably the safer bet to go with the relatively better proven technology of an internal combustion engine such as those currently in use on UL and LSAs.

  10. #20

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    I didn't say double, I said 25% boost. A motorglider type design might maintain altitude on 25% or at least extend glide.
    Some are going all electric, some hybrid. It depends on the aircraft class.
    Sounds like electric might not be for you. In the low power range (10-20 hp) electric is competitive, I think.

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