Wanted Wanted Bede bd5 kit or parts

Discussion in 'For Sale & Wanted' started by lisa, Jan 31, 2019.

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  1. Feb 22, 2019 #41

    TFF

    TFF

    TFF

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    It’s a different audience, prop or jet. Prop people are wanting a $20K airplane or that is what they think it will take. A jet person says” under $100k, what a deal!” Any drive system has to be thought out. The biggest problem is there is not the market at the price it needs to be.
     
  2. Feb 22, 2019 #42

    daveklingler

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    You have to admit that's not very reasonable advice. The vast majority of aircraft builders have some concern for cost, and few of us have even $60K to pony up for the jet engine. Beyond that, a BD-5J is faster and hotter, with half the range and a quarter the flight time, and costs at least twice as much to fly. It's a very different airplane.

    Kent, this is technically incorrect. Further, the Yahoo thread is an attempt by the guy who designed the drive system (and did a good job) to point out that the guy who was almost killed in the crash was blaming the wrong piece of the airplane. The fault lay with the propeller, which had been thrice thinned, and with the test pilot, who had not even bothered to look under the cowl, and ultimately with the owner, who had had his wood prop thinned so many times.

    I sometimes design electric motor-driven systems with driveshafts and resonances that have to be dampened, and with one long-ago stint on a motorcycle design team. I wouldn't claim anything near expertise, but here's a better explanation, to the best of my ability. (Note that there are better and longer discussions of torsional resonance elsewhere on HBA.)

    All mechanical systems have resonant frequencies. In cases where the resonances can cause harm, they have to be moved to a frequency where they won't be harmful. In an airplane, it's a bad thing to have a resonance at, say, cruise RPM.

    So the drive system engineer's task is usually to dampen these resonances, i.e., move them to lower frequencies where they won't do harm, say, below the lowest normal RPM of the drive. An alternative is to make the system stiffer, moving the resonance up to a higher frequency that never occurs.

    One thing I DON'T notice in the Kauth drive is any sort of dampening devices, so that may need to be added. --> The aluminum driveshaft in the Kauth drive is fine, if and only if the system is properly damped. Note that all metals will undergo hardening and crystallization at some point, not just aluminum.

    Also note that a sprag clutch won't solve resonances. A sprag or overrunning clutch's job is to prevent drive backlash from working its way back into the engine. In the case of the BD-5's drive system, which has a driveshaft, that means it's a good idea to have both a sprag or overrunning clutch AND some rubber in the system to dampen torsional resonances.

    Here's a decent list of all the BD-5 accidents:

    https://aviation-safety.net/wikibase/dblist.php?AcType=BD5

    If you take the time to take a more in-depth look at the list, you'll notice that almost all of the accidents are engine-related. An incredibly-sobering number of pilots died because they failed to do a walkaround. Another thing that struck me is that almost all of the crashed BD-5s use engines like yours that cause the empty weight of the airplane to climb by 55-85% - they flew fine until they had engine problems, but then the pilots had no margin because they were 200-300 pounds overweight in an airplane that's supposed to weigh 350 pounds.

    What I take from the list of accidents is not that the BD-5 cannot be built safely without using a turbine. What I take is that redesigning the BD-5 by building it 200-300 pounds overweight is a good way to get yourself killed. Incidentally, my kit came with a Yamaha Nytro engine like Dave Mischke's (the pilot you refer to below). I immediately put it up for sale.

    In the case of Dave Mischke's drive system, I didn't see any attempt to shift resonances, but that might have been there and I just didn't see it.

    I think there's a lot of really bad information floating around the community about BD-5s, both among non-owners and owners as well. Here's the advice I would give:

    1. Don't redesign your airplane unless you're qualified. Most importantly, don't build it overweight, and you'll have more time to make decisions if something goes wrong.
    2. Pay proper design to drive system dampening. If you don't know how to do it, find someone who does.
    3. It's easy to test your airplane for resonances before you leave the ground. That's not a cure-all, but it will tell you if you've skipped anything obvious.
    4. Don't do sloppy workmanship. Saving a few minutes on your wiring may kill you. Your choice.
    5. Develop a checklist for your airplane, and use it, and for *$#& sakes, do a (&*#$(*& walkaround!!!

    Last of all, I was struck by the fact that Dave Mischke started flying his first BD-5 at 60 hours of logged time. It's actually a fairly mellow little airplane, and many BD-5 pilots have said so.

    SOOOOOOOOO...there's one last thing I'd like to add.

    If you allow me to make a model of your Kauth drive in Solidworks, I or somebody else will be able to use Solidworks to do a resonance analysis and improve or fix its shortcomings. Other people could mate various engines up to the drive system and test them in Solidworks for torsional resonance.

    That would be a lovely thing to be able to give back to the community. It might make the BD-5 less frustrating to build, and it might save a life or two some day.
     
  3. Feb 22, 2019 #43

    BJC

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    The information there is just ugly.

    Too many stall/spin events too, even if the initiating event was a powerplant problem.

    One concern with the BD-5 design is that there is no crush zone or other protection between the bottom of the fuselage and the pilots spine.

    Question for the BD-5 enthuasists. Has there been a customer built and flown short wing?


    BJC
     
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  4. Feb 23, 2019 #44

    Victor Bravo

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  5. Feb 23, 2019 #45

    daveklingler

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    Well, yes. The wing loading with a regular BD-5B should be about 7.5 lbs/sq. ft. Guys who drop in a Yamaha 3-cylinder, along with the accompanying lead in the nose, end up at about 11.5, and the Honda-powered BD-5 ends up at close to 14. Both of those exceed the wing loading of the BD-5A (11.25), which a lot of people consider way too twitchy.

    Correspondingly, the stall kicks up from 55 to 85, and there's just little margin for error any more, especially with the hard stall of the original (non-Riblett) airfoil. Add an engine-out or a disintegrating prop, and fatal accidents occur with frightening consistency.

    If you land gear-up, yeah, there's not a lot between you and the ground, but I think that's safe to say about any RG aircraft. OTOH, the BD-5's gear is remarkably reliable and easy to use, uh, if you're not trying to exit a spin when you're 50 feet AGL.

    I have the impression that a fair number of A-wings have been built. I've personally spoken to a couple of people who owned and had flown both types.
     
    Last edited: Feb 24, 2019
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  6. Feb 24, 2019 #46

    Victor Bravo

    Victor Bravo

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    I am not an expert on the BD-5 in any way, but I do believe the BD-5 mission would be much better accomplished with a new design.

    IMHO there are just too many things about the BD-5 that need changing, or that need to be dealt with in a complicated way, or that need to be worked around, or that need to be not thought about.
     
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  7. Feb 24, 2019 #47

    Himat

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    Then I have to ask, apart from looking cool, what mission is the BD-5 designed for?
     
  8. Feb 24, 2019 #48

    BJC

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    Collecting customer deposits, based solely on looks and a dream.


    BJC
     
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  9. Feb 24, 2019 #49

    TFF

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    It’s a 40 year old kit that only a scratch builder would think is a head start. They did not expect to sell 500 in the entire life of the design. I bet a quarter of the EAA membership of the day put in a deposit. Just flat overwhelmed the system. But accepting the deposits was the downfall. Should have not done that. Someone today could do much better starting with the engine first. Problem today is it would never sell without the second seat and pretty much only a wife that could fly it would get in it , so it’s a big no to design one for kitting.
     
  10. Feb 24, 2019 #50

    Hot Wings

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    I can confirm that statement! And at the time it wasn't uncommon to hear that the kit should never have qualified under the 51% rule.

    Times sure have changed.............
     
  11. Feb 26, 2019 #51

    E28POWERM20

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    I heard recently from someone at Bede Aero, that they are looking into reintroducing/supporting the BD-5. I don't know what that means, but they haven't 100% abandoned the design.
     
  12. Mar 6, 2019 #52

    daveklingler

    daveklingler

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    The BD-5B is, from all reports (I don't have a finished airplane), a very nice little plane if it's finished in a similar fashion to the way it was designed. Bede Micro sells a Hirth engine package (the 3503, IIRC, and formerly the 2706) with about the same weight and HP that the plane was designed for. Cooling isn't that big an issue, and the plane doesn't drop out of the sky if you have an engine problem. Neither does it stall as abruptly as it does when it's way overweight.

    I seem to remember that Alturair makes the same recommendations. Follow the advice of the people who have been building them for a long time.

    But I do agree that it could use some modernization. Buying pre-drilled pieces from Bede Micro or Alturair will knock off a lot of time, and that was a big improvement. But if I were selling them I'd probably redesign the mainspar and a few other parts that cause problems. I might even pay for some fluid dynamics studies to modernize the wing; the KR-2 is an example of an old design that has greatly benefited from that kind of attention and still holds up well because of it.

    Skeeter told me a few years ago that he just doesn't make enough money on the BD-5B to merit his attention. He pointed out that the same amount of work goes into manufacturing both the prop and jet versions, but he makes much more on the jet, so he doesn't bother advertising that BD Micro still makes a very nice and very complete prop kit, albeit one that's a little bit pricey. But if you start with one of their kits or at least send your skins in to have them pre-drilled, you'll save years of work.

    I think Alturair supplies similar services. Both firms were very cordial to me when I reached out to them after getting my own kit.
     
  13. Mar 6, 2019 #53

    daveklingler

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    Bede Aero gets really good reviews for their BD-4C kit and support for it. I think they'd do extremely well with a BD-5 update similar in quality to the BD-4C - after all, a huge number of people look at that pretty little airplane and find it enthralling.
     
  14. Mar 11, 2019 #54

    Victor Bravo

    Victor Bravo

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  15. Mar 11, 2019 #55

    kent Ashton

    kent Ashton

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    He is likely blowing smoke that his "experamental" kits are "complete". One has the short wings; pretty much unusable. He may be missing parts like the formed saddles that attach the centerspar to the fuselage--a lot of kits were missing those. For sure, many parts that you might expect to get are in the form of raw materials--a 4130 bar, or a bar of 2024, for example. Plans are often incomplete. Any BD-5 can be called a "jet" before you start building but if they are pristine kits they might be worth acquiring. Then $80-100K later you'll have a jet BD-5. I know nothing about his engines but I would bet a modern PBS jet engine would be a lot easier to use. No pics either. If the cat pees on your kit, it's toast.
     
  16. Mar 29, 2019 #56

    Victor Bravo

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  17. Mar 29, 2019 #57

    delta

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  18. Jul 14, 2019 #58

    Phenomdriver

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  19. Jul 14, 2019 #59

    Phenomdriver

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    Mr Ashton,

    Being new to this forum, trying to figure out the PM thing.

    You can email me at simon261@comcast.net

    Interested in what happened to Dave Mischke’s project with the Nytro engine and failed Sprag clutch.

    I have a Bede 5 kit on the gear with wings ready to close, but long term looking at buying a microturbo TRS18 or maybe the PBS TJ100 to go jet.
     
  20. Jul 15, 2019 #60

    CharlieN

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    Umm, there was no 51% rule back then. This was one of the first comprehensive kits offered.
    Yes, unfortunately the powerplant and drive were not ready for market but this was pioneering that has led up to the kits we have today.
     

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