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Thread: A Hummel Bird for cross-country ?

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    A Hummel Bird for cross-country ?

    Hello everyone !

    It's been quite some time now that I'm seriously thinking about buying the Hummel Bird plans BUT I still have doubts :
    The plane fulfills all of my desires except the cross-country bit.
    I know it has not been designed for this purpose, however, me living in France, cross-country is not quite what it is in the US...

    Then I came across Bruce King's bird and his full VW fitting...as i'm not quite found about fitting a larger, heavier engine unit on such a small bird, I was thinking about something else:
    What about about reducing the drag ? It would improve speed and thus range.
    And so, after some photo viewings, I came to the conclusion that in addition to covering hinges, control rods, wheel struts and engine cylinders, I "could" redesign the wing shape to make them wider at base and shorter (keeping the same surface though) in a Mustang-like shape.
    Moreover, a VW conversion isn't an option for me as VW engines are rare in France...which would lead me to design additional tanks for better range ( 2-strokes are not as economic, fuel wise).
    I would appreciate some advice on this as it is quite the only thing keeping me from cutting metal:
    Would the fuselage need to be longer with a wider wing ?
    What about the engine ? Anyone has an idea ? ( i've seen that a Mac could be an option while browsing the forums)

    Thanks to you guys and best of luck with your projects.

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    Registered User Bob Kelly's Avatar
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    Wish i could help but Fixted wings are out'a my leag... i have a gyro !

    as far as engines go the Subare ea-81 is supposed to be a great engine when equiped with a reduction drive .
    ....
    there is also the Masda Rotory engine but from what i understand they are harder to find than a VW now .
    You might consider a Motorcycle engine I saw a pic of a Yamaha Roadstar 1200cc engine used to power a fixed wing the feller just hooked the prop to the drive shaft ... flew it in 2nd gear ! he was quite pleased !

    sorry I'm not much help !

    Bob......
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    My Momm'a alwayse told me "the impossable is only a little bit harder Son ! "... and ya know ... i do believe She is Right !

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    Site Developer Jman's Avatar
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    The Sub and Mazda are out for size- Way to large for that airframe. The hummel is surprisingly fast on just 37 HP. I believe there are folks using the Hirth F23 and the Rotax 477. No doubt there would have to be modifications to the airframe to accommodate them. If it were me I would have a 1/2 VW built by Hummel aviation and shipped to me. It's a proven airframe / engine combination that I would be comfortable with.

    Whenever I read an article about improving speed in aircraft, the author almost always references a book called "Speed with Economy". I have not read it yet, however it seems to be the classic text for homebuilders who want to eek out every knot.

    As for the HB for cross country. Most will tell you it's not a good aircraft for cross country flight. My perspective is that just about anything can be flown cross country if you like to fly enough. I just flew from Louisiana to New York at 80 kts (slower than a hummelbird) in an aircraft that if you were to release the stick, within seconds you would be spiraling into a flaming death because there is no inherent stability. Had to FLY each and every second. Most would call that a horrible cross country platform. I call it fun .

    Good luck!

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    Hey guys, thanks for the answers !

    Concerning the airframe, after some google-searching I came across this "Speed with Economy" book...I'll buy it as it seems to fit perfectly the mods I want to do on the HB !
    Concerning the airframe, seeing Roe's Bird, widening the fuselage for a larger tank seems to be a good idea seeing that 1/2 VW parts are virtually inexistant in France and all my friends are flying Rotax, 2-stroke will probably be the engines I'll end up with.
    I've also found some bike engine conversions on a French homebuilt forum but I can already see my instructor yelling about how it's suicidal !
    As far as cross country goes, the idea would be to have enough speed/fuel to reach my scattered family and eventually do some sightseeing trips over the Alps "for fun"..done it on the MCR-01 prototype..man it was beautiful, this bird is a mini fighter (constant speed prop...) !
    All of this meaning having a range of about 400 miles.
    Just like Mr. Roe did, I would balance every moving surface, cowl everything that can be and build in the cleanest possible way (I will apprentice myself to the aircraft building company where I fly since I'm still a newbie to metal frames).
    I was also thinking about reducing the airfoils thickness and the wing area a bit (narrowing the whole wing) or something to reduce leading edge drag.
    If anyone has done some mods on his projects' wing or could give me infos about Mr.Roe's bird, please feel free to express yourself

    Thank you all for your answers !

  5. #5
    Super Moderator orion's Avatar
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    I would urge caution in any wing modifications. Reducing an airfoil's thickness may actually have the opposite effect from what you're after. The highest cruise lift-to-drag ratios for most sections that form relatively lightly loaded wings are for airfoil families that fall in the 12% to 15% range. Reducing that thickness may actually increase the cruise drag and will especially hurt you in the slower parts of the envelope such as in climb-out, where the thinner section's drag curve tends to rise very rapidly.

    Reducing the area may also not be recommended just due to the low power that this aircraft generally operates with.

    Yes, there might be a bit of tweaking you could do, but there are other areas that will contribute more to reducing the drag than modifying the wing. These include paying particualr attention to cooling and cowl drag, putting maximum effort into the quality of the build, sealing fuselage leaks and protuberances, building fairings to reduce the wing-to-fuselage interface, building a more optimum wing tip, etc.

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    Hi Orion !

    Thank you for your valuable commentary and I will follow your advice concerning the thickness of the airfoil ( I believe the one used by the HB is a modified Clark-Y which indeed seems one of the most efficient profile for lightweight, low-speed aircrafts).
    After some thinking about firewall-forward options, I have reduced my choice to the Hirth F-23 or a Rotax from 50 to 65 hp mainly because of availability issues in my country.
    As you can see, both options increase HP from 25 % to 60 %... there's the dilemna : these powerplants mean high consumption leading to low range but also high HP leading to increased structure stress.
    As I have little knowledge about where to add structural reinforcements, my first reaction was to think "hey, why not reduce the drag-induced structural stress ?".
    Concerning the fuselage drag reduction, the ideas are there (thank you Orion and the "Speed with economy" book)
    However, concerning the wings, apart from designing better wingtips, root and control rods fairings as well as ailerons balancing, I have found no other way of modifying it to reduce drag and use the full potential of the powerplants without transfering HP (energy) to the structure through drag.
    Any thoughts are welcomed as I am quite inexperienced in this field.

    Thank you everyone and good flights !

    P.S.: I have often encountered this "low aspect-ratio wings" thing...can anybody explain what this means to me ? Many thanks

  7. #7
    Registered User StRaNgEdAyS's Avatar
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    Low aspect ratio refers to the ratio of span vs chord length.
    Here is a quote from the centennial of flght website that might help you understand it better.
    The aspect ratio of a wing is defined as the square of the span divided by the wing area. Itis a measure of how long and slender a wing is from tip to tip. For a rectangular wing, this reduces to the ratio of the wingspan to the chord length. High aspect ratio wings have long spans (like high performance gliders), while low aspect ratio wings have either short spans or thick chords (like the Space Shuttle). Gliders have a high aspect ratio because the drag of the aircraft depends on this parameter. A higher aspect ratio gives a lower drag and a better glide angle. The Space Shuttle has a low aspect ratio because of high-speed effects.
    Last edited by StRaNgEdAyS; July 17th, 2005 at 10:16 AM.
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    Super Moderator orion's Avatar
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    While the definition quoted above is correct, it also gets into the trap that many designers fail to notice. The equation for "induced" drag (drag due to lift) is the lift coefficient squared divided by the quantity pi times the aspect ratio times the Oswald's factor. Now, everyone seems to be locked in on the aspect ratio and ignores the numerator.

    Simply stated, the wing's area also has a bunch to do with induced drag since with more area, the cruise lift coefficient goes down, thus also reducing the induced drag value. Yes, the lift area has to be balanced with surface friction issues but sometimes a bit more area will do wonders.

    The other issue to deal with here is weight. High aspect ratio wings require more structure. Short chords result in small structural section heights. The long spans result in high bending moments. Those two issues coupled together result in the requirement for a lot of structural mass. As an example, an airplane we worked with recently, the Caproni two place glider, has a center section stub (the spar carry-through section that mounts on the fuselge - the wings attach to it) that weighs over 400 pounds - my back certainly did not like that each time we had to move it.

    And of course the a high aspect ratio is not the total solution to the induced drag story. This can be best demonstrated by a classic school example of the Avro Vulcdan and the Boeing B-52. When you normalize all the numbers (account for the difference is size, configuration, mass and scale), it turns out that the Avro Vulcan is actually more efficient in cruise than the B-52.

    For most general aviation applications, it is generally of minimal benefit to go to an aspect ratio of any more than about seven. After that you start getting into weight issues, as well as those having to do with handling (wing clearance, ability to judge the wing's reach, etc.).

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    Thumbs up

    Hey guys !

    Thanks for the replies ! I think I now grasp the aspect ration concept !
    After a bit of searching on the web I finally found a study that correlates both of your explanations.
    In fact, it stated that unless you fly at a really high altitude (less air pressure = small denominator = higher wing induced drag) all means commonly thought to reduce wing drag like wing tips, elliptical wings and so forth are plain useless and at most dangerous (the stalling patern of an elliptical wing is unfriendly).
    Finally, regarding this artical and your advices, I better keep the wing untouched and concentrate on parasite drag.
    One last question however : what would be the advantage of building a PC-7 shaped wing(effectiveness vs. construction time) ?

    Happy flying !

  10. #10
    Super Moderator orion's Avatar
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    By PC-7, do you mean tapered? In this scale the difference would be minimal.

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    Thank you for your tips Orion, I won't touch the wing ( yes i did meant tapered...didn't know the word, sorry >< ).

    Dunno if I can post this question here but oh well :
    I recently "discovered" the Suzuki GEO conversion and it seems attractive (water-cooled 50 hp at 2.2 gal/h, 118 lb with PSRU). Anyone has heard about this type of engine for a Hummel Bird ?
    If it doesn't fit i'll guess i'll have to get my hand on those Rotax...

    Thanks for your answers and good flights !

  12. #12
    Super Moderator orion's Avatar
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    I've heard of one or two companies producing this engine option and have seen one of them in actual use on a scale P-38 (pictured on the first page at our site - I did some of the scaling design work). At last report (which was quite some time ago) the owner was very happy with the performance and reliability. Keep in mind though, by the time you get everything on, the install weight with this engine is significantly above the other alternatives you mention and as such may be well beyond the typical engine for the Hummel.

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    Happy to hear that it's reliable !
    Concerning weight issues, i heard that Bruce King fly his HB with a 1835 cc VW from great plains (a full one) weighing around 160 lbs with little increase in stall speed. Also, with a more aerodynamically "clean" airframe, stall speed could get even lower at the same weight if i'm not mistaken.
    Anyway, considering your experience if this engine is not to be fitted on a HB, i'll have to start looking for cheap 2-strokes (= less reliability + more fuel needed). Wouldn't the excess of weight be compensated by less fuel carrying on a GEO ? ( i'm talking about the "small" 1000cc 58-62 hp engine)

    Thanks for your help !

  14. #14
    Super Moderator orion's Avatar
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    My reply has more to do with the structural capability of the airframe than with the performance. Most airplanes can tolerate heavier engines without seriously affecting the stall and cruise speeds. Some may have to be slightly adjusted (wings shifted) to account for the heavier nose, but that's relatively minor.

    But if the engine is significantly over the allowed weight, then you have attachment issues, as well as those affecting the overall structure, especially if it forces you to fly at a higher gross weight.

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    That's exactly what I was worried about... And so gaining HP without the drawbacks of overweighting the firewall and such would only be achieved by 2-strokes... (I guess I won't find a 4-stroke with more power for the weight of a 1/2 VW).
    Another question regarding this 2-stroke option: i'll obviously need a wider fuselage and maybe bring the firewall forward a bit...have any thoughts about this ? Will I need a larger stab ?
    Ideally I would like my Bird to look a bit like David Roe's one with a narrowed nose (should be OK with a Rotax 582 or less ) a bit like the AR-5.
    I'm giving you the links to the pics if your not familiar with the planes.

    David Roe's Diva:http://www.contactmagazine.com/Issue76/roe-1.JPG
    The AR-5:http://www.ar-5.com/ar5-4.html

    Btw, thanks for your quick replies Orion !

    edited: added the fuselage mod question.
    Last edited by NACA; July 18th, 2005 at 07:53 PM.

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