Tandem Wing Pusher

Discussion in 'Aircraft Design / Aerodynamics / New Technology' started by Starman, Oct 30, 2010.

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  1. Nov 5, 2010 #101

    Starman

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    I guess it was the styling that was throwing me off. With a stock glider style fuselage you can hide the engine inside a P-51 style scoop. This design is converging nicely now, and it will be at the big fair this summer.

    Also, Autoreply said there were no long drive shafts that have any proven reliability, I recommend looking at Porsche 928s or Corvettes with rear transaxles, or boats.

    Not reliable, HA!

    Edited to remove oudated drawing, see end posts
     
    Last edited: Nov 7, 2010
  2. Nov 5, 2010 #102

    autoreply

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    I'm basically designing such a thing too.
    Comparing apples to whales. A prop isn't a rubber wheel, firmly on mother earth... You don't have to believe me, but take a look at the huge trouble actual very qualified engineers went tru with the Bede. There's no free lunch or easy solution.
     
  3. Nov 5, 2010 #103

    Starman

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    That's neat, are you starting with an existing glider cockpit or building your own ... or just designing? OK, cough it up, lets see what you have so far

    I've been in this fireplace door business for WAY to long, I never really found fireplace doors to be all that thrilling even at the start. So I'm getting in to this airplane business as soon as my next custom door order is done, and I'm going to work full steam at it

    It's a very simple design from a very simple person, and with a little help from you guys I can get it done in three months. The official start date is Jan 1, and if, with the help of my friends here, we could find, cough, cough, a nice glider fuselage with a broken rear end by then I'll see if I can scorch some build time records. Hoping for three months.

    Autoreply, does your design have a driveshaft or on putting the engine in the back?

    Corvette and Porsche driveshafts do apply, check it out; and concerning the engineers Bede hired to figure it out for him, I tested smarter than all the engineers, mechanics, and executives that ever worked at Chrysler ... so keep your fingers crossed. Bede probably didn't give his engineers free reign either.

    Edit, also, a prop IS like a rubber wheel, in that they both have a lot of momentum behind them. The prop has the momentum of the blade ends and the tire has the momentum of the Earth, and if a Corvette can handle that then it's good enough for me,

    STANDARD drive train from a corvette, standard engine, standard prop, standard everything. I'll might make my own drive system first anyway and fall back on the Corvette if need be.

    Edit: removing surplus picks to save server space
     
    Last edited: Nov 7, 2010
  4. Nov 5, 2010 #104

    Jay Kempf

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    I actually have a Porsche 928. That prop shaft is one of my favorite parts of the car. Engine speed driveshaft right under your right elbow next to your right hip. Helps not to think about it when the outside view goes plaid.

    I really like the underslung belly scoop view. That is gorgeous. Just one thing. That engine needs to be about 6 feet aft of where it is if you want any chance of your weight and balance to come out. So the engine is behind the rear spar basically. With the rear wing under the engine you've got exactly what I have been drawing for years. Long nose gear that is attached to the front spar and short mains in the back in the lower main wing. Two rudders on the top of the main wings. Basically a small Valkyrie. You got right through all the compromises right to the conclusion fast. The two place glider front end is a great twist on it. I have also drawn up a cargo version of this and it still works. One nice thing about this sort of Tandem setup is the WIDE CG range and that it doesn't tip over onto either it's nose or tail when the occupants aren't in place.

    Anybody have a 3d model source for twin glider front ends? I could be modeling this thing. I have a basic V8 model.
     
  5. Nov 5, 2010 #105

    autoreply

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    Ground up own design. Either I use proven stuff, the way it's intended to be (engine, prop, maybe LG), or I design it the proper way.
    Mine looks like a glider, but the wing is roughly at 2/3rd of the height of the fuselage. The canopy looks the same but actuates in a very uncommon way, I expect to get a lot of benefits there. Fuselage looks (compared to a glider) enlarged. Roughly 1ft both immediately aft and forward of the wing. Forward will be a bit of luggage space, aft will be the engine.
    Speed, 200 kts flat out (912, no turbo), range, 3000 NM, high up @ 175 kts.
    I won't. There are numerous reasons for that, but amongst them is that I won't be subtracted too much by people, talking about my design. I've though about it quite thoroughly though and my configuration is far from unique, just better and different. All my numbers are realistic, compared to existing and proven aircraft. I just make other choices...
    Just to give you an idea; I have a couple dozen sketches about construction techniques I plan to use (skin layup, spar layout), hundreds of calculations (numerical iteration for most parts, like wing torsion, bending, a start of flutter, all that for the H-stab, V-stab, fuselage, landing gear).

    I am planning using a driveshaft. Gave it quite a lot of though, but my knowledge is lacking for a proper theoretical design. Have to learn more about that first, might in the end give up and adapt the "let's combine testing with designing", but for now I first want a theoretical solution and then test it.

    Regarding my comment about "people, talking about my design"; if I start a discussion, I want to argue/inform on correct information. This is an example, where in the end, still not all information was given the first time.

    So no fancy sketches. The first assembled 3D model you'll see is probably when the design work itself it mostly done.


    @ Jay, I do have a model for a Discus 2B (single seat glider). Is a catpart file.
     
  6. Nov 5, 2010 #106

    Jay Kempf

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    @ Jay, I do have a model for a Discus 2B (single seat glider). Is a catpart file.[/QUOTE]

    Cool, for some reason my head went to an old dual canopy Grob. So how does one transfer a large file in a forum? I'll have a look around the web too. Must be at least a surface model I can scab from somewhere.
     
  7. Nov 5, 2010 #107

    Toobuilder

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    ...and I have a Corvette - never thought about the driveshaft spinning at 6500 RPM inches from my body...

    THANKS!;)
     
  8. Nov 5, 2010 #108

    autoreply

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  9. Nov 5, 2010 #109

    Starman

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    Thanks Jay! I'm glad you like it. It's true these types of tandem wing designs have a wide CG range, which is what makes them so adaptable.

    I moved the engine forward so the weight distribution is changed, now I'm aiming for 80% front - 20% rear at gross weight and around 90-95% on the front with a single lighter person and no fuel.

    This makes overall wing size come down from 145 ft to 125 ft with the same stall speed of 54 kts. 80 ft on the front wing and 45 on the rear wing. As you can see that's not so far from a conventional plane, but this one has a lifting tail, full span slotted flaps, and the pitch control on the front.

    I finally settled on the design so it's more or less locked now. Thank god for that! Going with what was behind door 'B', with shark fin styling on the manifold/turbo exhaust and tail.

    Centerline wheels with outriggers on the front wing tips. Rear wheel retracts into tail or could be fixed and inside some clam shell doors.

    I decided to go with your twin boom idea too, but mine are only two feet apart. :)

    Edit, I was just wondering, have you or anyone ever heard of a Porsche 928 drive shaft breaking? I'll bet there aren't any, but even if it did it's inside a protective housing.
     

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    Last edited: Nov 5, 2010
  10. Nov 5, 2010 #110

    Jay Kempf

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    Working in Catia eh? Not me. I am in SW 10. Both Dassault and there is no clear way to get between the two. Astounding!

    Got file thanks. Trying to find a translator.
     
  11. Nov 5, 2010 #111

    Starman

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    I'll admit I haven't done a detailed weight and balance yet, but that's hardly needed on a design like this, until the very end when you hang the engine.
     
  12. Nov 5, 2010 #112

    Starman

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    Have you ever heard of one of them breaking?

    My computer won't open that file from Autoreply.

    Umm, so how fast do ya'll think it will go with 250 hp and 125 ft of wing?
     
  13. Nov 5, 2010 #113

    Jay Kempf

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    I have heard of a driveshaft breaking but it was because someone put a whole lotta boost on and was running on the track.

    The file is Catia native. Little chance opening that. Autoreply needs to open and save as a STEP or IGES if he has access to Catia. We can go from there.

    What program are you working in. Your details look very nice.
     
  14. Nov 6, 2010 #114

    Starman

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    :) I got that backwards, cg shifts to rear with a single person so % on rear is larger.

    Do you Porsche and Corvette aficionados eve rev it up, stomp on the gas, and drop the clutch? Yes. OK then try this: go out and warm it up, then redline it, floor it, and pretend like you're drunk and stick it in third or fifth gear, and dump the clutch; :roll: let us know if anything breaks.

    I'll give fifty fifty or better that it holds, I mean, the factory may have tested for that.

    Edit: Jay, I'm using an antique, unsupported, AppleWorks drawing program for MAC. I got one of those Viacad software packages, but I couldn't figure out how to make it draw a 2D angle iron end view with it, so maybe later.
     
    Last edited: Nov 6, 2010
  15. Nov 6, 2010 #115

    Sky High

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    When this thread began I started on a single seat version in XFLR5 just to see what was possible....just found the time to finish it. The following is just my opinions and hasn't necessarily followed the direction the thread has headed in.
    First up, XFLR5 is getting more accurate and can produce results if the sections you use and the approach used is sane, to within 2-5% of stuff that I have wind tunnel tested....but that's it, its a useful first pass tool but not something to replace some real engineering with. That said, all these pics were generated in XFLR5 as are the results.
    Second, I don't believe you need to consider huge HP V8's to power these designs with. This design is showing that a 189 knot cruise is possible on about 43 hp assuming an 85% efficient prop and an extra .65hp thrown in for the electrical load.
    Third, the wing area's mentioned seem overly large, this has just 10.2m^2 in both wings with a span of 7m, and it will still stall/mush at around 62 knots at its gross weight of 544 kg and 9.6 deg alpha.
    The flap on the fwd wing is just 15% chord, and I have serious doubts about the huge 45% chord flap shown in the thread.
    Stuff that still remains to be fixed or changed, probably a smaller higher lift fwd wing will speed it up in cruise and lower the the stall speed appreciably (perhaps 8-9 knots?), the aft wing tips need specialised sections to avoid the tip stall that occurs now which is a function of the wake interaction between the 2 wings.
    As shown in one of the pic's, I started with the assumption that you could power this with a couple of AMT Titan jets which output about 392 N of thrust, so the cruise drag of 272 N is well under the assumed 784N available, but probably not adequate for decent climb rates or grass runway operations. Anyways, XFLR5 doesn't like modeling nacelles, so all the results and other pic's show the results minus the drag of the engines, real drag numbers will be slightly higher.
    Lastly, all the sections were modeled at an Ncrit of 10 so that the assumed surface finish doesn't have to be as good as a glider, also so that the predictions are not overly optimistic either. I'm not likely to finish this or develop it, was just done for the pleasure of playing with it and to see if the basic thrust of the thread was valid.....enjoy the pic's
    Cheers
    Richard
     

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  16. Nov 6, 2010 #116

    Sky High

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    Forgot a couple of things, glider sections are not useful here as they generate too much lift/drag to allow any sort of a good cruise speed, the sections I used were my own and very low camber (0.7% to 1.1%), the cruise CL's are also low. The fuselage is similar to an ASG-29, but the nose is a bit different and was designed by Boermann at Delft for a standard class glider a few years back.
     
  17. Nov 6, 2010 #117

    Jay Kempf

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    Wow! cool thanks for that brain load of stuff to review. I thought the size of the lifting surfaces to the task was a bit much when this discussion started. But it is Starman's project so we'll stick with the extra area. Can't hurt anything other than top end in the end and with a ton of cheap HP it won't matter.

    As far as your question above: I don't think that anyone was thinking about using a glider section. The wing might attach at the same place but the section would have to be altered for the task. At least that was what I was always thinking. Been bastardizing fiberglass fuselages for other wing sections for a long time.

    What is interesting is the front view of your analysis. The interaction of the downwash or the separation front to rear is the toughest part of the aero design. Cruise is relatively easy but max downwash conditions is tough. Separation due to stall and blanking can be tough. But getting those two modes under control (not really speed dependant) is key and if they work then everything else would work. I still think geared flaps is the way to solve all that. Take off level and land basically level using the throttle is what I am talking about.
     
  18. Nov 6, 2010 #118

    autoreply

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    http://www.jarno nieuwen huize.nl/temp /D2B.igs

    Remove the spaces.
    That seems extremely low. Even the AR-5 or Reno racers need considerably more.
    The lowest drag aircraft in history (Diana II) still needs 40HP of thrust.
    Those results don't seem correct. That would be a Cl of 0.9 Even non-flapped airfoils achieve at least twice this Cl. I suspect, the lifting of the canard isn't taken into account?
    Also, 62 kts is extremly high, it'll fly like a rocket and need 3000 ft runways. I end up with exactly this stall speed too, but that's with half the wing area and with an extreme fuel load. 45-50 kts will be the normal stall, with 4 hours of fuel or so.
    I don't agree
    Typical design points for modern standard class gliders are 2-3 times the stall speed (in cruise). That's 40 stall and 80-120 cruise, even a tad more for modern gliders. This fits almost every aircraft.
    Often people argue that sailplane profiles aren't suited for powered aircraft, because they're designed for a wide range of speeds (or Cl). While this is correct, sailplane profiles are so much more refined, compared to the typical aircraft used on GA that they're still superior to even the laminar airfoils used in GA.
    The reasons (I think) people don't use them are:
    *People can't maintain laminar flow. (Very accurate profile, need to keep the bugs of)
    *Sailplane profiles don't tolerate fowler flaps, they just accept straight flaps.

    Cool pics by the way.
     
  19. Nov 6, 2010 #119

    Jay Kempf

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    Thanks,

    I think you are correct that if the design is to be in the sub 200mph regime that a flapped, reflexed glider profile will work just fine.

    Is Diana 2 the lowest drag airframe or the highest L/D for that S? There are some tiny power planes with less than half that span and area with pretty tiny FPE numbers.

    jfk
     
  20. Nov 6, 2010 #120

    autoreply

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    Well, straight flaps mean that you need large chord or drag brakes to get the required drag for landing. It also means your wing is slightly bigger as a fowler-flapped wing. In total though I expect it to have equal or lower drag as an advanced fowler-flap wing.
    The only means to compare (different) aircraft fairly is flat plate equivalent area.
    Mike Arnold claims 0.806 sqft of drag area, which seems realistic. The Diana II has - based on measurements - a frontal drag area of 0.61 to 0.62 sqft. It's induced drag is (of course) also far lower than any powered aircraft.
    Even most 2-seat open class gliders are around 1 sqft of frontal area only. I wouldn't be surprised if a 85 ft, 1900 lbs open class glider has lower drag as most formula 1 racers....
    Which is exactly why I'm advocating more glider technology. It's far more advanced as most GA technologies in structures and particularly aerodynamics.
     

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