Corsair/Spitfire hybrid

Discussion in 'Aircraft Design / Aerodynamics / New Technology' started by Will Aldridge, Oct 16, 2010.

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  1. Nov 23, 2010 #61

    addaon

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    How far off are you on sufficient fuel capacity in the wing roots? If it can be fixed by just adding a few percent thickness, I'd seriously consider that; that section is going to be more "interesting" structurally anyway, and putting the complexity (fuel tanks, gear mount, outboard wing mounts) in one place might just push you to simpler, localized heavier structure (aluminum, for example).
     
  2. Nov 23, 2010 #62

    Will Aldridge

    Will Aldridge

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    I'm about 5 gal short in the wing roots. If there were a way to make the fuel tank structural I might be able to but that makes me nervous. Of course I still don't know how to attach the landing gear so maybe some way will open up when i figure it out, but till then just looking at it I don't think it will work.

    The root chord is 52 inches and the spar is a little more than 8" deep so it is already pretty deep.
     
  3. Nov 23, 2010 #63

    macdonca

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    Fixed gear or retract?

     
  4. Nov 23, 2010 #64

    Will Aldridge

    Will Aldridge

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    It'll be fixed gear. I was initially planning on retractable but the whole design philosophy of this plane is that since the wing is going to be so difficult everything else has to be as simple as possible.

    Regarding attach points my plan has been to have a relatively thin cored shear web in the main spar and have the wing mostly hollow except for where the landing gear attaches. My idea at the moment is to have solid foam core from the main spar out forward to the landing gear attach point, which will obviously reduce volume for the fuel tank.
     
  5. Nov 23, 2010 #65

    autoreply

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    Integral (wet wing) tanks are by far the easiest way to go. Just make sure that your foam can stand the fuel (and epoxy can stand ethanol).
     
  6. Nov 23, 2010 #66

    autoreply

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    Integral (wet wing) tanks are by far the easiest way to go. Just make sure that your foam can stand the fuel (and epoxy can stand ethanol).
     
  7. Nov 23, 2010 #67

    orion

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    http://www.oriontechnologies.net/devpics/p40.jpg

    Here is an idea that's somewhat similar in scope to your hybrid. It's one of the last iterations of the P-40 ("Q" model) I was trying to see how well it would scale down to a general aviation type two place tandem. I also decided on a fixed gear for one of the variants of the aircraft, blending the gear in something akin to some of the 30's racers.
     
  8. Nov 23, 2010 #68

    Hot Wings

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    I like Orion's thoughts on the main gear. Simple and pretty well streamlined. Since you already have a gull wing the "leg" should be pretty short. If you make the wheel pant a structural item, similar to the outboard wheel pants on a Q, you can embed some trailing link suspension pretty compactly.

    As for the fuel tank, there are 2 schools of thought on placement with regard to fire danger. Putting fuel in the wings, particularly the leading edge "D" cell makes rupture almost certain if you hit something like a fence post or tree during a forced landing. In this scenario if fire erupts it's the crew has to exit through it.

    Putting the fuel in the cockpit may seem dangerous at first but the tank is in a well protected location and is less likely to get crunched in a less than optimum landing. If it does get broken chances are fair that the crew is already dead for other reasons. This assumes the instalation was done taking lessons from the Pinto's history.
     
  9. Nov 23, 2010 #69

    Will Aldridge

    Will Aldridge

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    I've been thinking about something like this and have been wondering if the extra wetted area and weight is worth it? Small gear legs with well designed fairings have been proven to work quite well. What are the advantages of the larger more blended type fairings? I haven't really drawn either out yet so I haven't decided which look I like best, although I think the gear legs are long enough that I like the look of smaller fairings better. If the gear were quite a bit shorter I would be more likely to emulate Lovings Love and Tom Aberles Phantom.

    There simply is not enough room in the fuselage for all the fuel I want so there is going to have to be some in wings no matter how it's done. The safety side of putting it in the outboard wing section is that in a crash if the wing gets hit it will most likely be ripped off and take the fire danger with it. The fire danger from the tank in the wing root is another reason I have been a little loath to put it there(aside from volume issues).
     
  10. Nov 23, 2010 #70

    Topaz

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    Is there any objective reason you can't simply scale up the aircraft a little to accomodate the needed fuel volume? I realize that the required fuel volume will go up as well, having to drag more airplane around, but in your sizing process you should be able to find a happy medium.

    Or simply cut back your range requirement. Do you REALLY have to travel "that" far non-stop?
     
  11. Nov 23, 2010 #71

    Will Aldridge

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    That's a slippery slope I really don't want to walk out on(making the plane bigger). There is plenty of internal volume for fuel tanks without driving the cost up considerably. I am designing the plane with the Corvair in mind and according to the numbers on the fly corvair.com website the fuel burn during cruise is about 7 gal/h. Although this is basically an around the patch plane not a serious cross country one I still intend on taking it to Oshkosh and I figure that 2 hours of flight time (counting reserve) is pretty reasonable, any less is too little.

    About the most I can squeeze in the fuselage as currently designed is 10 gal. and that just doesn't cut it.
     
  12. Nov 23, 2010 #72

    Topaz

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    Increase the thickness of the root section, then. Something's gotta give, slippery slope or not.
     
  13. Nov 23, 2010 #73

    autoreply

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    Well, there's always a lot of talk regarding this topic amongst pilots. I thing most of it is pretty useless. The margin of crashes that are severe enough to rupture a tank (if properly designed), but mild enough to survive yourself is pretty small.

    Putting your fuel out 2 or 3 ft isn't going to help you much either. The big majority of the pilots that could have survived, but burned are severly injured and thus can't get out. An intense fire at 3 or even 8 ft away will still kill you.

    Why not have a 10 gal header tank (many crashes occur because of typical low-wing problems)?

    A completely different take; why not have a "bomb" under the fuselage (with the rest of the fuel). Looks great for your design.
     
  14. Nov 23, 2010 #74

    Will Aldridge

    Will Aldridge

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    Given the comments on survivability and all I am becoming more convinced to go with 3 tanks, 2 in the wing roots and 1 in the fuselage. We all know the compromise game, and given the options I'm liking this one the best.

    I beleive what I said was that if the most easily ripped off part of the wing had the fuel tank in it when it parted company with the rest of the plane that would be more of an advantage, not that 3 ft farther away would make me a whole lot safer.
     
  15. Nov 23, 2010 #75

    Hot Wings

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    Fuel systems in small planes like this are always a problem due to space and CG issues. If you want simple and reliable that points to a header tank, but the capacity is limited.

    Putting fuel in the wings means pumps and plumbing. It also means that you have to find some way of remotely indicating the fuel quantity. Complexity is one of the things most builders are trying to avoid by building small single seat planes.

    If it were me I'd opt for a fair sized header tank for local flying and use Auto's suggestion of an external aux tank for long flights. Put the fuel pump in the aux tank and then you only have one electrical connection and 2 quick connect fuel lines (one feed and one overflow from the main tank) to contend with.

    A "bomb" would look right at home on your design. :)
     
  16. Nov 23, 2010 #76

    Will Aldridge

    Will Aldridge

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    Yeah but would the FAA think so?

    I may have been a little too quick to pass off the header tank. I'm trying raising the fuselage profile in front of the canopy to add more volume. Might be worth another gallon or 2.
     
  17. Nov 23, 2010 #77

    Topaz

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    It's the goose-stepping SOBs at the TSA and DHS you have to worry about, not the FAA. Ooops. Did I just say that out loud? :speechles
     
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  18. Nov 23, 2010 #78

    zk-jkw

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    The T51 has optional functional drop tanks so presumably the FAA doesn't mind (you cant actually drop them though!)
    Personally I'm not a big fan of fuel in the fuselage...
     
  19. Nov 23, 2010 #79

    Topaz

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    It should be pointed out that most smaller cars have fuel in the passenger compartment. The reasoning goes that if the vehicle is crushed enough to rupture a tank there, the passengers have "already left the vehicle", if you take my meaning. That's played out well in the automotive arena, while exposed "outside" tanks... well, there's the Pinto for you.
     
  20. Nov 23, 2010 #80

    zk-jkw

    zk-jkw

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    Agreed. From what I have seen the tank itself is not necessarily the weakest link in a crash rather the fuel lines/pumps and systems that run through the passenger area
     

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