CAR-251: The Cheap Air Racer Discussion thread.

Discussion in 'Hangar Flying' started by nerobro, Sep 10, 2014.

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  1. Sep 10, 2014 #1

    nerobro

    nerobro

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  2. Sep 10, 2014 #2

    Himat

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    The big question as I see it, how are the class kept as a cheap class?

    An observation from radio control airplane and boat racing. Very often a “cheap” entry class evolves into an expensive class as some spend money to be more competitive.

    Only one make or very stringent rules like list’s of approved stock engines and propellers have kept cost escalation at bay. The other option is rules that introduce a certain amount of randomness in the race results, but competitive people often dislike that weather and other “outside” factors decides who wins.
     
  3. Sep 10, 2014 #3

    Topaz

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    I think this thread is meant more as a discussion of this particular design and design process. The discussion about the racing class itself is over in the Cheap Air Racing Class thread referenced above.

    Nerobro, if I'm wrong about that, please correct me.
     
  4. Sep 10, 2014 #4

    nerobro

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    There are a few things adding up to a "I don't care if you throw money at it, you're still going to have to fly your butt off."

    First, it's a spec airframe. Your plane is built to plans, or you don't race.
    Second, takeoff weight will be mandated to be 500, or 550lbs. (depends on how the rest of the math goes.)
    Third, you use the spec engine, with the specified modifications, and prop hub.

    How do you deal with cheating?

    Say.. water ballast that's pumped into the exhaust during flight? Or sand that rattles out the back of the plane in flight? Well, if you win a race, we can weigh your plane. :) If you're lighter than the empty fuel load, we'll know something is up.

    How about some bigger pistons in that engine? Or a larger throat carb? maybe some port matching? Well, it's a spec engine. If someone thinks you're running a "hot" engine, for a nominal charge, we'll exchange a "series owned" motor, that we know to be in spec, for that racers engine. Since this can happen at any time, it's not to your advantage to invest heavily in your engine.

    If the race series becomes a real thing, with events, and sponsors, a motor pool would be the ideal option. Motors are leased to racers for the season as part of their entry fee. If it breaks, you swap it out with us. If we think you've done things to it, we tell you to swap the motor.

    Eh, I"m happy to discuss it here too. The planes value is directly tied to "fun" racing. But yeah, the cheap air racing thread is probably a better place for rules. :)
     
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  5. Sep 10, 2014 #5

    Matt G.

    Matt G.

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    The vintage sailplane guys discovered a guy in Florida that, given an existing frame and a few sketches or pictures, will blow a canopy for about $300. That seems like a fantastic deal to me.

    All of your other problems were already solved 50 years ago by the glider manufacturers. In the early to mid 60's, quite a few gliders had one-piece plexiglass bubbles mounted to a steel frame. The entire assembly is removable and quite light. The latches are simple and light and allow the canopy to be easily jettisoned in an emergency. A glider canopy vent window will solve your ventilation problem, too.
     
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  6. Sep 10, 2014 #6

    BBerson

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    I think someone should investigate the tip stall potential. The moderate taper and low Reynolds tip combined with the aileron at tip could cause a nasty tip stall.
    Suggest bringing the aileron inboard some. The roll rate should not be a problem.
    Maybe increase tip chord.


    Tail surface position: possible spin recovery issue.
    Suggest moving horizontal aft of vertical somewhat.
     
  7. Sep 10, 2014 #7

    nerobro

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    I hadn't done aileron sizing yet. Moving them inboard is really tempting, as that really gets away from surface flutter. (shorter control rods, stiffer part of the wing..) And this plane.. may have some nasty stall tendencies. I still need to think about how I want to deal with that.

    Since the design is going to switch to tricycle gear, the space under the tail gets opened up to help deal with spinning. Already, the actual rudder sticks out a foot below the elevator, so that should remain in effect even in a spin. Getting another 6" or foot under that would be easy. Moving the tailplane forward is a lot easier than backwards. Moving it forward also exposes more fin and rudder area. To get reasonable fin and rudder exposure I'd need to move the tailplane back a long ways, and I'd lose the active rudder area once the plane was in a spin.
     
  8. Sep 10, 2014 #8

    BBerson

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    Yeh, designing for spin recovery isn't easy.
    I always liked the Schweizer 2-33 glider with aft tail. I don't think it would spin at all, as I recall.
     
  9. Sep 10, 2014 #9

    Rienk

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    Definitely try to make this thing spin resistant. I'm fine with a T-tail, or a far rear H-tail like a TBM700 or others.

    Wing span should allow for some decent tips (even if it's just cloth over a bow). That will allow a foot or two past the 8' panel you're so eager for, and help with AR and aileron effectiveness.

    I think there needs to be the allowance for several spec built designs.
     
  10. Sep 10, 2014 #10

    Topaz

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    It will, but you really have to work at it.
     
  11. Sep 11, 2014 #11

    nerobro

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    T-tail comes with some pretty serious weight penalties. They are really pretty though. :)

    Stretching the wingspan much also means getting long enough that you can't keep the wing one peice. Perhaps 2x6 wood blocks, and leave them "free to interpretation" Let someone have a round tip, square tip, curved tip, reverse cut, etc... And you get "free protection from hangar rash" If the tips are bolt on they're also easy to replace.

    I think spin resistance is a hard thing to design for, especially when speed is the goal. My attempt with the lower rudder is to provide solid spin recovery.

    I'll see what I can look up for spin resistance after I get the math for this round done.
     
  12. Sep 11, 2014 #12

    danmoser

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    Happy designing.. a very worthy goal.

    Perhaps you already know of this, but the late Dr. Alex Strojnik has a set of 3 books and many of the same same goals as you, though his focus was clearly on attaining laminar flow..
    The 3 books have a lot of good practical as well as more scientific content, although they are a bit peculiar in writing style & organization.
    He developed the S-2 motorglider and Laminar Magic speed record setter, and a few other low cost race plane projects have spawned from that work.
    If you haven't yet.. take a look.
    John Washington is carrying on the legacy..
    check it out here: Aircraft, www.ReactionResearch.com
    Strojnik laminar design books, www.ReactionResearch.com

    Lot's of link to other resources there too.
     
    Last edited: Sep 11, 2014
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  13. Sep 11, 2014 #13

    NoStealth

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    Light pilot(s) help for rear cg. Not sure I qualify anymore :)
     
  14. Sep 11, 2014 #14

    cheapracer

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    Why didn't you go with a non-tapered wing for ease, strength and lower cost?

    If it's to be a class and they are all the same then a design that's 5 knots slower doesn't matter but if it's $1K cheaper it certainly does.
     
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  15. Sep 11, 2014 #15

    cluttonfred

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    Ditto what cheapracer said. In my mind this design would work best as basically a pastiche of the Sonerai I but even simpler--boxy fuselage, one piece wing bolted on top of the fuselage for easy disassembly for transport and storage, etc. Constant chord and full-span ailerons connected to small pushrods at the wing root make a lot of sense in that context. But feel free to use a tapered wing and outboard ailerons, I'll save the other set-up for MY cheap racer. ;-)
     
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  16. Sep 11, 2014 #16

    Victor Bravo

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    Tricycle gear? Really? On a lightweight, low power, inexpensive race aircraft?

    As I said before in the other thread, any class of air racing, from Mini-Maxes and Airbikes to IF-1 to 4360 powered Corsairs... is NO place for a new pilot. The very first fatal crash will kill the class, and 100% absolutely dead-to-rights HARM general aviation instead of promote it.

    Just like scratchbuilding a V-173 replica, or a Falco, or a hand-hammered cowling for a Gee Bee is no place for a brand new homebuilder...

    Someone can start a new thread about a cheap "air rally" or "air treasure hunt" competition class, where nosewheels are the norm. All the energy that had been misplaced into the cheap racer thread promoting Clark Y wings, 180 square foot wing areas, two-control Ercoupes, biplanes, and the Winter Zaunkonig can be funneled into that thread.

    To go fast on 30-35 HP, and make (even 2-3G) pylon turns, USELESS weight and drag are the kiss of death. These airplanes need to look like gliders, or Arnold AR-5's, or SD-1's, or MC-30's, or Moni's, or Cassutts, or EZ's, or even RV's.

    Some of us, myself included, strongly support general parameters instead of a fixed "one-design" racer. How many builders are you going to have if they can only use one construction method and design? There will not be any race pilots until after there are builders.

    (edit) Sorry, this was NOT meant to insult or belittle anyone. I stand by my reasoning, but if I let the sharp tongued smart-aleck a little too far out of his box then please forgive any unintended nastiness.
     
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  17. Sep 11, 2014 #17

    Victor Bravo

    Victor Bravo

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    This was my sketch of a sport-plane designed around the Briggs V-twin a few years ago, to get some decent performance and a little "wow factor" when you roll up to the gas pump. This one obviously would have been moldless composite, or perhaps even molded if it was worthwhile.

    If I drew this today I'd have to drop to one knee, bow my head in respect to Michel Colomban, and steal the offset longeron-mount tail design from his MC-30 instead of the T-tail. Colomban's tail has no more intersections than mine, but is lighter and cheaper and safer and easier to build.

    Old, wise, experienced, trained, successful aeronautical engineer figured out something that a wannabee amateur overlooked... go figure.
     

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  18. Sep 11, 2014 #18

    cluttonfred

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    VB, I like your racer sketch a lot (that's one heck of a spinner), I agree with you about the MC-30 tail (though I prefer the other way around, aft stab and forward rudder like a Miles M.20) but I disagree with you about the cheap air racer logic.

    A design like this is not a pure racer, it's a racy sport plane with the opportunity to run a race if you like. And if it were a successful desgin then many of them would never race, and even those that didwould spend the vast majority of their time just messing around like any single-seat sport plane. And if I remember correctly from the initial premise, this is ***not*** intended for Reno-style packs around the pylons, simply individual time trials over a closed course, and presumably the types of course would vary with each event.

    Given that premise, a clean, simple design emphasizing ease of construction and ease of piloting (hence the trigear) over absolute performace makes a lot of sense.
     
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  19. Sep 11, 2014 #19

    Hot Wings

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    This is the kind of race plane I was envisioning. Your example* would fit right in! But it seems there is much interest in a "one design". If this were to ultimately go down this path I'd suggest adopting an over all wing, fuselage and empennage shape and then let the designers come up with the structure in wood, tube/rag, composite, and aluminum. Then the builder could choose the medium they like to work in.

    But this decision is up to whomever puts up the money and time to actually get this started. That isn't me. I have too much to do already. (HBA is important so I can't give that up!). I would be willing to serve on a board of directors ............ if this ever got that far.

    * It looks like it could be done in aluminum sheet as well and still look very good.
     
  20. Sep 11, 2014 #20

    Hot Wings

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    This is the kind of race plane I was envisioning. Your example* would fit right in! But it seems there is much interest in a "one design". If this were to ultimately go down this path I'd suggest adopting an over all wing, fuselage and empennage shape and then let the designers come up with the structure in wood, tube/rag, composite, and aluminum. Then the builder could choose the medium they like to work in.

    But this decision is up to whomever puts up the money and time to actually get this started. That isn't me. I have too much to do already. (HBA is important so I can't give that up!). I would be willing to serve on a board of directors ............ if this ever got that far.

    * It looks like it could be done in aluminum sheet as well and still look very good.

    Edit: Sorry for the off topic post. This should probably be in the "Cheap racing" thread.....The all seem to run together:ermm:
     

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