Discussion: Conceptual Design of an "Inexpensive" Single-Seat Motorglider

Discussion in 'Aircraft Design / Aerodynamics / New Technology' started by Topaz, Sep 10, 2014.

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  1. Apr 14, 2016 #581

    Hot Wings

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    And maybe that is why the corporate world has been so successful getting new single engine planes to market in the last couple of decades? :gig:

    Give him time! He has a very regimented process he is following and will get to the hard numbers and detail design.
     
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  2. Apr 14, 2016 #582

    Jan Carlsson

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    it is getting there, just as the metric system is taking over the imperial lands, inch by inch, :) Topaz is doing it the right way, start from almost nothing, see what is needed. change as we go. different opinions and thoughts is what drive it forward. Topaz is not designing a ASW-xx or a SF-25, why would he? they are already designed.
    It is educational ...
     
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  3. Apr 14, 2016 #583

    Topaz

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    Yep. This is "conceptual design" in the sense that Raymer uses the phrase in Aircraft Design: A Conceptual Approach. I've never seen any two designers define the phases of designing an airplane with the same terms and with the same start-end points for each phase. Orion broke the phases about the same as Raymer, but called this stage I'm in "Configurating" or "Configuration Design".

    My recent excursion into crashworthiness is definitely more detail than you'd normally see at this stage. An experienced designer would already have a high degree of familiarity with the material and could jump right through it, whereas I needed to bring myself up-to-speed on the issues before I could make intelligent decisions. All this detail you saw was mostly that research being done.

    Why is it here at all? As you've recently seen, choice of crashworthiness technologies is influenced directly by the characteristics of the design at-hand, and vice-versa. Someone jokingly said to just put an arrow on the drawing with a legend noting, "under-seat load attenuator goes here." I very well could have done that. Stuff like that is done all the time, on much bigger projects than mine. But in the end, I'd still have slammed into the issue that an under-seat attenuator just won't fit. It wouldn't just disappear. I'd far rather find that out now, when the airplane design isn't "locked down" very much, than later when making a change is more difficult. So yeah, a little more detail now was in order, IMHO.

    What's next? I still need to write up the rest of the ways I'll be handling crashworthiness in this design. What's holding that up is time for me to finish up the rest of the inboard and outboard profiles of the airplane (I'm still working ahead of my thread a bit), just to make sure there are no more surprises. So far, so good on that score. I like the way the look of the airplane is shaping up.

    After that, things should return to a more-conceptual level. I need to do quick calculations of vertical and horizontal tail volume, then update the drawing to reflect those. Then we get start getting into stability and control, trim plots, drag, and more-detailed performance estimates. I'll also be starting to build a weight and balance and wetted area summation for the airplane, and that will also begin to start the accounting process for material costs, since it will be similarly itemized to the W&B and areas of surfaces. You'll recall that the cost of an airplane of this capability is the entire point of this design study. Can it be done within (or at least close) to an $8500 budget? I don't know yet.

    Once that's all done, there will be another, less extensive, redraw to reflect any changes in the numbers. Lastly, there will be a Raymer-style optimization of the wing and weights, dialing the airplane in exactly-as-possible for the requirements and specification document.

    Then one more redraw to reflect those changes, and this phase will be completed. At that point, I decide whether or not the airplane is worth taking through to build. If it is, I determine loads and more-detailed structural configuration in the "Preliminary" design phase, and final detailed structural analysis and individual part design in the "Detailed" design phase.

    I mentioned at the beginning that this would not be a quick project. I do want to "do it right", and I'm willing to put in the time necessary to accomplish that.
     
    Last edited: Apr 14, 2016
  4. Apr 14, 2016 #584

    cheapracer

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    Sorry, I have a bad habit of not following through with my thoughts because I arrogantly believe it's obvious.

    My thought to use paper pulp on your own mesh mold to suit your craft was of course then coated with a laquer or resin to seal it.

    Me, I will be testing a group of aluminium cans in short time, may even do it next week. They would be easily arranged obviously for individual applications. I intend to try a few different hole sizes in otherwise sealed cans. Note that a car aluminium radiator with the header tanks cut off, is actually an approved (and required) crush barrier for frontal impacts for race cars in Australia.
     
  5. Apr 15, 2016 #585

    proppastie

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    Might mount the results at that other thread, I would be interested to see your method of test, and calculations. Because not being much more than a "handbook Engineer" (look it up in the handbook, not hand job) I need worked examples.
     
  6. Aug 10, 2016 #586

    Himat

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    Quoted from post #67 in the conceptual design thread:

    A question here, what do happen to the pilot’s back as it slides down the seat back (main fuselage bulkhead) in case of a crash? I do see potential for injury to the pilot if he hit something as he move or just by the friction forces.
     
  7. Aug 10, 2016 #587

    Topaz

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    Ah, good eyes, and thank you for pointing this out. It's an error in my post. Originally, I was going to include a stroking vertical energy absorber for the seat pan, but it turns out there simply wasn't any space for it. I discuss this in posts #65 and #66 in the design thread. I forgot, however, to edit out that sentence from my draft for today's post, and didn't proof-read the post again before I added it here.

    I've edited the post to reflect the correct information, but in such a way that your question above still makes sense. Thanks for the help!
     
  8. Aug 10, 2016 #588

    Swampyankee

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    Most large aircraft tires have pretty high pressures -- iirc, it's about 219 psi in a Learjet 60 (https://www.nbaa.org/ops/safety/tire-pressure/). The rough ride may well because of the remainder of the suspension.
     
  9. Aug 31, 2016 #589

    autoreply

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    Just some inspiration:


    ;-)
     
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  10. Aug 31, 2016 #590

    Topaz

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    Beautiful. I'd be tempted to do something like that with a hybrid drive, and the ICE buried just aft of the wing and used as a range extender for the batteries. If the combo could get the range of my DS54 here, that'd be a neat ship. Ah well, a project for another day. :gig:

    Thanks for sharing this!
     
  11. Sep 1, 2016 #591

    Swampyankee

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    An interesting extension of this thread would be one for a two-seat motorglider with similar performance to Topaz's.
     
  12. Sep 1, 2016 #592

    Topaz

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    That's likely next for me. A project I've been working upon for some time. ;)

    I'd love to see other people's takes on the same general requirement, though (In other threads though, please. This one is for this particular project.). Motorgliders can be a real gateway to low-cost aviation, through the ability to keep the motor small and still maintain a good climb rate.
     
  13. Sep 1, 2016 #593

    Swampyankee

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    Well, I wouldn't start a different design in this thread; that would be both rude and confusing. For me, alas, it would be only an academic exercise. I am thinking of giving a design exercise for a motorglider to my high school engineering students. Of course, one of them would want it to be rocket powered, which is unlikely to be optimal.....
     
  14. Sep 1, 2016 #594

    Topaz

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    From the point of view of a teenage boy, rocket power is always highly optimal. :gig:

    Awesome of you to consider that for your students! For what little it's worth, IMHO I'd give them a sportplane instead. Something along the lines of an RV-x or similar. Motorglider wing optimization is a couple of steps harder than doing so for a sportplane. If you think they're up to it, then awesome. I've never taught, so I don't know what's realistic.
     
  15. Sep 1, 2016 #595

    Jay Kempf

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    Well, you know me, always in parallel with your efforts... But a little higher up the performance food chain.

    This one is beyond a cartoon and this isn't the latest version of it but only some aero-nuance has changed due to some heavy CFD analysis of late. Been sitting on it for a while. Amazing how getting married adds a seat to your design studies. Notice no unjoined inverted V tail... :)

    010 mg touchdown 18 may 15 hi res.jpg
     
  16. Sep 1, 2016 #596

    Topaz

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    Oh wow, that's really developing nicely, isn't it? I can guess why they are where they are, but are you concerned about "tunnel effect" (not sure what else to call it) with the propwash between the relatively closely-spaced vertical tails?

    That's likely to end up in the 40-50:1 arena, isn't it?
     
  17. Sep 1, 2016 #597

    Vigilant1

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    The acute angle formed by the pod/wing root interface and the decrease in planform of the fuselage prior to the TE of the wing would be things a traditional "rules we've come to abide by" designer would question due to possible interference drag concerns, but if the fillets are really generous or some type of modelling shows all is well, then perhaps all is well.
     
  18. Sep 1, 2016 #598

    Jay Kempf

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    That would be the goal. Not worried about the prop wash. Prop size, vena contracta, and separation will handle all that, tails are 7' on center so not as close as the perspective actually show. Drag so low at high speed cruise that it really isn't a large issue anyway. I'll start another thread or concat my earlier single seat one if anyone is interested. I am way past optimizing and running CFD on the wing root junction. I think I have that quantified enough to move forward. Turbulent transition is a deep rabbit hole to fall into requiring a ton of processor time. Pressure gradients and streamline optimizing, repeat.... But there are some really good precedents out there to exploit.
     
  19. Sep 1, 2016 #599

    Jay Kempf

    Jay Kempf

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    All is a qualified well. That is the crux of the entire design and is astute of you to have extracted it. Spent a ton of time in the computer solving that (I think) with the help of some people that are way up the academic food chain, industry practitioners, and way above my pay grade. The qualified part is that the solution fits the overall design goal not the best in the world class of current sailplanes. I also got lucky and was able to tuft and video something that had similar geometry at the root and similar transitions in exactly the same size and speed regime (Re). So I have a real world starting place.

    I purposely picked that camera angle to share so as not to let people see the aft end of the current design of the root fairings, which is where all the magic happens. No claims could be verified without building, tufting and measuring.
     
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  20. Sep 1, 2016 #600

    BJC

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    I like it. It looks similar to an evolution of one of my favorites, the Song.

    Song.jpg

    BJC
     

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