Build, then design, then build

Discussion in 'Aircraft Design / Aerodynamics / New Technology' started by addaon, Aug 28, 2008.

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  1. Aug 28, 2008 #1

    addaon

    addaon

    addaon

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    As some of you may have gathered from my questions, I have a long-term plan (5 year, hopefully, while doing my PhD) of designing and building a single-seat tailless design focusing on efficiency (goal of 160 kts on 4 gph, with all the compromises that entails). I'm now 95% set on a basic design, and 100% set on doing all-metal construction.

    But I know that I'm a better theoretical engineer than I am a hands-on person. That can be fixed, of course, and I'm planning on going to all the local EAA workshops, and I'm very (very) excited to have signed up for a workshop this fall through tinmantech.com. Still, I can't help but wonder if I should do a kit build first, just to get the building time in. It seems to be a good idea...

    So, here's the story. I'd want to keep both my "kit plane" and my "custom plane", and have them both useful to me. Since the custom is a single-seat, high-speed, nothing-near-STOL, IFR-ready, tri-gear design, the kit plane shouldn't be. However, the two should share the same construction (all-metal, blind rivets mostly) and engine (Jabiru 2200 and 80 hp). What I want from the kit plane, then, is:

    1) A very good kit. Zenith or Rans level, from what I've seen described.
    2) A reasonable price. I'm a college student, and there's no way I can afford this regardless, but there's different levels of broke.
    3) All-metal, blind-rivet construction.
    4) Reasonable performance on 80 hp, which probably means good 1040 lbs for happiness (just pilot) and 1200 lbs as an absolute max weight (with passenger).
    5) Tandem seating. I really like being in the center line. Pilot sits in front.
    6) Decent STOL performance. I don't need to be able to handle 300 ft, but I should be able to get into a 1000 feet field without stressing. Grass is a must.
    7) Conventional gear.

    Other than the construction, it's basically an Aeronca Champ. Other than the seating, it's pretty close to a Piper Cub. What's the closest thing in the "kitplanes by reputable companies" category?
     
  2. Aug 28, 2008 #2

    addaon

    addaon

    addaon

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    [I tried to post this as an edit, but it wouldn't stick.]

    When forced to compromise, #1 and #2 can go first... I won't enjoy building a plane that doesn't fit #3-#7 at this point, but #1 and #2 will just determine when I can actually start. As a further compromise, #4 can be revised to "safe performance, with reasonable performance on a 95 hp ULPower 260i"... I'd rather do the Jab, but I intend to buy one of each for my "custom plane" anyway.
     
  3. Aug 28, 2008 #3

    expedition2166

    expedition2166

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    well I'd recommend going with solid rivets because of the sheer cost of pop style rivets aside from that looks like you want an Rans RV got everything you want and kits are popular and help is easy to find there is a ton of people building them.
     
  4. Aug 28, 2008 #4

    Dana

    Dana

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    If "all metal" can extend to "all metal structure with fabric covering" then a Kolb FireStar II sounds perfect, though I'm not sure if the kit is still available... Kolb seems to be concentrating on the Mark III (side by side seating) and the new Flyer SS.

    -Dana

    Refuse Novocain... Transcend Dental Medication.
     
  5. Aug 28, 2008 #5

    addaon

    addaon

    addaon

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    I think I'd go with pop-style rivets for my "custom", so I'd like to go with them for the "kitplane" also, but I'm nowhere near 100% set on that.

    I must admit, it never occurred to me to go low-wing for this plane. It doesn't strictly contradict my requirements, but it somewhat goes against the spirit of #5, being great visibility. I do like the view from a low-wing, but I really love being able to look straight down for short-field and off-field operations, and I rather envision this as a "low and slow" type of toy.

    [Side note: Does anyone else confuse "Ran's" and "Van's" constantly? Just me?]

    The RV's also seem to specify outrageously large engines (150-200 hp in the 1120 pound RV-8!?); I'd have to do some research to see how they perform with about half that, but if nothing else, the CG would be skewed something awful. [Edit: The RV-8 is 1800 pounds; so sane engine size, but then much bigger than I want.]

    So, the RV's are an option (and maybe the best option, I agree) if I go low-wing, but I'm interested in high wing options still.
     
    Last edited: Aug 28, 2008
  6. Aug 28, 2008 #6

    addaon

    addaon

    addaon

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    On further consideration, the closest I've gotten to "all points" is probably the CH 701, which (I believe) does have a tailwheel option. In this case, all that's missing is tandem seating, which I'd really, really miss... but could possibly live without. Still, there has to be a "tandem seating 701", doesn't there?
     
  7. Aug 28, 2008 #7

    Tom Nalevanko

    Tom Nalevanko

    Tom Nalevanko

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    I don't think that you will ever get to your performance goals without using composites for your design aircraft. So I would suggest that you build a composite aircraft.

    A better idea may be to just help someone build a composite plane and buy a certified plane, perhaps an LSA. Homebuilts are continuous work and it would be hard to make progress on a new design while keeping the homebuilt going. Also the homebuilt will take a LOT more time that you think...

    And better yet, just knock off the PhD in good time (like 2 years) and move on with your life/career/aircraft design & building.

    I built a composite plane, sold it and am working on a design of something better. But I will probably buy into a Cessna T-210 to fly while doing this. Been there, done that....

    I have a good friend; ex F-15 driver, long time test pilot, yada yada. It took him 10 years to build his Lancair 2 place. I said that it would never take me 10 years to build my Stallion. And it didn't, it took me 9 years!

    Life is short, go for it!
     

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  8. Aug 28, 2008 #8

    Norman

    Norman

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    If you're sure that your long term project will be tailless You may want to modify your short term goals to get experience in composites and flying in ground effect.
    The reasons being:
    1... composites: The extent of laminarity is a stability factor in flying wings. No mater how wave free a metal skin is before the first flight it'll grow waves over time. Might as well start with something that can hold its shape under stress. That means at least a composite D-tube
    2... ground effect: Since 'wings usually either have thick center sections or a minimal pod to carry the stuff with short landing gear they experience a lot of ground effect. In spite of what many students claim after a bad landing high wing airplanes do not get a lift boost from ground effect and only feel a very slight reduction in induced drag. If you want to experience ground effect before your first landing in your original design get a low wing plane, preferably one that has the wing less than one chord length off the ground while siting on the gear.
     
    Last edited: Aug 28, 2008
  9. Aug 28, 2008 #9

    addaon

    addaon

    addaon

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    I must respectfully disagree. While metal and composite have very different properties, I can think of very few aerodynamic designs that are really only possible in one or the other.

    After long consideration (several years), I've realized I have no interest in this. If I truly cannot meet my performance goals with metal, I won't build a custom design, as I cannot meet my comfort and build goals in plastic. Absolutely nothing wrong with composites -- some of the production planes I like most are plastic -- I just don't want to work with it.

    This is entirely about getting the building experience in. Having planes to fly is not an issue, I just wouldn't want to build something and never use it.

    Five years is a good time for a PhD. And the entire PhD is about having a good time. If I didn't consider it more important and more enjoyable than even building airplanes, I wouldn't do it at all. I'm choosing to do a PhD because being a PhD student is how I currently like my life/career, not because I want some nebulous future. ;)

    Couldn't agree more, but remember, that means different things for different folk!
     
  10. Aug 28, 2008 #10

    addaon

    addaon

    addaon

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    As mentioned, I'm sticking with metal, even if it makes things more difficult. I'm definitely not planning on laminar flow airfoils, either.

    I'll keep this in mind when choosing what to fly, but it's not really relevant to what I'm going to build.
     
  11. Aug 28, 2008 #11

    Joe Kidd

    Joe Kidd

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    I had pretty much made my mind up that I wouldn’t build anything unless it was all metal but the more I researched matters and objectives I came to realize the versatility and utility of a tube and fabric design with fabric covered wood wings. Then I applied that same focus to all wood designs and recognized that they also offered simple but strong construction as well as an overall utility that makes them perhaps the most economical of builds.
    What you choose to build is your own choice and no one else’s as you will be the one doing the work and flying the plane afterwards. Now, with respect to the 701 or even the 750 if you have the engineering background and appropriate computer software you can install a different wing with a chord that offers less drag and greater speed as well as fuel economy. It may not be a true STOL afterwards but it will be a nice flying airplane as Savanna Aircraft has done something similar with its long wing version.
    JK
     
  12. Aug 28, 2008 #12

    addaon

    addaon

    addaon

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    Yep, I know the wing on the 701 is way towards the STOL side of the lift/drag compromise. I'd probably build slatless+VG, original airfoil, if I went this route, to maximize use of the kit.

    Here's an idea... the main reason I want tandem seating is so that I can be on the centerline. But 90% of the time I'm going to be alone anyway. How hard would it be to build a 701 (or any narrow two-seater) so that a single pilot could sit on the centerline? Issues seem to be:

    1) Rudder pedals. If I could reach the outer rudder pedal of each seat, that would work fine, but it seems like an awkward position....

    2) Seat belts. Perhaps a third seatbelt (centered) permanently in position, and just hooked over into the baggage compartment when the side belts are in use instead? Don't know what the attachment points are like.

    3) Stick position. The 701 is center stick, which is great, but I'm not sure it would be clear of, um, crotchal concerns when being straddled.

    4) Visibility. The whole point is visibility, of course... if downward visibility is blocked by the seat to either side, no gain here.

    Thoughts about this?
     
  13. Aug 28, 2008 #13

    nik.kruhmin

    nik.kruhmin

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    A Sonex maybe? It meets all your requirements except tandem seating, but they have a version (the Acro) where a single pilot sits centerline.
     
  14. Aug 28, 2008 #14

    addaon

    addaon

    addaon

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    Hm. I like the Sonexes (Soneces?). Didn't know about that version. Will look into. I'm currently leaning heavily towards tailwheel 701, but...
     
  15. Aug 28, 2008 #15

    addaon

    addaon

    addaon

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    Wow, thanks Nik! The Sonex Sport Acro has the centerline pilot / side-by-side two seat exactly like I described... very tempting. Now I just have to decide if I want that "hot" of a bird. Very tempting...
     
  16. Aug 28, 2008 #16

    dgeronimos

    dgeronimos

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    Be sure to look at Klaus Savier's Long-EZ:
    http://www.lightspeedengineering.com/News/News.htm

    That's 204kts on 4.2gph.

    -Danny
     
  17. Aug 28, 2008 #17

    addaon

    addaon

    addaon

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    Here's my current thinking. I really like the sonex, and I don't particularly mind the extra $4k (or rather, I do, but it's manageable)... but having to buy up front, or having it be an extra $8k (a full year's "toy money") is pushing the limit. Anyone have comments about kit quality and reality of build time between the two?

    Code:
    			CH701				Sonex					Point
    Price			$14k + engine			$18k + engine				CH701
    Price in sections	+ $1500				+ $5500					CH701
    Jabiru 2200 support	US Jabiru FWF			Sonex is dealer				Sonex
    "Supported" mods	Some required:			Some required:				Toss-up
    			Taildragger			Aerobatic ailerons
    			Bubble doors			Center seat	
    "Unsupported" mods	Some required:			One optional:				Sonex
    			VG wing/elevator		Differential brakes (maybe)
    			Slat removal
    Useful weight		Great (520 lbs)			Good (480 lbs)				CH701
    Performance		Excellent STOL			Good all-around				Toss-up
    Kit quality		Seems good...			Seems good...				Toss-up
    Build time		350-400 hours			800-1000 hours				CH701
    GOAL VIOLATIONS (-1)	Center seating			Cost
    
    Score is 3 pts CH701, 1 pt Sonex. Yes, I'm triple-counting price, but that's deliberate to reflect my situation, and is not a particular bias against the Sonex. Yes, I'm calling the performance differences between two planes designed for completely different missions a "toss-up"... both would be equally fun first planes for me.

    So, it looks like unless I get more info (please provide it!) or other ideas (still open) I'm going to be building a CH701.
     
  18. Aug 28, 2008 #18

    nik.kruhmin

    nik.kruhmin

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    Where are you getting your pricing info from? I'm guessing the 14k from Zenith is the airframe and finishing kits, but you'd still need, engine, prop, misc fwf, instruments, upholstry, etc. The Sonex airframe kit is $13,995 plus $794 for misc hardware (http://www.sonexaircraft.com/kits/pricing.html) to get the same as the two zenith kits for $14,789, only a $799 difference.
     
  19. Aug 28, 2008 #19

    addaon

    addaon

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    Prices are with a bit of interpretation. Zenith lacks FWF, I didn't add that, you're correct. Oops. Sonex lacks hardware, which I added... but also, if I went that way, I would definitely do the pre-assembled spar and machined angles, just to keep building time somewhat sane (and more comparable to the Zenith); that's where the discrepancy comes from. In practice, with engine, instruments, etc. I figure I'd run to about $32k on the Zenith and $35k on the Sonex; but the bigger issue is that I just can't do more than $5k or so upfront at this point without difficulty. Sonex clearly recognizes the value to builders of Zenith's buy-as-you-go plan (they mention it in their FAQ), but their substitutes just aren't good enough.
     
  20. Aug 29, 2008 #20

    nik.kruhmin

    nik.kruhmin

    nik.kruhmin

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    Have you considered scratch building at all? I'm in the same position as you with regards to school (though I haven't commited to sticking around for a phd yet) and that's the direction I'm headed in. Likely either a modified Sonerai (the I comes very close to your goals for your own design) or a Vision. The stol designs are neat and I'd probably really enjoy building one but there's more airports around here than open space with sympathetic property owners:depressed
     

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