+ Reply to Thread
Page 1 of 10 1234567 ... LastLast
Results 1 to 15 of 137

Thread: New design project: Aerobatic ultralight biplane

  1. #1
    Moderator Dana's Avatar
    Join Date
    Apr 2007
    Posts
    5,189

    New design project: Aerobatic ultralight biplane

    Like many pilots, "I want it all". Unfortunately nobody's making the low cost fully aerobatic ultralight amphibian bush plane I want , so I guess a few compromises are in order. After the UltraStar I'm flying now only meets two of those criteria (ultralight and low cost). One could put floats on nearly any airplane, "aerobatic" to me means basic loop roll spin kind of stuff, not Pitts Special, and reasonable short/rough field is "bush plane" enough, not Alaskan gravel bars. There have been precioius few aerobatic ultralights (the Quicksilver Super is the only one I know of that was really built for it, and they're pretty rare).

    A concept has been forming in my head lately that I can't quite get rid of. Ultralight (for freedom from regulation), pusher (half the fun of an ultralight is the great visibility without any sort of cockpit or windscreen, which makes a tractor design too windy), and biplane (not only because they're cool, but they can have tremendous structural strength and good roll rate). Starting to sound like Mark's biplane, but where he optimized for super light weight and low speed performance, I'll be happy if it just barely meets the 103 limits (using the AC103-7 calculations if not in reality).

    The closest thing in appearance would probably be the 1914 Beachey-Eaton "Little Looper", though I'm not interested in building a historical replica:


    Unlike the Beachey, however, I would use equal length wings, single bay wire bracing, conventional ailerons, and conventional (tailwheel) landing gear.

    Construction... hmmm. I'm currently leaning toward built up wings with doped or Stits fabric like the Kolbs, with a welded steel center structure (engine, seat mount, landing gear) and aluminum tube tail structure. Semi-symmetrical airfoil, gotta find a compromise between low speed lift and inverted flight, perhaps with flaps or flapperons on the upper wing. 2 stroke (depending on what I can afford, 447 or Cuyuna or one of the Simoninis, maybe) and diaphragm carburetor for inverted flight. Hard points for future float attachment (the twin boom tail fits in nicely with that; no acro with the floats though).

    Another goal is reasonably easy disassembly for trailering (though not on an everyday basis). I envision removing the forward (cockpit) structure and tail, keeping the wings together and rigged. Room for some camping gear, too, even if it's just a place where I can lash my hiking backpack.

    It's not going to happen any time soon as I have far too many non aviation related projects right now competing for time and money... but dreaming and designing costs nothing.

    -Dana

    Aviation has made the world a lot smaller, but it's still hard to miss it if you fall.

  2. #2
    Registered User PTAirco's Avatar
    Join Date
    Sep 2003
    Location
    Corona CA
    Posts
    2,647

    Re: New design project: Aerobatic ultralight biplane

    Seems to me that the biplane is the logical choice when it comes to a Part 103 UL, for the reasons you mentioned above. Structural strength in a small package, lots of wing area with small span for maneuverability. And looks cool....
    I always come back to the biplane when doodling on napkins - the only downside is lots and lots and lot of parts.
    "Aeronautical engineering is highly educated guessing, worked out to five decimal places. Fred Lindsley, Airspeed."

  3. #3
    Registered User
    Join Date
    Apr 2007
    Location
    Northern California
    Posts
    327

    Re: New design project: Aerobatic ultralight biplane

    Except for the pusher requirement the SNS-8 comes to mind. The Hiperlight also had the permentaly attached wings and removable tail. Neat little plane.

  4. #4
    Registered User mstull's Avatar
    Join Date
    Jun 2005
    Location
    West Texas
    Posts
    1,263

    Re: New design project: Aerobatic ultralight biplane

    That sounds like a worthy challenge, Dana,

    When you say "built up wings", do you mean mostly wood? My biplane was heavier than it needed to be because I chose the quick and easy aluminum ladder frame. Wood would be more weight efficient. But I did save some weight by making the upper and lower wings single piece and having no fuselage. I'd suggest using flaperons on all four wings, like I did, to improve roll rate and to help keep the plane small. Without the flap feature, the wings would need to be bigger to pass the stall speed limit. And bigger wings add weight and slow your roll rate.

    If I stuck a diaphragm carb on mine so I could push negative, it would have done a decent roll. Diaphragm carbs are very sensitive to bubbles... and it might be hard to do a roll without releasing a few into the fuel line. It's not an insurmountable problem.

    As to the design... while you're still in the early stages... You can save weight and drag with short main gear. The plane looks better too. But to do that, the engine will need to be somewhere in the no-mans land between the wings to provide some prop to ground clearance. It's better to have it there anyway, so the thrust is near the center of drag. Maybe the engine mount can be part of your steel fuselage assembly. Keeping the CG low with short gear allows a narrower main gear too.

    Biplanes are inherently inefficient. The wing tip losses are tremendous. You also lose efficiency because of the wings' proximity to each other. And all the struts and wires add drag. Spacing the wings about 1 chord length apart is pretty standard. Much more and the struts and structural wires get pretty draggy, and the plane starts to get top heavy on the ground. Much less is so inefficient you might as well just have a single wing.

    Those inefficiencies affect stall speed a lot. The formulas in AC103-7 only apply to monoplanes. You have to add at least 20% more wing area, if you care about being truly legal... plus any area of the lower wing that's blocked by the pilot. I added 6' total span on mine to account for that. All that wing area adds weight. You can save some weight if you use ordinary tubing for all the struts, with Lexan strut fairings.

    The MZ201 engine might be an ideal choice for you. It comes with a diaphragm carb, and is much lighter than a Rotax. With the stock, belt, reduction drive and a big prop, the thrust is pretty tremendous. I tried that combination on an earlier monoplane (the one with the deep under-camber I named "U/L") just to see what would happen. It would climb at about a 40 degree angle, and that's flight path, not just pitch attitude. Of course it would break the U/L speed limit by a mile. You might need one of Andy's active speed governors if you want aerobatic thrust yet stay with a legal top speed.

    I designed my biplane for just 1.5 negative Gs to save weight and drag, since I didn't intend to fly inverted. In addition to the extra structural weight for higher negative G loads, you'll need a multi-point pilot restraint system.

    With the 4 flaperons to get an aerobatic roll rate, you'll really notice how much drag they create at high deflections. The plane decelerates abruptly. With the extremely low momentum of an U/L, you'll need lots of spare thrust to overcome that.

    That lack of momentum plays havoc with loops too. When you pull up into vertical, the induced drag is pretty tremendous, slowing your plane instantly, unless you have gobs of extra thrust. So when you get to the top of the loop, the plane is at or near stall speed. Fortunately you'll be near zero Gs up there. So it's not that hard to avoid a stall if you use the right technique. But expect your loops to look more like a written e than a circle.

    I ended up compromising a lot of things on my design to make it truly legal in every way. Achieving just that was quite challenging.

    Good luck with your project.
    Mark E. Stull
    mstull@wtxs.net

  5. #5
    Moderator Dana's Avatar
    Join Date
    Apr 2007
    Posts
    5,189

    Re: New design project: Aerobatic ultralight biplane

    The wings on my Kolb have a 5" aluminum tube spar, tube leading and trailing edges, and ribs made of smaller tubing, attaching to the spar with a square plate with a flanged hole that slips over the spar. I'm envisioning something similar, probably with a smaller diameter tube for the spar since the wings will be shorter and due to the biplane configuration, better supported than the single strut the Kolbs use. As it is, the Kolb structure is very strong, having been tested to 6 g's. I would want at least +6/-3; possibly more negative since the structure will be largely symmetrical top to bottom. Also I may be able to build the wings in one piece instead of halves, which would make them stronger (though it might make the construction unacceptably complex).

    My thought on using flaperons on the upper wing only is twofold. First, using significant flaperon deflection reduces aileron authority. Having them only on the top wing would mean I would still have the full effectiveness of the lower ailerons. Also, having them only on the upper wing means the negative pitching moment the flaps create would be countered to some extent by the added drag being up higher. I'm really less interested in the effect on stall speed than the added drag, for glide angle control... but any flaps at all allow me to use a Cl of 1.8 in the AC103-7 stall speed calculations, instead of the 1.4 I'd have to use otherwise (I see nothing in 103-7 that says the formulas only apply to monoplanes).

    I definitely plan for the engine mount to be part of the steel cage, it would be silly to do it any other way. With a belt redrive, I have some flexibility on where the prop goes, simply by altering the belt length (within reason, of course). The landing gear length will be determined by the stall angle of attack, in the conventional manner, which may end up determining just where the engine (or at least the prop shaft) has to be. The MZ201 is a likely choice, as is the Simonini Victor I. If the calculatons show it'd be too fast I can always add additional struts as some others have done (easier on a biplane, anyway).

    I'm not worried about round loops, I just want something solid enough that I can thrash around in the sky without worrying about it coming apart.

    -Dana

    Televangelists: The Pro Wrestlers of religion.

  6. #6
    Moderator Dana's Avatar
    Join Date
    Apr 2007
    Posts
    5,189

    Re: New design project: Aerobatic ultralight biplane

    Dave, the Hiperlight is indeed a very cool aircraft, but it's very different from the direction I'm trying to go here. It's interesting that it's quoted as being stressed to +6/-3 but the manufacturer says it's NOT aerobatic,

    -Dana

    Televangelists: The Pro Wrestlers of religion.

  7. #7
    Registered User mstull's Avatar
    Join Date
    Jun 2005
    Location
    West Texas
    Posts
    1,263

    Re: New design project: Aerobatic ultralight biplane

    Dana,

    I wasn't suggesting you actually use the flap feature of the flaperons. I never used mine, other than to try them once. It's just a way to get away with smaller wings. I made all my ailerons into flaperons to pass the 60% of span calculation. It works out easiest with the linkage system to just slave the upper flaperons directly off the lower ones with a simple push rod near the trailing edges of the control surfaces.

    I reviewed AC103-7, and agree that it doesn't specifically address biplanes. But the formulas are obviously only intended and correct for monoplanes. I know that you are smart and experienced enough to know that biplanes are inherently less efficient at generating lift per wing area. Maybe an FAA inspector won't know. Most U/Ls aren't completely legal. And the FAA still hasn't assigned any manpower to enforce Part 103 operations. So go for it. I won't tell.

    As far as gear length... if you use short gear, you can just mount the tail higher to get the proper angle of attack for landing. It looks okay to do it that way on a biplane. I always liked the squat gear on the KR-2. It looks cool on the ZJ mono-wheel too. I shortened the gear on my biplane after I moved the engine up, and it looked WAY better.

    My biplane was the most fun U/L I've ever flown, by a very wide margin. I'm sure yours will be too. The sporty roll rate is to die for.
    Mark E. Stull
    mstull@wtxs.net

  8. #8
    Registered User
    Join Date
    Apr 2007
    Location
    Northern California
    Posts
    327

    Re: New design project: Aerobatic ultralight biplane

    Probably the manufacture doing some CYA. I know the Hiperlight is very different, but your goals sort of reminded me of it in some ways.

    In some ways I would think that formed sheetmetal ribs and a C channel spar (extruded or bent up) would be a bit lighter for the same strength. Pounding the ribs out isn't that difficult and the flat shearweb of the channel would make convenient attachment for struts and such. Just a thought.

  9. #9
    Registered User flyvulcan's Avatar
    Join Date
    Aug 2007
    Location
    Adelaide, Australia
    Posts
    336

    Re: New design project: Aerobatic ultralight biplane

    Check out the Australian Lightwing Pocket Rocket bipe on their website. There are some photos there ( Australian LightWing Gallery & History ) and more info on this page http://www.lightwing.com.au/aircraft.html It may be of interest to you. It is aerobatic. It doesnt look like what you want but may give you some ideas. Good luck!

  10. #10
    Moderator Dana's Avatar
    Join Date
    Apr 2007
    Posts
    5,189

    Re: New design project: Aerobatic ultralight biplane

    The Lightwing doesn't look like an ultralight (at least not by U.S. standards). It looks to be more in the class of the Smith Miniplane or Baby Lakes (I almost traded my Taylorcraft for a Smith years ago, but I had just gotten a new girlfriend, and the Smith is a single seater...)

    I could definitely see myself in a Hiperlight. 25 years later the girlfriend is still my wife, but she's not all that interested in flying with me any more, so a single seater is OK. Not likely that I'd build one, but if a nice used one came my way...

    -Dana

    People in cars cause accidents. Accidents in cars cause people.

  11. #11
    Registered User olgol's Avatar
    Join Date
    Nov 2007
    Posts
    86

    Re: New design project: Aerobatic ultralight biplane

    Dana, if you could settle for a tractor biplane, I have a great design for you :-)


  12. #12
    Moderator Topaz's Avatar
    Join Date
    Jul 2005
    Location
    Orange County, California
    Posts
    8,200

    Re: New design project: Aerobatic ultralight biplane

    Quote Originally Posted by olgol View Post
    Dana, if you could settle for a tractor biplane, I have a great design for you :-)
    Wow. Now that's a neat little airplane that would do well with some modern updating! I'm not so sure about the lower wings being quite so low to the ground (FOD), and the landing gear included, effectively, in the spar, but there's a lot of good stuff to work with here.
    "If you have built castles in the air, your work need not be lost; that is where they should be. Now put the foundations under them." - Henry James Thoreau
    Member of the Lake Elsinore Soaring Club.

  13. #13
    Moderator Dana's Avatar
    Join Date
    Apr 2007
    Posts
    5,189

    Re: New design project: Aerobatic ultralight biplane

    That's... interesting...

    Olgol, is there any other information, like if it ever flew? Not much wing area and a tiny engine, makes me rather skeptical...

    -Dana

    Daddy, what does "Formatting Drive C:" mean?

  14. #14
    Registered User bmcj's Avatar
    Join Date
    Apr 2007
    Location
    Fresno, California
    Posts
    6,948

    Re: New design project: Aerobatic ultralight biplane

    Quote Originally Posted by mstull View Post
    I designed my biplane for just 1.5 negative Gs to save weight and drag, since I didn't intend to fly inverted.
    Better make those landings soft Mark!

    Quote Originally Posted by olgol View Post
    Dana, if you could settle for a tractor biplane, I have a great design for you :-)

    Hey Olgol... nice find. That is one of the two planes I've been looking for a picture of (as a suggestion for Mark). Problem is, I can never remember the designer's name, so searches have been futile. I have to admit that I have never seen this particular photo. The pictures I have seen were taken from different angles. BTW... WHAT IS THE NAME OF THIS LITTLE PLANE OR THE DESIGNER????

    Thanks,
    Bruce
    Last edited by bmcj; April 21st, 2009 at 10:27 AM.

  15. #15
    Registered User billyvray's Avatar
    Join Date
    Aug 2005
    Location
    Newnan, GA
    Posts
    287

    Re: New design project: Aerobatic ultralight biplane

    That little gem is the DePischoff Aviette - good luck finding a lot of info on it!

+ Reply to Thread
Page 1 of 10 1234567 ... LastLast

Similar Threads

  1. Small aerobatic biplane kit?
    By pequeajim in forum Hangar Flying
    Replies: 10
    Last Post: May 2nd, 2013, 11:15 PM
  2. Best ultralight Biplane!!!!
    By cowboy22 in forum Aircraft Design / Aerodynamics / New Technology
    Replies: 27
    Last Post: April 26th, 2009, 02:50 PM
  3. 57lb ultralight biplane glider
    By Birdmanzak in forum Aircraft Design / Aerodynamics / New Technology
    Replies: 4
    Last Post: September 13th, 2008, 07:54 AM
  4. Low drag ultralight biplane
    By BBerson in forum The light stuff area
    Replies: 19
    Last Post: March 3rd, 2008, 11:10 PM
  5. Ultralight Design Books?
    By Brad_Bock in forum Aircraft Design / Aerodynamics / New Technology
    Replies: 4
    Last Post: January 26th, 2008, 08:30 AM

Tags for this Thread

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts