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I would like to design an ultralight airplane, which probably the total mass will be around 400kg. The speed should not exceed 200km/h. Forget about what the engine I will use. I intend it can land and take off in a small road and/or in a common road, which the road line not more than 2.5m each direction. If I have to occupy both direction, mean the road width is just around 5m, plus small space beside the road in both side. Beside the road, normally many electrical poles. So, not many space available.

To tackle the situation, I need to change wings design without reduce the wing area (A in m2). Was discussed earlier here some of the triplanes that were used during the WWII. If they were used during the war, that mean that such design was safe enough. But, I have a bit confusion regarding how to place the wings' stack? Here are the three options design.

  1. The wings stack are lean to the tail.
  2. The wings are stacked exactly over another.
  3. The wings are lean to the nose.

Another thing. We know that the closer wing to the ground will produce what is called earth deflection (CMIIW about the terminology) during take off. That will make the plane requires longer time to take off. In my opinion, the same effect will occur if we stack the wings too closed one to another, especially if the wings are stacked lean to the nose, the deflection will hit the lower trailing edge if there is no enough space. So what is the best design in this case? And what is the best space? Wings stack of a triplane

AirCraft Lover
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  • Ultralight at 400kg? In which country? In the US that would definitely not qualify as an ultralight, but I know other countries have different rules and definitions of "ultralight." – Juan Jimenez Dec 03 '18 at 14:21
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    I am not sure actually what is the definition of ultralight and I don't know how aircraft is classified. 400kg would be included the pilot (I myself if 71-72kg, the engine probably will be 75kg). But forget about it. Just see the 400kg regardless of the class. I am just concern about the triplane wing, and what is the best configuration to make it fly savely. – AirCraft Lover Dec 04 '18 at 00:18
  • The reason I ask is that in the US an ultralight aircraft cannot exceed 115kg empty weight, including engine, not including fuel. I don't know of any ultralight triplanes made in the US and designed to meet part 103 rules. Your design would probably have to be certified as experimental/amateur-built. – Juan Jimenez Dec 04 '18 at 11:43
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    Definetely my plane is amateur, not intended for selling. My plane will more than 115kg as the engine itself already around 75kgs, a car engine. I am not in US. I am in Indonesia, that aviation rules in our country also I don't know. But I will find it once I can build my airplane, or at least after the calculation is fixed. This is just amateur, not commercial, or not even experimental. – AirCraft Lover Dec 04 '18 at 17:29
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    But if I put a real airplane engine to my airplane with probably 50HP 25kg, probably I can redesign and recalculate so the weight will not exceed 115kg. But the most important thing now, what is the best choice from those 3 options? – AirCraft Lover Dec 04 '18 at 17:42
  • Have you looked at any of the available bi-plane and tri-plane kits that currently exist? http://aircraftproducts.wicksaircraft.com/category/aircraft-kits – CrossRoads Dec 04 '18 at 19:20
  • The HoneyBee is pretty close, with 19 foot wingspan: The H-2 Honey Bee is a strut-and cable-braced aerobatic biplane with four, equalspan, 8-foot wing panels... The prototype and early versions used engines in the 40-46 horsepower range, but the designer later moved up to an engine of 65 horsepower. In 1992, an H-2A Honey Bee was named "Best" in the combined Ultralight/Lightplane category during the EAA East Coast Fly-In at Wilmington, Delaware. Wing Span is 19 Feet, Fuselage Length is 15 Feet, 9 Inches, – CrossRoads Dec 04 '18 at 19:25
  • Also, in the US the speed of an ultralight is restricted to 55 knots/102 km/h. – jamesqf Dec 04 '18 at 19:37
  • Another collection of planes here https://www.pilotmix.com/tag/aircraft-database/biplane Kiebitz is only 118kg! Have to browse their website to find dimensions. – CrossRoads Dec 04 '18 at 19:40
  • http://www.kiebitzflieger.de/ 7.6meter wingspan. That will fit your road nicely. – CrossRoads Dec 04 '18 at 19:44
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    Thank you all my friends. Your comments are very useful. – AirCraft Lover Dec 05 '18 at 01:23
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    @jamesqf, thank you for the info. Thats quite interesting to know such many info have to be considered regarding aircraft. – AirCraft Lover Dec 05 '18 at 01:29
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    @crossroads, I think I will make it from scratch, except the engine, of however. Even the propeller I will make myself. – AirCraft Lover Dec 05 '18 at 01:34
  • Indonesia will let you design, build and fly your own airplane? I am impressed. :) Good luck! – Juan Jimenez Dec 06 '18 at 08:41
  • @JuanJimenez, that possible as long as no town we pass. I am stay in a village, and sometimes I have to check my plantation which the distance around 600km from my home. I also need to check the plants from above to see if all the plants are grow properly, uniformly, healthy. Of course I can not fly it in a town, especially in the capital. – AirCraft Lover Dec 07 '18 at 00:10
  • @AirCraftLover For this application I would recommend that you consider building a gyrocopter instead. Easier to design and build, lightweight, easier to land in a small area, and it will give you the kind of visibility that is more appropriate to check your plants from the air. – Juan Jimenez Dec 07 '18 at 19:38
  • Dear @JuanJimenez, I was thinking that one too, so do trike, but I think both are not so reliable. I am so sure to the rotor of the gyro copter, I can not rely on it, so do with wing of the trike, the strength and less controllable. But also I realize, to monitor such plantation from above for short time fly, also considerable. – AirCraft Lover Dec 07 '18 at 23:50
  • The rotor system on a gyro is much simpler than on a helicopter, and much more reliable. I used to work on military helos, and I've examined both. Gyros are infintely simpler to build, operate and maintain. They are also safer. If you run out of power with an airplane over your plantation, good luck. With a gyro you can land on almost any clearing. 600km is pushing it, but with a gyro you can land on a road in 20 meters and pull up to a gas station to fill it up. :) – Juan Jimenez Dec 08 '18 at 09:58
  • Is that save enough to fly around 600km with gyro or trike? That very interesting if is. I have watched many of them before I came to a conclusion to build airplane. – AirCraft Lover Dec 08 '18 at 11:08
  • Dear @JuanJimenez, which one is cheaper and easier to build a gyrocopter than a trike? In my mind, build trike is cheaper and easier. – AirCraft Lover Dec 08 '18 at 14:45
  • You will not get the necessary range from a trike, IMO. – Juan Jimenez Dec 08 '18 at 20:06
  • That what is in my mind. So, that one is drop from option. – AirCraft Lover Dec 08 '18 at 22:58

4 Answers4

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Wing stagger was mostly chosen to improve pilot vision: In single-seaters, a positive stagger would allow to place the upper wing ahead of the pilot, improving the field of view.

Large bi- and triplanes had no stagger. Here the pilot sits ahead of the wing and large aircraft fly mostly straight, reducing the need for the pilot to observe the airspace around him.

However, if you look for a proven design of a very compact triplane, I would like to suggest the Italian Pensuti triplane. It had a wingspan of only 4 meters and a total weight of just 230 kg. Emilio Pensuti, a test pilot with Caproni during WW I, designed it as an easy to fly aircraft for the common man. Therefore, it is sometimes also called the Caproni-Pensuti triplane. The first version was powered by a 35 HP Anzani engine while a later development, the Breda-Pensuti 2, used a 80 HP engine.

Of course, its wings had no stagger.

Drawing of the Pensuti triplane

Drawing of the Pensuti triplane (picture source). Yes, it did fly!

Pensuti triplane in flight

Pensuti triplane in flight (picture source)

If you build one, I would strongly suggest to change the wing airfoil to a thicker one with the same amount of camber.

Peter Kämpf
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  • Little worried about that one in a cross wind. Might need a good set of ailerons. Not bad in terms of symmetry though. With wheels cross wind might actually roll in slightly windward, but push it sideways. – Robert DiGiovanni Dec 04 '18 at 23:49
  • Thank you Peter Kampf. Very nice. There is one comment by @pilothead which referring the physic analysis regarding triplane as below. It is very nice. https://www.fullsizeplans.com/images/nffs/Lift%20EfficiencyBiplane.pdf – AirCraft Lover Dec 05 '18 at 05:19
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Do note that total wing area of a multiplane (biplane or triplane) wing configuration does not give the same performance as that same area with a monoplane. For a monoplane, all the wing deflects air downwards yielding lift. For a bi- or tri-plane, the wings all deflect the air together, reducing the effect of each. So a Cessna 152 with a 33 foot span would not fly if converted to a biplane with a 16.5 foot span or a triplane with an 11 foot span, to give an example.

Thus the concept of span loading. All fixed wing aircraft get their lift by deflecting air down as they pass. The amount of air they can deflect depends on their speed, their span and their weight. For minimum airspeed, the use of high lift devices is more effective than adding multiple wing planes. The main reason biplanes and triplanes were common in WW1 was for strength with the materials and understanding of aerodynamics at the time.

You might also note that many single place experimental aircraft designs have 5M spans already.

user31011
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    Actually, the real reason for triplanes was the desire to reduce span and with it roll damping. Dogfighting favors the fastest possible roll response. You are right about the limited understanding of aerodynamics, though. Caproni triplanes were really a folly. – Peter Kämpf Dec 04 '18 at 19:52
  • Age old question of turning vs speed. Triplanes were very difficult to deal with one on one in a turning situation, but were slower. A very common theme in aviation history. But these "follies" did have their moment, until continued progress changed designs once again. – Robert DiGiovanni Dec 04 '18 at 23:45
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    @PeterKämpf I always thought that the good roll rate was an unintended bonus, and that the driving reasons for multiplanes were materials and misunderstanding airfoil interference. Could you elaborate on your comment? Why were Caproni triplanes a folly, or more so than, say, Fokker triplanes? – AEhere supports Monica Dec 05 '18 at 11:04
  • @Peter Kampf may have been talking about the 3x3 flying boat, that one may have been a little off – Robert DiGiovanni Dec 06 '18 at 00:24
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    @AEhere: Comments are not ideal for elaborate answers; better ask officially. Caproni started with biplanes, made the Forty-series triplanes to carry their weight but returned to biplanes with the Fifty-series. And Fokker only made the Dr I triplane after pilots encountering the Sopwith Triplane expressed their desire to have such a thing, too. – Peter Kämpf Dec 06 '18 at 15:12
  • @PeterKämpf Thanks, I'll ask once I know what my question is :) – AEhere supports Monica Dec 06 '18 at 16:09
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To answer your explicit question, I'll note that both the Sopwith Triplane and the Fokker Dr.I are arranged in the 'lean towards nose' style.

However! The Wainfan FMX-4 Facetmobile might be of interest.

Wingspan: 15 ft (4.6 m)

Empty weight: 370 lb (168 kg)

Gross weight: 740 lb (336 kg)

Wainfan FMX-4 Facetmobile

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Roger
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  • I read about it. Very interesting. But seems it still beyond my knowledge. There are more researches to build such aircraft. But thank you anyway for the info so I have another insight and it open another option what to do. – AirCraft Lover Dec 05 '18 at 03:24
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    While this link may answer the question, it is better to include the essential parts of the answer here and provide the link for reference. Link-only answers can become invalid if the linked page changes. - From Review – jklingler Dec 05 '18 at 09:12
  • I've always wondered about the aerodynamics of the Facetmobile. Seems like the sharp angles would create a lot of drag. But something with the same body plan, but a smooth profile? – jamesqf Dec 05 '18 at 18:14
  • Dear @jklingler, can you please explain more? Is your suggestion you intend to me? – AirCraft Lover Dec 06 '18 at 23:49
  • @AirCraftLover My comment is a reply to Roger's answer. IMHO the post doesn't really answer your question about the differences, benefits and consequences of the wing-designs. It would be better suited as a comment since it provides additional information that isn't totaly off-topic. – jklingler Dec 07 '18 at 06:24
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A good starting point would be the Curtiss JN-4 "Jenny" biplane. Plenty of wing here, no need for triplane. You want long wings for easy slow handling. Warplanes designs generally are not as stable and do not make good recreational aircraft unless you are a very good pilot.

Stacking wings leaning towards nose reduces interference and maintains airflow over lower wing at higher Angle of Attack, making for a gentler stall. This design is the fore runner of slats, which are also very effective. You also want wings spaced as far apart as you can for better lift (get rid of the third wing).

It is surprising that there are not many recreational biplanes around these days, as they offer simple, rugged, reliably safe construction and lower flying speeds.

I would recommend continuing to research this, particularly to get a good engine/aircraft match. Good luck!enter image description here

Robert DiGiovanni
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    But the OP states that he wants a short wingspan to enable landing on roads. – jamesqf Dec 04 '18 at 19:38
  • Landing on narrow roads is more a function of landing gear width. You need to be under control. Very concerned that these "brilliant" triplanes aren't around very much these days. Pilot will probably get killed "landing on road with many electrical poles". Simply not a good idea. – Robert DiGiovanni Dec 04 '18 at 23:37
  • @robert-digiovanni, I understand that very hard to land it in a very narrow road. That my main concern how to make it can land safely. In order to "guarantee" it, I have to do some modification to the airplane so can fly with very slow speed, probably in just 20 mph. I have studied some eagles and birds how the expand their wing during "landing". Have a lot of study to be done here. – AirCraft Lover Dec 05 '18 at 03:00
  • Another advantage by applying bird's wing principle, it can land very short. Not sure whether can take also very short as there is distinctive different between how aircraft fly and how bird fly, especially the catapult generated by the legs power. – AirCraft Lover Dec 05 '18 at 03:04
  • This is why you want forward "lean", also called stagger. This, like slat, will help lower landing speed! Also, lower aspect ratio wings (shorter and wider) with undercamber will give you the lowest landing speed. The longer, thinner "albatross" wing, though more efficient (better gas milage), stalls at a higher speed. You don't need triplane to do this. I would recommend balsa models to get lowest speed for a given weight, and a large field to practice landing on your first flights. – Robert DiGiovanni Dec 05 '18 at 08:19
  • Plane in picture does not have forward lean, but flew 250 feet from a highway overpass (around 22 feet drop). – Robert DiGiovanni Dec 05 '18 at 08:30
  • @Robert DiGiovanni: I disagree. Landing on narrow roads, as the OP explains it, is about not hitting telephone poles, fence posts, or roadside brush with the wing tips. (I think we both agree that landing on such roads is not the wisest possible course of action :-)) But if you have adequate wingtip clearance, just about any SEL plane has suitable gear width. I've certainly landed on a number of dirt strips with wheel tracks no wider than a typical rural road. – jamesqf Dec 05 '18 at 18:08
  • Just a little worried about wing interference in the small triplane when the relative wind shifts. Notice, in a cross wind without the stagger, there would be a lot of turbulence around the lower wings in a slip. I do not think the Pensuti made it to mass production. The Curtiss JN-4 biplane has a wingspan of around 44 feet. That is less than 15 meters. I think I'd rather find another place to land if it was that tight. – Robert DiGiovanni Dec 06 '18 at 00:35
  • Dear @RobertDiGiovanni, there is one explanation that is very good regarding monoplane, biplane, and triplane. You may find it here. There are quite detail and reasonable explanation regarding the wing's gap and the stagger. – AirCraft Lover Dec 07 '18 at 03:56
  • Again, I have to thank to @pilothead as his info has helped a lot. Thats all requirement we need. Gaps, stagger, and and the wings area requirement are comprehensively compared to monoplane. – AirCraft Lover Dec 07 '18 at 03:59
  • @RobertDiGiovanni, unfortunately is not easy to find landing space in my place. This airplane I will use from my home to my plantation. In the plantation itself still possible, but not at my home are. – AirCraft Lover Dec 07 '18 at 04:13
  • Excellent paper on biplane and triplane efficiency, thanks! – Robert DiGiovanni Dec 08 '18 at 00:37