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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

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    $\begingroup$ 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. $\endgroup$
    – AirCraft Lover
    Commented Dec 4, 2018 at 0:18
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    $\begingroup$ 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. $\endgroup$
    – AirCraft Lover
    Commented Dec 4, 2018 at 17:29
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    $\begingroup$ 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? $\endgroup$
    – AirCraft Lover
    Commented Dec 4, 2018 at 17:42
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    $\begingroup$ Thank you all my friends. Your comments are very useful. $\endgroup$
    – AirCraft Lover
    Commented Dec 5, 2018 at 1:23
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    $\begingroup$ @jamesqf, thank you for the info. Thats quite interesting to know such many info have to be considered regarding aircraft. $\endgroup$
    – AirCraft Lover
    Commented Dec 5, 2018 at 1:29

4 Answers 4

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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.

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  • $\begingroup$ 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. $\endgroup$
    – Robert DiGiovanni
    Commented Dec 4, 2018 at 23:49
  • $\begingroup$ 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. fullsizeplans.com/images/nffs/Lift%20EfficiencyBiplane.pdf $\endgroup$
    – AirCraft Lover
    Commented Dec 5, 2018 at 5:19
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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.

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    $\begingroup$ 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. $\endgroup$
    – Peter Kämpf
    Commented Dec 4, 2018 at 19:52
  • $\begingroup$ 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. $\endgroup$
    – Robert DiGiovanni
    Commented Dec 4, 2018 at 23:45
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    $\begingroup$ @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? $\endgroup$
    – AEhere supports Monica
    Commented Dec 5, 2018 at 11:04
  • $\begingroup$ @Peter Kampf may have been talking about the 3x3 flying boat, that one may have been a little off $\endgroup$
    – Robert DiGiovanni
    Commented Dec 6, 2018 at 0:24
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    $\begingroup$ @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. $\endgroup$
    – Peter Kämpf
    Commented Dec 6, 2018 at 15:12
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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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  • $\begingroup$ 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. $\endgroup$
    – AirCraft Lover
    Commented Dec 5, 2018 at 3:24
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    $\begingroup$ 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 $\endgroup$
    – jklingler
    Commented Dec 5, 2018 at 9:12
  • $\begingroup$ 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? $\endgroup$
    – jamesqf
    Commented Dec 5, 2018 at 18:14
  • $\begingroup$ Dear @jklingler, can you please explain more? Is your suggestion you intend to me? $\endgroup$
    – AirCraft Lover
    Commented Dec 6, 2018 at 23:49
  • $\begingroup$ @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. $\endgroup$
    – jklingler
    Commented Dec 7, 2018 at 6:24
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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

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    $\begingroup$ But the OP states that he wants a short wingspan to enable landing on roads. $\endgroup$
    – jamesqf
    Commented Dec 4, 2018 at 19:38
  • $\begingroup$ 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. $\endgroup$
    – Robert DiGiovanni
    Commented Dec 4, 2018 at 23:37
  • $\begingroup$ @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. $\endgroup$
    – AirCraft Lover
    Commented Dec 5, 2018 at 3:00
  • $\begingroup$ 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. $\endgroup$
    – AirCraft Lover
    Commented Dec 5, 2018 at 3:04
  • $\begingroup$ 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. $\endgroup$
    – Robert DiGiovanni
    Commented Dec 5, 2018 at 8:19

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