# Interest in a plansbuilt, LSA/microlight amphibian?

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#### WurlyBird

##### Well-Known Member
This thread has actually had me thinking of how I would configure an amphib if I were to design it from scratch. I am thinking Buccaneer or Searey sized hull only about 1/2 to 2/3 as long after the step as before. The engine mounted to give as low of a thrust line as possible while keeping the prop out of the water. There would be water wings instead of sponsons to keep water from splashing into the prop as well as house the landing gear which would probably be trike fashion, here's why. The tail could be mounted on two booms trailing from the wing similar to a Quicksilver but without all the flying wires hopefully. This way the prop can be lowered to where it would normally interfere with the tail boom on most other designs. Honestly, you probably cant get it much lower then they did with the Icon, but what's the point of copying something already out there (almost)? The lift struts could mount somewhere mid point or farther out on the water wings leaving a pretty open area immediately around the cockpit. Something like the Searey sliding canopy until I figure out something better.

After I wrote all that above I sketched it out, pretty poorly, but it looked familiar. I did a quick search and apparently I want a small version of the Sikorsky S-38.

That is a good looking sea plane. I like the way the wing is raised above the engines and everything above the cabin is supported with struts. Very open looking and while it certainly has more drag then a nice pylon or fairing you would get more unobstructed air for the prop as well as a larger wing area. I guess it can be a tail dragger as well, even better. And forget LSA, mine will be a 2+2 so it can be used for the whole family.

#### cluttonfred

##### Well-Known Member
HBA Supporter
Or to bring it down to LSA scale, how about an amphibious version of the Ramsey Flying Bathtub! I'm not entirely serious, but not entirely joking, either.

#### WurlyBird

##### Well-Known Member
I like it! You would have to either move the engine up on top of the wing or make prop tips that are water compatible though.

#### Rick McWilliams

##### Well-Known Member
Seaplanes always want more power. The water drag at hump speed is often the limiting force. An aircraft with a gtow of 1430 pounds will need more than 220 pounds of thrust at about 18 knots speed. The normal long hull will have the lowest hump drag.

A low power seaplane will need to be very light and might benefit from some kind of short term power boost. JATO would be really fun.

#### oriol

##### Well-Known Member
In case you decide to use the long nose configuration you can do like many launch boats (Picture 1), use the nose as a sitting/solarium area: only use it when the amphib is on the water not during the flight (weight and balance issues etc...).

The nose area can provide too a way to get in/out the airplane, like in launch boats, so that you don´t have to build side doors (picture 2), the nose height would be equivalent to side windows: it would be equally difficult to get in/out the cabin in both ways.

Another option if you are compelled to put the prop above the cabin is to benefit from that and keep the nose clean of any item that restricts the occupants view.
You can subsitute the standard config of the long hull by using two big floaters ,a catamaran like solution, most amphibian modificated Cessnas do that (picture 4). The result might look like (or better!) this russian ekranoplane (picture 3), to be able to land on the ground also you should need four wheels, like most Kamov helicopters or again amphibian Cessnas (picture 5).

Oriol

#### Himat

##### Well-Known Member
The choices out there for amphibious homebuilts are pretty limited if you don't have deep pockets for a sophisticated kit. I am primarily thinking of boat-hull amphibians, not regular landplanes on floats. Among the plansbuilt options out there, most are decades old and too heavy for U.S. LSA/Sport Pilot limit of 1,430 lbs (648 kg) gross for seaplanes. Even the Volmer VJ-22 Sportsman, while it could work if built light, is too heavy if already built and certificated at 1,500 lbs gross. Just about all of them are way too heavy for the European microlight limits of 495 kg (1091 lbs).

If I were tackling an amphibian, I'd want to keep it light to stay within microlight limits and get adequate performance from an inexpensive engine like a 2.1 liter VW (Aerovee, Great Plains, etc.). A Rotax 912 would probably be a better choice for this application, but at two- to three-times the price. The VW engine also implies generous wing area and modest speeds, which has the side benefit of keeping the hulls stresses down (water is "harder" than it appears!). I think I'd want to go with a light plywood hull and either wood-and-fabric or aluminum-tube-and-fabric wings and tail surfaces.

Let me stop there. Would anyone else be interested in a light amphibian along these lines? If so, what other characteristics would you like to see? Modern or retro? Monoplane or biplane? Open or closed cockpit? Tractor or pusher? Side-by-side, staggered or tandem seating?

Cheers,

Matthew
Ok, you want a two seat aeroplane within the microlight or LSA rules. To me a Dornier Libelle inspired aircraft look promising. First the specifications of the original airplane, from Dornier Libelle - Wikipedia, the free encyclopedia (Dornier Do A):
• Crew: 1
• Capacity: 2 passengers
• Length: 7.18 m (23 ft 7 in)
• Wingspan: 8.5 m (27 ft 11 in)
• Height: 2.27 m (7 ft 5 in)
• Wing area: 14 m2 (150 sq ft)
• Empty weight: 420 kg (926 lb)
• Gross weight: 640 kg (1,411 lb)
• Fuel capacity: fuel 42 kg (93 lb)fuel + oil 10 kg (22 lb)
• Powerplant: 1 × Siemens-Halske Sh 4 5-cyl. air-cooled radial piston engine, 45 kW (60 hp)
The airplane is too heavy for the microlight, but within LSA rules. But observe, it is a three seat airplane. Today it should be possible to build it down to the microlight weight limit. 60hp is close to the VW engine, and at 495kg MTOW the VW should be sufficient.

#### cluttonfred

##### Well-Known Member
HBA Supporter
Yes, absolutely, the Libelle is one of the designs cited as inspirations in my early posts in this thread. The flat bottom is perhaps most appropriate for this type of very light design on modest power that would be limited to very smooth water in any case. There is an argument here for this type of metal hull, as it can be noisy but does not absorb any water. The external stringers on the hull are also used in some simple plywood boat designs. Even as designed and built in 1921, the original would meet LSA specs if you just removed the third seat and used the weight saved to install manually retractable landing gear for amphibious operation and perhaps a full canopy.

Ok, you want a two seat aeroplane within the microlight or LSA rules. To me a Dornier Libelle inspired aircraft look promising....

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#### Himat

##### Well-Known Member
Yes, absolutely, the Libelle is one of the designs cited as inspirations in my early posts in this thread. The flat bottom is perhaps most appropriate for this type of very light design on modest power that would be limited to very smooth water in any case. There is an argument here for this type of metal hull, as it can be noisy but does not absorb any water. The external stringers on the hull are also used in some simple plywood boat designs. Even as designed and built in 1921, the original would meet LSA specs if you just removed the third seat and used the weight saved to install manually retractable landing gear for amphibious operation and perhaps a full canopy.
I am not sure about that flat bottom. That is one thing I would change to get less slamming in the waves. There is also a question if a V hull would be “stronger” for given weight than a flat bottom. With a modest deadrise angle, about ten degrees at the step the planning qualities should not suffer if the hull design otherwise is sound. What hull material to chose is difficult, there are pro and con with all. Whatever is lightest is difficult to determine as secondary strength issues may limit the dimensioning. With secondary strength issues I do think of beaching loads, puncture by a sharp rock on the beach and that the deck better be possible to step on.

#### Rick McWilliams

##### Well-Known Member
The flat bottom hull is not a good idea. The peak water loads are proportional to V2 / tan(beta). Beta is the hull deadrise angle. V is landing speed. With no deadrise the forces are limited by the flexibility of the hull. Deadrise thus gives a smoother ride and reduces hull weight.

Landing gear must carry significant loads. At least 3 times the static load on each wheel. I would expect the landing gear system and structure to weigh at least 60 lbs.

#### leifarm

##### Well-Known Member
The aptly named Nordic Aircraft Omsider (means eventually in norwegian) is a very interesting consept to me.. However there is so far only one of them flying and the website is very seldom updated. I think they are in the process of changing the engine from an HKS 700E to a Rotax 912. omsiderbilder Claimed performance:
Wingspan 11m, Length 6,8m, Heigth 2m
Empty Weight 290kg, Max Weight 495kg, Payload 205kg
Cruise speed 200km/h, Max speed 270km/h, Minimum speed 65km/h, L/D 20:1
Take off land 100m, Take off water 150m, Climb 4m/s, Minimum sink 1m/s
Engine 60hp, HKS 700E, 2 cyl 4 stroke boxer, consumtion 6-8 l/h

#### cluttonfred

##### Well-Known Member
HBA Supporter
Very interesting, but the web site does seem a bit light on details.

The aptly named Nordic Aircraft Omsider (means eventually in norwegian) is a very interesting consept to me.. However there is so far only one of them flying and the website is very seldom updated. I think they are in the process of changing the engine from an HKS 700E to a Rotax 912. omsiderbilder Claimed performance:
Wingspan 11m, Length 6,8m, Heigth 2m
Empty Weight 290kg, Max Weight 495kg, Payload 205kg
Cruise speed 200km/h, Max speed 270km/h, Minimum speed 65km/h, L/D 20:1
Take off land 100m, Take off water 150m, Climb 4m/s, Minimum sink 1m/s
Engine 60hp, HKS 700E, 2 cyl 4 stroke boxer, consumtion 6-8 l/h

#### Himat

##### Well-Known Member
The aptly named Nordic Aircraft Omsider (means eventually in norwegian) is a very interesting consept to me.. However there is so far only one of them flying and the website is very seldom updated. I think they are in the process of changing the engine from an HKS 700E to a Rotax 912. omsiderbilder
”Omsider, om sider, til vaaren ein gong.”

There is probably more than just an aptly name on this airplane. It’s playing with the words too. In the region where they designed and built this airplane the farmers grow a lot of apples. Part of this apple harvest is pressed to get apple juice which is fermented to get apple cider. To some the wait before the drink is finished seems very long, but well wort it.

Links to some more pictures, with text in Norwegian:
Hardanger Mikroflyklubb Omsider
Omsider

The Web page is rather static, but not the airplane. I have not noticed any changes on the web page the last years, but a search revealed that Omsider LN-YZX did fly 18 hours and have 25 sorties in 2012. Less than previous years, I checked back to 2006. From the data I found the airplane must have flown at least some hundred hours.