I was bored last night so I designed a seaplane

I was bored last night so I designed a seaplane...

Specs; red, black and pink.

Main build materials; Electrons.

Development time; From dinner until just after normal bedtime and getting yelled at for not doing my Husband duties.

Development costs; 2 small cakes and a coffee with honey and missing out on Arnie beating up some bad guys in a movie on TV.

All comments welcome. Except for ignorant negative ones that don't pamper my large ego. I shall refer to the poster's of such with names such as "Billy Bob" and mention your close relationships with relatives.

 

You didn't tell what are the mission requirements. I think a glider approach could be interesting and you'd got a very versatile amphibious aircraft.



"for not doing my Husband duties", Ok, I won't joke.

 

Telegraphic opinions:
+ (Plus)
- good anti-spray config.
- comfy cabin
- nice outside visibility, despite the propeller placement

- (Minus)
- complex drive
- smallish H-stab (for the relatively short-coupled formula)
- no step on the hull

Conclusion: I'd buy/fly one, if it would've had two direct-drive engines on the flapped wings (in an upper position and with small props - with let's say 5-7 blades).

 

Things I like...

--Integrating the twin floats into a hull to create a catamaran flying boat.
--Thinking outside the box with the internal engine and belt/chain drive prop for a nice, big, efficient prop well out of the spray.
--Large comfortable cabin, great visibility.

Things I don't like...

--Belts and chains and long shaft harmonics, oh my. I'd prefer a plain old direct drive prop.
--That prop placement will be awfully dangerous when approaching a dock or a beach.
--Tail volumes seem low to my eye.

For what it's worth, I have some notebook sketches of a twin-hull flying boat that grew from musings about using a single salvaged metal float (perhaps available cheap because the other one was damaged?) as the hull of microlight flying boat. That led to using two hulls with a cockpit forward and a rudder aft in each one, joined by the wing and a high-mounted tail and with the engine mounted as a pusher just aft of the wing center section.

I stopped there because I was leery of the massively strong wing center section and horizontal stabilizer that would be required to withstand uneven loads on the two hulls, such as hitting a big wave diagonally on takeoff or landing. Still, it would have been very cool, a microlight homage to Italo Balbo’s Savoia-Marchetti S.55s. ;-)

 

Mission requirements, umm , land on water and fly in the air pretty well covers it! Just a good time fun plane with plenty of vision and room to move your feet around, carry some fishing/camping gear etc.

Tunnel hull with low CoG for soft, safe landings and short take offs. That hull was one I already had in 3D and is a 4 meter Biel Tunnel hull, IMO a tunnel is a much better option than what is currently used because they sit on a bed of air very stably.

www.youtube.com/watch?v=8Jxd8R_MCz4

Thanks for the picture too, been looking for at least 2 that I have seen but can't find in that configuration.

Just a mock up as mentioned only took a few hours, wings and tail just imported for layout purpose and not modified nor indicative of reality. Drive is not complex, nothing more than a belt drive PSRU only bigger. Step on the hull is valid point.

Meant to be a mid positioned, single engine plane. Wanted to push the CoG back to get the wings back for people forward/better viewing and safer water landings.

Thanks for both your comments.

 

https://www.google.es/search?q=QT-2...S47AbThYCwCQ&ved=0CAkQ_AUoAg&biw=1024&bih=673

From:

Schweizer X-26 Frigate - Wikipedia, the free encyclopedia

I think the position of the step is some behind the CoG. vertical to allow the aircraft rotate on take off. If this boat has a CoG located near the whole AC perhaps could work, otherwise you'd need plenty of power and flaps or, the glider approach.

 

You're welcome, cheapracer - and yep, I thought too that some details are gonna be fixed after the initial general configuration phase (don't forget that the V-stab is also too small, as cluttonfred very well noticed).

Anyway, various compromises are needed for seaplanes - in your project, the relatively low thrust-line and the pronounced forward position of the single propeller is bought with the price of the drive complexity.

P.S. A V-tail would be perhaps more simple to build?! (I've thought that for an older multi-engines microlight hybrid amphibian project, "deleted" now for local burocratic reasons - no landing approval on the lake nearby. :dis

 

Thanks for the reply Fred.

I point blank refuse to use a direct drive based on the economics of a modern automotive engine, so it it what it is.

One of the lines of thinking is using an auto engine in the middy position where simple strong mounting can be incorporated within the main fuse design rather than hanging out front with the required supporting structure saving a few kgs. With water cooling of course this is more practical than air cooled engine. This also opens up more realistic diesel engine options with their weight and TV issues.

Not for this plane of course, but for others an aerodynamic advantage is gained offsetting the weight disadvantage and that's why I was interested in getting a hold of Vapour Trail's model ...

 

Great first sketch. That would be much easier to dock because it can dock PARALLEL to docks.

Just a suggestion about refining your hull design. Most seaplanes mount their main step under the centre-of-gravity or slightly aft of the C of G. Step placement affects rotation for take-off similar to the main-wheels of tricycle undercarriage (usually 17 degrees aft of C of G). Angling the aft hull up a few degrees (17) also helps rotation for take-off.

We are having a similar discussion over on the Amphi-Camper thread.

 

Agreed, though 17deg might be a bit too far unless you're limited on nose gear load or configuration/retraction kinematics, between 12-15 across your CG range is probably an ideal.

Interesting design, my one suggestion would be to not forget to increase the dead rise angle towards the nose.

Have you considered lowering the tail boom to form part of the float after body and making the prop a pusher instead? I can see maybe an issue or two with evacuating the aircraft with the engine running with it mounted so close to the front of the canopy and you may be able to reduce any torsional gremlins with a shorter shaft.

What Length/Beam is that running at the moment?

 

Interesting and innovative design!

Somehow I wonder if there is a subtle joke behind this that I have not been able to recognize.onder:
Even if so, the post is a good starting point on seaplane design raising one fundamental question:

• Why not start the seaplane hull design with copying an existing suitable planing boat hull?

Next the post raises a question about sizing, should not a seaplane hull be sized as planing boat hull carrying the same load?

I’ll leave the two questions for later, now first commenting on the design.

Is the airplane centre of gravity placed where the boat would have its longitudinal centre of gravity?
I found some pictures of the boat stationary on the water and it look like the boat CG is aft of 1/3 chord from the leading edge on the drawing. I do think the engine should go all the way to the stern, after all the boat has an outboard engine hanging of the stern. The wing must then be moved back too.

Others have raised objections about the step placement and the possibility of the aircraft to rotate for takeoff. I’m not sure if that really is a problem. I had a look at the hull of different Dornier seaplaens, the Do 24, Do 24ATT and the Seastar. All of these seem to have the step well behind the CG, actually well aft of the placement recommended in textbooks and old NACA papers. Actually there in a book on Russian Ekranoplanes there is a picture of a homebuilt aircraft along the same lines, but with the engine in a pod above the wing.

 

The tunnel effect of the twin hulls may give enough ram-air lift to let the plane get by with less takeoff rotation during the initial liftoff, and the profile of that wide cabin could be tweaked a little into a Burnelli or Horten type lifting fuselage.

 

I like the placement of the prop...

 

Firstly thanks for all the input, wonderful!

No joke other than it's assembled as a motley crew of parts only to offer the overall concept, it is not scaled or pretending to be able to be flown as it is shown.

Because I don't believe any existing hull is best. Just because somethings work well for 100 years doesn't mean they are the optimal choice and can't be improved upon. A tunnel hull creates a bed of air to travel on and this will help lift the plane out of the water decreasing drag hence increasing STOL ability and offer a softer ride and safer landings. I looked at it more from a flying boat angle rather than a plane that runs on water.

Answering some at random,

The prop was set like that to maybe help lift by charging air over the top of the wide wing shaped fuse, comments on that welcome from more aero savvy people?

I don't believe a step is a requirement as the thinking is a lot of the hull will be out of the water sitting on a bed of air as mentioned. I have watched a few seaplane takeoffs now and not many of them rotate anyway, just lift flat after a long runup.

i wouldn't be concerned about the static balance of the boat in the video, only it's excellent running balance when the motor is trimmed in unison with the hull's characteristics.

 

It's clever. I would have some concerns about rough water landings. Having the space to catch water might make it slap.. and that could cause damage on the center of the hull.

 

I think that that massive engine mount must play a role in reinforcing the center-section as it supports the two hull under differing loads.

What I've seen of the tunnel hulss, especially the pickle-fork racers, is that they look a bit unstable, prone to each side being bounced separately, creating an uncontrolled rolling. This is not as critical with a floatplane because you have the massive wings providing stabilizing forces and moments of inertia.

 

Seaplanes can get "stuck" to the water long after they reached stall speed. Especially on smooth water. Some seaplanes can't take off if the water is really smooth.

Being able to rotate would be useful...

Also, planing boats need the CoG near the back of the hull. There's a book on designing boats by dave gerr that might be useful for you.

 

Most of the boats you refer to are racers that try to minimise everything except with massive central engine making for a very low moment - and they are going very fast with that limited design and can get upset quite easily.

You are right, the weight much further from the center creating a much larger moment along with dihedral will dampen those oscillations you see in those boats.