My Flying Boat

[Othman]

Hello everyone,

I just wanted to share a sketch of my ultralight (Canadian rules) flying boat design. It doesn't use any sophisticated means to get off the water (it's pretty traditional in that way). I wanted to design something small and fun to fly. For reference, the wing span is 24ft.

The biggest challenge will be to design the drive system from the engine, housed in the fuselage, to the two remote prop shafts.

Your thoughts and comments are welcome.

 

[Sonnyj]

WOW Othman
That is an exceptionaly nice design.I have always had a place in my heart for boats espescially flying ones.
I have always wondered if someone has ever tryed to use hydrolics for that twin prop application.Heat may be a problem but one could use a couple of coolers under the wings.
Please keep use posted on your progress.
Waiting to see it done
Sonny

 

[Othman]

Thanks Sonnyj.

I also share an interest in boats... which I find strange since I have always felt haunted by large bodies of water (I'm a prairie boy, and was never to strong of a swimmer).

Using hydraulics to power the props is an option; however, since I'm trying to keep light, I think that might be too heavy and complicated of a solution.

Right now I'm leaning towards belts, or chains... but I didn't completely toss away the idea of drive shafts.

 

[orion]

Many years ago we also looked at hydraulic power for a remote prop location. While from a configurational standpoint this seems an easy solution, from a practical one it is far from it. There are two primary issues - weight and efficiency, and both are interrelated.

The best hydraulic pump and motor add up to about 80%, give or take a bit. But that's under ideal conditions. As soon as the operating temperature rises, that number decreases, sometimes by quite a bit. Some of this can be optimized for by slelcting the right size lines and designing a system that attempts to minimize the hydraulic losses, but that can only go so far.

Now, if you only get 80% of the generated power to the props, that means that the rest is heat that has to be dissipated. So now you have to deal with not only the heat of the buried engine, but also that of the hydraulic system. In short, the install and systems can add up to quite a bit of weight.

For the configuration you show (which by the way is quite attractive), your best solution will most likely be two smaller direct drive engines or a serpentine belt sytem.

The drive shafts are also a possibility but all the gear boxes you'll need can add up in price and weight. Remember that with gears you have to lubricate the boxes and cool that oil too. We designed that type of system for the hydrofoil we were invovled with some time back, so I am very familiar with what's involved there.

 

[Othman]

Thanks Orion,

I think the serpentine belt drive is the easiest and most practical solution.

I avoided using two engines in because I didn't want to introduce the OEI problem into the equation (although you could argue that one belt might snap and I'll end up with only one prop operative).

The reason I chose remote props was to avoid having an ugly pylon mounted engine... and the reason I went with two props was to keep the prop size down, and bring the prop shafts lower to reduce the trim effects due to changes in power setting.

The props are located just above the wing TE to protect them from spray. I believe that the position of the props will not have a negative effect on the aerodynamics of the wing (the props may help keep the flow over the wing root attached at higher angles of attack, and therefore delay stall - not verified).

Cooling the engine should be taken care of by air entering the scoop located behind the cockpit, then directed around the engine, and back up to the air exit just aft of the wing TE on the top-side of the fuse... provided that the intake and exit areas are matched well.

 

[CAB]

One engine- two props

What about using a drivetrain out of a front-wheel-drive automobile? you could even use the transmission as a reduction drive. 90 degree gearboxes from a HUEY and off you go. I know, a buncha weird engineering needs to be done- but the thought always interested me. Imagine a 400 hp. blown Cadillac Northstar driving 2 props...........

 

[Leighton]

pretty creative idea using Huey gearbox's, i like it.

keep in mind that the Huey 90deg gearbox's also give a reduction of 2.6:1.

 

[Othman]

400 HP !!!!!! haha... divide that number by 5 and you'll be in my ball park power

 

[Midniteoyl]

Nice design...

Question: In the 'top' view, it looks like a gullwing, but not in the 'front' view. Were you originally gonna go with gullwings?


I like the belt/chain idea. Simple and effective. Do like the Wrights and simply twist one belt/chain.

If you went with toothed belts, the problem would be added weight on one side if you wanted counter-rotating props. Unless you went with a centerline mounted gearbox to reverse one prop, but then its still added weight and possibly less power to the reversed prop.

 

[Othman]

It's actually not a gullwing. There is a "bite" taken out of the leading edge, at the wing root, to improve visibility given the relative placement of the pilot and wing. The root airfoil is deformed to have a shortened chord while maintaining the same thickness as the rest of the wing.

Counter rotating props is not at the top of my priority list. The propellers will probably have very little inertia, and there will not be much to gain from having them rotate opposite to each other.

Thanks for the comments.

I want to thank everyone who has written in this thread... it's this kind of discussion that will help me work out the bugs!

 

[orion]

Just two other quick notes:

Keep in mind that for most people, the most comfortable sitting position is one where the heels are some significant distance below the butt. Airplanes that tend to place the occupants' legs out straight (like sitting in a kayak) tend to be uncomfortable for elongated flights. This tends to be true even for recumbant positions. I've been told this has something to do with the blood pooling in one's mid section but of that I'm not sure of.

One airplane that is less comfortable for me than what I originally figured is the Glastar, where you sit a lot flatter than it looks on initally climbing in.

The other note is regarding your hull - you'll most likely not need those sizeable spray rails you show in the front view. A hull has an ideal l/b (length to beam) ratio for every Froude Number. Making it any wider than it needs to be for the service just allows the spray to be attached to a larger surface area, thus creating drag and poorer performance. You'll most likely just want to incorporate two small longitudinal spray rails on each side that will deflect the sideways flow about twenty degrees below the horizontal.

I have a very simplified hull design document at our web site. I don't know if it'll be of any use but it's there for anyone to browse through that's interested.

 

[Othman]

Thanks for the notes Orion,

You are right about the seating. I’ll for sure have to study that further, and carefully examine where I will place the rudder pedals and seat relative to each other. I don’t really want to deviate from the fuselage design that I have, I want to keep it as small as possible.

The pilot shown in the drawing is about 6ft tall… I’m about your height Orion (6’4”) and about 180lbs. The fuselage should fit me well, and should fit a beefier person a little more snug like an F1 race car… well hopefully not that bad. Somebody told me once that the most comfortable cockpit they sat in was in a sailplane (I don’t know which one).


The Hull Design:

The additions on the side of the hull are partially intended to act as spray rails, but were really added for increased beam and buoyancy.

My initial hull design was just 24” wide (same hull as in the drawing, but without the additions); however, the length-to-beam ratio was not adequate for the weight of the ship, and it would end up sitting too low in the water, thus requiring extra power to get started and causing messy spray while doing so.

By adding the additional structure on the hull, I increased the max beam to 36”and increased the available buoyancy substantially, while still keeping the frontal area to a minimum (I could have easily widened the whole hull, but that would defeat the purpose). I used my static displacement calculator to predict the draft and trim of both hull designs.

So all in all, the hull design evolved after going through the design iterations (lots of literature research, including your summary document Orion – thanks!!, and looking at lots historical data). After I came up with this shape, I found a good reference book (by Holden Richardson*) from the hay day of flying boat design, which showed a number hull shapes that were tank tested, and were presented along with generalized attributes of their performance. I was quite satisfied when I saw one tested hull with the same configuration as mine, and was listed as having good spray characteristics.

Another benefit that I see in having the hull additions is that they will provide additional fuselage lift. The additional lift will also produce a nose-up pitching moment, which will assist/unload the short-coupled tail during flight.

So there you have the evolution of my hull design in a nutshell… or two


* www.nationalaviation.org/website/index.asp?webpageid={F3401AC2-408C-42A7-AD0F-CDDC7942F110}&eID=317

 

[Sonnyj]

Hello Othnan
Ha,and I call mayself a mechanic.I never even thought about serp.belts.Sized properly that should be the best way to go.You will need to ficure 8 one to counter rotate for tourque cancelation(Hope I spelled that right).The one on my 1984 Jeep CJ7 is the OEM and has 182000 MI.on it,pulling A\C,P\S W\P,ALT and fan.So it should be reliable in my opinion.
What power plant do you intend?Will it have wheels,or just load on the trailor,fold the wings and go home?I'm realy exited about this project,it looks like a lotta fun to build and fly.
Lets get a move on and giterdone.:ban:
Cya later
Sonny

 

[Othman]

Thanks Sonnyj,

I haven’t settled on a power plant yet. All I know so far is that I want to install 60HP-80HP. I have my eye on the MZ202 60HP light-weight engine available from Compact Radial Engines in British Columbia:

http://www.compactradialengines.com/engines.html

The specs look appealing to me, it’s nice looking, and costs about $5K USD; however, it’s a 2-stroke. I would really prefer a 4-stroke.

Do these kind of 2-strokes have messy exhaust like radio control airplane engines? I’m interested in hearing what you guys suggest for an engine. Keep in mind weight and of course, price J

As for landing gear, I thought about making the ship amphibious; however, the Canadian ultralight rules state that you can have retractable landing gear, or flaps, but not both. I intended to use flaps, but I may add some additional wing area and go for the retractable gear as shown in the drawing bellow… although the gear will for sure weigh me down more than the flap mechanism. I intended to use full-span flapperons as shown in the 3-view drawing. In the future I would like to incorporate both flaps and retractable gear on a heavier, non-ultralight version.

I think I want to keep the gear off this version. As I work out the design, I’m keeping in mind that I want to make it a good flyer, and perhaps enter the design in the Piccolla Coppa Shneider (Mini Schneider’s Trophy) race some day (http://www.aviogatti.it/coppa.htm), so I’m being careful to meet Italian rules as well as the race rules.

 

[Sonnyj]

Hello Othman
How ya coming on the anphib?
Yea those 2 strock engines will make a mess,but it will clean up good.
Have you considered an HKS or a Honda gold wing?The HKS is a 2cylinder 4 strock aircooled about what your looking for.And ofcourse you know the gold wing motor is water cooled,but makes enough more HP to haul the extra things like the radiator and coolant.With some machine work you could even get rid of the trany.Hey how about an outboard engine?Should be plenty of them where you are.
Regards
Sonny

 

[Othman]

Things are going well on the design... but slow.

I'm working on performance and stability analysis at this time.

Propulsion system selection and integration is NOT my favorite part of designing an aircraft, yet it's not something I can neglect cause I know it'll come back and bite me.

I had a quick look at the HKS engine, and so far looks promising, however I couldn't find a lot of specs during my initial search.

At this stage I'm not convinced about taking engines from motorcycles or boats and moding them to be used in an aircraft. The remote prop configuration I've chose already requires additional work for designing the drive system, I don't really want to introduce more components into the equation (and more things to go wrong). Basically I'm looking for a "plug-and-play" engine (inexpensive would be great too!).

I found an interesting thread in this forum covering the remote prop configuration, in which Orion provided a lot of useful info ( https://www.homebuiltairplanes.com/forums/showthread.php?s=&threadid=643 ). The aircraft in question didn't really need to use the twin remote props located aft of the cockpit, but in my case I think it would be advantageous... even though there are efficiency losses due to the drive system.

Thanks very much for your input Sonny

 

[David Martin]

pretty neat! the hull looks like an osprey my dad is building.

 

[StRaNgEdAyS]

Great idea Othman!
Concerning your need for power, have you given thought to a VW or Corvair conversion?
They have enough powewr to meet your requirements and are air cooled, and if reduction is required, your serpentine belt drive could accomodate that too.

 

[Othman]

Thanks for the comments guys.

I'm still doing research (when I can) on engines. I don't want one that I have to convert myself... the last thing I want to be doing is cutting up engine blocks and fiddling with home made engine parts.

The VW looks like a nice option, provided that I could get the engine "ready-to-fly" from a reputable dealer.

I found one engine that got my attention, the MZ202 from Compact Radial Engines, but the only problem is that it's a 2-stroke. It has the right specs, size and form that I am looking for. I wish they made a 4-stroke version

 

[everyman_flight]

Indeed, how's the plane coming along. I'm looking for a very small floatplane to build, just to get me started, and that design looks a beauty!

I wonder though whether you might like to mount the wing a little higher or give it quite a bit of dihedral to keep the wings clear of the water.

I might modify the hull a bit though, as I'll usually be coming down on comparatively rough water. I'm happy to trade rough water handling capability for taking longer to get off the surface.

I'm also thinking of making the creature from aluminium and have some nice cutout models of the

Best Wishes,

one keen to get to West Loch Tarbert and the Garvellachs more frequently than conventional transport permits.