Discussion 1912 Donnet-Leveque biplane kitbash

[mcg]

Thank you, Sam.

This is my second attempt. I messed up my first Leveque, and never finished it, tho I learned where some of the pitfalls are. So I am trying to take extra time with this one.

What would be a realistic weight target?

Michael

[Megowcoupe]

Hi Michael

Mine is 9 oz. I would actually prefer something a bit lighter for ease of water landings and to soften the stall a bit (yes, I do have some washout in all 4 tips), although I have gotten away with the last several landings- a gentle plop and a taxi back to shore- very cool I must admit. So be careful with the amount of detail you add unless you want a hangar queen. Also note that flying off water is probably a bit rougher on an airplane than a hand launch and landing on grass. I knew that if I added a lot of detail, the likelihood of flying the airplane diminishes (yeah right- when do I ever do that?) but this is an individual preference.

Be very careful with your power system. I suspect some of the folks who went considerably more aggressive in this area- i.e. 100 watts pay the penalty with a very hard to control airplane. I wouldn't be surprised if the Axi is a bit much- doesn't it do 75 watts? Lighter is better in terms of flight characteristics- I've noticed as I've gone to lighter batteries (but that also moves the cg aft on my airplane too.) The airplane was designed as a modestly powered free flight- and whoever flew one that way had guts! The large lifting stab right in the airblast is going to make an overpowered airplane very touchy.

Sam

[mcg]

Maybe it can be built at 8 oz. Waterproofing seems to adds a lot of weight. I am going to try to waterproof it with Balsaloc and LiteSpan, to avoid multiple coats of thick and heavy stuff. May work, may not.

Here is a table of motors. Kind of nebulous numbers, but. My Axi is the smallest one. I specified it because I happen to have one, though, it was not much of an engineering decision.

Richard -- its great that you are building one. Do you have a powerplant in mind for yours?

[Megowcoupe]

Hi Michael

I used Deft Interior sealer with some pigment added- think I gave it 3-4 coats. It's pretty light and has been fine in terms of waterproofing.

I'd do a test sample of the balsaloc and litespan first- a fabric doesn't come to mind as particularly waterproof. That's why I went with So Lite for the wings and tail on my bird.

What I remember about my Axi was that on 3 cells and a 7" (6"?) prop, it had enough power to pull my Sin Naps vertical. (A nice airplane, BTW) I went with a lighter HC motor (fewer watts) and the airplane now flies better. I'm pretty sure the Sin Naps is comparable in weight to the Leveque- so my hunch is that the Axi is overkill. Also bear in mind that you don't want to go larger than a 6" prop- don't want to get water in the prop and also you need some room for the hull.

Sam

[rszanti]

MCG -

No specific motor picked out yet. I have quite a few brushless that might work but I could use more specifics so I can select one. I saw somewhere that 100 watts is about the right size (?) but I thought 3-4 watts/oz. is about right for a sport flyer like this - at an 8 or 9 oz AUW, typically 25-30 watts would work.

But as an amphibian, maybe a higher power loading is needed. I keep watching for someone to say "I had a successful water takeoff without problem" and then mentioning what they used for power.

Richard

[mcg]

I have not personally seen a report of a successful ROW with electric power, but maybe it has been done.

Here are the hull modifications I am musing over. Keith Sparks' Macchi M5, referenced above, is published in the March, 2006 issue of Flying Models. Using his curve for the tunnel hull, proportioned to the Donnet Leveque in Rhino3D, this is what I get.

It looks so far like a fairly simple mod, with a 1/64 ply hull bottom anyway. Not sure it could be done with 1/32. The original aircraft appears to have had a pair of skids for beaching, or maybe hydrodynamic fences, on each edge of the step. I have not included these.

Here is a link to a bio of the Canadian inventor of the tunnel hull. Not quite clear if he was aware of the experiments going on in France.

http://www.rina.org.uk/c2/uploads/w%...0_%20final.pdf

Net of it. If the tunnel adds speed on the water, and thus gets the aircraft closer to its flying speed, it would help.

Keith Sparks says in the M5 article that he can take off from the water after a run of just a few feet.

[rszanti]

Read the M5 thread, that plane looks as good as the Leveque. In fact I liked it so well, I ordered a short kit from Spark's.

I've been considering going to the tunnel hull - after all hasn't speed boating moved to tunnel hulls for the fastest racing. Maybe the boaters know something !

[mcg]

Here is the proposed modification. Since the aircraft is already under construction, the formers cannot be easily replaced, so I have added a pair of partial formers to be glued behind the existing formers. These two partial formers establish the new concave bottom curve.

New parts are indicated in yellow. The points on the existing formers are then sanded down to conform to the new step curves, as defined by the added half-formers.

Works okay in CAD. Whether it works in balsa and plywood remains to be seen.

[wallis_100]

Hi, i've just found this and been reading it with interest,

I reminds me a little of what myself and Paul are doing.
I'm a masters undergraduate in aerospace engineering, with an interest in RC planes, and water flying in particular.
Paul has an interest in the Short brother hull development. see:
http://www.rcgroups.com/forums/showthread.php?t=1062431

we are currently developing a system of testing out different hull forms/steps to improve model performance/scale

The reason you might find this interesting, is that due to the difference in reynolds numbers linked to our flight speeds, and model sizes, the air is a lot 'thicker' and more viscous for us, then for real airplanes.
Secondly, the surface tension/viscosity of water, scales to a simmilar way.
This is the reason the real plane flew off water in 1912, with only 50bhp, yet we fail. Because, in order for the full size one to experience the 'stickyness' associated with the scales we use, it would have to try and take off from 'TREACLE' ... something i don't think it would have much luck with

scott

[Megowcoupe]

Michael

I'm not sure, but it looks like your step location is the same as shown on the plans. If this is the case, then I suspect you're going to have trouble getting it off the drink. Most float design calls for the step to be located aft of the cg. Realize that you want the float to be on plane before the airplane takes off, and you do need some volume in back of the cg, otherwise it's real hard to get there. Note that volume aft of the step is irrelevant when the hull is on plane.

Sam

[mcg]

Yes, I see this Sam, you are right. With the proposed structure in place, I think I can use a balsa block, or a series of them, to experimentally extend the step aft.

Scott, I think treacle turns into Molasses in North America. You are doing fascinating science on the Short hull step. Reynolds numbers and surface tension are certainly in this story. However, flying boats in sizes comparable to the Donnet Leveque model do in fact ROW. Our question is, what is it about this specific design, as kitted, that resists taking off from the water?

I am also wondering about a related problem -- how the flying tail affects the position of the center of lift at various speeds.

[Megowcoupe]

Hi Michael

I can answer the question about the tail-

There is one speed effectively for this airplane- probably something between 15-20 mph give or take. Add throttle- it'll climb, cut throttle, it'll descend. It doesn't fly fast and the climb speed and the stall speed aren't really all that different. Hence the tail works fine.

Your idea about experimenting with blocks should work fine, although I'd find it a bit frustrating. Maybe I'll get off my duff and lighten my airplane up, but I think the window to evaluate ROW performance is closing rapidly here for this year.

Sam

[mcg]

Some years ago I had a conversation with a Canadian pilot who had flown a PBY during WWII. He told me, laughing, that the PBY had only one forward speed, and that it was 70 mph. Stall speed, 70. Takeoff, 70. Cruise, 70. Top, 70.

[rszanti]

I got curious about what Motocalc might show for a drive.

So I entered 205 sq.in. (total area of Leveque wings) at 30" span (top wing) for the wing. I used a weight, less battery and motor, of 13 oz. (assuming the worst). I limited the prop size to 5" diameter, the biggest that will still clear the fuse, and limited the motor choice to Turnigy (from my favorite supplier HobbyKing ).

Motocalc spit out a Turnigy 28-26 1900kv motor with a 5 x 4 prop and a 2 cell 910mAh battery. This combination absorbs a maximum of 36 watts, produces an optimum flight speed of about 22mph while generating up to 5 oz of thrust at the prop. (if I use a 50" wing span, 30" top + 20" bottom, the optimum speed drops to 20mph but other changes in calcs are minimal).

Motocalc has no way of looking specifically at a bipe or an amphibian so these calcs may be useless. But I thought it might be a good start.

Richard

[mcg]

The Moto Calc results look promising, Richard.

Here is a brief update on the aft fuselage. The fuse is basically jigged by the cockpit floor, and by the bottom panel of the rear fuse behind the step. So a complete fixture in unnecessary. I did screw down some jigs on one side only, to use in beveling the edges of the formers.

Two servos are designed in. They are very light and positioned behind the prop. This is ok for this test mule, but in a future build I might move the servos forward, in the interest of dryness and weights and balances. Beside the fuse in the photo of the servos is the laser cut 1/16 top plate for the fuselage.