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Jan 03, 2020, 11:31 AM
treefinder
springer's Avatar
Thread OP
Discussion

SuperTwin redux


I thought I had started a thread some time ago detailing my adventure with repurposing a trainer1.5 wing, but apparently didn't- or at least I can't find it! So, here goes, with a little history first.

This started something like 10 years ago, when I built a gpw Trainer 1.5, a 56" span version of the venerable Trainer 1 that was the plane that i learned to fly with. A simple profile undercambered wing ultra light and floaty plane, it was a good flyer, but incredibly boring to fly after the first few test flights as it fleww incredibly slow and only well in dead calm. Unfortunately, I have no pictures of the original. It sat around the "hanger" for several years, until I decided to either bust it up or do something more interesting with it. I decided to make it a twin and a waterplane/candy bomber (odd combination that!) Salvaging the wing, and scrapping the profile fuse, I built a new fuse that was essentially a full fuse version of the side view but inverted. (too much time sitting with a can of pop studying it I suppose...) This plane flew really well, and was a fun water plane. As a candy bomber it only flew once. With over a pound of candy, hand launch in gusty wind, I didn't have enough speed and she doinked, busting up the original wing. What to do? build a new wing! I decided to make a more durable wing, full airfoil, and as with too many plan-less builds scope creep induced larger wing span and chord. I finished the wing and updated the fuse a couple weeks ago and made the mistake of painting it before trying to fly it, so, of course, she needs lots of "tweaks".

The first tweak was after a first flight taking off from grass, she flew, but was horribly erratic. Would fly straight and level, then "randomly" dip or drop a wing. Correcting was always over correcting. Managed to get her down in one piece. The CG was about 40% of chord, that I thought would be worth trying - it wasn't! I added a second 2200mah lipo to nose to move CG forward, and got to about 30%. Next flight also off grass, better, but still not stable as I like, and when I did the dive test, she stayed right on the down angle, no nose up at all. no more room to move anything forward, so surgery called for. I added 5" to fuse nose, and this morning tried again. Fortuitously, the weather has been warm and pond was not frozen, so tried a first water test. I found that she sits "about right" in the water and nicely as long as I don't power up or a cross wind blows. As soon as either happens, she dips a wingtip and the weight of water droplets keeps the tip in the water. I had to pull the plane out of the water and wipe all water off the wing to get it to sit right again. Sponsons obviously not doing their job. After that aborted test, I did two grass takeoffs and after a 30 foot runup, she took off and flew well. Got the CG correct, I think.

All that brings me to the next needed "tweak". I need to change the sponsons to make them effective in holding the plane upright in water, or cut them off and add tip floats. At this point I can use some guidance from those who have used the fuse mounted sponsons successfully. You guys got any ideas?

The sponsons are 6" span, 6" chord and about an inch thick. Wing span is 65" I recall from a thread in waterplanes forum that increasing span is more effective than thickness, but I don't want a biplane!
Last edited by springer; Jan 03, 2020 at 12:25 PM.
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Jan 03, 2020, 12:35 PM
Retired CAD guy
birdofplay's Avatar
So forget about the Spruce Goose

Now we have the Styro Storch ;>}
Jan 07, 2020, 09:12 PM
treefinder
springer's Avatar
Thread OP
Well, No guidance, so we have to improvise. I guess that's the fun of scratchbuilding!

I decided to wrap the sponsons with another layer of MPF, and extend them another 2" outboard. Finally, looking at the boeing 314s, i figured I could wrap the tip to make a "bulb" like they seem to have. At this point these are just shoved over the original sponsons, so can be removed and reworked. I took her out to the pond this afternoon for a float test, but the pond was frozen! I didn't think we had freezing weather last night, but I guess was wrong. Since I couldn't try the sponson upright float test, I decided to try another ROG test. This time I got her off in about a 20 ft run up. I think the "deeper" sponsons were on the grass and keeping the plane level as previously she would taxi out with one tip down until enough speed to start "flying". She flew well, in spite of gust winds, so the larger sponsons didn't hurt flight performance so far. Temps to be up perhaps to 50 on weekend, so I may get her in the water then, vs "on the water", hard water that is!
Jan 08, 2020, 09:38 AM
Retired CAD guy
birdofplay's Avatar
Contra rotation ?

Plans ?

Specs ?

;>}
Jan 08, 2020, 11:29 AM
treefinder
springer's Avatar
Thread OP
Couldn't find the CR props, so both spin ccr. My experience on a couple of other twins is it makes no difference functionally. Looks cooler, though, of course!

No plans, this has been my anti planning experiment. The fuse is just a upside down T1.5 fuse made into a box - with lots of modifications for various reasons. The wing was a remake of the T1.5 wing as full airfoil, expanded dimensions, added ailerons and flaps, etc. It has just grown like topsy! While I frequently go about designing, documenting and building in a disciplined way, every once in a while I like to just wing it (pun intended)

Not sure yet if I will even want to do plans of it. Still not doing all I want. Now I lost my ice clear pond (weather had been warm enough enough to keep it ice free til yesterday) I won't know if latest changes worked til at least the weekend if it warms enough to remedy the ice. Ah well, that is the fun of scratchbuilding!

I will compile specs, though, still haven't weighed it, but it is heavier than most any other plane I have done. Still, seems to fly well now I have the CG forward enough.
Jan 09, 2020, 12:27 AM
Registered User
Looks like you are making nice progress.
Jan 12, 2020, 05:48 PM
treefinder
springer's Avatar
Thread OP

1/12/20 update


An interesting adventure this is!

Today, after the rains/freezing rain/ sleet of the last two days, I saw that the pond was clear of all but a bit of ice at one end. Must try out the enlarged and extended sponsons! Got everything ready, and set plane in water. Good news is that it now stays upright! I motored around using the differential motor thrust steering - all well. Got to end of pond facing into the 2mph wind ( if that). Power up and she pushes a wave of water into the props, and motors ahead with sponsons clearly stuck I water, props sputtering and spewing. Ran the full length of pond with no hint of getting on step. Back and tried various things like full up elevator, full flaps, bouncing off wake. No joy. Although the plane stayed upright through it all

Motored to shore and picked it up. I discovered the spray had frozen on wings, fuse side, etc. The plane had nearly doubled it's weight!. There was still ice and "snow" on grass, so I tried a ROG. Took a hundred feet to build speed, but she got off. At first it took full throttle to maintain/ slowly climb. I suppose some of the ice fell off, because she became less sluggish in a couple circuits. I flew a couple minutes and brought her down on the grass full flaps and she still hit, skipped and landed. No damage to see.

So now I have a quandary: change angle of attack of sponsons (could be a major structure redo) or cut them off and add tip floats. I am leaning toward the latter as I think the sponsons are adding so much water drag she may not get on step even if they are pointing up another 10-15 .
Feb 03, 2020, 03:57 PM
treefinder
springer's Avatar
Thread OP
Finally got some actual flight video! You can see how much runway she takes sliding on grass with the sponsons, and how smoothly she flies. I haven't tried any advanced maneuvers, although it might look a little silly to see a big twin seaplane do loops and rolls! I finished the shrunk cowls and 3d printed a pair of receivers for them. Normally I just screw them into the wood of the motor mount, but thought adding "wings" to the receivers would both stabilize the cowl mounting and provide a retaining screw location. So far so good. Next project, Tip Floats! may leave a stub of the sponsons for removable landing gear - thinking of dual tandem wheels like C130 main gear. I will be using the tip floats from the original version, and increasing the angle of attack to insure they don't try to dive. Might look a bit odd, but hopefully will work well. I did a similar high angle on the 48" MPF Seabee tip floats and they work super.

(2 min 33 sec)
Feb 04, 2020, 09:27 PM
Build straight - Fly twisty
Whiskers's Avatar
Nice!
The right tip floats will sort it out.
Feb 11, 2020, 03:07 AM
Registered User
No cockpit? Maybe that is part of the problem? :-(
Feb 11, 2020, 02:22 PM
treefinder
springer's Avatar
Thread OP
Ha! Yup just doesn't look right, does it? I have one made to be velcroed on , but not satisfied with it yet. Matching the fwd fuse top and the fwd portion of wing has been tricky.
Last edited by springer; Feb 11, 2020 at 02:41 PM.


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