1QwkSport2.5r

It is indeed balsa. In the picture the sponson is upside down and hard to picture it's size. There is much more to it than you can see. The old sponsons had the boat floating perfectly. There was just too much drag at the boom tubes grabbing water and the bow of the sponsons wanted to submarine. Floatation was not a problem. The new sponsons actually have more displacement (volume) than the old sponsons so it should float as well as before or better. However, I am prepared to use a launch ramp if needed to get it going on plane. The only time I'd let it slow enough for it to drop off plane is when I'm bringing it in. The new sponsons will also be significantly lighter than the old ones so I have a lot more going for me now than I did before. I have a ton of progress done so when the epoxy cures I'll have some better pics up of how they look now. Vastly different than pictured above.

1QwkSport2.5r

Here's my current progress so far. Most of the frame work is done. They are quite strong and very light so far.


Overall length is the same as the old sponsons at 18", and sponson width is the same at 2 1/2" depth was increased to 2 1/2" from 2 1/4". The tail of the sponsons is 1" deep (aft of the step) which is the same as the old sponsons. I am pleased with how they're coming together so far.

arcdude

1qwksport2.5r From the comparison pics it's not hard to see why the original ones failed, the new ones look great though. I wasn't aware balsa wood could be used but I guess if it's entirely encapsulated by stronger material it's nothing more than a frame to line things up, excellent I'll have to keep that in mind. I sense success in your future!

1QwkSport2.5r

With the exception of my SI3's, my other builds are balsa frame/birch plywood construction. I've used .46 2-strokes up to a 1.20 CI (20cc) 4-stroke on my boats and have not had a single problem with them coming apart. Most of my boats are fiberglassed over but this outrigger is not. Nary a concern though.

Old sponsons were skinned with 1/8" liteply and then 1/32" birch ply over that. The new sponsons will be 1/32" ply skin over the balsa frame with 3/16" birch ply doublers at the boom tubes. I may add a layer of liteply on the inside and outside of the sponsons before the birch ply skin, but not on the top and bottom if I can help it. I'll wait and see. As they sit right now, the frames will hold up a 4lb bag of sugar without crushing. The old sponsons are so strong I can stand on one of them with 175# of weight (me) and they don't so much as crack. That's strong enough I think.

1QwkSport2.5r

Here's the weight of the sponsons at the current stage in grams:


This is the most weight I could get the scale to read before it went to Overload. It's got an 11# capacity but it reads to 12 1/2#. Just my bare hand pushing down on it. Should stay together for awhile I hope.

PS; photo bucket blows. Pics coming soon.

fuma

ran ok on water but was extremely fast on ice

1QwkSport2.5r

Looks nice! Airboats are ludicrously fast on snow and ice. I don't like running on snow - no brakes really sucks.

What engine are you running on that?

fuma

os la 46 with 3 blabe 10/6

1QwkSport2.5r

Sponsons are sanded and trimmed now. Hung them on the booms to see how it looks. They might be a tad too big but I don't think that will be a problem.

arcdude

Hey those look fantastic, great job! I sure hope they work for you this time after all the work you deserve it! What size are you boom tubes and what are you using for plugs? I have been having a miserable time trying to find either aluminum or carbon and a suitable match for plugs, EXASPERATED is more like it. Are you going to skin with balsa and then lite ply? Looking good

Oh ya almost forgot, here's a suggestion for you don't know if it will be of interest or not, but what I anticipate doing is wrapping the hull and sponsons with saran wrap and doing a float test prior to skinning the surface that way it'll allow an opportunity to make it smaller or larger should it need it, just a thought....

1QwkSport2.5r

I used Aluminum tubing from my local Menards home improvement store, I think its 1/2" O.D. For the inner studs that I mounted onto/into the sponsons ended up being a tool used for water mains in residential neighborhoods. It was a solid aluminum rod with a fitting on the end. I couldn't find a suitable rod that would fit the tubing I had, and this was the closest I could find. The tools were on clearance for $6 each I think, I bought two. I have not seen these tools at the store since I bought these so I dont know what I'd do if I didnt have enough left over from the last time. Some guys use Carbon or aluminum arrow shafts for boom tubes but I hadn't seen any at any of the local archery shops that would be strong enough (IMO) to work well so I used what I had.

My skin scheme will be a thin layer of Balsa if I need it, otherwise I was going to do 1/32" and 1/16" birch plywood over the balsa frame and 3/16" birch ply for the boom tube doublers. I think the size is about perfect or slightly too large but should work just fine. I suspect they should provide a significant boost in lift and being that much lighter should help with getting it on plane easier since the engine is up front. The prop should end up right at the sponsons' step so I'm on par with where the CG should be. I have some adjustability with the engine mount so balancing it out should be a breeze for the most part.

Plastic wrap isnt going to be water tight enough to keep the framework from getting wet which I would not want to have happen. Being that the boat floated perfectly with the old sponsons, I suspect it should float as well or better than before given the fact that my sponsons will be lighter and displace more volume. The trick will be getting it on plane and thats why I have my launch ramp I'll use if it wont plane off on its own. I think the better thing to do to do a "float test" before progress gets too far along would be to ziploc the sponsons and suck all of the air out of the bag and seal the holes around the boom tubes with tape or something... Unfortunately there's not a good physical way to float test without having everything water-tight. Taking into account the weight, and the amount of air volume, one should be able to extrapolate that information to determine if there is enough buoyancy. I tend to build by the seat of my pants so I dont usually go to that step and just build it, finish it, and float it afterward.

arcdude

I can relate to building by the seat of the pants I never have a plan just a thought and maybe a scribble or something that resembles one Lol! Do you know by any chance how high the tub bottom is above the bottom of the sponsons (water clearance)? The only reason I mentioned some form of float test is you have gone to quite a bit of trouble with this rig so far and if we can prevent an additional disappointment all the better. I just happen to get lucky today after a very long search for boom tubes, I found 1/2 in aluminum at Canadian Tire store and a 3/8 solid rod that fits inside of it, may need a little shimming or soomething, should work though. Lucky find!!

1QwkSport2.5r

I think I'll have a working boat after this, if I don't.... Well, it'll be a lesson learned. It looks like your aluminum boom tube bits are nearly identical to what I'm using. ID of pipe is a smidge over 3/8" and the studs are 3/8", OD of pipe is 1/2".

Some more pics of my rebuild follows.

1QwkSport2.5r

Mock-up, showing the boats new attitude.

arcdude

That is lookin pretty darn good! The overall styling is well done. Sounds like the same tubes for sure, should be strong enough. How do you find your motor mount, seem pretty solid without cross bridging? Just considering different types of mounts when I get started on mine. I notice from the pics at the back of the sponson where the tube insert attach's it seems to be a pretty small attachment point, do you think it'll be strong enough?

1QwkSport2.5r

The motor mount was modified a few different times but strength-wise it handled a .46 at 17,000rpm okay. I normally use aluminum L channel to mount the engine onto and 3-16"-1/4" birch ply for the pylon uprights which works well. As for the sponsons' aft boom tube mount - it is reasonably strong as-is but I have some 3M '5200' marine adhesive/sealant that I used in the old sponsons. It is an incredibly strong adhesive I gooped around the boom tube mounts inside the sponsons and doubles as a waterproofer around where the skin meets the boom tube studs. I will use the same technique on v2.0 sponsons so I trust the strength will be good.

The 5200 adhesive is so strong, it will by itself hold a 250hp 4-stroke to the transom of a fishing boat with no bolts! (Engine was being pulled off the boat for maintenance thus the bolts being removed).

arcdude

Are ya done yet? The 3M adhesives sound pretty much like the construction adhesive PL###, don't know if your familiar with them. Where do you get the 3M is that only available at a marine supply type store? I looked back through the thread and I couldn't find whether it's written or not what the angle of attack is on your sponson's? I have done a lot of research and can't seem to find a common denominator, everybody has they're own opinion.

1QwkSport2.5r

No I'm not done unfortunately. Been sick with the flu and work has been crazy busy. The 3M adhesive is a urethane moisture cure (also called acid cure) whereas construction glues are a solvent based urethane. The normal 5200 takes 1 week to cure in normal climate conditions. Longer if it's real dry/low humidity. Home Depot now carries the 3M marine adhesives although I got my first tube at a West Marine store on sale for 50% off. The downside to the stuff is once the tube it opened, you have to use it up within a week or it will start to cure inside the tube. I was able to plug my first tube and "save" it for a month but I had to pick a bunch of cured adhesive out of the tube.

No common concensus on AoA. I looked too. I shot from the hip on mine.

arcdude

1QwkSport2.5r That flu is a nasty one, I still have a little congestion since before Christmas. I'm really quite surprised there is so little information online in regards to air boats, all a person can do is sit back watch someone else do it and if it's successful proceed and if it flops forget about it, who knows maybe with Hooty's don't know if it's spelled correctly or not your boat and mine soon to be started we could be starting a trend. Get well you have a boat to finish!

1QwkSport2.5r

Yeah, being sick sucks. Especially when everything is achy, sore, or feels like someone has a 150psi air hose plugged into your ear. Makes life unpleasant.

Most guys building hydros are wet propped, these are the guys to pick for info. And for some reason they aren't as willing to share info to the air propped guys. Tried in the past. They think air propped can't be fast so why bother? Jerks. I have favored proven designs with most of my builds although I had more "show" than "go" with a couple. I've learned a lot from these mistakes and all I can do is share my mistakes and related lessons with others in hopes nobody makes the same mistakes I did. So with a little luck I'll have all of my boats ready to rock this summer.

I decided to use some 1/16" balsa sheet on the top and bottom of my new sponsons to add a little cushion to the skin just in case it's actually fast. I had to re-build the inside of the sponsons on my Jett powered SI3 due to excessive speed cracking the skin (with fiberglass on it even!). Didn't want to have to do that again so I'm adding some lightweight beef. I am hoping to have a little time soon to get some work done on these sponsons so I can get the boat re-rigged and float tested. I need to get some fresh electronics and probably rebuild the engine mount again too.

arcdude

Personally I believe air engine drive has a greater potential for speed and certainly is far more simplistic in it's implementation in comparison to a wet prop drive system. All that is required is for someone to stumble on the correct design to fully realize the potential.

Are you sure the cracking you mention is speed related and not moisture related, I have built things in the past that had a higher than expected moisture content in the wood to begin with and had cracking as it cured. That may be one advantage to using styrofoam core sponsons, the added benefit of vibration absorption. What is the issue with the motor mount, it seemed to work o.k.?

1QwkSport2.5r

I dorked it when I skinned the sponsons and didn't have enough support. It's from speed/getting beat up
by thr water. Read here about 1/4 down the page: http://www.rcuniverse.com/forum/rc-a...t-hydro-5.html

The motor mount looks too redneck. I want it to look better. It will work as-is but not to the way I want it to.

1QwkSport2.5r

Not much progress due to illness, but this is where I'm at with my Sponson v2.0 rebuild.

Added some 1/16" balsa sheet to the top and some 1/8"X1/8" Mahogany "pin striping" as I did on the originals. I'm gong to use 1/16" birch ply for the bottom of the sponsons, and 1/32" birch ply for the sides and tops. These sponsons should be 25% lighter and at least 75% more efficient than the old ones.

1QwkSport2.5r

Getting some skin on too..

1QwkSport2.5r

Not a lot of progress, but I'm getting closer. The skin for the sides are cut, I just need to get the skin glued on and drill the holes for the boom tube studs. After that I'll just have some trim work to do and I can get it sanded and glassed.

So far, as pictured, the old sponsons are 250 grams each. The new sponsons are 137 grams each. Strength is good and I'm coming out pretty close to dead square.