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  1. #1

    New Builder/First Air Boat

    My son (12) and I are in the process of building our first air boat. We have a Nitro .40 size engine. What fuel tank size would be best suited?

  2. #2
    1QwkSport2.5r's Avatar
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    Quote Originally Posted by trapper7 View Post
    My son (12) and I are in the process of building our first air boat. We have a Nitro .40 size engine. What fuel tank size would be best suited?
    6-8oz is probably fine. A bigger tank will give longer runtime... Just make sure the tank is installed such that the center of the tank (think half full fuel level) is even with the spraybar in the carburetor. If the tank is too high, the engine will run rich and probably flame out at low throttle settings. If it's a little low (in relation to the carb), it will likely work okay except the engine may lean out a bit more when the fuel level is low.

    What engine is it and what kind of hull are you planning to build?
    GlowHead Brotherhood #3
    Real engines use glow plugs.
    R.i.P Jacob Wetterling #11 10/22/1989


  3. #3
    I have a German made engine...(HB .40 PDP) For plans I found the ones on this site and am copying them: http://www.rcuniverse.com/forum/rc-airboats-246/8234813-40-46-build-plans.html

    I am VERY open to any advice.

  4. #4
    1QwkSport2.5r's Avatar
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    Quote Originally Posted by trapper7 View Post
    I have a German made engine...(HB .40 PDP) For plans I found the ones on this site and am copying them: http://www.rcuniverse.com/forum/rc-airboats-246/8234813-40-46-build-plans.html

    I am VERY open to any advice.

    Ah yes.. An old HB. Good engines - I have a .61 non-PDP myself. I have a piston/liner/rod for the .40 PDP Blitz too. Keeping my eyes open for a good donor engine in need of said parts.

    With internal combustion as a power source, you should be okay with the plans as they're written. I friend had problems with that boat using electric power. I suspect the batteries and such threw the CG off pretty far. I highly recommend building the engine mount such that you can shift the engine fore/aft to adjust the CG. The CG should be roughly 1/3 hull length from the transom as a starting point. Keep your prop diameter and pitch reasonable. Don't try a big diameter or high pitch props - especially with an older cross flow engine like the HB. Look to a 10x4-10x6 or 11x4. I don't think a 9" diameter is going to give enough thrust. Also, build your hull as light as possible. Think balsa or lite ply for the stringers and such. Your main hull runners (that will attach to the engine stand) should be birch plywood and use thin birch ply for the sheeting. I use 3/16" or 1/4" for my main/high stress areas such as engine mounts and such and thin 1/32" or 1/16" ply for the sheeting. Best advise for adhesive is 15min or 30min epoxy for bonding the hull together and use a thinned 30 or 60min epoxy or a slightly thinned epoxy finishing resin. Thin fiberglass cloth inside the hull is a good idea - I typically use 1/4oz cloth for inside the hull and on the bottom sheeting for added strength.

    Hopefully that isn't info overload. I have built 9 or 10 boats with several running 50mph plus. So far I've been lucky and none of them have blown apart.
    GlowHead Brotherhood #3
    Real engines use glow plugs.
    R.i.P Jacob Wetterling #11 10/22/1989


  5. #5
    This is not info overload at all. Much appreciated. The original plans recommended 1/8 ply throughout. So would that be too heavy? i think the i have a 10x4 prop. I got the engine with a pile of other R/C parts from an old lady for $60. The engine is brand new. On another topic: there is an older Futaba FG gold series FM that came in the box including a charger, though no receiver. Would this have any value. I plan to sell it and buy a new Transmitter/Receiver combo.

  6. #6

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    Hi there. Hope your build goes as well as mine did. I chose the same one as my first airboat as well last year. I unfortunately did not get a lot of water time last year due to some issues, but plan on getting more this year. In case you were interested, this is the link to my first build as well. Good luck with yours as well.

    .40 Size Airboat Build : With Questions....

  7. #7
    Thanks! Did yours work well? What thickness of ply did you use for the skin?

  8. #8
    1QwkSport2.5r's Avatar
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    I like using thinner plywood for the sheeting because it bends significantly easier. If the bend of the plywood causes it to be under too much pressure, your adhesive is going to need to be that much better to hold the shape and stay together. You may find using all 1/8" is going to be too heavy. For an old baffled .40, you're going to want to keep your weight below 5-6lbs for reasonable control and speed. Figure a baffled .40 (PDP adds some power, but not enough to write home about) is about equal in power to a strong Schnόrle ported .30 engine..
    GlowHead Brotherhood #3
    Real engines use glow plugs.
    R.i.P Jacob Wetterling #11 10/22/1989


  9. #9

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    It did indeed work well in my opinion. I do however need to make larger air rudders. Mine is all 1/8" ply and it is doubled up on the engine pylon. It has an old MDS .40 that needs a good tune-up. I did thankfully have a lot of good help from people on here which I appreciated very much. As for going, I did use Minwax in Clear Gloss, despite the recommendation to use a satin finish, as it is what I had on hand. It is plenty fast for me. Overall I believe that it weighed approximately 5 1/2 pounds. The only thing I could really recommend is to listen to 1QwkSport2.5r in using thinner plywood for the sheeting. I did have a tough time with tne front curve on mine, but then soaked my plywood and secured it until it dried then applied it.

  10. #10
    It has been invaluable already reading the feedback here for my build, for ex rudder size. I was planning to use 1/8 ply for the skin but will go with 1/16 (on order). Two questions: what model of radio would be best (under $70) and where might I source the fuel tank (i'll get an 8 oz as that was recommened here).

  11. #11
    1QwkSport2.5r's Avatar
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    Quote Originally Posted by trapper7 View Post
    It has been invaluable already reading the feedback here for my build, for ex rudder size. I was planning to use 1/8 ply for the skin but will go with 1/16 (on order). Two questions: what model of radio would be best (under $70) and where might I source the fuel tank (i'll get an 8 oz as that was recommened here).

    Don't chimp on the radio. Use a good well-known radio. I am a Spektrum/JR guy - I use a JR XS3 and DX3S. The XS3 is a synthesized FM which means you can set a dial on the receiver for the channel. No crystals and it works well. It is a pistol grip style RC car transmitter. It will be cheaper than the 2.4GHz DX series of radios. Some guys use AM, but I don't like it over water and even 2.4ghz can be spotty on water. If you go with 2.4ghz, make sure they have marine receivers. They tend to have longer antennas (my Spektrum DX3S marine receivers have two antennas - one long and one short).

    Look around online and even on Craigslist. Just look for Sullivan, Dubro, or Hayes model airplane fuel tanks. Of those three, the Hayes are the best but are no longer made.
    GlowHead Brotherhood #3
    Real engines use glow plugs.
    R.i.P Jacob Wetterling #11 10/22/1989


  12. #12
    Thank you for the advice on radio. My local hobby shop recommended a SkyFly https://www.amazon.com/dp/B019TN2MRM?psc=1

    I am on a limited budget...but it would be devastating to have the whole project 'sunk' by a brown out over a larger body of water!! Any opinions on my hoby shops suggestion?

  13. #13
    1QwkSport2.5r's Avatar
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    Some guys use them without issue while others have all sorts of problems. I myself don't have any experience with them, so I cannot comment. I've used JR and Spektrum for years and have not had any problems with them, but other folks have had problems with them.. Same goes for Futaba - some like them and some don't. Best thing to do is use a radio with a built-in failsafe or if the radio you choose doesn't have a failsafe, get an external one and use it.
    GlowHead Brotherhood #3
    Real engines use glow plugs.
    R.i.P Jacob Wetterling #11 10/22/1989


  14. #14
    Looking at the FlySky link it appears the receiver is not waterproof.

  15. #15
    Quote Originally Posted by trapper7 View Post
    Looking at the FlySky link it appears the receiver is not waterproof.
    Perhaps I would rather aim in this direction: https://www.amazon.com/Spektrum-4210.../dp/B00JBBWY9Y

  16. #16
    1QwkSport2.5r's Avatar
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    Just put the receiver in a compartment and use foam tape (similar for sealing leaky Windows) to seal the lid. None of my receivers are waterproof. The marine receivers tend to tolerate being wet - I've had some boats upside down for a half hour and everything still worked after. I highly advise making your electronics compartment waterproof - you're in deep doo doo if your servos get wet too.
    GlowHead Brotherhood #3
    Real engines use glow plugs.
    R.i.P Jacob Wetterling #11 10/22/1989


  17. #17

  18. #18
    1QwkSport2.5r's Avatar
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    That should work. When you get the boat built, I would do a good range check with the radio to ensure you are covered. That radio should have a built-in failsafe, so make sure you set that up. Also use a good receiver battery pack - I'd highly recommend using a NiMH or LiPo battery pack instead of a AA cell holder.
    GlowHead Brotherhood #3
    Real engines use glow plugs.
    R.i.P Jacob Wetterling #11 10/22/1989


  19. #19
    Thank you, what NiMH or LiPo battery pack would you suggest i order to replace the AA cell holder? Looks like my won and I will start cutting plywood this afternoon! Getting exciting.

  20. #20
    1QwkSport2.5r's Avatar
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    I use 1600mah NiMH packs. I think the last 3 I got were Venom brand. MaxAmps makes premium packs with good warranty - they are worth it but not necessary. If you go with LiPo, look for a 2S (7.4v) pack around 1500-2000mah. Most receivers will handle a 2S LiPo pack okay... I don't trust LiPo though - so I would ultimately recommend a NiMH pack or LiFe (LiFePo4) pack. Life cells are 3.3v/cell, NiMH is 1.2v/cell, and LiPo is 3.7v/cell.
    GlowHead Brotherhood #3
    Real engines use glow plugs.
    R.i.P Jacob Wetterling #11 10/22/1989


  21. #21
    Well, my son and I cut out all the framing parts, and they fit together! Fun work. From what i see online, some people appear to use super-glue to tack the components together and then epoxy for stronger bond? A friend of mine asked why i wouldn't use thin fiberglass over the 1/16 ply for strength. I am worried about weight, so not sure i want to glass it.

  22. #22
    1QwkSport2.5r's Avatar
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    I don't use CA glue to tack parts. I epoxy them right out of the gate. You could use CA to tack if you wish, but I feel having epoxy inside the joint plus a little on either side of the joint is much stronger than just putting epoxy on either side of the joint with parts tacked in place. As for fiberglass - I use it. 1/4oz cloth and finishing resin thinned slightly. A couple thin coats of epoxy thinned down won't add much weight and is worth the strength it adds. If you are worried about weight, just epoxy the outside skin - 2 coats minimum (thinned finish resin) and use thin fiberglass strips on the inside of the hull - at the stringers and runners. It's a good idea to seal the inside of the hull with epoxy anyway. This will help prevent rot should water get inside where it isn't supposed to.
    GlowHead Brotherhood #3
    Real engines use glow plugs.
    R.i.P Jacob Wetterling #11 10/22/1989


  23. #23
    1QwkSport2.5r's Avatar
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    You can take a look at my last build and how I did mine. I didn't fiberglass inside the hull, but I did use balsa stock to brace the inside and I sealed the entire inner hull with epoxy resin. 9th RC airboat build - Selph Inflicted .40 series Tapered Flat Bottom
    GlowHead Brotherhood #3
    Real engines use glow plugs.
    R.i.P Jacob Wetterling #11 10/22/1989


  24. #24
    This is certainly helpful. Last night we fired up the .40 for the first time. its brand new. Ran fine. We are now waiting on the 1/16 ply as the supplier is backlogged, sadly. i ordered fiberglass cloth too, 3/4 oz. One thing i am wondering: what if I would cut out some of the interior bracing, bulkheads/stringers to make the ship lighter? I have seen some people do this cutting out ovals or circles. Any thoughts?

  25. #25
    1QwkSport2.5r's Avatar
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    Make sure when you run that engine that you break it in on a test stand first. It is a ringed engine that will require special attention to get the ring seated.

    You can do weight reduction measures, but I suggest building your first boat without doing that. Just to get a build under your belt and get a feel for how things should be per the plans. If you build too light, then you're adding ballast and that's no good either.
    GlowHead Brotherhood #3
    Real engines use glow plugs.
    R.i.P Jacob Wetterling #11 10/22/1989



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