.15 RC airboat build
06-13-2015, 12:08 AM
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.15 RC airboat build
Hi everyone, well after reading several articles on RC airboats I decided to have a go at building one myself. Generally I fly RC aircraft but we get those days when wind conditions leaves you hankering to do something else.
I searched thru my model bits and found a sweet little OS 15 engine which I had used in a couple of planes and I new it was reliable for such a project.
Next I found a 20mm thick sheet of polystyrene foam stored in the garage roof so project began.
I had read that a good size formula to start with was to make model approx 3 times the prop diameter in length and one and a half times the prop diameter for beam.
My intended model ended up being established as 650mm length and 250mm beam.
I cut a base from polystyrene at these dimension then cut two side strips 40mm height and cut a 30 degree angle on these to form bow. I then cut the base at the inrtersection of angle and cut mitre angles so that the base would rake up 30 degrees as per sides.
Next I cut several more 40mm width strips to use as transom and cross beams in the hull. I then glued the hull side pieces to the hull bottom and glued font section of hull bottom to sides and bottom of hull. After trimming deck line straight I cut a 3mm thick ply top and made cut outs in this for radio hatch and front cockpit area. I sat deck on hull and marked position of cut outs so that cross beams of polystyrene could be glued into hull.After hull was all glued together and glue had dried, I bevelled the chines also at a 30 degree angle and added a 12mm radius between the edge at lower hull and chines. This would stop chine digging in during a turn which could lead to boat flipping.
At this point I decided to make aluminium engine mounts so that I could position them along with engine fitted onto the deck and drill deck for fitting blind nuts to underside of deck to retain engine mounts before gluing deck to hull.
I made an aluminium prop guard from 40mm x 3mm material for trial purposes, then made a chair and fitted a Ken doll purchased from a toy store.
Several more hours work had radio gear/fuel tank in position and attention was the turned to making rudders. I had read the it was better to keep rudders low so that airblast from prop would not heel boat in turns so this is what I did. Rudders are hinged by short sections of tube glue top and bottom of rudder leading edge and suitable pivot holes drilled in hull transom overhang and engine extension brackets made for rudders. Rudders were the connected by a tie bar with ball links each end.
Where to put COG was the next problem but several people reckoned that COG 30% from rear was a good starting point. I found my set up was rear heavy so a hole was carved in hull as far forward as possible and a 6oz lead fishing sinker was glued into this hole as COG was then at 30% as recommended.
Finally a fine day so off to the local waterways for trials. Motor started, model was launched and to my surprise even at low throttle there was excellent rudder control. After a couple of turns I gradually opened throttle and it popped onto the plane with ease swinging an 8" diameter x 6" pitch prop. Steering was still responsive and it soon became apparent that these airboats have to be steered like a midget car. Cornering consisted of applying rudder then as boat began to slide you have to gently start applying opposite rudder then slide can be controlled further by manipulating throttle. After a short time jet boat type spins and nice cornering can be achieved.
On returning model to shore I noticed I had a senior moment as the prop had been fitted reversed. Swapped prop around the correct way and speed was the ballistic. Attached are some pics and video link below of boat as 1st trialled and boat as it is now finished with a new style prop guard.
https://www.youtube.com/watch?v=f_x0sO6hGfo
https://youtu.be/dzrzAUJtuug
I searched thru my model bits and found a sweet little OS 15 engine which I had used in a couple of planes and I new it was reliable for such a project.
Next I found a 20mm thick sheet of polystyrene foam stored in the garage roof so project began.
I had read that a good size formula to start with was to make model approx 3 times the prop diameter in length and one and a half times the prop diameter for beam.
My intended model ended up being established as 650mm length and 250mm beam.
I cut a base from polystyrene at these dimension then cut two side strips 40mm height and cut a 30 degree angle on these to form bow. I then cut the base at the inrtersection of angle and cut mitre angles so that the base would rake up 30 degrees as per sides.
Next I cut several more 40mm width strips to use as transom and cross beams in the hull. I then glued the hull side pieces to the hull bottom and glued font section of hull bottom to sides and bottom of hull. After trimming deck line straight I cut a 3mm thick ply top and made cut outs in this for radio hatch and front cockpit area. I sat deck on hull and marked position of cut outs so that cross beams of polystyrene could be glued into hull.After hull was all glued together and glue had dried, I bevelled the chines also at a 30 degree angle and added a 12mm radius between the edge at lower hull and chines. This would stop chine digging in during a turn which could lead to boat flipping.
At this point I decided to make aluminium engine mounts so that I could position them along with engine fitted onto the deck and drill deck for fitting blind nuts to underside of deck to retain engine mounts before gluing deck to hull.
I made an aluminium prop guard from 40mm x 3mm material for trial purposes, then made a chair and fitted a Ken doll purchased from a toy store.
Several more hours work had radio gear/fuel tank in position and attention was the turned to making rudders. I had read the it was better to keep rudders low so that airblast from prop would not heel boat in turns so this is what I did. Rudders are hinged by short sections of tube glue top and bottom of rudder leading edge and suitable pivot holes drilled in hull transom overhang and engine extension brackets made for rudders. Rudders were the connected by a tie bar with ball links each end.
Where to put COG was the next problem but several people reckoned that COG 30% from rear was a good starting point. I found my set up was rear heavy so a hole was carved in hull as far forward as possible and a 6oz lead fishing sinker was glued into this hole as COG was then at 30% as recommended.
Finally a fine day so off to the local waterways for trials. Motor started, model was launched and to my surprise even at low throttle there was excellent rudder control. After a couple of turns I gradually opened throttle and it popped onto the plane with ease swinging an 8" diameter x 6" pitch prop. Steering was still responsive and it soon became apparent that these airboats have to be steered like a midget car. Cornering consisted of applying rudder then as boat began to slide you have to gently start applying opposite rudder then slide can be controlled further by manipulating throttle. After a short time jet boat type spins and nice cornering can be achieved.
On returning model to shore I noticed I had a senior moment as the prop had been fitted reversed. Swapped prop around the correct way and speed was the ballistic. Attached are some pics and video link below of boat as 1st trialled and boat as it is now finished with a new style prop guard.
https://www.youtube.com/watch?v=f_x0sO6hGfo
https://youtu.be/dzrzAUJtuug
Last edited by Wayne Lester; 07-17-2015 at 08:35 PM. Reason: video link added
06-13-2015, 02:05 PM
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Yep surprised me and several others how responsive steering is.
Have found a small Thunder Tiger GP10 nitro engine also so will build a smaller version for this also.
Have found a small Thunder Tiger GP10 nitro engine also so will build a smaller version for this also.
06-19-2015, 12:07 AM
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Thunder Tiger GP10 airboat build.
Hi again everyone,well as I said earlier I would next build another airboat that would be powered with a smaller Thunder Tiger GP10 engine that I found in my cupboard.
My last design powered with an OS .15 engine was a real success so I decided that my new build would be made using the same design with a few small modifications that I hope will enhance performance of this new build.
If this build is as successful as my 1st build I will draw up some plans and post them on my forum for others to build.
OK here we go then. Firstly having decided that foam hull and ply deck would be used again, I scaled sizes down to suit the smaller .10 engine that I would be using this model and arrived at the following sizes:
Hull length = 530mm.
Beam = 230mm.
Hull depth = 50mm.
Hull was constructed same as my previous model, ie: hull bottom made from 20mm thick polystyrene, hull sides,transom and cross members would be made from 20mm thick X 30mm height polystyrene strips. Deck would be from 3mm thick ply.
This time I cut a the non trip chine angled at a 30 degree upwards from base of hull instaed of 45 degree angle as per my previous model. I am hoping this will further reduce chances of chine digging in during a cornering slide. Final water test will prove this theory right or wrong, however I notice by studying photos of full size airboats they tended to have approx 30 degrees angle also.
I retained the same type prop guard design but lightened the hoop frames but reducing the strip width of aluminum I used.
I retained the same rudder set up as per my previous model but simplified the design of top aluminum plate bolted to the motor mount pylon.
Driver used was a Ken doll from the Barbie & Ken collection available at most toy stores. His legs bend at hips but not at the knees so application of heat from my heat gun soon had that problem sorted as I wanted to reduce the height of seat by a further 15-20mm.
Driver seat has 3mm ply floor section and seat base/back. The 4 legs are made from 4mm fiberglass solid rod which are fitted/glued into holes drilled into base and seat bottom.
The driver has been retained to seat by a screw thru base and screw into back (ouch!)
The entire seat/driver can be slid forward and removed from boat so that electric starter can be positioned to start engine.
This time I have omitted the front cockpit from the hull and have added a spray and anti branch guard to the bow of hull. As I progress I will add more pictures and a video of hopefully another successful result on water.
More progress made over the past few days has seen fitting up of rudders and linkages, painting and detailing hull along with fitting of fuel tank and fuel lines.
All that is left to do now is fit servos for rudder and throttle control, add a fuel filter then hopefully it should be ready to water trial this coming weekend.
At the moment I have fitted a master airscrew propellor 7" dia x 6" pitch. This may be a bit too much pitch, a 7"x4" pitch would be best but this is the only small prop I have lying around.
https://youtu.be/dzrzAUJtuug
My last design powered with an OS .15 engine was a real success so I decided that my new build would be made using the same design with a few small modifications that I hope will enhance performance of this new build.
If this build is as successful as my 1st build I will draw up some plans and post them on my forum for others to build.
OK here we go then. Firstly having decided that foam hull and ply deck would be used again, I scaled sizes down to suit the smaller .10 engine that I would be using this model and arrived at the following sizes:
Hull length = 530mm.
Beam = 230mm.
Hull depth = 50mm.
Hull was constructed same as my previous model, ie: hull bottom made from 20mm thick polystyrene, hull sides,transom and cross members would be made from 20mm thick X 30mm height polystyrene strips. Deck would be from 3mm thick ply.
This time I cut a the non trip chine angled at a 30 degree upwards from base of hull instaed of 45 degree angle as per my previous model. I am hoping this will further reduce chances of chine digging in during a cornering slide. Final water test will prove this theory right or wrong, however I notice by studying photos of full size airboats they tended to have approx 30 degrees angle also.
I retained the same type prop guard design but lightened the hoop frames but reducing the strip width of aluminum I used.
I retained the same rudder set up as per my previous model but simplified the design of top aluminum plate bolted to the motor mount pylon.
Driver used was a Ken doll from the Barbie & Ken collection available at most toy stores. His legs bend at hips but not at the knees so application of heat from my heat gun soon had that problem sorted as I wanted to reduce the height of seat by a further 15-20mm.
Driver seat has 3mm ply floor section and seat base/back. The 4 legs are made from 4mm fiberglass solid rod which are fitted/glued into holes drilled into base and seat bottom.
The driver has been retained to seat by a screw thru base and screw into back (ouch!)
The entire seat/driver can be slid forward and removed from boat so that electric starter can be positioned to start engine.
This time I have omitted the front cockpit from the hull and have added a spray and anti branch guard to the bow of hull. As I progress I will add more pictures and a video of hopefully another successful result on water.
More progress made over the past few days has seen fitting up of rudders and linkages, painting and detailing hull along with fitting of fuel tank and fuel lines.
All that is left to do now is fit servos for rudder and throttle control, add a fuel filter then hopefully it should be ready to water trial this coming weekend.
At the moment I have fitted a master airscrew propellor 7" dia x 6" pitch. This may be a bit too much pitch, a 7"x4" pitch would be best but this is the only small prop I have lying around.
https://youtu.be/dzrzAUJtuug
Last edited by Wayne Lester; 07-17-2015 at 08:36 PM. Reason: progress update
