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Thread: Engine thrust


  1. #1

    Engine thrust

    Hi guys kind of new to the forum there is some pretty wild looking creations that I've noticed so far. I have a curiosity as to why more development isn't being put into using the airplane engines for their intended purpose. Why not put the motor approx 1/3 back on the hull and use the engine thrust angle to control boat pitch angle or hydro planing effects much like a hydroplane boat? I understand the concept of the swamp buggy but by the same token all the weight is being put on the back of the hull which has to be counteracted in order to get the hull running right. Anyone else tinkering with this idea?

  2. #2
    You have a valid point for discussion, and I'd like to contribute to that.

    There is a trend, a pattern that exists which has it's roots quite deep in the history of the aero engine, I've touched on this before here. If you take a grass roots functional full size airboat we are lead to the superb vehicles which are the only way to access wetlands in many parts of the world, and if you consider the means of controlling those your almost bound to result in a rear engined craft. Air rudders demand that flow, add the simple practicality of vision and the driver being out of that airflow then rear it has to be.

    But, to me almost exclusively to modelling, front engined boats are proven to be the most efficient when it comes to converting thrust to speed, and this predominantly developed in Europe. Tethered airscrew hydroplanes represent the fastest airboats on a thrust to speed ratio basis of any type, including real ones, and has been around since long before practical RC control came into existence. It is a simple fact that in regions where real airboats are used there is a tendency to head towards rear, even when the control method does not use the thrust, i.e. water rudders. As the sheer volume of such boats knocks the specialist European Hydros into a cocked hat in numbers the dominance of rear engines is easy to explain.

    Right now, there is a gap of enormous proportions between the effort that's gone into the development of rear engined boats and the specialist minority of airboat's specifically designed to be efficient, but it is going on in certain quarters, resulting in such current beasts as this:

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    Closer to your thoughts there have been attempts at front engined craft that use thrust to lift the boat by allowing propelled air to get under the hull, effectively a force fed tunnel boat., indeed some are almost working on a Ground Effect principle. But I've not seen reasons why these craft have not come to the fore.

    So I guess those those looking for a speed experience to nth degrees use forward engines, but those that like to share in what is a more traditional way will pretty much automatically head to back engines because they enjoy that as part of the real airboat experience, and those folk form the vast majority of airboaters.

    It's a hobby, fill your boots, do what gives you the fun and if that be pursuing forward engines and seeing if that can go up a level from where it is then I'm with you, let's do it

  3. #3
    Hi Jeremy_H Clearly I'm not alone in my thoughts on this idea. Is that your boat in the pic? I never considered a rigger with an air engine. Please understand I meant no disrespect to anyone's design or a person for what interests them in this varied hobby of rc merely exploring alternatives with available means of propulsion. I have seen some interesting creations here at rcu and it can certainly gets ones creative juices flowing that's for sure. I have built a 48" hydro and placed a 75 supertiger (inverted for lower CG) just behind the front sponsons at about 2 degree's up thrust and to be honest it scared the heck out of me, scary fast, too fast for fun unless the aim is to create the fastest water dragster. It was estimated to be over 70 mph in seconds and to my astonishment it actually worked with no sign of lift off, blow over and seemed to be exceptionally stable. Have you or anyone else experimented with this concept?, what was the outcome?, anyone have pic's of their creations?

  4. #4

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    Quote Originally Posted by arcdude View Post
    Hi Jeremy_H Clearly I'm not alone in my thoughts on this idea. Is that your boat in the pic? I never considered a rigger with an air engine. Please understand I meant no disrespect to anyone's design or a person for what interests them in this varied hobby of rc merely exploring alternatives with available means of propulsion. I have seen some interesting creations here at rcu and it can certainly gets ones creative juices flowing that's for sure. I have built a 48" hydro and placed a 75 supertiger (inverted for lower CG) just behind the front sponsons at about 2 degree's up thrust and to be honest it scared the heck out of me, scary fast, too fast for fun unless the aim is to create the fastest water dragster. It was estimated to be over 70 mph in seconds and to my astonishment it actually worked with no sign of lift off, blow over and seemed to be exceptionally stable. Have you or anyone else experimented with this concept?, what was the outcome?, anyone have pic's of their creations?
    No offence taken at all.

    The blue boat is a screen shot from youtube, I'll dig out the vid link plus any pics of some of the stuff I mentioned.

    Do you have any pics of your boat?

  5. #5
    Here is a couple pic's of my own creation, the boat weigh's about 4.5 lbs and as you can see from the pic's I'm trying to create some form of body. Initially in the construction and experimentation of the hull I had to redesign the riding surface of the front sponsons due to a strange duck walking effect, after changing the ride surface angle it went without a hitch as mentioned earlier. I found that the 2 degree up thrust angle of the engine was just enough to lift the hull and still maintain adhesion to the water surface all in all a great successful experiment. Anyone else have a contribution?
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  6. #6
    1QwkSport2.5r's Avatar
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    For speed applications there is no specific engine placement rule. Many are rear engine because it's generally easier. Some folks prefer pusher prop setups for the more scale type of boat and almost always require rear mounted engines. Other designs such as the Selph Inflicted 3-point hydro use a rear engine/front sponson design and are incredibly fast and stable. The prop thrust on the SI's actually holds the bow down. They're generally set up to be a tad light at the bow for top speed which really is the point of a hydrofoil. Below are my SI3 boats. .20 series SI3 with Jett .35, .60 series with SuperTigre S90K both on tuned mufflers. Also is a picture of my custom built outrigger hydrofoil. The outrigger needs a sponson makeover so it's a shelf queen for now. Hull sizes respectively are 16"wX22"l, 22"wX29"l, 22"wX39"l. The .20 series has gone 49.8mph with a 3" wet rudder. I expect 55-60mph or better with the now 1.625" wet rudder with a 9x6 prop.


    GlowHead Brotherhood #3
    Using Dynamite, Enya, Fox, Jett, K&B, SH, Super Tigre, Thunder Tiger, and Traxxas engines.


  7. #7
    My First SI3 is finally on the way and I can't tell you how much I'm looking forward to that!

    Fantastic looking things Mr 1QwkSport2.5r!

  8. #8
    Quote Originally Posted by arcdude View Post
    Here is a couple pic's of my own creation, the boat weigh's about 4.5 lbs and as you can see from the pic's I'm trying to create some form of body. Initially in the construction and experimentation of the hull I had to redesign the riding surface of the front sponsons due to a strange duck walking effect, after changing the ride surface angle it went without a hitch as mentioned earlier. I found that the 2 degree up thrust angle of the engine was just enough to lift the hull and still maintain adhesion to the water surface all in all a great successful experiment. Anyone else have a contribution?
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    Now that is very interesting to see . Keeping us posted is now a net obligation my friend!

  9. #9
    1QwkSport2.5r's Avatar
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    Here is an Italian model dubbed the Cobra. I believe it was designed in the early-mid '70s and is a front engine shovel-nose type hydro. I think it was designed around a .40-.45, iI appears this one has a Super Tigre .61 or larger judging by the cylinder head. I have the plans printed and had the intention to build one but life got sidetracked a bit so it hasnt been started.
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    GlowHead Brotherhood #3
    Using Dynamite, Enya, Fox, Jett, K&B, SH, Super Tigre, Thunder Tiger, and Traxxas engines.


  10. #10
    1QwkSport2.5r That is an interesting rigger you have is that an original or an adjusted plan of some sort? may I ask what is wrong with the sponsons? I followed your build on the SI3, quite interesting and I also watched the vid that thing moves, how's the turning at speed? Here is a thought if the motor was inverted and the hull modified to have a 1" deep divot for lack of better terms the CG would be lowered considerably. I wouldn't be one bit surprised that the outrigger will do in excess of 60 without too much difficulty. Thanks Jeremy_H unfortunately I have promised that hydro to my son and it has been downgraded to a TT 46 so it'll be a little more fun for the beginner, too much speed for the new person can be a dangerous thing for all concerned. I do have several motors including a couple 90 4 strokes without a home so a new build in the future is a great possibility once an idea pops into the old grey matter! Has anyone used 4 strokes and power response is there a great deal of difference in response? I have the motors for a couple of planes that I have lost interest in and likely going to part with them, I guess I could always sell the 4 strokes and get a 2 stroke of whatever size needed. Another option that has occurred to me is has anyone tried a PTO and placed the engine down in the bottom of the hull?

  11. #11
    The cobra is one of the designs that uses a portion of the thrust to lift the hull.

    A pto is doable, and certainly could be interesting. I'm looking at a toothed belt arrangement on a water prop boat and the speed thing is an unknown for this drive method, they specify a tensile force but apparently not a speed, so the centrifugal (or is it centripetal?) force on the belt is probably the limiting factor. For this purpose I'm guessing plodding four stroke engine better than a screaming stroker.

  12. #12
    1QwkSport2.5r's Avatar
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    The sponsons on my rigger aren't quite big enough and the profile is wrong. It wants to submarine instead of plane out. More show than go as built.

    4-strokes work great! My first boat; a Kamikaze. Designed by the same guy that designed my rigger. The rigger was built from scratch without plans. The original rigger went over 80mph with a Jett .90lx. Mine had a TT .46 though my Jett .35 is as strong or stronger than the TT .46 so I may use it instead. The little 3-pointers turn pretty well if a turn fin is used. Else it suffers a good bit in turns.

    Kamikaze flat bottom run with the two 4-strokes I own. First video is on water using an Enya 60-4C.
    http://youtu.be/fVadTr40eQw
    Same boat but with an Enya R120-4C. Twice the displacement, 13x7-13x9 APC props and a whole lot faster. On grass:
    http://youtu.be/Ub0mfQ7Lp1g

    Boats with 4-strokes need to be really overdisplaced over a 2-stroke to get as good or better performance. Example: if it runs great with a .60 2-stroke, it'll ROCK with a .90 2-stroke. In place of a .90 2-stroke I'd use a 1.20 4-stroke.
    GlowHead Brotherhood #3
    Using Dynamite, Enya, Fox, Jett, K&B, SH, Super Tigre, Thunder Tiger, and Traxxas engines.


  13. #13
    1QwkSport2.5r In regards to the sponsons not getting on plane would possibly adjusting the engine a couple of degrees up not assist in getting on plane? Could the back end be too light? As I mentioned earlier the issue I had with the hydro doing a strange porpoising type walk I adjusted the ride planes on the sponsons to about one degree by sanding down the surface and adding an additional layer of lite ply and adjusting the engine up about 2 degrees up, just a thought. I had also considered curved turn fins on the sponsons to aide in turning and to prevent roll overs.

    Jeremy_H I also considered a design similar to the cobra with a vent down through the hull further back ie end of the sponsons rather than at the very front, I would think water pickup may be an issue. The PTO idea was to keep the engine CG down providing a much more streamlined hull, another consideration that may be incorporated into a cobra type design may be the use of an inducted fan rather than a prop.
    Last edited by arcdude; 01-17-2014 at 08:48 PM. Reason: forgot something

  14. #14
    1QwkSport2.5r's Avatar
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    Quote Originally Posted by arcdude View Post
    1QwkSport2.5r In regards to the sponsons not getting on plane would possibly adjusting the engine a couple of degrees up not assist in getting on plane? Could the back end be too light? As I mentioned earlier the issue I had with the hydro doing a strange porpoising type walk I adjusted the ride planes on the sponsons to about one degree by sanding down the surface and adding an additional layer of lite ply and adjusting the engine up about 2 degrees up, just a thought. I had also considered curved turn fins on the sponsons to aide in turning and to prevent roll overs.
    I tried adding almost 10* of upward thrust angle to the engine mount (prop) and it got no better. The hull sits low enough in the water that the book tubes are in the water and the surface tension is too great to overcome which then makes it submarine. Me and a buddy tried for a couple hours trying to get it up on top and no such luck was the case. There is nothing else that can be done with it as-is; it just needs new sponsons.
    GlowHead Brotherhood #3
    Using Dynamite, Enya, Fox, Jett, K&B, SH, Super Tigre, Thunder Tiger, and Traxxas engines.


  15. #15
    1QwkSport2.5r Is there a plan for the SI3 or is it only available as a kit? I would like to hear how you make out with the rebuild of the rigger and she ends up working for you....always looking for new ideas.

  16. #16
    1QwkSport2.5r's Avatar
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    Quote Originally Posted by arcdude View Post
    1QwkSport2.5r Is there a plan for the SI3 or is it only available as a kit? I would like to hear how you make out with the rebuild of the rigger and she ends up working for you....always looking for new ideas.
    SI3 plans and kits are for sale at www.rcairboats.net You can do it either way. Plans are around $35 and the .20 series kits start at around $80. Haven't checked pricing lately so those figures are approximate. Chris (the designer of the SI3) sells a flat bottom kit/plans as well as other stuff. Check out his site (there's a forum too). Lots of builds with pics in the forum. Chris is a super nice guy to deal with too.
    GlowHead Brotherhood #3
    Using Dynamite, Enya, Fox, Jett, K&B, SH, Super Tigre, Thunder Tiger, and Traxxas engines.


  17. #17
    1QwkSport2.5r I have been drawn back to your outrigger several times and am intrigued by the design. May I inquire what materials were used in it's build, wood thickness and so on. If it's top secret and you'll have to kill me I'll pass. What speed range do you expect? and is there a current speed record for these style of boats? I have started a 20 size outrigger some time ago and am having difficult with finding matching tubes inner and outer for the booms to the front sponsons, any suggestions would be greatly appreciated?

  18. #18
    1QwkSport2.5r's Avatar
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    Here's my main build thread on RC Airboat World's forum: http://www.rcairboats.net/phpBB/view...hp?f=50&t=2012

    Not top secret, but there are no plans either. I copied the boat Hooty301 built but smaller for a .46 size engine. Hooty's Jett .90 powered rigger has gone 84mph so far. I'm hoping to see 60mph from mine using a .46. Everything I used materials-wise should be listed in that thread. If not, ask and I'll fill you in.
    GlowHead Brotherhood #3
    Using Dynamite, Enya, Fox, Jett, K&B, SH, Super Tigre, Thunder Tiger, and Traxxas engines.


  19. #19
    Quote Originally Posted by 1QwkSport2.5r View Post
    Here's my main build thread on RC Airboat World's forum: http://www.rcairboats.net/phpBB/view...hp?f=50&t=2012

    Not top secret, but there are no plans either. I copied the boat Hooty301 built but smaller for a .46 size engine. Hooty's Jett .90 powered rigger has gone 84mph so far. I'm hoping to see 60mph from mine using a .46. Everything I used materials-wise should be listed in that thread. If not, ask and I'll fill you in.
    I do have a couple of questions if you would be so kind, there seems to be quite a debate on the sponson angle, I respect the experience of others however the sponsons on my hydro are only 1 degree (side to side) angle at the rear and gradually increase toward the front at an approx up angle of 2 degrees from the back and increasing as it goes forward, that boat has done over 70 mph. If you would like some close up pics of the ride surface I'd be most happy to oblige. You state a fellow by the name Hooty301 has built a similar rig? what are his sponson dimensions, similar to yours? I am considering a rigger build myself once I have done the research and am considering a ply over foam method, could be interesting!!!

  20. #20
    1QwkSport2.5r's Avatar
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    I freehand drew my sponson angles, no idea what my angles are. There are no dimensions of Hooty's hull other than the length is about 4 feet. Overall width is in the 20-24" range. Beyond that I don't know. Here is his rigger thread: http://www.rcairboats.net/phpBB/view...php?f=50&t=314

    I will say I'm making new drawings for the sponson rebuild and I will be using a very similar rake angle as my SI3 boats. A very smooth curve with no flat spots and sharp corners.
    GlowHead Brotherhood #3
    Using Dynamite, Enya, Fox, Jett, K&B, SH, Super Tigre, Thunder Tiger, and Traxxas engines.


  21. #21
    I've finally found the video of that boat I show above:


  22. #22
    Jeremy_H It looks like a good solid runner, is it the pond that is too small or is the boat that appears to be a little slow. Without having seen a lot of boats in real life it's hard to judge a video. There seems to be quite a wake behind the boat and running pretty wet. What I would like to accomplish is a method of using a traditional boat yet find some way of minimizing the wetted area of the hull by using the thrust angle to do it. Gotta be a way!!!


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