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  1. #1

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    Fastest Engine

    I am trying to break a speed record with a three point hydro airboat, I know this is an airplane tread so figured you guys would know what the fastest airplane engine around a .90 or engine of equivalent weight would be for my application.I read that the JETT engines were powerful but expensive. Ive got a flatbottom airboat gps'd at 45.2mph with a .61FX, I would like to get into the 70's so I need the most extreme airproped engine I can find. Any help with this one would be greatly appeciated.

    Here are some pics of my current boat....
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  2. #2

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    RE: Fastest Engine

    A Nelson is very expensife and will give you some insain preformance

  3. #3

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    RE: Fastest Engine

    What sizes and what power are these Nelsons? Where do you get one?Also do you think I would get more speed from the smaller engines or the .90's?

  4. #4
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    RE: Fastest Engine

    I would check out Jett. I suspect you need a throttle on a boat so a Sport jett would give you a good mix of both worlds.

    http://www.jettengineering.com/

  5. #5

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    RE: Fastest Engine

    I'm sure that if you call Dub (Jett), he can work up something. He can fine tune to your specifications. He does make the .90LX and 1.00LX which might be a good place to start. I'm sure that you have worked on the drag coefficient and determined what thrust is required. Prop dia. / Pitch / RPM. With this, talk to Dub.

    I feel the need... ... the need for speed.
    Revver Brother #45

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    RE: Fastest Engine

    Take a look at the OS 91FX. It will drop right in without mods, weighs the same as your .61, is much more powerful, costs about $200, and pulls my Delta Fighter along at 127 MPH confirmed with radar. I use a 12X8 APC prop, a Performance Specialties Ultra Thrust muffler and 15% Cool Power fuel. I realize you won't get near that speed in a boat but it will wake it up in a hurry. It's hard to beat the OS91FX and I own several Jett engines.
    Arthur

  7. #7
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    RE: Fastest Engine

    ORIGINAL: hooty301

    I am trying to break a speed record with a three point hydro airboat, I know this is an airplane tread so figured you guys would know what the fastest airplane engine around a .90 or engine of equivalent weight would be for my application.I read that the JETT engines were powerful but expensive. Ive got a flatbottom airboat gps'd at 45.6mph with a .61FX, I would like to get into the 70's so I need the most extreme airproped engine I can find. Any help with this one would be greatly appeciated.
    Hooty,
    A sleek airplane with that engine would be able to break 100 mph easily. So, I would suggest that you appraoch your problem from the viewpoint of how to keep a sleek 100mph airplane planing/skipping on the surface of the water rather than how to get a boat to go faster. The problem with most boats is that all their weight is in the back. This is a condition that we airplane-minded people call tail-heavy. This is an unstable condition for an airplane. Drop a playing card from shoulder height and it will tumble end over end to the ground. Put enough paper-clips on one side and it will become a stable glider. I know everyone here has seen video of those super-fast speed boats that hit too big a wave, nose up into the air and do backward somersaults like that playing card did before you added the paper-clips. They both do backflips for the same reason. Do a google search for "flying boat foamy" to get some ideas how to design one for your .61fx. I havn't seen anyone build a glow powered one yet. They all seem to be small electrics. Check out the Ezone forums there must bee some good threads there on flying boats. Build and learn how to fly one of these without telling your "boating friends" then show them your new boat. Fly it off the surface of the water and pretend you didn't know it could fly. It'll blow their minds!
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  8. #8
    Craig-RCU's Avatar
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    RE: Fastest Engine

    Hooty,
    Is this you?

    http://www.rcuvideos.com/view_video....4571bd98c4d548

    A tuned pipe and maybe a smaller higher pitched prop might get this one moving faster. Mounting the engine up front would make sure that it wouldn't do backflips if it caught air.

  9. #9
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    RE: Fastest Engine

    What size prop are you using now? What fuel are you using?
    Just as an example, if it were mine and I was using the .61FX I would try maybe a 10 X 9 and 15% nitro fuel?
    An Ultra Thrust muffler would really wake up that O.S. too...(wouldn't it? I know it works great on a Webra .50!)

    How about a Webra...do they still make the .91? (gonna have to go look-see for myself now... )
    < Wrongway Feldman's Kreider-Reisner KR-21...(on Gilligan's Island)

  10. #10

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    RE: Fastest Engine

    What size prop are you using now? What fuel are you using?
    Just as an example, if it were mine and I was using the .61FX I would try maybe a 10 X 9 and 15% nitro fuel?
    An Ultra Thrust muffler would really wake up that O.S. too...(wouldn't it? I know it works great on a Webra .50!)
    Im running 15% coolpower with a 12/4. Where could I find this muffler you speak of? Also what kind of rpm can be expected from .91fx with a12/6?

  11. #11

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    RE: Fastest Engine

    Hooty,
    A sleek airplane with that engine would be able to break 100 mph easily. So, I would suggest that you appraoch your problem from the viewpoint of how to keep a sleek 100mph airplane planing/skipping on the surface of the water rather than how to get a boat to go faster. The problem with most boats is that all their weight is in the back. This is a condition that we airplane-minded people call tail-heavy. This is an unstable condition for an airplane. Drop a playing card from shoulder height and it will tumble end over end to the ground. Put enough paper-clips on one side and it will become a stable glider. I know everyone here has seen video of those super-fast speed boats that hit too big a wave, nose up into the air and do backward somersaults like that playing card did before you added the paper-clips. They both do backflips for the same reason. Do a google search for "flying boat foamy" to get some ideas how to design one for your .61fx. I havn't seen anyone build a glow powered one yet. They all seem to be small electrics. Check out the Ezone forums there must bee some good threads there on flying boats. Build and learn how to fly one of these without telling your "boating friends" then show them your new boat. Fly it off the surface of the water and pretend you didn't know it could fly. It'll blow their minds!
    Talkin about backward flips, heres a good one of my flatbottom flippen and driving away[link]http://s131.photobucket.com/albums/p290/hooty301/?action=view&current=2005_0222boat30003.flv[/link]

  12. #12
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    RE: Fastest Engine

    Hey hooty!
    Go to the YS Support forum here in RCU and ask Dave Shadel about the Ultra Thrust.

    Try a smaller diameter / higher pitch prop too...that 12 X 4 isn't enough prop for that engine.

    Why doncha get a few different props to experiment with...if that .61FX is still "healthy" (good compression, runs well ) I would try an 11 X 7 APC and a 10 X 8 and 10 X 9 just for the heck of it.

    The fuel is O.K. but personally, I would add a few oz. of castor oil to it (to a full gallon )

    For now, if you are running the stock muffler, take the baffle out of it and drill out the "tailpipe" 1/16" larger. (do that in 2 x 1/32" steps because the alum. is hard and the drill will want to catch and bite )
    < Wrongway Feldman's Kreider-Reisner KR-21...(on Gilligan's Island)

  13. #13

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    RE: Fastest Engine

    Why doncha get a few different props to experiment with...if that .61FX is still "healthy" (good compression, runs well ) I would try an 11 X 7 APC and a 10 X 8 and 10 X 9 just for the heck of it
    The engines only about three months old so shes still healthy, Ive tried a 11/7 APC a12/5 and a 12/6 but get better speed from the 12/4 also I just switched too the coolpower I normaly run Byrun 15% cas/syn mix what fuel do you like? Watch the vid above and tell me if the engine sounds like shes turning where it should with a 12/4. I thought about drilling out the muffler wasent sure if it would hurt anything though, the first thing I did was remove the baffle. Im running a bit under proped becouse of the drag issue with it being on a boat.

  14. #14
    proptop's Avatar
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    RE: Fastest Engine

    Well...maybe you are already getting about as much as you're gonna get outa that engine? I have a .61FX and have had it in 2 different planes...a Top Flite Corsair and a scratch built original design...

    I have had as much as a 13 X 6 APC on it, and believe it or not, it worked on the Corsair. Try an APC 13 X 6 (same design as the 12 X 4 with thin tips so it will spin and throttle up better than a 12 X 6 )

    Either that, or hit it with a bigger hammer...(.90-.91 size) like you were thinking all along, aye?! ( I just thought maybe the .61FX wasn't quite optimized, but you have it close, so...?)

    edit: I have dial-up...(I know ) so watching the video is a !*%#@ pain...couldn't get it to work...

    How heavy and how big is this air boat anyway? (just outa curiosity )
    < Wrongway Feldman's Kreider-Reisner KR-21...(on Gilligan's Island)

  15. #15
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    RE: Fastest Engine

    ORIGINAL: hooty301

    Why doncha get a few different props to experiment with...if that .61FX is still "healthy" (good compression, runs well ) I would try an 11 X 7 APC and a 10 X 8 and 10 X 9 just for the heck of it
    The engines only about three months old so shes still healthy, Ive tried a 11/7 APC a12/5 and a 12/6 but get better speed from the 12/4 also I just switched two the coolpower I normaly run Byrun 15% cas/syn mix what fuel do you like? Watch the vid above and tell me if the engine sounds like shes turning where it should with a 12/4. I thought about drilling out the muffler wasent sure if it would hurt anything though, the first thing I did was remove the baffle. Im running a bit under proped becouse of the drag issue with it being on a boat.
    You said in your first post "I am trying to break a speed record with a three point hydro airboat". Maybe if you could be more specific about that. Are there specific "contest rules" that you have to follow? Do you have to use a specific hull with a specific engine mount location? If so, then all you can do is add horsepower to get more speed. If not, then there are lots of ways to reduce hull drag (google hydrofoil) which seems to be a huge problem based on your data here . A 12x4 is a "stump pulling" prop for an airplane and not a speed prop. Also, if you can only add horsepower and can't modify the boat to be at least aerodynamicly stable, you will come to the point that every speed run will end with an air-launch and a backflip. At this point aerodynamic stability will be the limiting factor and not horsepower.

  16. #16

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    RE: Fastest Engine

    Neat video and great flip. The motor sounds likes it running well, but that prop is a bit on the small size for that motor. You are most likely running it at an RPM that is above its best Power band. A standard airplane prop would be a 12x6 for that motor. I'm not a boat guy, but it looks like the boat is a bit on the big side for that motor, I would suggest a smaller boat, or a bigger engine if you want to go faster and the props aren't doing it. Drilling out the muffler won't hurt anything other than slightly less backpressure to your tank, but it won't make a big noticeable speed difference either.

    Then again, you have the GPS, test it both ways, and let us know.
    Dave Norman
    29w

  17. #17
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    RE: Fastest Engine


    ORIGINAL: hooty301
    Ive tried a 11/7 APC a12/5 and a 12/6 but get better speed from the 12/4
    This may be telling you that thrust is the limiting factor here since the theoretical speed is higher with more pitch. You can go to the Jett site listed above and get a tuned muffler for your engine for $85. The extra rpm of the muffler will not get you to 70+ mph though. My goal now would be to turn the 12x4 faster or even try a 13". Just as in aircraft, speed =$$$

  18. #18

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    RE: Fastest Engine

    Hooty:

    You are going for a record which implys there are some fast people out there that have gone the route of spending the dnecessary dollars to be number one. Seems like fast is a combonation of dollars and knowledge. There are only two high rpm engines made in the USA that should be a natural for high rpm and resulting speed. Jett and Nellson racing engines will give you 20,000 plus of reliable power for a reasonable dollar. They only come in a 40 size with respects to the real high rpm engines needed for you application. Size of the engine will limit the size of your boat, so most of the speed design must come from the boat design, same as the Q-500s and formula airframes. Now, there are always exceptions, they seem somewhat dollar related and are. Your OS 61 is a dog in intended applications and might as well yell at the moon here. If you gotta have a big block that turns rpms, gotta go for the king, the 90 BVM ducted fan engine, good for 20K plus. Quality again here equals dollars, you may find one on e-bay for around $500.00, they are $800 or so new. The OS 91VRDF is also a high rpm engine good for around 20K, but not with the pure power of the BVM, but much cheaper. There is a real art to getting high rpms out of the OS vrdf without burning them up. Chances are you will put more into the learning curve with the OS than buying the superior BVM outright. Again, quality and performance equal dollars. There are some guys in Germany that are hop up artists for the big engines who will make them scoot for a buck, gonna cost as much or more than the BVM in the long run. Recently bought a OPS 60 that is guaranteed turn turn 24 K and up. Thing has 8 induction ports, etc. After looking at the internals of this thing, it sits on the engine shelf. No question that it will blow up, just a question of when! Not gonna risk gear or me or buddys with the thing. Yea, am susre it will give you world record rpm's and speed for at least the first and second run which is what it's designed for. Did I get ripped? I don't think so, the engine will do what it's designed to do (I believe), just a few times. Just trying to give you a little feel for what the record holder types thinking is. Yes, you can do it!!! Get the best information you can and then go for it. In 1949, two 14 year old kids took the nats record for class B in U control with their inovation of a presssured fuel tank taken off the McCoys back plate. Shocked the old guys who really know engines and how to make them run. The next year, they all were running pressurized systems and the kids got blown away. Kids should have kept their equipment covered at all times!!! Such is racing and speed in general. None the less, you can do it. Ron Morrison did!!

  19. #19

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    RE: Fastest Engine

    OS91FX needs more prop than a 12x6 or 4. With a APC 12X8 it will turn about 16,000 with excellent response. Any smaller and it will over rev. Get a muffler from Jett or Performance Specilalists. Jet is prettier, both give 1K to 1.5K more RPM.
    Arthur

  20. #20

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    RE: Fastest Engine

    How did you get an OS 91 fx to run 16000 rpm with a 12/8 prop?

  21. #21

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    RE: Fastest Engine

    ORIGINAL: hooty301

    I am trying to break a speed record with a three point hydro airboat,

    ...

    I would like to get into the 70's ...
    Hello hooty301,

    here’s a suggestion to gain some serious speed:

    I’d like to recommend a .90 sized ducted fan setup – tractor type. There are several advantages involved.

    First of all, this solution keeps the CG very low supporting dynamical stability by reducing pitch and roll tendencies of your vehicle effectively.

    Generally an OS .91 VR-DF engine plus the JetModelProducts JMP 2 tuned pipe should be the right powerplant for your goals. This engine is quite easy to handle and spare parts are still available.

    http://www.jetmodelproducts.com/exhaust.htm

    Typical rotor diameters of .90 fans such like Dynamax or Ramtec are about 5 inches.

    http://www.jetmodelproducts.com/dynamax.htm

    http://www.trimair.com.au/index2.html

    Compared to the Dynamax the Ramtec fan blades do feature a slightly higher pitch meaning less static thrust but higher topspeed (224.98 feet/sec or 153.40 mph statically). 10.5 pounds of static thrust can be reached with the combo OS .91 VR-DF plus Ramtec at about 21000 rpms.

    By doing some trial and error tests, you could check out different ducting diameters and lengths to find the optimum setup. For instance a 4.5" inner dia ducting produces more static thrust than 4.0β€œ but lower β€žexhaustβ€œ velocity.

    But the absolute highest β€œexhaust” velocities (at the expense of static thrust) are achieved using the BVM .91 and BVM .96 engines and the well matched VioFan fan unit. This unit is slightly smaller in diameter than Dynamax and Ramtec. It is not advisable to combine the OS .91 VR-DF with the VioFan unit because the VioFan reaches its best degree of efficiency not below 22000 rpms.

    http://www.bvmjets.com/Accessories/viofan.htm

    NOS or slightly used 90 sized ducted fan assemblies and engines can be found frequently in the large EEE-BAAYY.

  22. #22

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    RE: Fastest Engine

    An ignitor for the glow plug, an electric motor for starting, and a Hanger-9 tach. Try it. You'll like it.
    Arthur

  23. #23

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    RE: Fastest Engine

    Might want to check that tach. Mine will only read about 12300 rpm with a 12/8 apc.

  24. #24

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    RE: Fastest Engine

    Are you using an UltraThrust or Jett muffler? 15% CoolPower? It will do it.
    Arthur

  25. #25

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    RE: Fastest Engine

    What have you changed since the last time you posted readings on that setup?


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