RE: Fastest Engine
 

Ok, so thats what Ill do, this way Ill also be able to adjust the engine foward or back to get the balance right which is key in making the boat slide across the water most efficiently. Then after testing biuld some ducting for looks and to see if it helps with speed. Also how would you design the inlet lip that your talking about?

RE: Fastest Engine
 

Another thing I am concerned with is the placement of the sponsons or the points that touch the water. If you look at where these points are on the majority of the boats that are going for the speed record like the American Challenge compared to the Aussie Spirit. The American Challenge and the Quicksilver are biult like a trike with two points in the rear and one under the nose with the balance point in the front of the rear points, but the boat that holds the record has all three points towards the front of the boat and reqiures the thrust from the engine to lift the majority of the boat out of the water and skim the water on its chin. This set up seems like it would be more efficient than the trike design which would kind of pivot over the rear points plowing the nose in. The traditional canyard style would most likely be the easiest to setup though, just dont know if it would be as fast as a hydro like the Aussie.

RE: Fastest Engine
 

In case of a suggested circular inlet ducting of 17.8 inch^2 area, the inlet ducting would feature an inner diameter of 4.76”.

Assuming a 2:1 ellipse of 4” of length, a shortest possible inlet length would be 2“ and the inlet “lip” diameter would be 6.75”.

RE: Fastest Engine
 

Hooty,

you do have a load of speed boat specific questions concerning CG adjustment, best balance, least water induced drag etc.

So I would like to recommend the following site. One of the best sources for R/C nitro speed boating in the net:

www.intlwaters.com

Here many actual and former record holders can be found. You will notice that many also do like building their home brews...

I think you can start a very interesting thread over there too. But you should make a link to this extreme speed thread though [8D]

RE: Fastest Engine
 

Yes thats a good Idea but I am after a record and have got to keep an edge on them. Theres a lot of other guys going after the same record so Im going to keep this with us if you know what I mean. I told them some specs of one of the JETT motors but didnt tell them what kind it was and let me tell ya, they are icthn to know .

I put some pics of my flat bottom on the first post.
Heres a lil higher res vid that I thought you guys might like also...

[link]http://www.rcuvideos.com/view_video.php?viewkey=3196f05ac29810b924ac[/link]

RE: Fastest Engine
 

Ok, I plan to get the OS 91 fan motor. What do I need to know about tuning and setting this engine up with the pipe . I have read that it is easy to damage a engine getting the tuned pipe right if you dont know what your doing. Are the pipes pre tuned or do they have to be setup?

RE: Fastest Engine
 

Well please check out post #80 and 83 of this thread. Due to the fixed thus liner timing matched pipe length of the JMP 2 you can’t do anything wrong.

It is absolutely necessary to use at least 23% of oil combined with only 5 to 10% of nitro.

A proper break-in procedure though is very important for any high performance engine because the piston fit can be ruined right in the very first start.

So you need a tach that can measure 1-bladed props. The black Dynamax rotor spinner is large enough to locate a painted single white signal stripe (width about 1 cm).

Even at the very first start the engine must run on pipe, that means at about 18000 rpm at full throttle statically. Why? At about 18000 the engine on the one hand is already “on-pipe” on the other hand it still runs very rich (adequate internal cooling). That is optimal for breaking in.

The relatively high combustion temperatures right from the beginning lead the liner and the bordering aluminium housing to expand evenly. So the best operational piston fit is reached as fast as possible (within seconds) to ensure a long piston life. If you would run it at much lower (non-piped) revvs for the first time(s), the liner thermal expansion rate would be minimal and piston wear as well as well as the wear of the liner nickel surface coating would be excessive. This can lead to a busted piston/liner assembly due to lacking compression.

Fortunately the OS 91DF does come with only light piston pinch that reduces the break-in time to about 10 runs at 18000 full thottle, each 1 minute. Let the engine cool down (5 min) between each run.

However, there are also super hard pinched ABC ducted fan engines such like PICCO P90 which I recommend to heat the entire engine head with a heat gun before first flipping the piston over top dead center (TDC).

Usually it is recommendable to use a bladder tank to avoid any bubbles but in your application I believe it is sufficient to take a regular 500 to 800 ml tank which is well packed in soft foam. Pressurized tank is mandatory.

The OS .91 combined with the JMP 2 pipe is very user friendly, I don’t know a ducted fan engine of this size that handles that easy. As mentioned earlier the best insurance for a long engine life is a well visible white smoke trail at full throttle.

RE: Fastest Engine
 

Wow! this thread took off. Hooty, I think your are heading in the right direction. I seems that your have recieved a lot a great and useful info and look forward to your build.
Since Hooty took my flat bottom speed record away from me and want to wish him luck on the top speed build.
Hooty I don't know if you have every seen a picture of the Jap style airboat . They are using a .40 K&B and reached speed a little over 100mph. I have not seen a video but I thought you might like this photo.
http://img.photobucket.com/albums/v6...4/JapBoat1.gif

RE: Fastest Engine
 

That looks a lot like an airplane with no wings...:D[8D]

RE: Fastest Engine
 

Yeah, it looks exactly like an airplane without wings. You could bolt some wings on it and give that horizontal stabilizer an elevator control and you'd have an airplane! I like the inverted vertical stab. doubling as a water-rudder idea that this boat uses. That could be a good idea for float-planes too.

RE: Fastest Engine
 

You could build something very much like that, with a wing on it, and have sort of a modern version of a Schneider Cup trophy racer...[8D]

A pylon racer on floats...:D

RE: Fastest Engine
 

Thanks for sharing Asthmic....that looks very interesting, I may have too look into this one.

RE: Fastest Engine
 

Have you given any consideration of a name for your water craft? One comes to mind.

RE: Fastest Engine
 

No I really havent thought about a name yet, what comes to mind?

RE: Fastest Engine
 

hooty....I have one of those engines if you are interested. ;)

FBD. [8D]

RE: Fastest Engine
 

Name? Well considering that it's a water craft that is pushed along by air and your ID is Hooty, there can only be one choice.


BLOWFISH

RE: Fastest Engine
 

:D

RE: Fastest Engine
 

Hey Dave, yes I am intrested. I left a pm for you.

Thats a good one:D

RE: Fastest Engine
 

....here's the throttle arm that was missing in the picture. No hurry on it Hootie. ;)

FBD. :D

RE: Fastest Engine
 

I think there is an ARF seaplane that does exactly that. Forget the name. Splash? I recall a metallic iron on covering with maybe some blue trim.

RE: Fastest Engine
 

I think I have figured out what I am going to do

A japanese style airboat(the boat pictured above) fitted with a 91fx and a jett muffler. I want to do all my experimenting with this one, get my weight distribution right and soforth. Then build the same style using a ducted fan setup, with the fuselage being the duct.

But first I want to build for the 91fx so I wondering if you guys could help me with some deminsions on the fuselage and floats and anything else I might need to know.

thankyou

RE: Fastest Engine
 

I want to make the length total somewhere between 40 and 50 inchs but am unsure as to what would be the best shape and deminsions of the stabalizer and fin.

What I have in mind is basicly the boat pictured above exept with the fuselage down almost level with the spontoons and the engine sitting up on a pod above the fuselage.

If you guys could help me with the stabalizer and fin I would very much appriceate it. What do the ones used on a good and fast speed purpose built plane look like.

RE: Fastest Engine
 

I have been reading over a couple off threads discussing the 91VR-DF with a prop. Some of the guys make there own props and others cut off the tips on the wood zinger like the one below. I was wondering if there are any other props like the APC that would respond well to cropping in a puller setup.

Edit..the reason I ask this is becouse of water, dont wanna use wood just in case it comes in contact with a mist which would shatter it.

RE: Fastest Engine
 

Well I thought it would only be right that I shared my build with you guys since you have given me alot of good info, help on design and got me thinking in a more aerodynamic way. I went ahaed and got the .91fx which I will use with a tuned exuast and am going to use this engine for testing. Once shes ready for it I plan to bolt on a .91vr-df with a prop.

It will look something like the Eagle X rigger boat on post 55 except with a tail wing and fin. The engine will be on a pod just behind the rear of the sponsons.

I will upload as I go, here is the progress so far, framwork of one of the sposons...

RE: Fastest Engine
 

[8D] I'm looking forward to watching this...[sm=thumbup.gif]