du-groundeffect

Hey guys, why not adopt the attitude that the "lowly" airboat can go faster than a regular hydro? That roostertail may look impressive, but it represents a lot of wasted energy! How about an attempt at beating some of the existing hydro records? The Japanese craft show what can be done... It would be fun to set up some "rules" that we could adopt, and then go for it!

Paul and Joe Rice

Mr Cajun Gator

So for all of my airboats have been built to climb hills run the ground, and to play with in the back yard. But that is a spark, and I have a bucket of fuel in my hand. I do believe that a record can be made. After it is done, making it recognized will be the hard part, since in their rule book it states that it must use water to propel it.
I have room to start another project, and I will give it some thought. One question, what is the highest rpm that a prop can turn?

du-groundeffect

Hi haljmac,

What I had in mind was to make a point that for a given engine size you could go faster with an air driven craft than with a water prop. Certainly the water prop records would not be replaced, just compared to a comparably powered airboat. The challenge would be to compare speeds over a typical oval course and also a straight-away course. In the process, we could compare our airboat speeds and lap times via internet posts. Videos could be used to measure time between bouys of a known spacing, or some other agreed upon method. I'm sure we would all learn some new tricks in the process, besides expanding our fun!

Maximum prop speeds? Oh boy, they can get really wild! If you were flying a piped 2.5 cc speed plane with a single blade prop with a radius of 2-1/2", the revs can approach 40,000 rpm! On the tamer side, a hot 6.5 cc engine will turn a 9" x 6" two blade at about 20,000 rpm. One of our latest airboats uses an old Super Tiger .40 that turns a 9" x 6" prop at less than 15,000, and it works fine. We tend to avoid large diameter props, just to keep the CG lower. What prop sizes and rpms are you used to turning?

Bsmooth

well lets just define "airboat" here. Are we saying that it is simply a craft which rides on a surface of water propelled by a prop in the air? It could be possible to make a hydrofoil which uses a air prop to go REALLY FAST[sm=bananahead.gif]

du-groundeffect

Hi Bsmooth,

As to what types of craft qualify as "airboats", I agree with pro27; anything driven by an air propeller is an airboat. As different craft emerge, and especially if there were a lot of participation (wouldn't that be nice!), special classes could be recognized if there was a considerable difference in performance. But in the beginning, we should encourage as much inovation as possible... It would be a lot of fun to see what develops!

Mr Cajun Gator

this is what I have in mind, I have a .61 rossi, that has been mod into a .65. The only downfall I have is it has a water cooled head, not much of a problem because we are taking water speeds. I am not sure of the HP this engine is pushing, but I'm sure its a lot more than any regular aircraft engine. I was asking about what is the rpm's a prop can handle because this engines turns in the range of 36,000 - 38,000.
I started the hull on autoCad, working on the design, so for I'm having a good feeling about it. I'm still working on the drop engine stand(DES), and if I can get it to hold up to the torque and HP of this engine I will go with it.
The hull design is based on the outrigger, which is the hull that holds the top speed records. Its going to take some adapting to get it set up to run on the water, since it will be getting its force from the front of the hull instead of the rear.
I will need help on what would be the best prop. which will hold up, which will be the most efficient, what style will cut through the air easy. With water props I have a complete understanding of the physics of what happens as it passes through the water. Air and water props, the basics are the same, but we need more than just the basics.

Mr Cajun Gator

IDEA!!!!
Would need a pusher prop. That makes another????, what options are there?

du-groundeffect

Hey haljmac, that is some Rossi .61! I can imagine the engine might hold together at over 30,000 rpm, but what about maximum power? If you were going to try an run a prop at that speed I'm sure you would looking at a ducted fan. Or, you might be able to run a speed reduction...some belts can go to quite high speed. As for the head, why not trade the watercooled head for an airplane or car head? You would be able to eliminate the possibility of losing cooling if the pickup came out of the water, as well as the extra drag. Sounds like a hot project!

Mr Cajun Gator

Wrong RPM's, the 36,000 - 38,000 are for my cmb, sorry about that. the R's for the .61 are 28,000 -30,000 rpm's. Where is the best place on ducted fans?

du-groundeffect

Most ducted fans are made for engines in the .60 to .90 size range, commonly used in jet aircraft models. Those engines usually run around 20,000 to 25,000 rpm. On the smaller size, OS makes a .46 ducted fan engine rated at 2.5 bhp @ 23,000 rpm. A ducted fan arrangement would make a lot of sense for a really high speed airboat due to the low CG. You wouldn't have the low speed thrust of a prop, but who cares if you're shoot'n for 100 mph?

Mr Cajun Gator

I was just checking out the ducted fan units, come across one that has a .91 engine, stated that it holds a record of 225MPH. Water and air resistance, big difference. The price tag on this set up is just under $1,000.00 Never the less I will still start on the hull, then maybe one day I'll be able to afford it. I'll have a lot of time to work on the hull.

du-groundeffect

Yes, those ducted fan units are expensive, all right. As an alternative, you might consider if a three blade prop of say 9" dia. and around 8" pitch would work on your engine. It would be cheap enough to experiment with. Master Airscrew makes a 9 x 7 three blade that sells for $7. Just buy it, fire up the engine and see what it will turn. You might be lucky! As for the water drag, If you design it just right you won't even touch the water anyway!

Good luck!

pro27

As far as props go (speaking from my peevious life as an U-control speed and combat flyer) you can throw out the MA's and go with APC or Bolly if you can find them. They are a pain in the Ass to work with (re-pitch, taper, tip mods and tip shapes) but there are few props stillout thre you can do this with and get away with it. You are looking for rpm, in the purest sense. Small diameter with a barn door of pitch. ( Super Tiger x15 with a 6.5d x 11 pitch flown at the Dayton Ohio AMA Nationals in 1976) Have no clue what the speed freaks are using these days.

pro27

Here is a list of something to shoot for...........

http://www.namba.com/web2001/records/Straightline.pdf

Mr Cajun Gator

IMPBA records are higher, the record was 120 set by nitro rigger, and now set by an electric at 122. Breaking that would put the airboat on the table. But IMPBA nor NAMBA will reconize that there record has been broke. And it will be hard next to impossible. The water has a stronger force and much more of the HP is used, the air less force much of the HP wasted. (cavation)

brother

Hi, There is a guy in Seattle, Wa. that designed a full sized craft that rides on a cushion of air, it's not a hovercraft. It has no air bag and uses an air prop, I can't remember all the details but I will try to find out more. Sorry for being so vague. If cavitation is a problem could this be the answer? The craft appeared to be about as wide as it was long, and looked similar to a delta wing that curved down. I want to say it used air rudders and an elevator, but I can't remember. Brother

du-groundeffect

Hi Pro,

I agree, Master Airscrew is not known for speed performance; APC would be a better choice. APC makes a 9x6 three blade, which might be about right for the Rossi .61. I have a rear rotor K&B 6.5 that turns a two blade 9x6 at 20,000 on 10% nitro; assuming the Rossi .61 had about 50% more power, it should turn similar speed with a three blade 9x6. In any case, testing a few props would be well worth the effort if the object was to avoid the high cost of the ducted fan unit.

du-groundeffect

Hi brother,

What you saw could have been the Klem Outrider 27 which rides on an air cushion and uses a surface drive, or possibly the Flarecraft L-325 which uses an air prop and is a true "WIG" (Wing In Ground) effect craft. That's the type of craft I've been experimenting with, and show on my web site. The models are fast, just tricky to keep in ground effect. We've had good success using a fixed elevator to adjust trim.

du-groundeffect

Like I mentioned before, water drag can be essentially eliminated if you make use of ram air pressure, and "fly" just above the surface. Full-size experimental craft are classified as "boats" as long as they can not fly out of ground effect.

brother

Du-ground, I would like to check out your web site, would you mind posting your web address? I have been tossing around the idea of building a WIG, a freind and I have been discussing possibe designs. I've considered a delta wing configuration or even modifying the Crusader that was built in the "50's" by the British. It sounds like you have experience in this area what do you think? Brother

du-groundeffect

Hi Brother,

My website address is http://www.du-groundeffect.com There are some links to other sites that you may find interesting too. We have some video clips of some of our test runs. Thanks for inquiring, and good luck with your projects!

Paul and Joe Rice

du-groundeffect

pro27,

Thanks for posting the namba records. Several of them look like interesting "targets", such as the A, B, C, X, and Unlimited Hydro. Anyone that builds an airboat that comes close to those speeds with a similar engine will definitely be noticed! I can imagine that RCBM would be more than happy to publish an article about the "evolution" in air boating! You never know, maybe a new market would emerge if the public saw the possibilities. No longer would the airboat be considered "lowly"!

TERBObob

My Feedback: (21)

[&o]
Speed isn't everything and I sure hope this forum , doesn't turn out like the BOAT DOCK , where everything is SPEED , SPEED and ONLY speed .
Fast is good , but lets not take the FUN out of this , ok guys ? Once the "fun" if gone , then so is the "wants" for new blood . Why ? Well , you only then want to be competitive and then we start talking HIGH DOLLAR hardware , and equipment . Take for example what has happened to water propelled boats . Fun ? Yeah ... but most of the boards now are only concerned with the "speeds" and the "clubs" ... the FUN BOATER has lost his place. Then the "newbie" is not going to get involved , since he will then need some HIGH dollar hardware and other misc items . ( Why am I saying high dollar ? again , look at water propelled boats and some of their hardware - $40.00 for a rudder ? $150.00 for a tuned pipe ( which only costs probably no more than $15.00 to make )
And does it REALLY matter if IMBA NAMBA or the other clubs recognizes airboats ?
Getting more folks interested in airboats is ALWAYS a super idea , but I don't think , at the expense of having to worry about the "clubs" recognizing airboats .... And then having to "join" one of them , pay them "due's" , so you can run on a local pond/lake and have to follow "their" rules .... ( Well , there went all the fun ! )
Again , fast is GREAT , but lets not solely dedicate ourselves to worring about HOW FAST , or about BREAKING records ...
If it happens ---- GREAT ... but if not .... oh well !
Right now , a fellow can build an airboat with next to nothing for cash , but start "breaking" speed records , and I GUARANTEE , those prices for items needed , will no longer be "cheap" and the fellow who "makes" his own , or own design , will get laughed at ( just like in water propelled boating ) and loose interest REAL fast ! ( unless of course , his/her pockets are deep ! )
Lets keep this a "hobby" and leave the record-breakers to the "racers" in those "clubs" . If , someday , this DOES come to that , then so be-it , but for now ... being such a OPEN form of RC'ing , lets try and keep it that way ...
With airboating the way it currently is .. the ONLY two requirements are - HAVE FUN and BE SAFE while doing it ! No hull size max or min , no motor size specs , no prop size specs ... etc , etc , etc .

( now , ya think I didn't know when I wrote this that I would get some kind of rebuttal ?? Sorry , but , yeah ... I DO expect it [8D] )

Mr Cajun Gator

Well SAID, thumbs UP. I do agree.
Myself this is for us guys that run airboats. I run my race boats witht he guys at the club, fact I was there today, after being gone for over a month, yes you are right it is hard to have a good time. My air boats I love them. I get my most enjoyment not from the speed of my boats, because they are not fast, but from the fact that I can run where the trucks and the water props boats go and then some. But I do want to see a air boat have all out speed, show that it can be done gain some respect then get back into running the ground, sliding across the water(frozzen in some places(ya, picking again)) and JUMPing the levee. Why?? Because!!! We ARE airboaters and we can do that!!!!

pro27

As far as the whole SPEED thing is concerned, I would like to try and design a hull with the right motor combination to go as fast as I could, just to try it. Not looking to making a record, getting my name published in a mag or something, but for my own satisfaction[8D]

I could probably satisfy this need for under $200 ( the bay and other swap boards) and not take a loss in the fun factor cause it would not be taken seriously by myself.

We are a diversified group here. Some like the gassers, and some like myself, prefer the .20 and under size. I am not going to trash someone because they don't like my engine choice. I like to run my airboats more on open water while a lot of you like to do the jumping levee thing and trim your shrubs with yours ( sorry Slayer.....just HAD to put that one in there)

We should be able to laugh at ourselves as well as others, but be able to learn from each other as well. That is one thing that I feel is setting us apart from most other type boaters, we don't take it seriously, and we have the most fun

I myself do not have the need for competition at an organized level, but when my friends and I get together at the water hole, you can bet there will be some FRIENDLY competition as well as some hull rubbing going on. All in the name of fun.

I don't think I have ever spent more than $200 on any airboat I have ever built! Am I a cheap A**? Or am I just having some fun ?