A topic to think about

[Carl Van Houten]

Hopefully this upcoming year things can get back to normal.

 

[RonShaw]

Carl, What would you be willing to pay for a factory production Glow Engine Outboard motor?

Its always good to ponder that kind of stuff.. what would you pay for a gallon of fuel?

What would you be willing to pay for a wood tunnel kit or a glass built tunnel.

No need to answer that here.. just good to ask yourself the question from time to time..

then.. what if it were hard to get those goods.. or in some cases it might take weeks, or MONTHS!

A bank account is easer to build then patience!

I suspect cost has had less impact then availability on the health of the hobby. Ron has worked hard to help fill the product void. (thanks Ron) and without people like Ron, Gary, Jerry, Stu, Gabe and many MANY others, we would ALL be staring down at cell phones 24 hours a day.

Merry Christmas All!

Grim

Thank you Grim. At the end of the day its a hobby and a great one at that with really good people!!!

 

[RonShaw]

Hopefully this upcoming year things can get back to normal.

Exactly right Carl. Cant wait to get a boat wet again soon. See you at the tunnel champs. You, Mike n Mike, and Martin will have a free place to stay!!! Just bring seasoning and grilling tools!!!...

 

[Carl Van Houten]

Hopefully we don't have a covid repeat of last year.

 

[Carl Van Houten]

I am going to leave this with you once more for guys that may be thinking about designing their own tunnel boats.

Think of it like a playground seesaw and how you have to use your legs to push your end off the ground when the skinny kid gets on and wants to ride. Its the same thing your engine is having to do when your boats aerodynamics are poorly designed.

Get out there and DESIGN SOME BOATS!!!
-Carl

 

[RonShaw]

Hopefully we don't have a covid repeat of last year.

Exactly

 

[john v]

good article carl but , you need to write a book!. i am collecting all this info and writing it down. a book would be much easier. good thing you dont live near me, i would be over your house every day . lol

 

[Carl Van Houten]

If you are bored and need something to look at while your boss is not in the office, Google search (wing in surface effect ship)

The craft in the video is not a racing design and is not an outboard either but you can see that the short wingspan airfoil has no problem lifting the craft clear of the waters surface. It does have small sponsons at the end of the wings that are similar to the sponsons of a tunnel boat. Some have said in the past that the air foil decks on the new style tunnel boats are not effective and are just for looks and that even if you build an air foil style deck on your tunnel boat the effect would be so slight that you would most likely never know you even did it. Well don't listen to this because it is just wrong.

We all know that the old string-line airplanes with flat wings did in fact fly but they produced no lift until you stalled the wings surface against the direction of air flow and if you have flown one with flat wings boy did it snatch the plane up when you gave it just the slightest amount of Angle Of Attack. That is because you were stalling the entire wings surface with very little AOA required. You may think well this is good right? WRONG! If flat wings were the perfect wing design why has billions of dollars been spent on airfoil shapes over the years and is still continuing today?

If you are planning to design a tunnel boat get ready for learning a lot because there is a life time of things to lean about these boats. When you figure it out you will have a boat design that for one requires very little nose weight. Like everything there will be a sweet spot with aerodynamic advantages and your sweet spot has to fall within your speed requirements. Everyone has had a tunnel boat that is great with a stock motor on it but when you put a good hot modified on that same boat it becomes completely worthless for racing.

-

 

[Terry Keeley]

 

[Grimracer]

Another thing worth noting.. the aircraft Carl describes all have operating control surfaces. The idea with that was to "maintain" ground effect flight.

The Russian's were light years ahead of us on that. I can not imagine that big dam plane honking down on a ship..LOL... in the end the idea (maybe it was timing) never really "got off the ground" with any usable military application.

Cool stuff... i have followed that for a number of years now.... I guy I know Peter Sripol made one from foam.. it "flew" but again.. like the rest.. was just not all that practical.

Grim

 

[Carl Van Houten]

Mike, I agree that it was not a practical design for what they were trying to do with it in the war but the point of bringing the video to the table was to show how much lift can be generated and with hardly any power while in ground effect and is where our tunnel boats live their entire angry little lives.

- Ground effect is trying to peel our tunnel boats off the surface and you have to formulate an over all shape that resist it. Have you ever thought about the cross section shape of our tunnnel boats (cut from front to rear)? There is no conventional wing shape there if you are running ASP's. So why are we going this direction? Most all of our blow off problems that we are trying to overcome is mostly caused from ground effects.

For those who are trying to design your own boats, what you are working with is a lifting body in ground effect oh and if that's not enough to deal with throw in a pillow of trapped air between the sponsons. The trapped air between the sponsons has nothing to do with creating the WIG effect because ground effect is there even without sponsons but the trapped air between the sponsons makes it even more effective for lifting the model.

Some have said designing tunnel boats is easy. If tunnel boats are so easy to design then why are there so few that work correctly?

Terry, Why doesn't your virtual streamlines show the turbulences behind the transom? It should look like spaghetti back there...

 

[Terry Keeley]

I'm sure it is turbulent back there, that simulation just shows the relative speed as the air speeds up over the top and bottom.

I did this to try and create some down force at the transom and from the simulation found an angle that worked. To test it I made a little wedge piece to fill it in, the boat hopped.

Air flow's a huge part of the equation but in my experience anything that touches or is dragged through the water is 100 times more "sensitive".

 

[Carl Van Houten]

My shop is full of molds where I have tried different things over the past 34 years. If you lived close by we could go out there and pull down one hull mold and build two hulls out of that same mold. Then we could pull two different deck molds down and build one out of each. Then put those decks on those identical hulls, rig them and go run them. I will pick the one I want to run . You would be shocked at how different they are.

New Airfish-8 (wig craft)

 

[Kris Flynn]

Carl, can you please show us a deck that did not work compared to one that did? (Same hull)

Then a simple explanation of why it did not work how you wanted it?

I am trying to visualize where and what changes you made to make them so different.

 

[Kris Flynn]

In light of a proper discussion...I would like your honest feedback as to why you think the deck changes did nothing noticeable to my 7.4LB tunnel at 70-75mph, yet removing 4mm (removed approx 20% of pad width, was 19mm) for about 150mm made the boat as stable as anything i have seen before and enabled me to push to 90mph.

Note, i never ran all 3 things shown here at same time, winglets were run 1 at a time (same both sides) at various forward and aft locations with no difference.

I was chasing a nasty "wobble" or "tap dance" at full speed which I tamed down alot by moving my COG forward alot more than i thought i could at first...but could never get rid of what you can still hear and see in my 84.xx ave SAW record passes (see here )

Anyway, very keen to get some feedback if you dont mind typing

Cheers
Kris

 

[Carl Van Houten]

Hello Kris,

First of all thanks for posting pictures of your tunnel boats and video. You have made some cool stuff and fast too. The reason I am posting anything here on this site is to hopefully help promote thinking about "overall design" of tunnel boats.

As far as the proper discussion mentioned, I do sell my boats and what I have learned anyone can do if they would just spend some time working with it. Me and you have both made boats for the R/C hobby and it is good that people can buy a ARTR boat but the down side of buying a boat instead of building a boat and playing with the pros and cons of design concepts is that the "plug & play" racer is not digging into his hobby. I know everybody does not have the "Build Bug" and there are many P&P racers out there that are super competitive and very into this hobby but I would like to see more people building because it is healthy for our hobby.

How many people could go up to the counter at KFC and ask for their recipe and expect the manager to come out and write it down for them? You have the chicken, you know what it taste like so you go home and try to make your own chicken taste as good as theirs or maybe better right? Its the same here.

Q: Does aerodynamics play a role in trim?

You don't have to answer this but just think about what would happen to your boat trim if you removed the "Boat Tail" deck design from your Dragon? Can you really say that nothing would change? Like I said you don't have to answer that here because that is your thing and I am just throwing that out there to think about because I am going to say that based on our experience with that exact feature that it plays a fairly significant aerodynamic role in your specific boat design and setup.

Your models are unique and not just a copy. Your ideas have produced some fast models and show a different way to fry the chicken. You are already doing what we need to see more of in this hobby!

-Carl

 

[LohringMiller]

Mike Bontoft and I did a lot of aerodynamic testing on our various designs. The ground effect is critical and Mike's designs reflect this. One of my articles on high speed boat design describes lift effects. Below are a couple of Mikes record holding boats.

Lohring Miller

 

[Kris Flynn]

Hi Carl.

I offer a free set of plans to an earlier dragon design to hopefully get the "juices going"... i am sure they would be happier to build a Vans Racing design than mine

What do you mean "boat tail" design? Do you mean the drop at the rear in the center section? I "removed" that from the center section with the white blocks...or are you suggesting the sponson tops also?
Cheers

 

[Grimracer]

A boat tail also comes in as well as down (and or up for that matter).. I would qualify your sponons as (rolled).

There are some VERY famous boat tail designs out there.. from the aft end to just the cab or cockpit.. the 1963 Split window Corvette was just one of those.. with.. tada! a rolled deck lid.

Dragon COREVETTE! (yea.. its a stretch.. BUT..I am a vette lover...) LOL

Grim

 

[Carl Van Houten]

Kris,
I have seen a lot of your boats around the South. I only make wood kits for prototyping these days.
Boat Tail is a term used by ammo manufacturers and it comes from the design of the bullets. If the rear of the bullet tapers down we call those bullets boat tails.

I am a reloader. My dad was a big time reloader because he shot so much it was too expensive to buy ready made ammo.

Any drop of the deck at the rear of a boat we call those types of features boat tails.