Rigger sponson angles and sizes.

[Ian Inverarity]

Does anyone know of a way to calculate the lift, and maybe drag, of various geometries of sponsons?

Is is better to run narrow sponsons at a higher angle of attack or wide sponsons at lower angles? Which has less drag? For prop walk compensation people reduce the angle of attack on the left sponson. Hammer would make his left sponson riding surface narrower, and I have seen this on SG's as well. both of these work by inducing more drag on the left. ???

Ian.

 

[MikeP]

This is all I could find, Propjockys formula.

--the reason I moved the rear sponsons back was to overcome the inherent drag coefficient that is a product of the sponson's location in relation to the hull's dynamic balance point, considering the !@#$%^&*(<>{}"?>+_)(*WEDRFTGYH 1256+_)(*78sdfg@#$%^gHJ$RTyhjblah, blah,

 

[Propjockey]

DISCLAIMER....

Propjockey Racing will neither confirm nor deny the validity of the aforementioned formula concerning sponson placement in any radio controlled marine craft.

Use of the formula and any adverse effects resulting from use of the formula are the sole responsibility of the end user, and shall in no way be misconstrued as liability on the part of Propjockey Racing.

That being said, it should be understood that the formula was carefully calculated by the Propjockey Racing R&D Division solely for the use of Propjockey Racing. Countless hours of tireless work went into the development of the formula by some of the most dedicated and knowledgable minds in the field.

Propjockey Racing.....you want fries with that? 8)

 

[TomMoorehouse]

Does anyone know of a way to calculate the lift, and maybe drag, of various geometries of sponsons?

Is is better to run narrow sponsons at a higher angle of attack or wide sponsons at lower angles? Which has less drag? For prop walk compensation people reduce the angle of attack on the left sponson. Hammer would make his left sponson riding surface narrower, and I have seen this on SG's as well. both of these work by inducing more drag on the left. ???

Ian.

I don't know of any calculations.....

wide sponson bottoms=better at rough water, narrower=less drag

low attack angle = better at rough waters, higher = less drag and usually more instability.

That only way to figure out what works best is to experimemnt that I know of. Over the years and many designs, myself I find being conservative with the numbers works best....

 

[topfuel443]

Well said PJ

(another useless post for me!)

~ James

PS wade you are not the only one bored at work

:

 

[Ian Inverarity]

Ah yes, I had forgotten the PJ formula! : Silly me!

I was wondering whether the combination of high angle of attack (say about 5 degrees) and narrow riding surface had been tried to minimise drag, but by the sound of it, that combination would not be good in rough water.

Nitrocrazed racing. Trial and error. Mostly error.

 

[Slideblues]

Ian here was my setup for my last rigger, thin long sponsons and tub, Smokin fast for a .12 class,

Well, till Glenn raised the bar a bit 8)

5.5 AOA

Length 24"

Width 8.5 to inside sponsons

Height 1.61" tub tapering aft to 1.33"

Tub 1 degree down angle

Sponsons 2 degree down angle

Gene ;D

 

[EatMyShortsRacing]

Ian,

You really want to go into that depth??? I can let you in on a little secret... THE EMS Racing method.

First start with a piece of ply and draw out your shape using the time calibrated optical micrometer (for those lay persons, the naked eye), glue a piece of foam to it, and use a 3 degree (again can use the TCOM) angle on the ride surface. Width of this surface again can be modified using the TCOM. Build in adjustment in the boat to allow 3-6 degrees angle of attack and take it to the lake.

Adjust to suit.....

EMS Racing Now the real secret is out...

 

[Ian Inverarity]

Craig,

Now your getting too technical for me! Do you take along a hacksaw for fine adjustment to riding surface width? Does this method work for twin 90 hydros? ???

Gene,

So maybe there is something to it? Glenn's boat had quite thin sponsons, I wonder what angle of attack he ran? ???

Nitrocrazed racing: Is PVA glue okay for joining the form to the ply....

 

[EatMyShortsRacing]

Ian,

I carry many fine tuning tools... the 12 oz hammer, the gas axe, and for those permenant adjustments, reverse gear in the SS!!!

EMS Racing Flat boats are faster???

 

[Ian Inverarity]

Craig,

I dont bring a hammer, I would be too temped to use it sometimes!

I have seen people make adjustments to the bottom of monos at a race metting with a rasp file. It worked too! ;D

Nitrocrazed racing: Large shifters can do the trick too...

 

[wavejumper]

I am currently in the same kind of dillema I am also working on an experimental sponson. I hope to have it done this week and you can be sure there will be plenty more of info if it works. Keep your fingers crossed and hopefully all others will be obsolete in the near future.

 

[Ozzy]

Ian

I have a rule of thumb the lighter the boat the lower the angle of atack and the narower the ride surface can be you must have enough width on the ride surface to suport the weight the only exception to this is if you can make moor power.

Ozzy

CHD Racing

 

[Ian Inverarity]

Paul,

I know what you mean, but if I understand it correctly there would be 3 main factors that affect the lift and drag of sponsons: Angle of attack, riding surface width and speed. Increase any of the factors and lift would increase. Drag increases with speed, but what I dont know is how drag increases with riding surface width and angle of attack.

It stands to reason that drag increases if a riding surface is made wider if that riding surface remains at the depth that it was at. However as it gets wider it will make more lift so the length of the riding surface in the water would decrease. What I am wondering is which situation is better for low drag?

At the same time as a riding surface is made narrower it could be increased in angle of attack so that it rides at the same depth. In this case is there more or less drag? Are other problems created in rough water ride etc?

Ian.

 

[TimD]

you know what would be handy on this thread?

Some actual dimensions regarding width for different engine sizes etc. and some weight measurements for the "dry" setup.

 

[Ozzy]

What do you want me to give away all the secreats???

ok ill try to explain it this way a plaining surface at a given speed will have a sertin amount of drag redusing the width of that surface will increas the drag at a given weight increasing the angle of atack will reduse the drag to a point but the side efects are less stabbility.

It stands to reason that drag increases if a riding surface is made wider if that riding surface remains at the depth that it was at. However as it gets wider it will make more lift so the length of the riding surface in the water would decrease. What I am wondering is which situation is better for low drag?

The best posible outcum would be to have a narrow sponson with a low angle of atack at speed but to get the boat to that speed you first have to overcum the drage indused by the narrow riding surface!!,It's a catch 22 sitchuation you can't get one without the other.

Ozzy

CHD Racing

 

[Propjockey]

Sooooooo...would a ride surface that narrowed from front to rear accomplish this?

 

[Ozzy]

Ahhhhhhh so sombody is thinking!!!!! yes this will help but there is always down side increasing the eairia will also increas the aerodinamic lift this can be a problem at high speed it is always a jugaling act.

Ozzy

CHD Racing

 

[Ian Inverarity]

Ozzy,

Yep, I want the secrets. 8)

I could think of a couple ways to achieve the scenario that you describe. A ride pad gives a narrow riding surface at high speed while the rest of the sponson can provide lift for launching. Probably the ride pad depth would have to be 1/4" or more to be really effective and I havent seen any like that!

I have seen pics of narrowing sponsons like PJ describes, at a guess they may also be a little 'darty'. Another way to do the same thing would be suddenly step down the width of the last couple of inches of the sponson so that the riding surface at high speed is narrow, but again the rest of the sponson can do the work at lower speed.

What about the combination of high angle of attack and narrow sponsons? Or is that too harsh in rough conditions? I was thinking this combo would be less affected by aero lift.

Ian.

 

[Ozzy]

Ian

narrow sponson and high angle don't do well in rough water.

The ride pads do work and i have tryed the deeper pads they improved the rough water handling but they did increas the drag .

Steped width riding surfaces i have tryed them but the increased aerodinamic lift wasen't what i wanted.

Keep thinking there are more answers out ther. ??? ???

Ozzy

CHD Racing ;D ;D