Eagle SGX/Rigger Tech 101

[Ian Inverarity]

Tom,

Yep, those were the pics I saw. Altho looking closely it is not the same boat as Anders showed, it has a different tub and different sponsons. But they do look to be built by the same person!

Ian.

 

[Slideblues]

The pic I remember had Andy holding the SAW rigger, I honestly cant remember if it had the dual booms or not ???

Gene ;D

 

[Ian Inverarity]

Gene,

Do you mean this one? At the top? Single booms there.

http://www.cmdracing.com/updated/race_report.htm

Hang on, wasn't this thread supposed to be about the sponson layout of the heat racing boats, not Andy Brown's SAW boats???? ???

Ian.

 

[Slideblues]

Yeah that's more like the one I remember, any how Ian's right, What do ya think, Rears or no Rears, sponsons that is!!!!!

Thanks Guys for the pics

Gene ;D

 

[Ian Inverarity]

Gene,

Many of the twin 90 boats in Australia currently have no rear sponsons. There is also a very successful 45 hydro that has no rear sponsons and uses a round bottom strut.

If I had to guess I would say it relates to weight distribution and CG. The SG's tend to have a CG more towards the rear of the boat and runs the sponson deeper than the strut, so it needs the sponson to help support the rear. At speed the prop still lifts them out on many boats tho. The boats I have seen without rear sponsons probably have a more forward CG, and many have downforce generating front sponsons and canopies.

Other hulls with forward CG's, like the Avenger Spider Cobra or Hummingbird, have rear sponsons but have the strut deeper than the sponsons so that they are lifted from the water at speed. I read in one of John Finch's books that the rear sponsons give a better ride with a consistent attitude in corners.

Ian.

 

[EatMyShortsRacing]

My last 45 Stinger (Aussie Stinger) was originally made with no rear sponsons. I added them once I started having cornering problems. I didnt see any loss of pace by adding them. With the design of those boats the rear sponsons will aso provide more downforce in the rear of the boat. So here I am confused as to whether the rear sponsons actually changed the ride height of the boat at the rear... The sponsons were about 2mm above the bottom of the strut.

I was also considering trying to run the strut a lilttle lower in my 45SG to get the rear sponsons (no centre sponson installed although it came with the boat) out of the water in the straights. Any SG owners tried this??? I would imagine you have to adjust the front sponsons a little to maintain the angle of attack but if you are only raising the tail one or 2mm That may not affect the boat too much??

The Aussies here will know my new 45 SG has only hit the water for the duration of the Australian Nationals so I am not claiming I have had a lot of time setting up this boat (new engine A45 Hydro as well) so there are a lot of unknowns for me. I think the first thing will be getting the engine going hard (and using a pipe that will allow me to hear the engine!!! LOL)..

EMS Racing More buck for your bang!!!

 

[TimD]

I was also considering trying to run the strut a lilttle lower in my 45SG to get the rear sponsons (no centre sponson installed although it came with the boat) out of the water in the straights. Any SG owners tried this??? I would imagine you have to adjust the front sponsons a little to maintain the angle of attack but if you are only raising the tail one or 2mm That may not affect the boat too much??

EMS Racing More buck for your bang!!!

Craig,

A lot of the guys running SG's are building them without the centre sponson to avoid the "SG HOP" in the turns. I built mine with the sponson for the simple reason that it allows the bigger props to unload at slower speeds and launch. ;D

I think that for SAW stuff that the single centre sponson would work well for that reason (turns aren't an issue).

The drag from the centre sponson verses two outer sponsons should be less I would guess.....

 

[Slideblues]

Ok, Tim brought up hopping, What about sliding and hooking? The secret world of turn fin design and placement? As far as Straight, Swept-Back, Curved in, Sharpen one side,

And placement, On the sponson, On a arm extending from the sponson, At the CG, A little before or after the CG, Ya get the idea,

Gene ;D

 

[Anders_Martinelle]

Well guys , the photo was taken of me when i asked Andy to bring his boat that he ran 126mph with to the Winter Nationals last year??

The boat that is a look alike is his older boat but he wrecked it some time ago....

Before that he had his blue SG45 as a saw boat.

Mr "Slideblues" the other pic you had is from the WC in Polen and that IS his SGX that he won the 45 class with.

Gene, i think this is the photo youre looking for.

Anders

 

[Anders_Martinelle]

And the engine is a Picco 80.

Anders

 

[Anders_Martinelle]

To continue the sponson question, my 2 cents???

NO rears.

Anders

 

[Slideblues]

Anders,

Yes thats the one, thanks for posting it !!!!

Sorry for my confusion with the WC boat,

Gene ;D

 

[TimD]

Ok, Tim brought up hopping, What about sliding and hooking? The secret world of turn fin design and placement? As far as Straight, Swept-Back, Curved in, Sharpen one side,

And placement, On the sponson, On a arm extending from the sponson, At the CG, A little before or after the CG, Ya get the idea,

Gene ;D

Are we still talking about SAW stuff or have we moved on to Oval racing?

 

[Slideblues]

I think it would be safe to say that if your runnin SAW center sponson and no rear's is the hot ticket, So

Its Oval time Dude !!!!!

Gene ;D

 

[TimD]

OK Gener,

Turnfins can make or break an oval racing boat - Hey Dale!!!

The only way to get it really dialed is to take a few different fins to the pond with you and try different things. With Dales boat we took 4 fins - all the same size and shape and just tried different bend angles and found the right one. Now the boat has lost it's tendency to pull the inside sponson under in the entry to the turn. It is still not perfect but it was good enough to win our nationals ;D We still have a few other things to try on that boat.

My SG just turns like it's on rails with the stock turnfin - I have not touched it at all. I had to turn the rates down on the radio by a long, long way. Waiting for the new motor before I make any changes to the setup so I can see the differences the power has on it.

Tim.

 

[Ian Inverarity]

On the subject of rear sponson/strut configuration, one idea I came up with a few years ago before I saw a single rear sponson was to curve the flex off to the left and have the strut coming out of the back of the left rear sponson. ie no external stuffing tube, it is contained within the left sponson.

This would give a boat with the fairly standard two sponson configuration, but without the aerodynamic and hydrodynamic drag of the stuffing tube etc, and the 'shading' of the prop effect that allows the launching of big props. Of course such a design only really suits narrow boats with sponsons under the tub like Mike P and Hammer's designs.

I never had the opportunity to try it tho, so it might be complete rubbish! ;D

Ian.

 

[Ian Inverarity]

On the subject of turn fins, I am no expert but I have tried a few things. The curvature of the fin is very important. When I was trying to tame my first edition 45 SG I made a fin of the same size and shape, but put a single bend in the bottom to approximately the average angle of the multiple bends of the stock fin. Thus only the bend was changed from the original fin. The boat was totally different. It needed more rudder to turn the corners, so it was less efficient, but it also made the boat more predictable. Unfortunately I destroyed the fin before I ever raced it, so I couldn't fully evaluate it. The down side to these highly curved fins seems to be an even higher aversion to going left!

The sharpen one side bit is a method of compenstating for prop walk. It works best as a bevel, but I like to blend out the bevel on the lower bent sections to reduce the lift caused by the bevel. I have only recently started doing this, but seemed to work well on my 90 Hummingbird before the sponson got out of alignment!

I think I read somewhere that Andy Brown said the swept back is purely so the fin rides over hard objects in the water! :

I have noticed that more modern designed outriggers have larger turn fins. My 45 SG turn fin had a similar are to my 90 Cobra! The fin on my Hummingbird is huge considering the size and weight of the boat. I think this is because the boat designers worked out that the extra drag of a larger fin is more than offset by the extra speed retained in corners!

Tim,

'Tis better to reduce the rates by moving the links on the servo and tiller arm than to wind the rates back on the radio.....

Ian.

 

[TimD]

Tim,

'Tis better to reduce the rates by moving the links on the servo and tiller arm than to wind the rates back on the radio.....

Ian.

Ian,

I did that when I built it ;D there is hardly any rudder movement on that thing and it still turned on a dime. Last resort was turning down the rates. That made it more drivable. Maybe my rudder is too long - it is at the same depth as the 5 other SG's I measured at the Nat's.

Tim.

 

[Ian Inverarity]

Tim,

I would not cut the rudder shorter, I think that was one of the problems I had with my 45 SG. If I had to correct left the turn fin seemed to somehow cause the back of the boat to lift and hop, then the rudder came out and it would spin! No fun at all....

Ian.

 

[Twin_k90]

Timbo/Ian,

turn fins are where it is make or break, my fin is too small now, having to apply too much rudder to make it around the turns and thats what is washing off the speed,

im going to make a fin like the one that Ian sent me, but with one bend and then some other shapes with different types of bends etc in them, ill find one eventually!!

Dale