Rigger Angle of Atack (AOA)

[larryrose11]

Team,
I just got a new rigger, a Ecomaster Hydro 1.
The boat came to me set up, and the AOA is 6.5 Degrees. Is this too much? What should I expect?
What should the sponsons angle of atack (AOA) be? I have seen some say that 2.8 degrees is stable, 3 degrees is fast, over 3 degrees is fast but too loose.
What is everyones expirence?
Larry

[NativePaul]

It depends on the boat and what you want to do with it. As yours came set up, try it out as is, Gromov is a multiple world champion and knows what he is doing. If your use case is similar to his, it will probably be pretty darned good.

I have heard 3-5 for SAWs and 5-10 for racing.

I used to start with 5 degrees for Naviga racing (what the Ecomaster was designed for) but always went up, and have switched to starting at 6 degrees, once off the building board I don't measure them so I couldn't tell you what I am actually running. I go up on the AoA till I get the pitter patter, move the CoG forwards to stop the pitter patter till the tail hops, then go back a bit to calm the tail, and go up on the AoA again till the pitter patter comes back and back down with the AoA till it goes away.

For SAWs I go with 4 degrees and I haven't built an adjustable SAWs boat, I haven't run into incurable pitter patter yet, so could probably go up as out SAWs speeds are lower here than they are in many other places, but I don't want to chance it as I like getting my boats back.

[RayR]

Depends on the boat. The JAE .21 size boat is 4.0 Degree's, the KEPS .21 size boat is 3.9 Degree's.

[larryrose11]

Paul,
What to you mean by 'pitter patter'

As for use case, Gromov is racing in EU with energy constraints and min run time.
I don't plan on that at all, and just want to go a fast as I can and still corner well for 3 min or so.

[larryrose11]

Putting info I found out on the web to make the forum better.

Aerodynamics of High-Speed Sponsons

rigger get to flighty,can changing front sponson attack angle fix it?

My Rigger has the hops

How to set outrigger angles

May be useful for setting up a rigger AOA and CG

Outrigger Hydro Turning Dynamics

[NativePaul]

Pitter patter is when a hydro has too much lift for the speed and/or the weight at the front, at the edge of a blowover it dances from sponson to sponson, spilling the air out from underneath the sponson as it increases roll angle which drops the sponson, and pivoting around the longditudinal CoG the opposite side raises till it spills the air, and drops, which raises the fist side, etc, etc, forever, or until either speed is reduced or a blowover occurs. It is an similar effect to chine walk in monos, and it probably has an proper name but I didn't go to school for fluid dynamics and don't know it, It makes a pitter patter noise like a seagull catching worms, or rain on a tin can, so my buddies and I call it pitter patter.

how set up did it come, are you using a Naviga sized motor 2860 ish or something bigger? I don't think you will fit 2p in it, so with a similar battery size and half the run time you could be making double the power, if you are at anything like similar weight you will want to reduce the lift a lot and reducing the AoA will certainly help with that, you might want to drop the strut too in order to run the tub flatter, IIRC this hull has a molded in off centre ski, if so you might want to build up the ski to go along with the increased strut depth.

If you alter the weight or balance much from intended, it may no longer be able to self-right, or you may have to add extra ballast or buoyancy to keep that feature.

This hull was designed and built for efficiency in the mid 50 mph range, with double the power you could be pushing it into the high 60s or low 70s you may want to consider reinforcement as any crashes will carry much more energy at these higher speeds even if the weight is the same. I know you have it already now, but for future reference Gromov is happy to add extra glass for a stronger layup on request.

[larryrose11]

Paul, It only came with hardware.
I was going to try something different. A TP 2935 (29.5 x 62 mm, 156 g) 1680 KV, a Castle 130 Light (water cool mod), and two 2200mha 3s batteries in series. It puts the weight about the same, batteries are 50 grams over spec.
I also have the option of moving up to a Neu 1115, 2184 KV, same setup and a small prop.

[eXoNerated]

Hi Larry,
The papers direction on the aerodynamics as it examines sponson design of one of the most experienced model boat makers in the game, Andy Brown. The Mongoose then the Eagles spoke for themselves. Theory is very useful but Andys work is empirically proven however later the JAE releases the flat plane technology and many scratchbuilders built from plans as the speed was there. The Keps rigger is the extension of flat plane technology. A better handling boat in my humble opinion. It seems to have amended the JAE flat plane sponsons and moved toward a better aerodynamic direction. I would build upon This using the 2014 thesis as a guide. A combination of the flat plane technology and tear drop aerodynamic shape would be the area of positive research. You could consider designing a symmetrical 3D sponson with a speed wing profile that has a channel to except a narrow flat plane shoe. If you make a detachable flat plane shoe you could have different angles shoes in a modular design.

Regards,
Hubert