1/8 Scale nitro - tunnel design

[dschigoda]

I am thinking about modifying a 1/8 Scale nitro hydro design. Its an early '80s pickle fork hull (1983 Miss Renault). Does the location of the "break" in the tunnel bottom, and the angle of attack of the front portion of the tunnel have much of an effect on the running attitude and lap speed of the boat? [This is assuming I have a decent motor, driveline, light hull, and driving skills].

In looking at the Newton scale plans it seems to me that the angle and height of the front portion of the tunnel is higher that it would need to be for a light "wood and foam" 1/8 scale nitro hull.

[Or maybe my vision of hydro design is tainted by my rigger design experience?]

Or maybe it doesn't matter - because the sponson angle, strut angle, and prop type have more of an affect on the running attitude?

Has anyone experimented with less tunnel angle and changed break point (forward)? Any general conclusions?

Dave

 

[Russell Bear]

I am thinking about modifying a 1/8 Scale nitro hydro design. Its an early '80s pickle fork hull (1983 Miss Renault). Does the location of the "break" in the tunnel bottom, and the angle of attack of the front portion of the tunnel have much of an effect on the running attitude and lap speed of the boat? [This is assuming I have a decent motor, driveline, light hull, and driving skills].

In looking at the Newton scale plans it seems to me that the angle and height of the front portion of the tunnel is higher that it would need to be for a light "wood and foam" 1/8 scale nitro hull.

[Or maybe my vision of hydro design is tainted by my rigger design experience?]

Or maybe it doesn't matter - because the sponson angle, strut angle, and prop type have more of an affect on the running attitude?

Has anyone experimented with less tunnel angle and changed break point (forward)? Any general conclusions?

Dave

I don't know all the theory behind it, but I can speak from experience. I built my scale from Newton plans and it also has a high AOA on the hull bottom. I couldn't keep it on the water without blowing over. Placed a small bow spoiler underneath and the problem went away. I would definitely make it shallower.

 

[Don Ferrette]

I don't know all the theory behind it, but I can speak from experience. I built my scale from Newton plans and it also has a high AOA on the hull bottom. I couldn't keep it on the water without blowing over. Placed a small bow spoiler underneath and the problem went away. I would definitely make it shallower.

That's one of the problems with scaled drawings of the real boats. On the big boats they need to pack air under them to "float" the hull, especially pre-turbine hulls. For us it's exactly the opposite as we need to get rid of most of that air pressure. Earlier style boats that incorporate high bottom AOA & air traps rails at the bottom edge of non trips should get reworked to eliminate much of that when doing the model. Think about it & do the math, an 1/8th scale running at 60 mph is equivelent to the real thing running 480 mph.

 

[Duck899]

I am thinking about modifying a 1/8 Scale nitro hydro design. Its an early '80s pickle fork hull (1983 Miss Renault). Does the location of the "break" in the tunnel bottom, and the angle of attack of the front portion of the tunnel have much of an effect on the running attitude and lap speed of the boat? [This is assuming I have a decent motor, driveline, light hull, and driving skills].

In looking at the Newton scale plans it seems to me that the angle and height of the front portion of the tunnel is higher that it would need to be for a light "wood and foam" 1/8 scale nitro hull.

[Or maybe my vision of hydro design is tainted by my rigger design experience?]

Or maybe it doesn't matter - because the sponson angle, strut angle, and prop type have more of an affect on the running attitude?

Has anyone experimented with less tunnel angle and changed break point (forward)? Any general conclusions?

Dave

If your going to go that far.....Take a look at the top of the hull as well....In particular, the angle of the tops of the sponsons from the sponson rear area to the tips of the sponsons and how they are when the hull is positioned at 0 degrees incidence (measured underneath from the sponson rears to the transom). If you can get some sort of negative 'rake' here it will help to hold the front end down at speed. Kinda tricky though as you have to adjust the angles of the bottom-sides so you do not lose length at the fronts of the sponsons.....

One of the guys here did that to his 1982 Pay n' Pak when he built the boat in 1983 and it still runs competitivley to this day....

There is a side shot of the 82 Pak in my gallery where you can see the effect of the tipped down sponsons....It holds the water very nice vs his older 1980 Pak which took flight quite regularily.....Hence the redesign.....I believe they were both Newton designs as well untill the mods to the plans for the 82 version.

 

[dschigoda]

Thanks guys! It sounds like I'm thinking along the right track. I had not thought about the angle of the top deck of the sponsons. Hmmmm.