NAMBA / IMPBA Tunnel Rules - Extra wings and spoilers OK?

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Christian Holmstedt

Well-Known Member
Joined
Jun 14, 2014
Messages
63
Straight question:

Do the rules allow for additional wings and spoilers to be added to a tunnel hull?

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Current IMPBA Outboard rules:

VII - Outboard rules

A. Engine and Hull Specifications

1: There are two outboard classes - tunnel and Hydro (Outrigger)

2: There are six engine classes - A, B, C, D, E and F

3: The tunnel outboard classes shall not lock down the engines nor use an auxiliary sterring system

4: The hydro outboard classes may lock down engine and steer by an auxiliary sterring system.

So to answer your question, it's not against the rules..
 
From the NAMBA rulebook:

Tunnel hulls will be of a tunnel configuration with no restriction as to size, weight, or
type of construction. A hull will be classified as a tunnel if it meets the following
requirements:
a. The general design of the tunnel hull should follow as closely as possible to
the design of the full sized OPC tunnel hulls.
b. The hulls will be stand-off scale, with no restrictions as to canted sponsons,
tunnel dihedral, air traps, strakes, stern stabilizing fins, etc.
c. Imaginative painting, striping, company logos, and lettering schemes may be
added and are encouraged.

d. A close to scale driver with at least the head and shoulders must be provided
unless proof of a reclining driver is offered as in OPC hulls. Boats without
drivers must be painted to include a darkened windshield to resemble a
closed-in cowl appearance.
e. The tunnel may be of any design, width, or depth, but must run the full length
of the hull.
f. The tunnel must connect two outer hulls or sponsons which are unbroken and
must also run the full length of the hull. Picklefork designs are acceptable.
Outrigger configurations are not acceptable.
g. Sponsons may be of any design and may include stepped surfaces on the
wetted running sponson bottom of not more than 1/8" in depth. The 1/8" steps
may not be less than 5" apart if used across the sponson. Only one step may be
used if used lengthwise on the sponson.

h. No hull will be allowed to have a recessed or picklefork bow which exceeds
30 percent of the overall boat length. Airslots in the center hull must be
subtracted from the overall hull length.

From part b I would assume small wings are allowed. I've seen tunnels raced with both front wings between the sponsons and rear wings over the center section. These pictures of Rod Geraghty's tunnel shows an innovative design that I'm sure could qualify anywhere.

Lohring Miller

Geraghty 3.5 tunnel.JPG Geraghty 3.5 tunnel1.JPG
 
LohringMiller said:
From the NAMBA rulebook:

Tunnel hulls will be of a tunnel configuration with no restriction as to size, weight, or

type of construction. A hull will be classified as a tunnel if it meets the following

requirements:

a. The general design of the tunnel hull should follow as closely as possible to

the design of the full sized OPC tunnel hulls.

b. The hulls will be stand-off scale, with no restrictions as to canted sponsons,

tunnel dihedral, air traps, strakes, stern stabilizing fins, etc.

c. Imaginative painting, striping, company logos, and lettering schemes may be

added and are encouraged.

d. A close to scale driver with at least the head and shoulders must be provided

unless proof of a reclining driver is offered as in OPC hulls. Boats without

drivers must be painted to include a darkened windshield to resemble a

closed-in cowl appearance.

e. The tunnel may be of any design, width, or depth, but must run the full length

of the hull.

f. The tunnel must connect two outer hulls or sponsons which are unbroken and

must also run the full length of the hull. Picklefork designs are acceptable.

Outrigger configurations are not acceptable.

g. Sponsons may be of any design and may include stepped surfaces on the

wetted running sponson bottom of not more than 1/8" in depth. The 1/8" steps

may not be less than 5" apart if used across the sponson. Only one step may be

used if used lengthwise on the sponson.

h. No hull will be allowed to have a recessed or picklefork bow which exceeds

30 percent of the overall boat length. Airslots in the center hull must be

subtracted from the overall hull length.

From part b I would assume small wings are allowed. I've seen tunnels raced with both front wings between the sponsons and rear wings over the center section. These pictures of Rod Geraghty's tunnel shows an innovative design that I'm sure could qualify anywhere.

Lohring Miller

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Geraghty 3.5 tunnel.JPG
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Geraghty 3.5 tunnel1.JPG
Click to expand...
E. and F. seem confusing to me.

After reading H., I gather that the "length of the hull" could actually be up to 30% less than the total length of the boat.

What about inset transom/tunnel floor? Does it figure in with the 30% rule just as a center airslot?
 
Thanks for the answers and yes, points E and F are somewhat contradictory.

So other than that auxiliary wings are allowed even if the intent of the rules seems to be in favor of having boats look scale.

I got some ideas I'm working on and wanted to make sure those are not dead-ends.

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You are right. I think the original idea was to reproduce a scale look. However, the Tommy Lee XT-460 had an inset transom and there is no limit to that unlike pickle forks. Inset transoms can only be taken so far since you want the wing's lift as far back as possible. All the measuring rulings I've seen used the overall length between perpendiculars as the length. This is an issue with electric tunnels length restrictions. It means that the hull length is the total sponson length.

In NAMBA there have been a lot of non scale tunnels tried. Front and rear wings turned out not to help much except on SAW boats. I believe Jimmy Johnson's record holding tunnel still uses an adjustable front wing mounted on the cockpit sides. With modern gyro stabilization I would expect a front wing to be useful, but I don't know of any testing. Then there's the question of does the front wing count in the pickle fork calculation? What's the difference between a front wing and a slotted center section?

Lohring Miller
 
Very useful clarifications here.
Max length for a P-Class tunnel is 34" from what can understand, and that would be including the center airfoil if it is set-back (instead of in-set).

Center of lift should according to theory be as far aft as possible. Preferably aft of CG to achieve stable flight, just as in an airplane, but that is impossible on a tunnel hull.
This can be fun.....
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Look at f above.

"The tunnel must connect two outer hulls or sponsons which are unbroken and
must also run the full length of the hull. Picklefork designs are acceptable.
Outrigger configurations are not acceptable."

In ground effect the center of lift gets pretty far back. I bet it's behind the CG in normal running. However, it doesn't take much angle change to get it to move forward causing a blow over. A rear wing above the transom should help, but in model sizes wings out of ground effect don't seem to be particularly powerful. My thought is that a servo actuated canard wing between the sponsons should be tried. Hooked to modern gyros or autopilots, it could adjust to keep the bow at a constant attitude.

An XT-460 is slightly over 34". It would be easy to trim the hull to 34". A Shaman is also a possible choice for a P tunnel.

Lohring Miller
 
Hi Lohring,

if a wing is allowed with gyro action . What about a gyro steared truster . Can be a impeller inside the cockpit aera or better a small quadrocopter motor with helicopter back rotor . So you can ad lift or downforce.

Happy Amps Christian
 
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I think that would be prohibited for most boats under the propulsion rule even though it's not technically air propeller driven. It would probably take a special ruling. Gyro driven airfoils should be allowed.

"Method of propulsion will be of the type that functions by propeller contact with the
water or air. Air prop driven boats will be limited to “1/2 A” or "A" class engines
only, see Section 10 – rule A.1."

Lohring Miller
 
Gyro controlled outboard tilt. That should be ok too I guess.
So much fun that can be done with new tech.

A Raspberry Pi Zero is $5 or so. That's got several times the horsepower of the computers on Apollo.

As for hull stability the Dynamic CG is the key. It should move around as little as possible and if it can be kept aft of the CL, all is good for stable flight.
 
Hi,

je ,new electronics are very funy to play with. The gyro controled outbord tilt is good i try it ,but for the next tunnel i will ad a prop high position system . Workes better i think. But at the end if Neptuns left fight straigt from the bottom of the lake you have never a chance to stay clear on the water.

Happy Amps Christian
 
The amount of tilt needed is tiny. The variable engine tilt system would be very sensitive. A wing has the opposite problem and may not be sensitive enough.

Lohring Miller
 
Just to be clear- that boat of Rod Geraghty's is a boat I built for the glass flat water of the Ft. Wayne In. internats and was later sold to Rod. Small-but great stock boat for flat water.
 
Tommy Lee said:
Just to be clear- that boat of Rod Geraghty's is a boat I built for the glass flat water of the Ft. Wayne In. internats and was later sold to Rod. Small-but great stock boat for flat water.
Click to expand...
A bit of history....

This boat is still alive and well serving as the current .12 tunnel record holder in IMPBA.....

I gave David Hall the boat and his .12 Novarossi gearbox motor is installed on the back.....

The boat is 21 years old and is still beautiful.... This little boat has been wrecked several times and repaired so it has gained a little weight...

When Tommy sold me the boat the sponson tips and cowl front were stacked in a separate pile....
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...but I gotta er back together....

Several things were learned with this amazing little boat.....
 
Tommy Lee said:
Just to be clear- that boat of Rod Geraghty's is a boat I built for the glass flat water of the Ft. Wayne In. internats and was later sold to Rod. Small-but great stock boat for flat water.
Click to expand...
I stand corrected. I got the pictures from Rod so I assumed he built it. It's still an innovative design.

Lohring Miller
 
It's all good Lohring-Rod and I are great friends and talk on the phone a lot.. Most of my dis-carded boats wound up at his house, The little orange tunnel is still being run by David Hall and currently holds the IMPBA saw record in A- tunnel.
 

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