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Tunnel Driving

Old 02-02-2013, 05:48 PM
  #1  
308jockey
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Default Tunnel Driving

Evening all,

I was out this afternoon trying to sort out the Hot Shots since the SOWEGA race is in a few weeks. I ran into some interesting driving problems. The Hot Shot Sprint which is a .40 powered boat, is incredible in the straights but shows a real reluctance to turn unless I back the throttle off to just under half, then it comes around very nicely. At speed at least the front half is out of the water, perhaps a bit more than that. I quickly discovered that full deflection won't make it do much more than slightly alter the line of travel. A little better at half throttle but I have to come off a little more and all of a sudden it turns great. Then I can hit the gas and go to the next turn and repeat. Fortunately it accelerates well. It would be a nice drag boat actually. You may have read my earlier thread on restoring the two Hot Shot .21's. One of them is still a little slow but I think that's a prop issue. The other is quite fast, pretty impressive I think. At speed most of it is out of the water as shown in some of the attached photos from this afternoon. This boat is showing similar turn characteristics but I find that backing off the throttle and using nearly all the turn throw turns it ok. If I pulse the turn from full right to just less than that several times it turns nicely but if I slow down too much or don't pulse it correctly it digs in and turns all at once killing most if its speed in the process. Then it's back on the throttle but I have to accelerate too much to stay in the race. So what am I missing here? Right now I feel like I'm not really driving but simply avoiding hitting the shore. Practice makes perfect and I'll be out several times working on it but is there something I should know or is this just how tunnels, especially these older ones, drive? Other question: I've been running 10% nitro and have been told that 50-60% is not uncommon. I'm still trying to get my head around those numbers and don't feel like melting my pistons but will probably try a little 30% heli fuel tomorrow to see what will happen. Will the extra oil content cause any problems with these engines? Any other hints or encouragement is welcome. Thanks.

Rick H.
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Old 02-02-2013, 09:39 PM
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Jerry Dunlap
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Default RE: Tunnel Driving

Is that the Hot Shot that calls for a turn fin?

JD
Old 02-03-2013, 07:45 AM
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308jockey
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Default RE: Tunnel Driving

Jerry I don't think so. The .21s are glass and I don't recall any mention of a turn fin. It's been a long time ago though and I don't have any of the plans or instructions. The Sprint was built by another club member who has passed away. He was a meticulous builder though and if there was supposed to have been one I suspect it would be there. No obvious signs of something missing from the boat. It probably had not been in the water in a decade until I got it. Seems like I recall a wood Hot Shot .21 that was a very different design, narrower and without what I used to call a pickle fork design. Never had one though. That may have called for a turn fin, I don't know. Are tunnels normally reluctant to turn at speed?

Rick H.
Old 02-03-2013, 08:44 AM
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rcguy1411
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Default RE: Tunnel Driving

i always found to get these types of hulls to turn you had to set the bow with the full size hulls we trimmed in the engine in with the rc versions we chop the throttle to drop the bow to get them to turn adding a turn fin will help with your turning isue as Jerry mentioned i am redoing an older tunneland am thinking about adding third channel trim im more of a sport boater and not a racer but i think the ability ti trim thr engune in when heading into a turn will help with corner speed just a thought
Old 02-04-2013, 08:47 AM
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308jockey
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Default RE: Tunnel Driving

All three of my tunnels seem faster by quite a bit the more out of the water they are. That same condition seems to limit controlability though. Running them yesterday and the black one came out completely out of the water, tumbled in three dimensions and splashed back down upright and backwards. I've trimmed the motor to push the foot forward a bit and am wondering if a little nose weight might be in order. Sitting still the tops of both .21's have maybe 1/4-1/2 inch above the water at the back. I have no idea how to balance these boats correctly, it's all T&E right now. Then again maybe this hull has a certain speed above which it just won't stay in the water reliably.

Rick H.
Old 02-04-2013, 11:37 PM
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Ron Olson
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Default RE: Tunnel Driving

In your pictures the hulls seem to be loose on the water (translation: flying too much) which is why it may have problems when turning. Try tucking the motor in a little or adding some weight to the nose. Keep track of your previous settings in case you might have to resort back to a previous one.
Keep in mind that right now you're not running in race water conditions. When you're going to be going against 5 other boats at SOWEGA it's going to get rough out there and you've got some good racers in that area in the OB classes.
Old 02-05-2013, 06:53 AM
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kroggs
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Default RE: Tunnel Driving

I had the same deal with my TS3 with the Thunder Kitty motor.  I had to add 6oz of weight and put a slight bit of negative on the prop shaft.  This slowed the hull down a bit so I raised the motor back up a touch and now it can turn at full song and goes fast on the straight...  The hull is also sitting nose level Vs. up in the air flying....  It also handles rough water better when the nose is sitting down...
Old 02-05-2013, 05:23 PM
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308jockey
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Default RE: Tunnel Driving

Sounds like I need to add noseweight. I'll start with some stick on weights on the insides of the sponsons, maybe 2 ounces per side to start. Both .21's porpoise noticeably all of the time unless they start really coming out of the water. Thanks for the information.

Rick H.
Old 02-05-2013, 09:00 PM
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Ron Olson
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Default RE: Tunnel Driving

Raise the engine up until it starts to cavitate in the turns then take it down a hair.

Those little motors LOVE the nitro so don't worry. Running 45-65% isn't uncommon as these aren't planes or cars. John Otto of Technology Fuels may be there so if you need some high percentage stuff, let him know and he can bring some along for you or order ahead of time. BTW, he might be the guy to beat there if he shows up.

Porpoising can come from the boat trying to catch some air as it quite hasn't packed enough under it yet. Dumas boats have been imfamous for doing this.
Old 02-07-2013, 12:04 PM
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308jockey
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Default RE: Tunnel Driving

I added 2 ounces to one boat and three ounces of weight to the other, inside of the sponsons on both boats. It sure is ugly. The one that got 2 oz. is still slow but I finally changed the prop and that should give me some extra speed. The boat with 3 oz. runs MUCH better, easier to turn, good speed but less tendency to go airborne. I might actually be able to get this one around the course properly. The Sprint is running and steering well, I'm happy with that one. I still may go pick up a gallon of fuel with more nitro and see how that does. Tried some 30% heli fuel and that was a disaster. Too much oil. I need to finish trimming and decide which .21 I'm going to race and get some more practice. I don't expect to finish ahead of last but don't want to look like the complete rookie I am when it comes to boat racing.

Rick H.
Old 02-07-2013, 06:26 PM
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kroggs
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Default RE: Tunnel Driving

You never know Rick.  Some times the slowest finishes first!!!  I was chasing Grim Racer once and had tooo much steering dialed in and the boat hooked and all them slow boats passed me...  Just keep working on the trim, try more weight and lift the motor till she starts to purpose and then set it back down a touch!

Practice them bouys and you might come out better then you think come race day!!!

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