20 kph zonda splash

[paulejr]

Crash? I didna see no stinkin crash ...Lake near by , wind about 18-25 kph. Zonda still stock but running good and I could not resist, waiting for glass about as frustrating as nailing jello to a tree....GPS has it about 48.8 mph just before going to jump school....

https://youtu.be/lSQjZVDIg10

[jkflow]

That's when you move batteries a lot further to the front, what was the wind speed that day?
Looked real tail heavy in this run.

[paulejr]

They had slid back when I got it in. needs to add some wheel weights to the nose next trip as it seems we dont get a lot of glass days here. wind that day was 15 kph and gusting to over 20 kph. I really need to get this one to settle in that type of breeze or only get on the lake a few times this summer . My other boats , sit and pout....waiting for wind under 10 k, or even the days of glass with less than 5 k wind.

[Panchothedog]

Is there some reason you can't get the batteries to STAY more up front.
Velcro, straps, blocks, ect. Makes more sense than adding weight.

[paulejr]

I understand about the batteries being moved further fwd rather than adding nose weights. We'll see when this low moves on and the winds die down.

[properchopper]

Even with no wind

https://www.youtube.com/watch?v=5wQrlZjnd6U&t=3s

[paulejr]

Oh man !!!!! what sortof speeds were you getting .. the one from left to right and it lit up right and kept going.... I was cheering !!!!

[Bande1]

motorcycle stick-on wheel weights on the nose. Hobby stores sell them for planes. get that weight forward and the stinger down.

[Peter A]

Sometimes an air dam in the tunnel is what is needed to balance the airflow and stop the blow overs.

[Notoriousone]

My Zonda speedrun setup.. Struts parallel with rearmost ride pad. Batteries far forward, only about two inches of the batteries is sitting on the tray. They are mostly in front of the trays sitting on foam pieces. I don't use battery straps, only cut foam pieces and pool noodles to hold batteries in place. Note long pool noodle pieces sitting on the trays, to keep batteries from sliding back. These will be strapped to the trays, once in the batteries don't move at all.. She's been over 100mph a bunch of times with this setup with no blowovers. It does run very wet when turning at lower speeds, but once over 75 or 80 it starts to pick up slightly and rides flat and stable. This is a speedrun boat, so handling isn't so important to me. Now that I feel comfortable knowing it wont flip, I can start moving batteries back incrementally after each run and see if it gets faster

[paulejr]

I have seen a thread about air dams but not sure the physics of it or where or how it is placed. I would like to see more info if you have some. For the immediate future , adjusting batteries, tweaking the stingers and such will be on my agenda for now. now. QUOTE=Peter A;768504]Sometimes an air dam in the tunnel is what is needed to balance the airflow and stop the blow overs.[/QUOTE]

[properchopper]

These hulls, like their full sized bretherin, have (when designed properly) the "tunnels" configured to aerodynamically provide just the right amount of aero lift for the speed envelope they will be normally operating in. When pushed past this speed envelope, as in this case, an aerodynamic "foil" can be used to reduce this lift and keep the hull from becoming airborne. Adding weight, or transferring forward existing weight is a counter-productive "fix" which ultimately disrupts handling (although most long/skinny cats already corner like King Henry VIII).

The Cheetah hull is a bit more of a "widebody" and corners relatively well 'tho I add a bit of air dam material to the ones I build.

cheetah strealth front cropped.jpg

[paulejr]

''The Cheetah hull is a bit more of a "widebody" and corners relatively well 'tho I add a bit of air dam material to the ones I build.''

can you give me some dimensions or ratios as they pertain to the size of the tunnel vs the size of the air dam ?

[properchopper]

can you give me some dimensions or ratios as they pertain to the size of the tunnel vs the size of the air dam ?

I use a less scientific method : Trial and error (plus years of experience making "educated guesses")

Realize that you're asking a basically hobby-grade item to exceed it's design limits and push into questionable realms of performance if you want to wring more speed out of it or just roll on windy days.. I sympathize with you on windy day running 'tho
sometimes it's just model boat motocross just for the fun of it

https://www.youtube.com/watch?v=qkiTfVT1LaE

I'd go ahead and tack something like a rubber wiper blade refill in front and see if it helps. That's an easy place to start and has worked for me in P-Ltd Cat competition.

[paulejr]

Added wiper to tunnel, only about 5.25 inches across .... i turned the struts down 3/64th. I left the batteries in about the same place and will test this afternoon. wind is at 10-14 kph. 8-10 mph ...

[paulejr]

Yea baby... flat as a pancake at 51 mph several full throttle runs. I had turned the props out ward and lost 6-8 mph, but, see the video... waiting on TFL for the next size prop as the port side was BO. I had a puff of smoke but nothing showed up overly hot except the plugs were at 125 after 4.20 minutes of run on batteries that were at 80%. waiting on U tube for the video to load...
https://youtu.be/gL80FY5MnxU