FC Cheetah Fail....

[Fluid]

Club Member Jim Stephens and I ordered Cheetah hulls earlier this year, and Jim finished his first. Yesterday we were running practice heats and general boat tuning, and Jim had his new Cheetah out. Now Jim is new to cats and he didn't understand that the Cheetah has a major design flaw which makes it run poorly. He did not rebuild the rear sponson pad like everyone knows has to be done to have a decent running Cheetah. He even cut the skeg off the strut! He put a TP4060/2200 Kv motor in with a Castle 240 and 4S2P batteries. Here is how it looks:

IMG_0324.jpg

Well poor Jim, not knowing any better, tossed his cat in the pond and started making some oval passes to get the feel of the boat. You can see the poor results below:

https://www.youtube.com/watch?v=PgQcXtuv8wY&feature=youtu.be

Even worse, later in the day we ran a cat heat and in race water the Cheetah almost won. The cat's top speed is low/mid 50s, just where the motor/prop should drive it and just right for our generally rough Texas racing conditions. Jim is very unhappy with his new Cheetah, he will probably keep it forever.

I am with Tony on this one, this idea that there is a design flaw in the boat is bogus. I have been successfully racing cats for over 25 years, and there is nothing wrong with the Cheetah's rear pad - at least not the ones on our boats. Like any cat the ride pads should be sanded smooth and flat, but this does not remove much material at all. Anyone having issues is simply using a bad setup or not spending enough time to tune the boat up.

I am reminded of the H&M Drifter "sponson mod" of a decade ago. Someone, somewhere couldn't get their Drifter to turn so they decided there was a design flaw with the bottom. The famous "Drifter sponson mod" was published online and the sheep followed. Plenty of folks never ran their new Drifter as it came from the mold, they did the "mod" and ran it not knowing if it fixed anything. Another waste of time. We oval raced Drifters and SuperCats (identical bottoms, different decks) for years and they ran just fine with the right hardware and setup. The SuperCats always ran better, but that was due to the different deck aerodynamics, not their sponson design.

Bottom line, spend your time changing the bottom of the Cheetah if you want, but it is a proven design and it works as molded. We will spend that time tuning and racing our new cats instead.





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[kfxguy]

Jim is very unhappy with his new Cheetah, he will probably keep it forever.





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I'm confused with this statement.

My cheetah ran great once I figured out it needs a long (6") rudder.

[Luck as a Constant]

I'm confused with this statement.

My cheetah ran great once I figured out it needs a long (6") rudder.

didn't detect the sarcasm there huh?

[kfxguy]

Just watched the video....running g very nice!

[kfxguy]

didn't detect the sarcasm there huh?

Was just making sure lol. Btw, I have another cheetah on the way. Lol

[flraptor07]

I don't know about the H&M Drifter but it's very proven that the ride pad mod on the Cheetah does improve the performance. With a single set up the Cheetah does run good right out of the mold but the mod deffinetly helps. The design flaw shows up more pronounced with twin set ups.

[Luck as a Constant]

Was just making sure lol. Btw, I have another cheetah on the way. Lol

man, i wish i had the loot some of you guys got

[flraptor07]

Was just making sure lol. Btw, I have another cheetah on the way. Lol

I figured you'd get another one I love mine, it's one of the best running boats I have!

[electric]

Hi, I am the Cheetah owner Jay is referring to at the start of thread. Couple of things I would point out. The first time I put the boat in the water the boat ran awful. It was just plowing the nose like crazy. The reason it ran poorly is I have never run a cat and had no idea how to set it up. After some reading(Thanks Tony), and talking (Jay)) I figured out two things. One, my strut was set Waaaay too far down. Two, my COG was too far forward. No wonder it was plowing. I made these two adjustments (and a small leveling of the rear ride pad, which I don't think did much as it looked fine to me so I just roughed it up a bit) and then the boat took off and ran great. I ran the boat at least four or five times yesterday (Jay had to show the one where it wrecked!) and had a blast with it! It ran and handled great! I just need a bit more time behind the wheel with it and it will racing soon. I also trimmed 1/8" to 1/4" off the nose so it is officially 34" long. Really a blast to drive!!!

[Fluid]

....it's very proven that the ride pad mod on the Cheetah does improve the performance....

Really? "Proven" by whom? Why does virtually every other R/C cat have the same rear pad design, yet they seem to work fine without "mods"? There is no design flaw in the sponsons. What is different with the Cheetah compared to most other small cats is the tunnel design. It is closer to that of a typical oval racing gas cat with almost no taper for the aft 75 percent. This creates less lift than the other designs and requires a bit different setup than other cats. For example twin stingers have to be mounted higher on the Cheetah than on narrow scale type cats to keep the bows up, otherwise it will naturally plow. Most owners do not seem to understand that the Cheetah was designed for oval racing, not for SAW-type running. Trying to force it into that role will generally meet with varying degrees of failure regardless of any sponson mods. This is not a hull to try to break the 100 mph barrier with.

As I said, feel free to mod to your heart's content, but don't perpetuate the BS about an imagined design flaw. The boat works fine as is.


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[kfxguy]

I just read where the owner did level the rear ride pad........the original thought from the first post is that no mod to it was done but seems like there was.....just sayin.

On a side note, my carbon cheetah ran perfect without touching the hull with a sanding block. Maybe only the fiberglass ones had an issue?

[flraptor07]

Really? "Proven" by whom? Why does virtually every other R/C cat have the same rear pad design, yet they seem to work fine without "mods"? There is no design flaw in the sponsons. What is different with the Cheetah compared to most other small cats is the tunnel design. It is closer to that of a typical oval racing gas cat with almost no taper for the aft 75 percent. This creates less lift than the other designs and requires a bit different setup than other cats. For example twin stingers have to be mounted higher on the Cheetah than on narrow scale type cats to keep the bows up, otherwise it will naturally plow. Most owners do not seem to understand that the Cheetah was designed for oval racing, not for SAW-type running. Trying to force it into that role will generally meet with varying degrees of failure regardless of any sponson mods.

As I said, feel free to mod to your heart's content, but don't perpetuate the BS about an imagined design flaw. The boat works fine as is.


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Like I said the flaw shows itself more in twin set ups. Have you had a Cheetah set up twin? Scott (Tiqueman) is the one that did the R&D on the mod and he is the one that "Proved" the performance improvement for oval racing not saw racing the thread is in this forum somewhere but I haven't found it yet, If somebody knows where it is please feel free to post it. I have a Twin Cheetah and ran it both before and after the mod so I know first hand what the mod does, Do You?

[flraptor07]

Video after the mod

Unfortunatly I didn't get any video before the mod but here's after the mod. https://www.youtube.com/watch?v=CWlCxsirqQY

[properchopper]

When I first read Scott's take on curing Cheetah plowing by re-configuring the rear sponson I was cornfuzed - I have plenty of respect for Scott's FE acumen but at the same time my Cheetah exhibited no such behavior :

(you may have viewed this ad nauseam but just for the sake of this discussion) :

https://www.youtube.com/watch?v=Cl5ebHR6wR4

My best guess, with apologies to Scott, is that with a relatively (compared with twins) lighter single motor setup the boat airs out just fine. Add the extra weight of a second motor, ESC, mo' battery, and the additional butt-lift of a second prop and there's your plowing behavior. And yes Jay is spot on in stating that the hull is very much an oval design ( most likely plagiarized from an Aeromarine Laminates hull) and settles waydown in the water when the throttle is chopped to set it for the trip around the turn buoys, the same way most all oval racing cats do in the land of (the) Insane

As far as the Drifter is concerned, both of my un-modded bottom Drifters do fine - Three NAMBA Nat'l records so far. Actually it does run a little wet - primarily from the cooling water output landing on the deck, otherwise it mostly just flies at low altitude over the H2O

drifter 10.jpg

[keithbradley]

Really? "Proven" by whom? Why does virtually every other R/C cat have the same rear pad design, yet they seem to work fine without "mods"? There is no design flaw in the sponsons. What is different with the Cheetah compared to most other small cats is the tunnel design. It is closer to that of a typical oval racing gas cat with almost no taper for the aft 75 percent. This creates less lift than the other designs and requires a bit different setup than other cats. For example twin stingers have to be mounted higher on the Cheetah than on narrow scale type cats to keep the bows up, otherwise it will naturally plow. Most owners do not seem to understand that the Cheetah was designed for oval racing, not for SAW-type running. Trying to force it into that role will generally meet with varying degrees of failure regardless of any sponson mods. This is not a hull to try to break the 100 mph barrier with.

As I said, feel free to mod to your heart's content, but don't perpetuate the BS about an imagined design flaw. The boat works fine as is.


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I built a number of Cheetahs with twin setups, and they all ran great without any sponson mods. I have heard of some with an excessive hook in the last step, but I haven't had my hands on any so I assumed that perhaps there were a few that were poorly molded.
In my experience if you run larger props with a twin setup, the nose can drop pretty hard when letting off the throttle suddenly, but I would not consider that a negative thing in regards to oval racing.

I have, however, encountered hulls that REALLY, REALLY needed modification to the bottom to loosen them up. The Hydrolift hulls come to mind. I modified the bottom on this hull, resulting in adding 27mph and lowering current draw:

https://www.youtube.com/watch?v=tsxarm-jEYw

Obviously this has nothing to do with the Cheetah, but I wanted to point out that it IS possible to get a hull design, straight from the manufacturer, that greatly hinders the performance of the boat.