Re: Hyper Viper's 1st Flights

roddie Thu Oct 26, 2017 7:02 am

Kim wrote:

Oh Yeah! I think I'm gonna put it on 40' when Vince and I fly this weekend. The KB really lights it up, but I'm gonna play with it's original engine just to see what I can get from it.

Hi ya' Kim. I watched one of Rusty's "Stunthangar" vids this morning.. and wanted to share some info with you. It was discussed that the choke-tube on the Sure-Start engine actually robs the engine of power due to the airstreams' passing-over the top; creating negative-pressure (vacuum) in the venturi. You probably wouldn't notice this when bench-running.. but you might when flying. You may want to try flying the model again with the Sure-Start engine.. and choke-tube removed. Do you have any short-style needles? I'm not sure whether a short needle would protrude enough from the cowling to adjust.

You could try angling (trimming) the tube to face forward a few degrees.. but IMO.. you're better off running the engine without it.

Kim Thu Oct 26, 2017 8:26 am

roddie wrote:
Kim wrote:

Oh Yeah! I think I'm gonna put it on 40' when Vince and I fly this weekend. The KB really lights it up, but I'm gonna play with it's original engine just to see what I can get from it.

Hi ya' Kim. I watched one of Rusty's "Stunthangar" vids this morning.. and wanted to share some info with you. It was discussed that the choke-tube on the Sure-Start engine actually robs the engine of power due to the airstreams' passing-over the top; creating negative-pressure (vacuum) in the venturi. You probably wouldn't notice this when bench-running.. but you might when flying. You may want to try flying the model again with the Sure-Start engine.. and choke-tube removed. Do you have any short-style needles? I'm not sure whether a short needle would protrude enough from the cowling to adjust.

You could try angling (trimming) the tube to face forward a few degrees.. but IMO.. you're better off running the engine without it.

Yo Roddie,

I could now see where that'd be the case, but never thought about the choke tube previously. I flew the Viper several times in the stock version, then stuck a K.B. on it which, of course, lit it up. May go back to experimenting with the original engine though, just to see what can be done.

Ken Cook Fri Oct 27, 2017 11:03 pm

Something doesn't add up with their findings. If they recognized these effects, there's no reason not to lean the engine out on the ground more to compensate. The impact of what they're stating is no different than having a tank mounted inboard on a profile. Many times when using a uniflow tank, the opposite happens and the engine goes screaming lean the instant the plane is released, so either you neck down the uniflow tube or try and launch with a very rich setting. The situation at hand here sounds as though the engine is underpowered. The choke tube if anything is improving fuel draw. The Killer Bee has a larger intake and this could certainly improve power slightly. The Sure Start certainly can afford to have it's venturi opening enlarged. If indeed air blowing over the top is causing this problem, one would just need to drill a pin hole in the back of the choke tube or in the vertical section. You can't properly use a straw when there's a hole in it.

Greenman38633 Fri Mar 29, 2024 9:37 pm

Wow. This is a old post. I’m surprised it has t been updated by the one who started it. At any rate I’m thinking about buying a Hyper Viper. Anyone got any new information or a update to this thread ? Thanks. Mark Green

**944_Jim** Fri Mar 29, 2024 10:57 pm

Southridge CNC cut these kits, but then stepped away from the business a few years back. Good luck finding an un-built kit.

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