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All Forums >> RC Airplanes >> Pylon Universe - RC Pylon Racing >> Club 40 >> GP Viper 500 with 25 FX questions
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GP Viper 500 with 25 FX questions - 8/28/2008 5:02:27 PM   
2-Stroke Freak


 

Posts: 26
Joined: 4/4/2007
From: Roseville, MI, USA
Status: offline 		I'm thinking about getting a Viper and would like to use a 25 FX for power. Will it work?? What prop is best??

What servo's are recommended. Lighter is better, right?

I also have a TT 46 I could use if the 25 is under powered. I'm new to Go Fast Turn Left and want to ease into it. I'm not looking to race just want a 100mph + fun flyer.
       Post #: 1

RE: GP Viper 500 with 25 FX questions - 8/28/2008 8:54:37 PM   
vicman



Posts: 6451
Joined: 12/8/2002
From: Valdese, NC, USA
Status: offline 		You will be pleasantly suprised with how well the Viper does with a .25FX. Not a barn burner but plenty fast (100+). You will need to either add lead or make a spacer for the motor mount to get the CG correct, here is a pic of mine. 9X5 or 8X6 are good choices to start.
If you ever think of going racing the quickie .25 class normally has a 3.25 min weight so standard servos are not a problem.
With the TT.46 you will want to hang on to your hat if your not comfortable with a fast airplane. Have your dual rates set up in advance. Your low rates will be at least half the low rates you would use for a sport flier. It came as a suprise to me too.

Be sure to review the Viper thread there are some other improvements you will want to make before you fly it. In my opinion the biggest one is throw the wheels away.

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Bigger Badder Meaner Faster!
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       Post #: 2

RE: GP Viper 500 with 25 FX questions - 8/28/2008 9:32:42 PM   
Jim Duda



Posts: 232
Joined: 4/10/2006
From: Austin, TX, USA
Status: offline 		This combination was flown against the Club 40 Raiders and is just a few MPH faster. Dallas / Ft. Worth has a dozen or so Q25 races each year...very popular in North Texas!

http://www.rcuniverse.com/forum/m_7537969/tm.htm

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< Message edited by Jim Duda -- 8/28/2008 9:35:44 PM >

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       Post #: 3

RE: GP Viper 500 with 25 FX questions - 8/28/2008 9:59:28 PM   
2-Stroke Freak


 

Posts: 26
Joined: 4/4/2007
From: Roseville, MI, USA
Status: offline 		Jim,

I just got home from my LHS with my new Viper 500!! Now I have to go back for more stuff......

Does the Hayes mount fit the blind nuts already in the firewall??

What wheels do I need to upgrade to??

I see you are using noyln wing bolts, is that the way to go 1/4-20??

Thanks again!!
Mike



< Message edited by 2-Stroke Freak -- 8/28/2008 10:17:54 PM >

(in reply to Jim Duda)
       Post #: 4

RE: GP Viper 500 with 25 FX questions - 8/28/2008 10:17:34 PM   
Jim Duda



Posts: 232
Joined: 4/10/2006
From: Austin, TX, USA
Status: offline 		The Hayes AL-25 mount and the Great Planes mount for the .40 size motors are interchangeable. Get the "Pizza Cutter" wheels from either Jett Engineering or Darrol Cady.

http://www.jettengineering.com/
http://www.darrolcady.com/Accessories/accessories_flight.htm

The 1/4-20 nylon wing bolts are DEFINITELY recommended! If you use the supplied steel metric (3mm?) wing screws, be sure and put tape over them before flying...too many have vibrated loose!

(in reply to 2-Stroke Freak)
       Post #: 5

RE: GP Viper 500 with 25 FX questions - 8/28/2008 10:20:29 PM   
2-Stroke Freak


 

Posts: 26
Joined: 4/4/2007
From: Roseville, MI, USA
Status: offline 		Is nylon used in the tail too??

How are you keeping the hatch covers on??

I appreciate the help!!

Will the 3mm blind nuts tap to 1/4-20??

< Message edited by 2-Stroke Freak -- 8/28/2008 10:21:27 PM >

(in reply to Jim Duda)
       Post #: 6

RE: GP Viper 500 with 25 FX questions - 8/28/2008 10:35:07 PM   
Jim Duda



Posts: 232
Joined: 4/10/2006
From: Austin, TX, USA
Status: offline 		Tail: Blue Loctite on the two supplied screws.
Tank hatch is epoxied on...you'll have to cut it off if you put your tank up against the firewall.
Servo hatch is attached with a servo screw.
Knock the 3mm wing blind nuts out...(screw in the wing screws a few turns and tap them out from the top.) Tap with 1/4-20.

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       Post #: 7

RE: GP Viper 500 with 25 FX questions - 9/2/2008 3:07:52 AM   
2-Stroke Freak


 

Posts: 26
Joined: 4/4/2007
From: Roseville, MI, USA
Status: offline 		I finished up assembly and maidened today. I set the CG at 3". First takeoff was hairy to say the least. It required all of the up trim I could give and it was still dropping. I mechanicly set up elevator to where I had trimmed it to and centered the trim on the TX and flew it again. It one or two clicks up to get level flight.
Also on approach it doesnt want to come down, and I almsot have to stall the wing to land. I never did roll it over inverted to see if it climbs or dives, but does it sound nose heavy??

Also upon take off it veers left and the ailerons dont really respond right away until the plane starts flying. I laterally balance the wing too.

I am flying off of grass.

Whats the problem with the stock wheels?? I only lost one on my last landing, and managed to find all the pieces.

(in reply to Jim Duda)
       Post #: 8

RE: GP Viper 500 with 25 FX questions - 9/2/2008 3:55:08 AM   
gunfighter


 

Posts: 646
Joined: 7/13/2002
From: Canyon Lake, TX, USA
Status: offline
quote:

Whats the problem with the stock wheels?? I only lost one on my last landing,


THAT is the problem!! The stock wheels are junk!

Regarding the up trim - did you read the threads noted?? You need to shim the back of the v-tail about 3/32" to get most of the vipers to fly correctly.

3" back for CG is a little too far back to start IMHO. try 2 3/4 or even 2 5/8 to start. Then adjust to suit your style.

Vipers fly fine off of grass. If it is turning hard left on take off, you might have some left thrust in the engine. Try to set every thing at 0-0 and do a lateral balance. That might help.

(in reply to 2-Stroke Freak)
       Post #: 9

RE: GP Viper 500 with 25 FX questions - 9/2/2008 4:26:02 AM   
2-Stroke Freak


 

Posts: 26
Joined: 4/4/2007
From: Roseville, MI, USA
Status: offline 		I have the latest version with the Pizza Cutter wheels. I think it was my fault. When I installed the wheels I backed off the collar to let the wheel spin more freely. After looking at them I need to put washers between the gear and wheel to give it some room as to not rub the gear. I need longer screws first.

I have some 1/32 ply I can use as shim stock for the tail. How big do I need to cut the shims and where exactly should they go??

Once I got things trimmed out and the plane got on step it was comfortable cg wise.

I ended up using a 32SX with a Mousse can pipe. A friend is going to loan me an Ultra Thrust
muffler to try. Maybe the added nose weight will help with landing.....

(in reply to gunfighter)
       Post #: 10

RE: GP Viper 500 with 25 FX questions - 9/2/2008 4:31:18 AM   
B EXTREME


 

Posts: 90
Joined: 3/10/2007
From: brisbane, AUSTRALIA
Status: offline 		Yep, the vipers have BIG probs as a far as V tail incidence goes. Most of the vipers need the V-tail to be raised by 3mm from the back. this will mean that the v tail won't be sitting flush with the fuse anymore but it will fly correctly...

good luck

_____________________________

B EXTREME

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       Post #: 11

RE: GP Viper 500 with 25 FX questions - 9/2/2008 10:02:53 PM   
daven



Posts: 7026
Joined: 12/7/2001
From: Andover, MN, USA
Status: online 		As to veering left on take off, set up your rudder so you have about 1/4" throw either way. On takeoff, hold full right rudder at full throttle. This will help keep you going straight without veering left. Adjust throw so that full right rudder creates a perfectly straight takeoff.

_____________________________

Dave Norman

klasskote.com
supertrc.com

(in reply to B EXTREME)
       Post #: 12

RE: GP Viper 500 with 25 FX questions - 9/2/2008 10:14:34 PM   
2-Stroke Freak


 

Posts: 26
Joined: 4/4/2007
From: Roseville, MI, USA
Status: offline 		Thanks Dave for the tip!! I'll try it.

I did shim the motor out on the left side with shims cut from a beer can. I have only put one in so far till I fly it.

I also shimmed up the tail, so today will be a re-maiden.

(in reply to daven)
       Post #: 13

RE: GP Viper 500 with 25 FX questions - 9/28/2008 6:34:16 PM   
2-Stroke Freak


 

Posts: 26
Joined: 4/4/2007
From: Roseville, MI, USA
Status: offline 		Heres a update on the Viper.

Daven thanks for the rudder on takeoff tip, works every time.

The 32sx hauls this thing around nicely. I'm using a Ultra Thrust muffler and a Hand made head that takes a Nelson plug. On a clipped 9x6 APC I'm getting almost 19,000 on the ground and it pulls the turns and accelerates well.

I took it to a club race, the course was a 600' 2-pole. No real rules other than 40 size planes and nothing bigger than a 46 size engine, no jett or nelson. There were 9 pilots. Vipers being the dominant air frame, with some vintage Scat Cats, and a couple Sonic 500's. Everyone else was flying either tt-46 or st-40-45.
Here I am the underdog with my little 32, the pylon gurus took interest in my plane when they saw me practice and we started playing with props. Ended up with a clipped 9x7 rev-up and it probably picked up 10 mph and still pulled the turns. When race day came I was second fastest in the field on radar at 109mph, with the fastest being 119 mph, we were the only two to break 100. At the end of the day I placed third, and had a great time. I wish there was more interest in pylon locally, I'd love to have a reason to assemble a real racer!!


(in reply to 2-Stroke Freak)
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