Viperhead performance compared to norm OS91 SZ-H Head

[Aviation addict]

Guys, I have a Stratus Kit and OS91 SZ-H p/p & reg on order and am trying to decide whether to mill the head to get it to fit the fan shroud or to simply use the ViperHead.

Has anyone used both of these heads on an OS91? Does the two glow plug design make the engine run any different / better?

[DavidH]

From my experience with the Viperhead on the YS 91 and the OS 91. It does allow the motor to run a little better ( smoother). I have not really noticed any power increase when adding the Viperhead.

I milled the sides off on my blue heads that came on the OS PS motors. They look like they were done at the factory. I also took off one fin on top of the head to allow it to fit in the MA shroud. Seen a couple that have been done on a belt sander and they look just like mine that was milled off.

4mm off each side and 1 fin removed off the top. Motor does not run hot.

David

[Aviation addict]

Thanks David,

Which fin do you have to remove from the top?

Once these modifications have been made to the head do you need to do anything to the Stratus fan shroud?

Do all 91 size Viperheads come with 2 glowplugs & which (OS) plugs would you use?

[R-4-L]

hey john, i hope you'r can find some decent weather conditions for flying over there! i'v lived in Aberdeen for 3 years, from those only a few days in the summer i found flyable! where are you at?

[Aviation addict]

Can't be too fussy about the conditions when living here. As long as its 'dry' and the wind is below say 25mph I'm out there making smoke. I wear ski gear in the winter (just used it the other day though - in May) and have a tranny mitt to keep my fingers from falling off. Where there's a will theres a way! :D

[Aviation addict]

I've been researching the Viperhead out of interest and as an engineer it seems to make some sense using two glow plugs, one Medium/Cold and one Hot. You can imagine the bias changing from the Cold plug to the Hot plug as you spool the heli up and go flying. After having a couple of dead stick Autos, it would be nice to think that that situation would'nt happen again either.

David has kindly provided a brief insight into the Viperhead. Does anyone else out there fancy giving us a quick review??? Cheers : :)

[Jerry]

You do not have to mill the stock head with a minair fan shroud. Just cut the shroud to end immeditaly above the cylinder head. No cooling issue at all.

Jerry

[angelob]

Jerry,

How is the shroud supported at the cylinder head? I'm interested because I have ordered my 91 SX-H.

Thanks,
Angelo

[Aviation addict]

How is the shroud supported at the cylinder head?


Hi Jerry, I'm interest in how the shroud is supported too. It must be attached to the frame at the aft end as usual - but then what happens? I guess vibration is a real possibility if this mod is done wrong...

[Jerry]

Its not a difficult mod. It involves drilling one hole in the frame and one hole in the shroud. You shorten the standoff. Bobby Watts, Jim Stark, and myself have all done this and had zero issues.

Jim Stark's (note how much he trimmed off. This pic was taken in PHX when OS was over here during testing of SZ last December.)

http://members.aol.com/ctseaplane/shroud1.jpg

here's Bobby's old Extreme. He drilled a hole in the frame.

http://members.aol.com/ctseaplane/bwshroud.jpg

After Bobby did his, I decided to make mine look nicer than his (LOL) In the Tempest CF frameset - there is already an existing hole

http://members.aol.com/ctseaplane/jshroud.jpg

Not only do you not have to mill the nice blue head....but you lose some weight too. Those shroud braces aren't exactly lightweight.

If you have enough vibration in your airframe for this to become an issue.....you have many more important issues.

Jerry

[Aviation addict]

Thanks Jerry. A picture paints a thousand words. Did you make the bracket yourself or could I buy one some place? Yours looks a nice neat job.

[Jerry]

That is the stock Minair fan shroud support. As pictured, the left side is cut short, to get rid of the extra slot for the normal second mounting support.

Inside the fan shroud is an M3 nylon nut. Once thats in the first time - it stays. You remove the shroud via the frameset nut/bolt. Forceps or a 5.5mm open ended wrench are required.

Jerry