Engine for Skyway 35

[Angelo Smyth]

Hi all - planning on building a SIG Skyray 35 soon. I have a brand new K&B .20 that I'm considering for this. I'll get a CL NVA and venturi for use here if it's a reasonable engine for this application.  I'm well aware that there are bigger / better engines out there,but this engine is feeling a bit left out and wants to fly! But if this is an unreasonable engine for this, I'll be happy to go another route. Thanks in advance for your input.

[Tim Wescott]

For learning how to stunt, the OS 20FP is perfect if you don't build too heavy.  The 25LA and 25FP are also darned good (I actually ran a 25LA in mine, because it was a tad heavy for my 20FP).  For contrast, a Fox 35 (so, 75% bigger than a 20FP) is considered not enough.  The basic engine design matters at least as much as displacement.

To add to the complication, if you just want a plain old trainer and not a stunt trainer, then a weaker engine than a 20FP would get you by.

I have no clue how a K&B 20 compares to the above engines in design, except that I know that K&B engines were pretty high performance for their day.  And I'm pretty sure that there's not just one K&B 20 -- I see at least two on the Mecoa site, and goodness only knows how many K&B made when it was still K&B.

So tell us which K&B 20 you have, and tell us what you want out of the plane.  Then someone who does know how your particular version of the K&B 20 will compare.

[Angelo Smyth]

This is what I have

[Angelo Smyth]

Instructions with it say K&B R/C Sportster Engine p/n 5600. No copyright data, but there's no .com on it anywhere on it either....

[Tim Wescott]

I found this review online.  It looks pretty similar to a FP20 -- so maybe it'll work.  I'd say go for it.  I would suggest you stick with the stock muffler; just put a venturi on it, use an APC 9-4, and see how it goes.  If worse comes to worst, you can always get a FP20 or LA25.

A typical 20FP should turn a 9-4 at around 11000 to 12000 at launch, and should pull the Skyray nicely through a pattern.  I'd hope for similar performance from your Sportster.

[Steve Dwyer]

Angelo,

You got my attention, I'm trying to finish the Skyray 35 I started last year, it is now covered but needs painting. I plan to use an OS FP 25 on it, in hopes it will have a little less kick than the OS LA 25 I have on a Flite Streak. I'd take stock in what the others are saying about weight and the 20 size engine.
Are you considering building the plywood kit wing version Skyray or changing to balsa? Keeping the plywood you might just find the 20 will be a bit underpowered.
Here's a shot of my balsa conversion wing, if you are interested there is a ton of information on SH regarding the benefits of building a balsa wing instead of using plywood.

Good luck and send some photos,

Steve

[L0U CRANE]

Angelo, Hi!

Tim has the good word on the K&B Sportsters. On another site (RCU) there was some discussion of the Sportster .28. Most liked it and considered it more of a torque/grunt setup than for very high RPM.

I had a .20 years back, and found it much easier starting without throttle, and quite happy revving. I'd cut my own suction venturii.  9-4 is a good suggestion, and it should be happy and "adequate" power for a Skyray - particularly if you keep the weight reasonable. Didn't get opportunity to fly mine, but the comments of others who flew the .28 may suggest the .20 could do well with a 9-5.

It is a "modern metallurgy" engine, so use the recommended fuel. It probably will not like a high castor-content fuel.

Luck! Enjoy! and "social distance"...

\LOU

[Angelo Smyth]

Steve, I haven't started yet, but the plan is I'll  be replacing the ply ribs with balsa. Painted fuselage, straight mylar covering for the wing with no paint.

[Angelo Smyth]

Angelo, Hi!

Tim has the good word on the K&B Sportsters. On another site (RCU) there was some discussion of the Sportster .28. Most liked it and considered it more of a torque/grunt setup than for very high RPM.

I had a .20 years back, and found it much easier starting without throttle, and quite happy revving. I'd cut my own suction venturii.  9-4 is a good suggestion, and it should be happy and "adequate" power for a Skyray - particularly if you keep the weight reasonable. Didn't get opportunity to fly mine, but the comments of others who flew the .28 may suggest the .20 could do well with a 9-5.

Thanks so much Lou - hope you and Penny are well.

It is a "modern metallurgy" engine, so use the recommended fuel. It probably will not like a high castor-content fuel.

Luck! Enjoy! and "social distance"...

\LOU

[Angelo Smyth]

Lou - thanks so much - hope you and Penny are well

[L0U CRANE]

... added thought: Stock muffler is quite light and effective; good source for pressure tap for tank. My choke should have had good fuel draw, but muffler pressure is nice to have available.

The original plywood-rib kit had two "good" points: cheaper than SIG's usually nice balsa, and as a design for beginners it was strong enough to survive building -  AND, perhaps, those first few inevitables...

\LOU

[Angelo Smyth]

Ty, Way too many scrubby Mesquite trees for FF around here! I prefer to damage my planes without the help of the local vegetation! 

[Angelo Smyth]

Tim - thanks for including the review. It was interesting.

[MikeyPratt]

Hi Angelo,
Their are a number of engines that work perfectly, the most commonly used is the OS 20 (BB) set up but also your K&B 20 will work just great as well.  Even  Veco 19 has more than enough power the fly the Skyray 35, I have one myself that runs very well.  The most important part is using the correct prop to use.  They all seem to like the 9 X 4 prop, 10 to 15% nitro, 60’ X .015 lines with lap times around 5.0.

Have a blast,
Mike Pratt

PS  You can use the stock carb and just hold carb open with wire connected to an mounting bolt.

[Dwayne Donnelly]

This is what I have

K&B 28 is good engine, with a 9X4, 9X5 is perfect for a Skyray.

[Angelo Smyth]

That's good to know Mikeypratt - thanks!

[Phil Spillman]

Hi Angelo and All, This has been a very interesting thread for me to read. I just happened to have bought a K & B .20 and .28 at a recent swap meet! I bought these two engines because a friend of mine has been flying a plane sort of like a Veco Tomahawk with a K & B .28 for power. This engine flies that plane very nicely! Another friend recently dug out has own Sky Ray, built with balsa not plywood parts and installed an OS .20 UC engine in it just to see how it would fly! It flies quite well with that little power plant!

With this plane first came out Sig sponsored a video called building and flying the Sky Rays which featured building and flying both the .35 sized release and the 1/2 A version! The producer of this video had me do the flying parts of both videos for the production! I was amazed at how well these planes flew! And they were quite fun to fly the .35 size especially because it performed the entire AMA PA pattern with ease!

Since I have become a real fan of the OS FP .20 I know you'll have a ball with this combination! As for me I plan to mount my K & B .20 on my own Tomahawk for some more flying fun!

Tally Hoi!

Phil Spillman