Skyray with my contest engine

JPvelo Tue Sep 10, 2013 12:21 pm

Built up a Sig Skyray so I can start putting some time on my contest engine. I lengthened the nose by an inch to account for the lack of a tanked engine and because I had read where Ken Cook said they build tail heavy. He was right! The cheek blocks originally butted up to the wing but you can see in the photo I added an inch to the front of the plane. I also doubled the size of the elevator as it looked to small. I went with a "Blue Angels" paint scheme because I had those colors on hand.
https://i.imgur.com/CdeuCiL.jpg
This thing flys suprisingly well for a sheet winger and looks great in the air. Watch how well it lands in the video. For the $14 cost of the kit I can highly recommend it.
I was having engine trouble today . Fuel is 18% nitro, 22% oil 66/33 castor/syn. Prop is master airscrew 6x3 cut down to 4.75x3. I think I may have over bored my venturi because even launching at 20,400 rpm it bogs and sputters under load. With a 5x3 it was dramatically worse. I don't think the engine can put out the rpm the large Venturi demands.
https://i.imgur.com/Cwu5Xk1.jpg
The engine slows in climbs, the power drops, the engine slows more, power drops more.
Anyway, here's the video:
https://www.youtube.com/watch?v=97h_xNKq6V8&feature=youtube_gdata_player

roddie Tue Sep 10, 2013 1:25 pm

That's a nice looking and nice flying plane, James!!!

OVERLORD Tue Sep 10, 2013 2:16 pm

Good job Jim, your modifications turned out well. Were these obtained by trial and error or was it just an estimated guess? It flies really well!

Lieven

Ken Cook Tue Sep 10, 2013 2:23 pm

A major problem with the Skyray is the weak nose. After it snaps off for the 4th time, the weight of the glue usually makes your CG correct. What I did to prevent this and to assist in the CG was to add 1/32" ply both sides prior to gluing the cheeks on. I extended them back to the bellcrank. This made for a ridgid front end that wasn't so prone to breaking and it balances correctly. This of course was with a Blackk Widow, so using a product backplate is going to shift the CG even more rearwards. At that point I would use finishing resin and glass all around the cheek blocks to aid in the strength and CG issues. Ken

JPvelo Tue Sep 10, 2013 2:32 pm

OVERLORD wrote:Good job Jim, your modifications turned out well. Were these obtained by trial and error or was it just an estimated guess? It flies really well!

Lieven

Thank you! The Skyray was originally designed for a tanked engine, like the Black Widow or Golden Bee. Engines with a product backplate like I use are a little over a centimeter shorter than a tanked engine and about 3 grams lighter. I knew I would have to extend the nose to keep the cg in range, especially if the plane has a tendency to build tail heavy as Ken had stated. The elevator looked to small and was just a lucky guess.

Jim

Mark Boesen Tue Sep 10, 2013 2:52 pm

i always thought if i built another one, i'd do like ken sez only i thought 1/64 on both sides to appx 1/2" behind trailing edge...they snap pretty easy, also bob the tail appx. 1-1.5"

Jim, you might want to look at a balloon tank, or swap backplate, 20k on ground is a lot of rpm for a reedie.

JPvelo Tue Sep 10, 2013 2:58 pm

Mark Boesen wrote:i always thought if i built another one, i'd do like ken sez only i thought 1/64 on both sides to appx 1/2" behind trailing edge...they snap pretty easy, also bob the tail appx. 1-1.5"

Jim, you might want to look at a balloon tank, or swap backplate, 20k on ground is a lot of rpm for a reedie.

Already swapped the backplate and dropped about 1000 rpm on the bench, can't fly it until tomorrow. It has a killer bee crank so it will probably ruin the case before it breaks the crank. I have about 50 spare cases.

Jim

Mark Boesen Tue Sep 10, 2013 2:59 pm

....ok, after watching video, i'm gonna wonder if it was just a little lean, actually sounded pretty good.

if you've tried to open it up a tad, and it still goes lean, you might have a fuel draw issue and might look at a low pressure balloon tank set-up.

**RknRusty** Tue Sep 10, 2013 3:04 pm

Mark Boesen wrote:....ok, after watching video, i'm gonna wonder if it was just a little lean, sounded pretty good.

I just watched it too. It does sound like there's more room to rich it up before launch. I'm guessing you are using your usual pressure bladder method?

JPvelo Tue Sep 10, 2013 3:24 pm

Mark Boesen wrote:....ok, after watching video, i'm gonna wonder if it was just a little lean, sounded pretty good.

That's what I thought at first, but launching richer only made it worse. It's set so pinching the line for a second speeds it up, the same way I fly a TeeDee on pressure.

Jim

JPvelo Tue Sep 10, 2013 3:28 pm

RknRusty wrote:
Mark Boesen wrote:....ok, after watching video, i'm gonna wonder if it was just a little lean, sounded pretty good.
I just watched it too. It does sound like there's more room to rich it up before launch. I'm guessing you are using your usual pressure bladder method?

Same setup as always.

**Cribbs74** Tue Sep 10, 2013 9:08 pm

Sounded ok to me Jim. Flies better than I expected.

Good Job!

Ron

JPvelo Tue Sep 10, 2013 9:23 pm

Cribbs74 wrote:Sounded ok to me Jim. Flies better than I expected.

Good Job!

Ron

Thanks, flys better than I expected as well! I think the main problem with the engine is that I've grown accustomed to flying with a Tee Dee!

Jim

**Cribbs74** Tue Sep 10, 2013 9:36 pm

Maybe, It sure didn't sound unusual to me. BTW I know you wanted to see my BC fly a while back. I posted a video the other day in Flying discussions. Not looking for feedback or anything just wanted you to know it's there since you were asking.

Ron

JPvelo Tue Sep 10, 2013 9:40 pm

Cribbs74 wrote:Maybe, It sure didn't sound unusual to me. BTW I know you wanted to see my BC fly a while back. I posted a video the other day in Flying discussions. Not looking for feedback or anything just wanted you to know it's there since you were asking.

Ron

I saw that, it was HAULING on 35 foot lines! Impressive flying.

Jim

**Cribbs74** Tue Sep 10, 2013 9:43 pm

Ok good, you did see it then. So what's your next project?

JPvelo Tue Sep 10, 2013 9:59 pm

Brodak F-82 twin Mustang. I'm taking my twin out tomorrow with left hand props to see if I can pull it out of stooge with souped up engines. Last time I flew it was with clones of my contest engine, #1 cylinders, killer bee cranks and bored venturis. The tourqe from the motors caused to fly into the circle as soon as I pulled it out of the stooge. I mean overhead damn near like a wingover into the circle. Broke the wing off so it's glassed back on now. I set it up with 5x3 3 blade pushers from Bernie, cut down to 4.25x3. That third blade really loads the engine! I had to trim that much to get two blade rpm numbers. They are flexy plastic props so I don't know how well they are going to perform. I wish someone made a good quality 5x3 pusher. Anyway, I'm hoping it tourqes to the OUTSIDE now and hauls ass with those engines. If that's the case that F-82 should be fun fun fun!

Jim

pkrankow Tue Sep 10, 2013 10:21 pm

Master Airscrew makes some 3 blade pushers in what might be suitable size.
6x4
http://www3.towerhobbies.com/cgi-bin/wti0097p?CATEGORY=&MANUFACTURER=MAS&FVSEARCH=PUSHER

and puller
http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXFTE7&P=7

The Cox prop is 5x3.5 so it's the same ballpark...

Phil

JPvelo Tue Sep 10, 2013 10:27 pm

pkrankow wrote:Master Airscrew makes some 3 blade pushers in what might be suitable size.
6x4
http://www3.towerhobbies.com/cgi-bin/wti0097p?CATEGORY=&MANUFACTURER=MAS&FVSEARCH=PUSHER

and puller
http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXFTE7&P=7

The Cox prop is 5x3.5 so it's the same ballpark...

Phil

Thanks, I will probably try those if I can't find any 2 blades. The problem with the cox ones is they have so much flex they flatten out and don't pull like they should.

Jim

JPvelo Wed Sep 11, 2013 2:45 pm

I redid my fuel system and it helped. I removed the line clip I was using for an on/off valve and it no longer wants to die when I fly inverted. Here it is with the original, bored as big as it will go backplate. Launch is at about 19.5k. I think I posted yesterday the main thing wrong with the engine is that I've gotten used to flying Tee Dee powered planes.
https://www.youtube.com/watch?v=paDJ9xL2X9k&feature=youtube_gdata_player
It survived the unplanned landing with minimal damage. A little epoxy and it will be as good as new. I wish I could say the same for the twin, flew directly overhead out of the stooge again so direction of prop rotation was not the problem. Not sure how I will address that with the Twin mustang.

Jim

pkrankow Wed Sep 11, 2013 3:14 pm

JPvelo wrote:... I wish I could say the same for the twin, flew directly overhead out of the stooge again so direction of prop rotation was not the problem. Not sure how I will address that with the Twin mustang.

Jim

Unless your controls are whacky, WAY tail heavy. Move the CG up significantly by shifting the engines or adding weight, say 10%-15% of total wing chord. Heck, balance it on the LE if you need to, you will change it repeatedly during trimming.

A nose heavy lead sled is more useful than a former out of control tail heavy machine. You can always adjust the weight back in increments till it is where you want it.

Phil

JPvelo Wed Sep 11, 2013 4:08 pm

pkrankow wrote:
JPvelo wrote:... I wish I could say the same for the twin, flew directly overhead out of the stooge again so direction of prop rotation was not the problem. Not sure how I will address that with the Twin mustang.

Jim
Unless your controls are whacky, WAY tail heavy. Move the CG up significantly by shifting the engines or adding weight, say 10%-15% of total wing chord. Heck, balance it on the LE if you need to, you will change it repeatedly during trimming.

A nose heavy lead sled is more useful than a former out of control tail heavy machine. You can always adjust the weight back in increments till it is where you want it.

Phil

So tail heavy will cause it to fly in? It built borderline tail heavy and was then made more so by a previous repair. The first time it came in was the first time it flew after the repair. So I will rebuild once more, with a big ass fishing weight epoxied to the nose. I just want to know I can pull a high powered twin from a wing stooge before I build the mustang.

Jim

pkrankow Wed Sep 11, 2013 4:23 pm

Yea, it will instantly sky, then it will have minimal control as it noses. I've destroyed a couple new planes with tail heavy. The controls will be twitchy and unstable.

Kinda sickening seeing hours of labor (or childhood memories) crash...get repaired, crash again.

Repainting makes them even more tail heavy. I peeled paint off the tail of the yellow zinger I destroyed without getting a good flight even once on it. After repairs and repaints it was as thick as a mechanical pencil lead (.5 mm or so) consider stripping the paint with chemical stripper suitable to the paint used and starting over with the paint job.

If you have bulkhead engines put a 1/4 inch spacer in to move the engine forward. On 1/2a this should move the CG about 1/2 inch forward or more.

Nose heavy the controls will be sluggish and not very responsive, but it will be predictable. Glide will be poor. Keep adjusting the weight back till the controls are light but not twitchy, and glide does not requires excessive elevator control to maintain.

Phil

Ken Cook Wed Sep 11, 2013 6:18 pm

Jim, I built the Brodak F-82. I actually flew it when John Brodak was present. A handful of us gave it a great little work out. I purchased another, and it will have tanks installed. The runs were two short on the Black Widow. I was flying with 50' lines however. It was moving out. All of us flew the pattern using it. We would just skip the in between laps and go right to the maneuvers. It was truly a capable flying plane. The gear was problematic and kept bending. My next one is probably going to be Big Mig powered with maple beams in the fuse. My Fox .35 twin Mustang has a 68" wingspan and it uses 4 wheels. One nose wheel and tail wheel on each fuse and it works very well. The gear is short and goes directly into the maple beams. Ken

JPvelo Wed Sep 11, 2013 6:21 pm

Ken Cook wrote: Jim, I built the Brodak F-82. I actually flew it when John Brodak was present. A handful of us gave it a great little work out. I purchased another, and it will have tanks installed. The runs were two short on the Black Widow. I was flying with 50' lines however. It was moving out. All of us flew the pattern using it. We would just skip the in between laps and go right to the maneuvers. It was truly a capable flying plane. The gear was problematic and kept bending. My next one is probably going to be Big Mig powered with maple beams in the fuse. My Fox .35 twin Mustang has a 68" wingspan and it uses 4 wheels. One nose wheel and tail wheel on each fuse and it works very well. The gear is short and goes directly into the maple beams. Ken

Cool, I am looking forward to building and flying this plane. I am hoping to figure out how to successfully stooge launch a twin and leave the gear off all together.

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