Just a few shots of the latest project to come out of the Butcher Shop...or what stunt builders build when they  are not building stunt planes. The Shy Fox MkII is a MkI with a lower aspect wing. Both were designed by Dave Hull. It has not flown yet but will be soon. Power is an Enya 25 SS, ABC. For comparison I enclosed a shot of the MkI and Mk II side by side. Plans for the original MkI version can still be ordered from Model Aviation magazine.

Very nicely done!  What sort of racing will it be for?   TS

Sorry, Super Slow Rat per NCLRA rules. 

She's a beauty, Pete. Hope she's almost as fast as a Mockingbird. 

Bill Bischoff

I got a close up look at both when Pete came down for the Bob Palmer Stunt Contest. He's raced the Mk I with us before, but the Mk II is right off the assembly table and it looks really good. We had hoped to get some flights in after the stunt rounds were completed but didn't quite make it. Hope you get it in the air soon Pete and work out any bugs.

My own Mk II just had the outboard wing rebuilt after the overly aggressive pilot person put it into the pits at warp speed. Even when the pitman has soft hands, there is a limit to what the leading edge can take!

Wingspan of the MkI (mine at least) is 38". If the tail moment looks a bit long in the picture, it is. I extended it by 1". If I were to do it over again I would build it according to plans. The extra length is not needed.  The Mk MkII plane is built per Dave's numbers  except for a slight change in wingtip shape due to having a couple of leftover wingtips in the scrap bin that needed to be to used. 

No plowing on either one of these, Motorman. They have plenty of span. I have flown "floppers" as a rent-a-pilot before and didn't like them at all. The induced drag goes thru the roof at the top of the racing zone and they slow down. If you bring a pig to that party, your pilot needs to be a good whipper. The reason each of the proud owners touted for the super low A/R was the low form drag from the reduced frontal area and that they shake down impressively. Both those claims are nebulous. If you want to win, you have to be able to pass without slowing down, or you need "liberal" officiating and a strong pilot. And if the pig stalls on the first shake and does not reestablish flow and flying before it hits the ground (in other words, it is a flopper) you basically get close to the pit and crash there and hope it is in reach of the pitman and nothing important broke off. Liberal officiating helps here too. And if you have staked your design cred on such a design, you build it stronger and heavier each year to keep it from breaking during successive flops. So now it slows down even more at the top. True race plane de-evolution!

Ok. I'm not a fan of super low A/R racing planes. It does get the wing out of the way of the pitman which is the only redeeming value I have found. This was pointed out to me after too many beers at Muncie—by a pitman....

If it helps anyone, the wingspan on the Mk II is 34 inches. The area and thickness are unchanged. It also used the stock stabilizer size. The rest is unchanged. I prefer the Mk II because it is easier for the pitman and it flies just as good.

McSlow

PS—Tell us about your 24" slow rat, Motorman

So where can one get plans to the mark 2 version?

I don't drink Beer

It's never too late to learn a new skill, Bob. 

George,

The ShyFox plans are available from the AMA. You can go into the Members Only section and see them in the archives, including a very complete build article in the March 2010 magazine. The Mk II differs only in the wing planform. There are no released plans for the Mk II, just two sketches that I made and gave to a few guys that were interested. The root chord is 10-1/4" and the tip chord is 9-1/4". The wing LE is moved 1/2" forward in this version to maintain the  balance. Neither of my planes required nose/tail weight. I tend to use firm wood in the fuse and tail. Spar construction is the same, just a bit shorter. Just make up some root and tip templates per the sketch and stack-sand your rib set.

Again, in the interest of full disclosure, I didn't follow the plans when I built the Mk I stab and elevators. Kind of like Pete and his wingtips, the piece of wood I had was a bit bigger than the plans so I used it. The plans actually show both, so take your pick. The Mk II used the smaller stab. No difference in the way the two fly, really.

For anyone who has not tried the exact sewn hinges shown in the plans, you should. They are really bulletproof when combined with the spruce spars. They work equally well on basswood surfaces that I use for Goodyear, Mouse, Rat, and Quickie Rat tails. The problem I have when I tell people about sewn hinges is that they remember carpet thread and a million stitches along the length of the surfaces. (Like Frankenstein's sutures.) This is unnecessary with modern materials, draggy, takes more time to do, and is butt-ugly. The second issue is that guys all fondly remember the "best" material to use. I try not to get involved in these conversations any more. People do what they know--even if it has long since been improved. When a guy tells me how great 1/2A Dacron flying lines work but won't try Spectra, the receive channel just isn't turned on. Or dental floss. Or carpet thread. Or, the super techie dude,  who has got to use Kevlar thread. Sure Kevlar is strong, but for a sewn hinge, it is harder to work with and you need some pretty small stuff. If you have a 100 year supply of Soviet Kevlar that you need to use up, go for it!

Well, I guess if Rad doesn't do beer, he must not have been the pitman in question. Or else I drank too many and can't tell the story right! Bob did a great job pitting the heat races at the Nats that year. Most races are won in the pits, so try not to hand a rent-a-pitman a plane with some unusual trick setup. If the teams have to split up for the final, that pitman may only get 5 minutes to figure out your setup. Less if he has to go fill up the refueling bottle. Most pitmen are very familiar with the setup shown in the ShyFox plans. This plane has probably been pitted by all of them!

McSlow

Dave,

Thanks for sharing the info.  I appreciate it.

George

So true about pitmen.  When Melvin and I were flying together  in the Shoestring event I would tell to set the prop to his satisfaction when he pitted my plane.  Other than mouse it was only event I would fly because of rules at the time.   Guess I will have to pull out plans of the Sly Fox.

Has anyone built a straight wing version of the Shyfox?

Not to my knowledge, Charles--you could be the first!

Be sure the wing meets the rules for area (300 sq. in.) and minimum thickness (1") and have at it.

If making the ribs for the tapered wing is troubling you, I can say that I stack-sanded a full set using a couple of templates and it is pretty simple. The hardest part for me was going thru the junk drawer looking for some long 4-40 bolts to clamp the stack. But there is no reason you couldn't use some 6-32 or larger hardware store bolts.

Dave "McSlow"

For stack-sanding the "bolts" are DuBro 4/40 threaded rods.  You can stack as high as you want.  I typically do two planes at time. 

I always do one-sided templates and flip them.

Also, the blanks are held in alignment with a little bit of clear dope that can easily dissolved.

If you have the rib drawings you can just cut out the ribs and sand each one smooth. It's not like you're making a stunt ship.

MM

I am going to see if I can get a gentleman to laser cut me a couple sets. I really like the bird. I am going to give SSR a shot. I have been pestering Bill Bischoff for help with some of the stuff he offers. Does a really nice job. My local club (North Coast Control Liners) is dipping our toes into Flying Clown racing this season. I will see if I can get some interest in SSR. I will see if I can pick McSlows brain a little on building thoughts. 

Slim Pickin's there, Charles!

Have you read the Model Aviation article? I tried to include a lot of info, and they published it pretty much as written. But if you have specific questions or need more photos, then just ask about it here.

The Divot McSlow

Dave, I sent you an email. I will be looking to start building in April. I am going out of country for a short time, but will start when I get back, Also a sport Goodyear.

Charles,

No email yet...?  But I'm not sure how to find private messages on the "new look" board. Maybe that is where you went?

Dave

I asked Bill if he had your email. After some arm twisting he gave it to me (don't blame bill for that). I downloaded your Mk II drawings. I am having trouble finding the CF strips for the LE. I may punt on that and use some tow?

Charles,

CST Composites lists the .007x.250x36 carbon laminate as CL-1033. You can reach out to them and see if it is in stock. They are in Tehachapi CA, not the one in Aussieland.

The tow would work. Some uni-tape would also be very good. It's essentially tow that is already spread and laid out flat. That makes the joinery of the parts easier since the carbon is sandwiched in the middle and having the carbon a controlled thickness makes things easier.

Truth be told, the wing is strong enough in bending using the spruce wing spars without the carbon inner reinforcement. The leading edge carbon is there to try to minimize damage from rough handling during a race. It helps, but a bigger, harder balsa LE would accomplish much the same thing. But then you can't tell everybody how much carbon reinforcement is in your plane and how cool that is. Of course, it might be a lot cooler to have the $30-$40 bucks in your pocket instead, but....

The products in the parts list were readily available at the time. Like much of the "build it yourself" part of the hobby, that has changed in recent years.

Thank you Dave. I go by "Chuck". I will check with CST. I appreciate the insight on harder balsa might be enough, especially with the Mk. II wing modification. I am intending to use a shut off as well. That might minimize harsh handling by a pit crew. If that is not allowed in the rules, I will adapt. I will look into having the aluminum front end fabricated as well. I really like the design elements of the SF plans!

Chuck,

I just sawed, filed and drilled the engine mounts on my two planes. I used the aluminum plate sold at the hobby shop from K&S. It has good strength and temper. I do the same with all the Quickie Rats and other racers....

Was the aluminum 2024, or 6061? I have some sheet identified with Aircraft S&S. Meeting with my buddy on Monday to talk rib cutting. We are embarking on another project for our local club that should yield some fun stuff with our guys. The Shyfox project is the next build I would like to get them engaged with. There are plenty of stock .25's around that would make this project exciting!I also downloaded your Mk II mods and like them. I was going to build a Mk i to get my feet wet, but I like that version a little better!

K&S says that their 1/8 aluminum sheet is 6061-T6. Their SKU is 83072. The 2024 would work even better (it is stronger), if you have some. It has added copper, which increases the strength and fatigue resistance, but is more susceptible to corrosion in full-sized planes. But that's not really an issue with models....

I will note that the gear will handle some abuse, but if your pilot is in the habit of slamming the plane down right in front of the pitman, you CAN bend the gear leg. If that is the case, a single wire strut might be a better choice. If you are considering that, then I would suggest using 5/32" music wire for a single-strut setup.

Thanks for the alloy clarification, Dave! I will follow the plans for the first built. I always follow a recipe for the first meal and tweek things later for my taste. I like the look of the bird. I am meeting with my dear friend on Monday to discuss the build. I think I will make the Mk II version out of the chute to gain some experience with SSR. I flew fast rat MANY years ago, so I need to learn how this works, and then promote to others in my club to join in the build. We may start with virtually any airplane with 300 squares or more to "get in the game"! We are starting with the Flying Clown event as a club racing event, and there are 7 or 8 builds going on. I have gotten a lot of help from Bill with providing our guys with tanks and shut-off's to get started.

SSR and to a lesser extent Clown are both "floaty" design forms due to the size of the wing that is required by rule and the normal weight that these come out. That means that the landing approach and landing gear have to take that into account. That makes these fly much different than the more traditional "rat" classes. For example, in shakedowns. But, the SSR rules also prohibit the use of shutoffs which means you need the glide lap anyway. The rules for Clown apparently changed to allow the use of shutoffs which makes things easier on the pilot at the speeds the things were going.

True, with no shutoff in SSR, you need to be prepared to hit the pits no matter where the engine quits. But, with the wheel in the right place, you can put it on the ground faster without bouncing if you practice a bit. A half lap of gliding is better for your race time than a lap and a half of gliding, as long as you know you can do it. I have a selection of SSR gear legs with different sweep angles and wheel locations so I can find the "sweet spot" for the wheel.

Bill,

I guess I was trying to discuss durability issues, not wheel trim issues. The caution was that an SSR was going to float, and if the pilot's inclination was to slam it on the pavement and feed it to a pitman too fast, both the aluminum gear and the wing (if that's what the mechanic decided to grab) were going to take a beating. That said, a really good pitman with a soft touch is invaluable. Especially when the pilot gets excited (ie. wants to win!) and really stuffs it into the pit.

As to the correct wheel placement, I can say that on both my Mk I and Mk II prototypes the balance and wheel location were good without adding tail or nose weight. The plane balances on the wheel in the normal range of 15 degrees or so ahead of the CG. (I would have to measure again to verify.) Those dimensions are shown on the plans for the Mk I. I think the Mk II nose is slightly shorter, measured from the LE. And, as I previously noted, the tail on the actual Mk I prototype was a bit oversize from the plans, so a bit heavier. I use firm wood for the fuselage, and the tail and fuse are glassed with 1/2 oz. cloth. So there is pretty good info on where the balance comes out, where the plane handles well in the air, and why the wheel location isn't a random guess. If anyone needs measurements or weights, I can do that.

Your point is a good one that if the plane flew well, but wouldn't set down and stay stuck, I would have had to make another engine mount/gear leg piece. The wire gear is more forgiving of swapping those out or even bending to suit.

I have a quick question, Dave. I was discussing with my rib cutter last night this build. He had a question about the Mk. II build. The new ribs are longer than the Mk. I version. Is the placement of the bell crank and lead out position still relative to the Mk. I version? And if the wing placement of the Mk.II version is a half inch forward of the Mk. I version, the spar location is still in the same relative position in the fuse? Are those good assumptions?

The lead out position should be calculated as a percentage of the root chord to be the same on both planes. Same with the spars, belcrank and balance point.

MM

The location of the bellcrank mount is immaterial to how the airplane will fly. The position of the leadout guide relative to the CG is what matters. The bellcrank can be anywhere as long as the leadouts don't bind in the guide. Trust Mr. Hull's measurements. He knows what he's doing.

Thanks. I know the bell crank does not matter, as long as it is structurally sound. Lead out position is most important. I made some assumptions that lead outs stayed in the same relative place?

Charles,

Let me get the plane down off the wall tomorrow and take some measurements for you. I might have to make a sketch to make sure I am giving you the correct interpretation of the changes.

Dave

That would be awesome, Dave! We are like to get a best understanding of the changes to the Shyfox! I think it is going to be an awesome bird! I have started getting supplies for the build and wrapping up some late winter builds for the upcoming contest season. 

A few measurements on the ShyFox I and II for comparison:

The fuselage overall length of both versions is the same. Including the rudder, they are 24" long. Note that by rule, the fuse must be at least 22" from the drive hub to the hinge line of the elevator.

The nose on the Mk II is 1/2" shorter, as measured from the wing LE. The original is 6" and the Mk II is 5-1/2".

The aft edges of the wing spars are in the same place on both the original and the Mk II. Both are 8-3/4" back from the nose.

You can see where I mounted the bellcrank on the plans for the original. I'm pretty sure I used the same mounting system for the Mk II, relative to the spars.

Essentially, the redesign was a change to the wing and some minor shaping changes to the nose for improved streamlining. The design approach was to locate the new wing on the same fuselage so that no other changes (ripple effects) would be needed. So the wing grew forward from the spar, and grew aft from the spar, until I got to the new root chord/area/span that I wanted. The rib grew more behind the spar to maintain proportions.

I assume you have the sketches of the root and tip ribs of the Mk II. Sorry they are not cleanly drafted. I might look for my "kit" box and see if I can get a cleaner tracing from the templates. I think I used aluminum templates as I normally do.

I also assume you have the planform sketch of the Mk II wing. I generated that for someone a few years back that was building one.

I hope this helps. If you have more questions, ask away.

Dave

Awesome! I think that is great info! Let the building begin! I will try to figure out how to put pictures on SH to show my work. I will share with T.J. So he can post on NCLRA newsletter! I am looking forward to it! I already have a tank I got from Bill. I have a few more things I need to reach out to Bill for the Clown build we are working on.