Matt
I did use the .035 wall aluminum tubing. My first attempt at bending the thinner (.014" wall) failed as the tubing would buckle and split.
The "stinger" will be held in place by the silicon coupler (a Dubro exhaust diverter section) and rubber grommets at the pipe tunnel floor and at the bottom of the fuse. I thought I was smart and bought 7/16ID grommets for my 7/16 OD tubing. But a 7/16 OD tube at a 45 deg angle is much wider as it passes through the wood. I'll grab some 1/2" and larger grommets to figure out which one fits the best. I am also planning on inlaying some 1/16" plywood where the grommets are for more support.

Yup! Exactly how I envisioned it..., albeit too long ago now.

Jeff,

once finished, it might be worth considering a little silicone between the stinger exit and the grommet to prevent oil from seeping into the fuse if the plane is inverted before cleanup - minor detail. I also suspect that nitro might eat into rubber much more easily than into silicone so they will eventually have to be replaced. This, of course, assuming that you will be flying this beauty for a looong time!

Hopefully, the temperature of the stinger won't be such that it will wear out the grommets too quickly.

Matt,

you don't have to bend the stinger at an "offset angle" in order for it to exit the fuse bottom on one side of the pushrods, you simply have to get the bend angle where it enters the fuse correct.

Getting the stinger to exit the fuse bottom slightly offset from centerline is a simple matter of rotating it slightly!

Thanks for the info and photos Jeff! I'll get the same size tubing and give it a try. Did you have to heat the tubing before bending it or did you just use the coil? It looks from the photos you used the coil over the tubing instead of inside the tubing?

It is really cool to see your Skymaster come together. Just thinking about how the exhaust is routed is pretty sophisticated work, from the inverted engine back up to the pipe on deck, and then back down to exit the underside of fuse. Quite a bit of work especially in the 25 size plane! The Magic is the other one that I recall having this same config, everything after that went with the belly mounted pipe...

Matt

David,

Understood on rotating it to get it to come out the side.

I meant to say that the exhaust for the Arrow will also come out to one side at the bottom (rather than center). I remember reading Jeff had to deal with this and found the best solution to be existing to the bottom side. I looked at his setup and compared with the Arrow and concluded that the Arrow is the same way - exhaust out the side. It doesn't look as good as center but when I looked at photos from Wolfgang he also had it out the bottom side.

Now if Jeff did the twin exhaust nascar style for the Skymaster it would be awesome!

Matt

Originally Posted by Huang

Just thinking about how the exhaust is routed is pretty sophisticated work, from the inverted engine back up to the pipe on deck, and then back down to exit the underside of fuse. Quite a bit of work especially in the 25 size plane! The Magic is the other one that I recall having this same config, everything after that went with the belly mounted pipe...

Matt

That's right Matt. The one thing that bothered me and others too was the fact that the 25 size MK Magic was designed to use a side exhaust side mounted engine. This sort of breaks with the idea and lines that Hanno originally conceived for the Magic. The 40 size was designed with a similar engine/exhaust configuration as the 60 but the 20 wasn't. We have been fooling around with a CAD version of the MK 20 Magic to see how the front end could be modified to adopt the same configuration as the larger Magics and the Skymasters.

Interestingly, the early Skymaster 40 (which I originally believed didn't exist, but it does, or rather, did), breaks this configuration too using a side mounted engine. I don't really get the reason why Kato went back and forth on this front other than perhaps whatever engine he may have had available and wanted to use in the particular designs.

OS VF's existed in 21, 25, 40, 46 and 61 at the time so there was really no reason to design otherwise. I've always wished that YS had made a 25 or 32 in addition to the 45 and 60. A little YS 25 FR just like its bigger brother, the 45 FR, would have been very cool!

David

Originally Posted by doxilia

Yup! Exactly how I envisioned it..., albeit too long ago now.

Awe come on, I only started in June (of THIS year)!

Originally Posted by Huang

Now if Jeff did the twin exhaust nascar style for the Skymaster it would be awesome!

Matt

You don't know how long I mulled over that idea. I spent countless hours scouring the internet for aluminum and copper wye's.... I even called Jtec who offered to make me a custom wye in 7/16" aluminum.

Is it too late to patch those holes????

Originally Posted by Huang

David,

I meant to say that the exhaust for the Arrow will also come out to one side at the bottom (rather than center). I remember reading Jeff had to deal with this and found the best solution to be existing to the bottom side. I looked at his setup and compared with the Arrow and concluded that the Arrow is the same way - exhaust out the side. It doesn't look as good as center but when I looked at photos from Wolfgang he also had it out the bottom side.

Matt,

Got it.

I've been thinking some about this business because I've been drawing up a CAD version of the 40 size MK Arrow. I haven't touched it in a quite a while but I wanted the exhaust to come out the bottom and debated whether it would be better to offset the exhaust and keep the pushrods closer to the fuse center or vice versa. In the end, I decided to go with Jeff's SM approach primarily due to how the tail boom is built (the bottom is contour sheeted rather than flat) and it made it easier to keep the pushrods centered and not make a hole in the center of the fuse bottom.

On a 60 size Arrow though, one option would be to use a pair of mini servos to actuate the elevators. If placed close to the sides of the fuse, the pushrods would run down the length in such a way that the exhaust can exit center bottom with the pushrods on either side. One could presumably do this with a single servo too but with a little more pushrod routing.

In any event, if your Arrow is built and flying, it's probably irrelevant and I should stop digressing Jeff's excellent thread!

David

Originally Posted by doxilia

Yup! Exactly how I envisioned it..., albeit too long ago now.

More of a comment on the length of time I've wanted to build one of these puppies rather than the length of your build... Hey, anyone who can get a pattern bird framed, geared up, finished and in the air in 6 months is cool in my books!

Originally Posted by doxilia

Matt,

Got it.

I've been thinking some about this business because I've been drawing up a CAD version of the 40 size MK Arrow.

David

David,

Quit thinking about the Arrow and start thinking about the Super Chipmunk!!!

(Sorry to mess up your thread Jeff.)

Doug

Originally Posted by Fatherof4

David,

Quit thinking about the Arrow and start thinking about the Super Chipmunk!!!

Doug

He, he...

Behold, for the mind is an expansive thing... plenty of thinkin' to go around!

I will be bouncing some ideas off you in the not too distant future.

End of digression,

David

Originally Posted by doxilia

That's right Matt. The one thing that bothered me and others too was the fact that the 25 size MK Magic was designed to use a side exhaust side mounted engine. <snipped>

You know David actually most of the MK 25-sized planes used a side exhaust configuration even if the original 60 size was rear exhaust. The MK Aurora 25, for example, used the side exhaust configuration with an S-header.

I think I know exactly why this is -- it is mostly a sales/marketing reason. In Asia and in Japan, the most popular size by far for R/C aircraft is the 30 class (.25~.36). It is like a .40 size is the most popular size in US. There are dozens engine choices in that size and modelers all had them. However they were all side exhaust - OS 25VF being the only rear exhaust. If limited to OS 25VF it restricted the modeler to the only one expensive DF engine. If using side exhaust, everyone had many cheaper Enya 30BB or OS 32F laying around to use and Hatori made matching S-headers for each. It's like if you made a kit in US only for a rear exhaust 40 how many would you sell. Now if you made it a side exhaust, you had a much bigger market. The 25-sized planes were not really for pattern competition but a cool looking sport plane, so by making it side-exhaust it was more practical and MK had a much broader market to sell to.

This is what made the Skymaster 20 so special and why there were so few... it is truly unique in this configuration. In Hanno's write up on the Magic in '81 he said he designed the inverted engine with enclosed pipe on top deck because it reduced pipe temperature by separating engine cooling and pipe cooling (vs. a design like the Arrow). He also said the inverted engine reduced noise because it was cowled, something that if true would carry over to the Skymaster 20.

All in all it just looks so damn cool, right? So that we can continue here chatting about Jeff's cool plane and pollute his thread...

Originally Posted by Generic Member

You don't know how long I mulled over that idea. I spent countless hours scouring the internet for aluminum and copper wye's.... I even called Jtec who offered to make me a custom wye in 7/16" aluminum.

Is it too late to patch those holes????

Haha... Jeff it would just be cream on top of an already super rare classic! Macs might actually make you the Y out of a header pipe if you show him the project. Would be super awesome!

Those hobbico exhaust stacks you mocked up are hilarious, I almost fell off my chair when I saw that.

David, on the Arrow 60 I even thought of using an MK bell crank and offsetting the center horn and pushrod so that I can make space for the exhaust to come through in the middle. But as you said it's already built and flying so it's too much work. And if coolness was the factor, the Arrows look coolest with the exhaust straight out back!

OK no more polluting Jeff's fine build thread!

Originally Posted by Huang

You know David actually most of the MK 25-sized planes used a side exhaust configuration even if the original 60 size was rear exhaust. The MK Aurora 25, for example, used the side exhaust configuration with an S-header.

Quite true, but I don't intend to keep it that way. For example, the Aurora 30 that we've been redesigning is going to be more like a mini A60: glass pan, plug-in wings, inverted RE engine (OS 25, MVVS 28, OPS 29, Enya 32), Hatori 300, all the cool stuff. As for the Cosmos, it uses a SE engine but with a pipe tucked into a tunnel in the fuse under the wing. The Skymaster, well, it's taken care of. The Magic, we're modifying. Last but not least, I will one day create an Arrow 25 setup like the Arrow 40 except for the 25 VF or MVVS. The Blue Angel, Mattlas and Curare are vintage classics ('70's), smaller and I plan to leave them as is with SE engines and fixed gear.

I think I know exactly why this is -- it is mostly a sales/marketing reason. In Asia and in Japan, the most popular size by far for R/C aircraft is the 30 class (.25~.36). It is like a .40 size is the most popular size in US. There are dozens engine choices in that size and modelers all had them. However they were all side exhaust - OS 25VF being the only rear exhaust. If limited to OS 25VF it restricted the modeler to the only one expensive DF engine. If using side exhaust, everyone had many cheaper Enya 30BB or OS 32F laying around to use and Hatori made matching S-headers for each. It's like if you made a kit in US only for a rear exhaust 40 how many would you sell. Now if you made it a side exhaust, you had a much bigger market. The 25-sized planes were not really for pattern competition but a cool looking sport plane, so by making it side-exhaust it was more practical and MK had a much broader market to sell to.

Makes perfect sense. But this market just loves RE engines (myself included) so I want to have true mini pattern ships. Not for competition, just because, like you say below, they are so damn cool!

All in all it just looks so damn cool, right? So that we can continue here chatting about Jeff's cool plane and pollute his thread...

Matt, you should post more often, your thoughts and contributions would be great! We want to see that Atlanta going together!

David

PS Jeff, I think I mostly kept it within the realm of MK 20 size classics. Please don't lynch us for our transgressions!

Originally Posted by doxilia

Jeff, I think I mostly kept it within the realm of MK 20 size classics. Please don't lynch us for our transgressions!

Guys, it doesn't bother me at all. I enjoy the conversation.