RickP

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Hey Thanks for the reply!
According to the Dick Sarpolus article the first painted airframe came in at 30oz, but it did fly. His second using monokote came in at 25 oz. He claims that it might be possible to do better, and of course I hope I can do so. I remember the A4 as well, but it looks to me like the airframe is just too heavy. Do you know how much that weighs? Can you weigh one of your models for us? It just seems to me that the F16 wing loading and weight looked favorable to something that might actually fly well. After all it hardly looks like a F-16, it doesn't have the complicated and heavy dual inlet for the fan either. I'm hoping pumping it up to a .090 and keeping the weight low I'll have something that can fly reasonable. If I can do split ess's and perhaps even a half cuban with the aircraft I'll be estatic. I'll yield on the half cuban but if I can manage that It would be a total success.

I thought a lot about the Kadmax unit, but I really couldn't find one. Then I thought a lot about the hopped up .21's for use in cars and they looked promising 35 to 40K RPM but the weight was astronomical compared to the .090 and I wasn't increasing the wing area, so I bailed out on all of that. So I have designed my own version of the RK-709 for use here.

The design of my fan unit is complete. But I want to go back and have another run through it. Try to reduce some weight and make it a little simpler. I think I am going to reduce the rear stators from 5 to 4 and carve some hardwood out of the motor mount. The overall package fits the existing design well (see attached Pic). When I am finally done with that I want to design a test stand and some tooling to help assemble it. Then I'll send it all out to a kitter to have it all laser cut.

I have purchased a 3oz bubbless tank and Fueler (see pic). A lot of my research showed that the pod fuel tank was a real source of frustration. I think the bladder tank will eliminate that. I think there is a lot of room for it up front, but I'll have to mount it above the needle valve and I hope I don't have a problem with that.

That's where we are to date. I hope by next weekend to have all the drawings out to the cutter.
Rick

RickP

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Here is the photo, I had technical difficulites uploading it last time.
RP

Jaime_Arenas

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Rick,

where did you get the fuel tank?

Thanks,
Jaime

Jaime_Arenas

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By the way, there's a Kamdax Mig 15 for sale on ebay right now; it's the one with the DF unit and engine. Just search for Kamdax and you should see it. Depending on where your having the parts for your fan made it may be cheaper to just buy this thing.

Regards,
Jaime

RickP

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Jamie,
From my old Quickie 500 days. Darol Cady http://www.darrolcady.com/index.htm Look at the Tetra tanks. I was suprised that he had a tank as small as the 3oz but I think it will be perfect. Too bad I lent my fueler out and never got it back, $35 I shouldn't have had to respend Darol is a great guy.
Rick

RickP

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Thanks! I'll watch it, but if it's more then $150 I'll just get a habu. This is more of a nastoga thread as mentioned earlier. With that said common sense has been tossed out the window a long time ago. Amazingly RK-40's keep popping up on Ebay all the time. They seem to - increduliosly - go for more than $80 each time.

Rick

Jaime_Arenas

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I get the nostalgia bit. I'm building a Sterling Corsair; it's a terrible kit, but I'm having great fun building something that reminds me of why I got into the hobby. I may follow your lead if I get my other projects knocked out. I have a Kamdax fan unit and engine that need a new home. After reading your thread I rummaged through the shop for my Kress F-16 short kit that I bought years ago. After looking at the plans I decide that the Kress F-16 would be too large for the little Kamdax DF unit; but it may be perfect for the E-flite 32 EDF unit.

jaime

RickP

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The Kamdax jet went for $100, a little to pricy for my taste.

I finished my DF design, created the drawings and sent them in to have them laser cut. I am getting 1 Mini F-16 short kit and enough parts for two of my DF designs. I'll start assembling the DF first and see if it produces any thrust.

Attached is a PDF of my fan assembly. Included with the DF kits I designed some assembly tools too. A test stand and a drill fixture for the stator blades.

I have to get an adapter machined for the TD and I need some machining work done on the fan rotor.

RP

RickP

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Hello All,
I got the laser cut parts today. I also should be getting the rest of the balsa and plywood I ordered from balsa USA soon. I attached pics of the laser cut parts. A few items to note, first the horizontal stab came in busted up, too bad. not too upset, it should be easy enough to cut that myself. I was hoping to see the fuselage sides and doublers, but they seem to not have been included. To my surprise he also cut the fins to the missiles which get fixed to the wing tips, but there are only two, I need 4. I dropped him a line so lets see what he says. With all of that said the Ducted fan parts look amazing. More so the tooling I ordered looks great, I have the engine stand / assembly fixture and the drill fixture looks great.

The next step is to get the 1/64 ply and form the cylinder for the fan. I should have that soon. I need an exactly 3" OD mandrel with witch to wrap it around and it's not too easy to find. I bought some PVC fittings at Home depot today. Not quite the right size but maybe I can build it up with something.... More to come
RP

RickP

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Looks like my Balsa should arrive tomorrow, not much I can do untill then. I built an adapter or mandrel to wrap the 1/64 ply around but it's not perfect. I think I am just going to use the rings I had cut and some clamps with some hardwood. Lets see how it looks once I get some material in my hands.

Also I purchsed off of Ebay a CD of Ducted fan design articles including the Kress design documents. Interesting stuff. According to cres the annual area of the fan sweep should be equal to the OD of the tail pipe for a zero restritcting flow. The way I designed my fan I'll need to choke off the taip pipe a bit. Plus it looks really important that I get the inlet fairing right. I'm not sure how I am going to do that. I was thinking a large foam block but maybe Balsa would be easier to deal with. I'm not sure how I am going to do that yet.

Rick

RickP

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Still no Balsa yet [] - Worse yet I am all out of glue, so not much I can do. Good news is that I should have all of that today.

I did however read all of the articles I purchased from that CD and from Kress's design criterior (I know his graphs are highly contested) I can see that the fan I have chosen is a reasonable choice. It's a 6 blade 3" od fan with a 50% diameter hub. Also according to this I need to reduce the OD of the tail pipe to 2.6". This is in contrast to the existing design, so I'll have to cut 3 new formers for the tail pipe, I'll give it a conical shape to reduce from 3" to 2.6" at the exit.

Also, from his graphs its clear I should get close to 24oz of thrust with the .090 and 3" OD fan. That would be a 1:1 thrust to weight ratio which would be outstanding. I really doubt I'll get that good of a deal, he has published his RK-049 he calculated 22oz of thrust and the best he could manage was 17oz of thrust. Even if I get 17oz I think I can call this a success. I think 17 would be a good worst case senario and as such worthwile building this misfit!

I am also going to have to carve a good inlet. This should be fun. I ordered some 2X4 blocks to laminate so I can begin to hog them out and get started on that.

I did start building my assembly Jig / test stand - untill I ran out of glue.

No real progress to show but the end result is becoming clearer in my mind!

RP

RickP

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Okay guys, spent a little bit of time working on the Ducted Fan cylinder. I think it went together pretty smoothly. I had decided to build two along the way, and good thing! I messed one up! Glued the rings on in the wrong order, that's going to take quite a bit to fix so I'll just shelf it for now. I am really happy with how the seam came out on the inside.

Rubbernecker

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And what might that amber colored beverage be in the background of picture 4? Now I see why you messed one of them up. Looking good.

John

skaliwag

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Amber liquid is accelerant

combatpigg

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Rick, it looks perfect...! Is the seam fiberglassed..?

Skaliwag, the amber liquid is "retarder".

RickP

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Hello,
Nope, I cut a small 3/4" strip of 1/64 plywood to back the seam up. I put a relief in the 1/4" rings to allow for it. I drew it all up in 3D Autodesk inventor. I used the sheet metal module for the cylinder and the "contour flange" command. I then unfolded it and printed it all out and just traced and cut it out. it's amazing it all fit perfectly! I glued the backing strip to one end of the unfolded tube material first and then slipped all the rings over and tack glued it!

I think the liquid is Green Flash IPA. ;-)

RP

RickP

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So I finished the outer ducted fan body. I hogged out all of the cylinder body under the dome with a dremel from the inside. All I have to do is fuel proof and paint it. The inner motor mount will be next, but before I can start on that I have to drill out the stator supports. I need a drill press for this and am going to have to buy one. I have to drill several 4-40 clearance holes 1 1/4" long. It's going to be a tricky operation, gonna need to make a few practice runs first.

I also put the motor and fan into our machine shop with the adapter drawing. They said no problem they can do it for me, but one guy is on vacation next week and it's probably going be three weeks before I can get it. Oh well, I guess beggars can't be choosers. I should have given it to him a couple of weeks ago when I first dreamed it up. Anyway I can't complain for free.

I think next up for this project will be the tail pipe and formers. After I bought the laser cut kit I dreamed up the tapered tail pipe so all of the hole diameters in the three rear formers need to be a different size. Thank god for the unfold command for the tail pipe, it's tapered so only the long stream is straight. I already cut that out. I have to make the three 1/16" formers next.

RP

RickP

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Here is a better shot of how I backed up the seam. If you look close you can see where the laser cutter made a relief for it. And yes, more "Retardant" in the background
RP

RickP

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I am working on like 4 projects at once. It drives me nuts! but that is the way it is at the moment... I started the motor mount last night. You can see the arraingment I am planning on below. I have started second guessing myself. But I don't know what else I can do at the moment. I have to be able to service this thing, so the front mounting plate must be removable. Hence, I have designed it with two 4-40 screws to remove the front mouting plate. I had hoped to be able to get some thread insert into the maple runners but there is just no room for them. So I will have to use wood screws. I know over time wood screws don't hold up too well in this application but not sure what else I can do. I can't go through to the back and use tee nuts. Any comments would be appreciated at this point!

combatpigg

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Rick, if you repeatedly harden the threads in the wood with thin CA you can't do much better than that.
Even if the threads lose their grip, you can pack the holes with stainless aircraft safety wire pieces and that will give those screws something fresh to bite into.

juanjulian

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Rick,

Nice build! Seems you are having a blast designing and building. Envy your building time.

Test your fan before installing in plane.

You are the king of nostalgia projects.

Cheers,

Juan

RickP

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Thanks Guys,
With this project when it stops being fun, thats it! So far so good!

Yes, my first order of business is finishing up the fan unit. I am going to make sure it runs and produces some appreciable thrust. If so, I'll move on to the tail pipe and inlet. I plan on bench running it like that and trying to make some kind of thrust measuremnt. Provided both of those are favorable I'll proceed

Combat Pigg, thanks for the suggestion. Sometimes on these smaller things you have to make some exceptions to keep it light and reliable. Somtimes I forget that I can always go back and fix it!

Rick

combatpigg

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Rick, the hardest thing is to find good New England Rock Maple any more. It used to have such a tight grain it was almost like working with aluminum.
The stuff that the hobby industry sells now is like cottonwood compared to the old stuff.
In our area there are hardwood suppliers who can still get the primordial wood, but it is getting scarce.

Crosscheck

Hi RickP,

Nice Project ![8D]
I am following along...

R.E: 'getting removable bolts in your Maple motor mounts'... question...:

-back in the 70s!, I had an upright .35 CL stunter that pulled out 6in. too low, one outside loop ...

-the engine bolts ripped out of the 'buried' cheap/soft T-nuts.[]

Long story short, One of the 'old then!' Experts told me how to fix it[8D]:

-drill out the holes to the brass tubing larger than your mounting bolts.

-rough up the outside of the brass tube... plug the ID with a balsa 'peg'.

-glue in with '24hr Epoxy' ( the longer the cure, the stronger the epoxy, 5-minute is like cheddar cheese !)

-drill out the balsa peg, then tap for your bolt...

That is it !

Done it several times.

Not sure if it is the epoxy holding, but I know the brass tubing looks more like a heli-coil...

Anyways, I could remove/re-tighten engines...

Hope this helps...

Take care,
Have fun,
Dave'crosscheck'Fallowfield
Maac 6437
Unabashed Combat Team

RickP

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Ahhh,
You got me! I misspoke, it is Birch! I ordered all of my wood from Balsa USA. They have Birch Motor mount stock. It's Okay, but now I wonder if it's too soft. Is there something better I can use?
Rick