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  1. #51

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    RE: Mini F-16 vintage project consideration


    ORIGINAL: gkamysz

    The original RK-049 had a paperboard shroud with a few reinforcing rings made of plastic(?).

    Plywood.... pretty low tech. IIRC, the directions show that the rotor is the same as the RK-709 but you trim the blades to get the RPM up on the .049.

  2. #52
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    RE: Mini F-16 vintage project consideration


    ORIGINAL: Toysareforkids

    *You must also stop the air from spinning from the fan, to straight air to get foreward thrust. (rear stator blades)*

    *My Rk-049 is a hard thin cardboard with plywood rings around it.

    * Pat
    Pat,
    Do you know how "thin" I am thinking 1/64 lite ply?

    The plans for the RK-049 are very specific about the angle of the front and rear sator blades. I assume it's for this reason. See the attached photos, it came with some aligning fixtures as well.

    Rick
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  3. #53
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    RE: Mini F-16 vintage project consideration

    The fact is that The very first guys designing fans and compressors did it it somewhat blindly. That quickly changed as study developed proper formula to get the work done. This is in the early WWII days.

    CP, yes, you can get something done by trial and error. If accepted design methods are not desired here, I'll keep it out of the conversation. I think a rather simple 30+ year old design has some room for improvement but that's besides the point as we are not designing a fan here, just assembling one. I have the fan design paper published by Robert Kress. It should be possible to find it on the net, especially over at the other site where it's been brought up several times. It works and appears to be the method he used for his products.

    Stator blades become more important at high power loadings. I'd just follow what Kress had in his design, even so I think it only removes half the swirl. Few model ducted fans have optimized stators due to limitations in manufacturing. Even straight stators have some of the desired effect. The total swirl loss if left unrecovered is small, but could be useful if the overall system is marginal.
    Greg

  4. #54
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    RE: Mini F-16 vintage project consideration

    This has got to be the longest build thread without any building yet! I just got my .090 today and fan parts will arrive tomorrow. From there I can get on with laying out the fan. There are some extra fan parts thrown in so I want to take an inventory on what I have before I get started.

    I have to travel on business, till next week, so not much else will be happening here for the moment.

    RP
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  5. #55
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    RE: Mini F-16 vintage project consideration

    Well I just got delivered a box of assorted "old" 1/2 sized DF parts. Of most interest / use is the fans themselves. If I can assure I have the right fan, then I can perhaps proceed. There are several in the package, but it seems to boil down to 4 varieties. I would like to identify all of them before I proceed. The blue ones appear to be RK 709 fans which is exactly what I a looking for. I say this because the seller told me he thought they were, one is Identified with RK-709 written on it and is blue (as far as I know they are the only ones which are blue), of the right approximate dimensions and number of blades. From what I can see from pictures on the internet this is what I have. and if so I am in luck.
    The "White" one he tells me is an .049 fan but kit is unknown. I only have this one. I also have two different orange blades and would like to ID those. I believe they are RK 20 fans. not sure. The big difference between the two are the thickness of the fan. One is thicker than the other.
    If you guys can help me ID or confirm the ID of these fans I would appreciate it.

    Kind regards,
    Rick
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  6. #56
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    RE: Mini F-16 vintage project consideration

    The RK-709 fans I had and have seen were orange. I do seem to remember something about a blue 709 rotor and some kind of difference. The one on the lower right looks like it could be a RK-709 rotor. The blue one then looks like it has less pitch. The white rotor is an ancient Morley unit, these were sold as electric. And I do remember at least one article or advert showing a Cox TD or some sort installed in the Morley. The leaves the top left which would probably be the RK-720. I remember something about the 709 being a trimmed 720 rotor.

    Greg
    Greg

  7. #57
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    RE: Mini F-16 vintage project consideration


    ORIGINAL: gkamysz

    I remember something about the 709 being a trimmed 720 rotor.

    Greg
    Greg,
    It could be, I took an inventory of the fans I have, and attached it below. Look at the difference between what I labled the 100-101 and 102 fan. They all look ground down to some extent, but I think it's clear the only difference is the OD in these three blue fans. The 100 fan is labled (by hand) 709. I am going to assume that this fan came from an RK-709 kit. Take a look at a RK-709 kit picture I found on the web. Looks alot like it.

    Apparently the TeeDee .090 was a motor choice for this fan and dimensionally it is the same as the RK-049 which is called out for in this kit. So I think I am going to give it a try. I'll build a DF with the .090 and Blue -100 fan above and if that is remotely positive perhaps I'll continue.

    Rick
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  8. #58
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    RE: Mini F-16 vintage project consideration

    Ducted fan design,
    I'll start the design of my fan before I build it. First thing I need is a 3D model of the Tee Dee. None exist so I modeled my own. next up and a bit more challenging is the fan. it doesn't really need to be exacly to scale, but it's what I do, it's fun and I'll give that a whirl next.
    RP
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  9. #59
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    RE: Mini F-16 vintage project consideration

    Guys,
    It's going to be fun trying to adapt the fan with a 1/4 bore to the output shaft of the Tee Dee. Anyone have any suggestions on a design that won't let the fan spin on the motor? I only have, what is it.., a 8-32 screw on the motor?
    RP

  10. #60
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    RE: Mini F-16 vintage project consideration

    If the 8-32 will hold a prop it will hold the fan. The torque and power output of the engine is the same. I'd start with a simple bushing and see if the fan mounts square. What are you drawing with? How many of the rotors have aluminum inserts?

    I think it will work well.

    Greg
    Greg

  11. #61
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    RE: Mini F-16 vintage project consideration


    ORIGINAL:
    What are you drawing with? How many of the rotors have aluminum inserts?
    Greg, I am using Inventor. I have Pro E too, but I like Inventor for simple tasks.

    The rotors are about 50/50 with the inserts. I'll upldate my chart later.

    Already two design issues. My fan choice hits the carburetor venturi and the head of the Tee Dee sticks compleatly outside of the 3" ducting. My choices for the fan are to either turn it back so it fits and change the blade profile, or space it out. I'm not happy with either choice. And with the head for the Tee Dee I am going to need to duct air over and around it right? Otherwise it will overheat? Not much room in the airframe there, I think the wing spar is right above it.
    RP
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  12. #62
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    RE: Mini F-16 vintage project consideration

    You do have the prop driver on there right? Props would hit the venturi too?

    This is what the parts looked like. A couple photos from the net. There were a few versions it seems. Some with orange rotors, some with blue, some with the preformed head recess in the duct, some without.

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    Greg

  13. #63
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    RE: Mini F-16 vintage project consideration

    Okay,
    Great pictures! I've been searching for two weeks now and didn't find any RK-709 pictures. Where did you get those or what did you search under?

    So I'll add a recess for the head, gotta pull the plans out and see what that does to the airframe. maybe I can move the whole fan back since I'm not using a tail mounted tank.

    Yes, prop spacer is on here is a cut away view. I think the best thing to do is just add another spacer and move it away from the venturi. That is just alot of mass spinning way out there on a motor which has no ball bearings, and no way to dynamically balance the spinning mass. I'll mull it over a bit more....

    Thanks!
    RP


  14. #64
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    RE: Mini F-16 vintage project consideration

    I just typed rk709 and rk-709 in the google image search. One is from a french site the other from a classified ad here at RCU. Looks like the section didn't make it.
    Greg

  15. #65
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    RE: Mini F-16 vintage project consideration

    Made some progress on the DF design on Friday, forgot to take some screen shots so I'll post some next week.

    Quick Question, how the heck am I supposed to attach the glow plug clip if it's recessed inside the DF unit?

    RP

  16. #66
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    RE: Mini F-16 vintage project consideration


    ORIGINAL: RickP

    Made some progress on the DF design on Friday, forgot to take some screen shots so I'll post some next week.

    Quick Question, how the heck am I supposed to attach the glow plug clip if it's recessed inside the DF unit?

    RP
    One is to have a small hatch that will allow you access to hook up a glow clip and to change the glow head. Use a rare earth magnet to hold it closed.

    You could also modify a glow clip to be wired to a remove connector.

    Unfortunately either way will add weight.

    Hogflyer
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  17. #67

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    RE: Mini F-16 vintage project consideration

    And with the head for the Tee Dee I am going to need to duct air over and around it right? Otherwise it will overheat? Not much room in the airframe there, I think the wing spar is right above it.
    I would rotate the engine 90deg if it suits the airframe, and not worry about head cooling too much- you have the most ultimate forced fan cooling known to man on the cylinder- it should be fine, and at 90 from vertical, you can address that later if it isn't. With the head on the side of the plane, it should be easier to attach a glow driver, and avoid accidentally flooding the engine too.

    J.M

  18. #68
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    RE: Mini F-16 vintage project consideration


    [/quote]

    One is to have a small hatch that will allow you access to hook up a glow clip and to change the glow head. Use a rare earth magnet to hold it closed.

    You could also modify a glow clip to be wired to a remove connector.

    Unfortunately either way will add weight.

    Hogflyer
    [/quote]

    Excuse my ignorance, this is my first 1/2A in 30 some odd years. Looks like a bunch of guys are just using standard glow plug adapters but they have to hold them on. Like the normal ones... http://www3.towerhobbies.com/cgi-bin...&I=LXJ799&P=ML

    is this the case? I'll have to pull out my old glow stuff and try it. I've been flying gas for quite some time....
    RP

  19. #69
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    RE: Mini F-16 vintage project consideration

    Did you get the venturi interference sorted?
    Greg

  20. #70
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    RE: Mini F-16 vintage project consideration


    ORIGINAL: gkamysz

    Did you get the venturi interference sorted?
    Hello Greg,
    Yes I decided to make a spacer for the fan. I have to make some kind of adapter to get the fan to fit to the motor anyway and I have access to a full machine shop at work so I designed a spacer / adapter to resolve that issue. Before I get it made I want to finish the entire fan design.
    I'll attach where I am so far. I have to spend some time looking at how it fits in the airframe at this point, before I get to far along with the details. I have a feeling I have it designed too long and I want to see how the bump out for the cylinder head fits.
    Rick
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  21. #71
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    RE: Mini F-16 vintage project consideration

    OK, I see now. I've never seen a recessed Kress rotor. If you don't have a convenient source for the spacer, contact me. I'd make the rings from 1/8" aircraft ply. Leave a short lip on the ends of the shroud to allow a sleeve to slip over the fan shroud. This will make connecting the ductwork much easier.

    Greg
    Greg

  22. #72

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    RE: Mini F-16 vintage project consideration

    Wouldn't it be easier to machine some off of the venturi? I mean, you've got a FAN in front of it so machining a little flat for clearance isn't going to hurt breathing efficiency much, if at all.

  23. #73
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    RE: Mini F-16 vintage project consideration


    ORIGINAL: DeviousDave

    Wouldn't it be easier to machine some off of the venturi? I mean, you've got a FAN in front of it so machining a little flat for clearance isn't going to hurt breathing efficiency much, if at all.
    I thought about that breifly. I was going to need to file away almost half of it. More than I was willing too. I'd rather turn down the fan at that point, but I am going to need some kind of an adapter anyway, So i think this is the path of least resistance.
    Thanks!
    Rick

  24. #74
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    RE: Mini F-16 vintage project consideration

    Okay Guys,
    Thanks for all of the advice. I think I have the external design / package finalized. I moved the rings back to allow some lip for the fan unit to interface with the model (Thanks Greg). I moved the "seam" up to the top and added a cap strip over it, I have to cut away a fair amount of it anyway and the cylinder head structure should stiffen it up. The OD is good and I'm a little bit longer mainly because of the bump out for the cylinder head, but I think I am just going to leave it. I modified my rings to work in the structure. The little cylinder head bump out fits in quite nicely under the wing with no need for further modifications.

    What's left, I have to come up with the motor mount and how that is going to interface with the stators. I am using an external fuel tank so that should not be an issue. Speaking of which since there is no fuel tank I don't really think I need that riser behind the cylinder head so I am going to delete it. I ordered a 3oz bladder tank and fueler used in Plylon planes for use here. I think it will solve the notorious fuel problems these things had. Plus I will use the crankcase pressure.

    So as soon as that is done I'll draw up the parts I need and convert them to a DXF for the laser cutter and order the fan and the kit at the same time. I'll keep you posted as I go.
    Rick
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  25. #75
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    RE: Mini F-16 vintage project consideration

    I just saw your project and I love what your doing. I was a huge advocate and early adopter of the RK049, unfortunately it wasn't a great performer. I certainly remember the F16 plans and always wanted to do one but my plane of choice was the A4 by Midwest, I must have stared for hours at the ad in the 1984 RC guidebook. When I finally built one the results were typical and disappointing, most often you got an extended glide and sometimes I had it settle back in with the engine still screaming away. In addition to the fan unit weighing about as much as it produced in thrust, you had a full sized RC system and battery pack. Today with all the gear available I can promise you that it is possible to build a great flying 1/2a jet. I picked up the Kamdax Mig and found that it flew OK with the wheels on and very acceptable with the wheels off. I have a pretty nice collection of Midwest A4s and RK049s on my collection wall. I did build another A4 totally original and set it on display never to be flown. I built another one electric and of course it flys great. But wanting to have one flying with a 1/2a fan I built what I call the 1//2a A4+. I replaced all the wood in the kit with contest wood, used a Kamdax/Norvel fan, lithium flight pack, sub micro servos etc. The result is a 1/2a ducted fan that can taxi out, rip off the runway and really fly. I am not sure of the airframe weight for the F16 but if you build it light you can be sure of a good flying plane.

    Where are you at with your fan choice, have you tried the Kamdax unit? I suggest it for its performance and weight. I think it would be difficult to beat Kamdax on weight for the fan unit with anything built by hand.
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