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  1. #26
    RickP's Avatar
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    RE: Mini F-16 vintage project consideration


    I think it's about 120 watts at 28kRPM, but with the RK-709 the engine would run much slower and make less power.
    I think you might be right, no way to tell. Do we know what the power output of the .090 is at 18.5K RPM? I see the problem. If Kress did his homework on the RK-709 the output of the fan should be matched to the output of the .090 at 18.5K Before the Picco can get past 18.5K it has to at least match that power output. I doubt I'd be that lucky, it probably has very little mid range that motor.

    So I did as much as I can at the moment. I took the scaled up silhouettes of the .049 and .090 which I received on a separate thread and took a look at them on the plans. The .090 is 1/4" bigger than the .049 and the OD of the RK-049 seems like it is 3 1/16" approx. So say a 3" ID tube. So I would guess I would need a 3 1/2" ID tube for the .090 but I'm at a standstill until I get those fans. They should ship today. I'll report back when I get them.

    RP
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  2. #27
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    RE: Mini F-16 vintage project consideration

    I wouldn't make the shroud any larger for the .09. The RK-709 shroud had a recess for the head.
    Greg

  3. #28
    RickP's Avatar
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    RE: Mini F-16 vintage project consideration

    I've read some success stories using the car nitro motors like the picco .12 in these units. Performance seems undeniably better. However that motor is 8 oz without the muffler or pipe. the .090 is 2.5 oz. It seems to the key with this air frame is to keep it light. Keeping it simple will help too. Then I'd need a throttle servo and the pipe, it's making this too complex, so the .090 is going to have to be it.

    Okay, we will keep the shroud the same size. I should have the plans for it shortly so I'll know what to do. How think do you think the plywood Shroud should be? Is 1/32 ply sufficient?

    RP

  4. #29
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    RE: Mini F-16 vintage project consideration

    Hy Rick P

    I understand nostalgic and that is why I always check on this forum.

    Started into Rc with the cox .049 control line, and always wanted a small .049 RC plane. 25 years ago this was impossible since there was no small rc equipment like today.

    You can´t FIND any good fan for a .049 or bigger engine SINCE THEY ARE OBSOLETE, having to coform with old stuff. THE ONLY WAY TO GO AND HAVE A GOOD PERFORMING PLANE IS BY GOING ELECTRIC.

    You can have the best of both worlds, a nostalgic and classic design plane, with TODAYS PERFORMANCE.

    For sure going electric will be cheaper and less effort, than finding old stuff highly overpriced since are colector items for nostalgic persons, and then trying to match a high performancesmallglow enginethat are hard to find since electric hasovercome this size ofdisplacement.

    MYPROVEN RECOMENDATION FOR A ELECTRIC FAN FOR YOUR PLANE( almos plug and play)

    HET OR WEMOTEC FAN 70MM(diameter of fan 6 mm less than the RK)

    Electric motor: het 2w brushless motor (400 watts)

    Speed controller: 40-60 amp.

    Battery:lithium polimer 3S 2200-32000mah

    The easiest is to buy a combo like http://www.ejf.com/index.php?main_pa...roducts_id=449

    Battery can be purchased here http://www.hobbyking.com/hobbyking/s...arehouse_.html

    The best EDF information is at RCGROUPS since here at electric jets is mostly foam toy edf planes.

    Hope this info works,

    Cheers,

    Juan

  5. #30
    RickP's Avatar
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    RE: Mini F-16 vintage project consideration


    ORIGINAL: THE ONLY WAY TO GO AND HAVE A GOOD PERFORMING PLANE IS BY GOING ELECTRIC.
    Juan,
    You speak the truth. But honest is, that if I am going EDF (and I will in parallel with this!) is to just get a modern foam EDF. Already less then I have spent! I just watched a well used Tee Dee .090 go for over 65 bucks. So I pulled the trigger on a NIB .090 for 155 bucks. Add that to the $90 I have already spent in fans and I am shaking my head. Well all I can say is that I am having fun.... My best buddy is flying a habu and has more flights on it than I can imagine. At some point I'll have to get some stick time in on it. When I stop having fun, i'll box it up and put it on the shelf
    Rick

  6. #31

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    RE: Mini F-16 vintage project consideration

    Hi Rick,
    Hey I missed this thread- I like what you are doing, and I think your ideas about keeping weight down in the engine dept. are dead right.
    It might be a good time to remind you that you have to be really careful with weight in the structure too when you are building DF- most people would balk at the idea of strapping a 130gm++ engine on a 1/2a plane, but that is the reality of what you start with when you make a ducted fan plane with the weight of the unit plus engine. You just have to keep the weight down on other parts of the plane and all is good- I think it is all part of the challenge- after you have made a ducted fan plane and flown it, making prop planes starts to seem kinda too easy.
    I am really looking forward to seeing how your plane turns out.

    J.M

  7. #32
    RickP's Avatar
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    RE: Mini F-16 vintage project consideration


    ORIGINAL: think your ideas about keeping weight down in the engine dept. are dead right.
    Thanks bro, I hope you are right. I did several other "nostalgic" aircraft and have not had the results I have hoped for. I hope this one is different.

    Okay,
    So I have purchased an NIB .090 and a box full of parts to an RK-709 fan.... My next step is to build the fan unit. and run it. I think I have pretty much committed to this step at this point and I will keep you posted here. I think a used .090 unit is next to fab up the fan unit and maybe even get the test stand running before I break the seal on a new engine is on order. A couple of questions.

    There are no dimensions on the plans for the fan units How much clearance should I design between the fan and the shroud?

    Should I use 1/32 or 1/64 plywood for the body of fan unit? (Ive looked at CF and it is too expensive and too heavy. Plywood seems to be the best answer so far...)

    Looking ahead:

    I've found a 3oz bladder tank used for pylon racing, I'll have to mount that remotely. Good or no? is 3oz enough?

    Radio gear: I am thinking about one servo per aileron as in the larger birds I fly, what servo would be good?

    I would love to add a rudder servo, worth the weight or no? I think not, but comments please (I am thinking nice axial rolls at the bottom of a split ess....) No throttle, no point in it at this point. Maybe I can mix in flaps if I use two servos....

    BTW, happy new years guys!!!
    RP




  8. #33

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    RE: Mini F-16 vintage project consideration

    Thanks bro, I hope you are right. I did several other "nostalgic" aircraft and have not had the results I have hoped for. I hope this one is different.
    I think the key here, is to realise that the TD09 and fan are probably going to only put out as much thrust as a TD049 with a prop. So approach the whole plane contruction with that in mind.
    A C/L plane might be built a bit heavy- see if you can cut out any weight in the design.

    About the tank. With a prop plane you would be fine with an off the shelf tank, but they weigh too much for a Df plane, and it gives you a chance to claim back some weight. I think a balloon tank might be a good option- there is room behind the engine for a tank or a cylinder (rolled cardboard thats been fuel proofed ) to hold a bladder/ balloon. I have read here about rolling tanks from sheet styrene- the glues and styrene are fuel proof as is, you this could be an option.

    Servos- I would use 5 or 6 grm servos in each wing- thats all you need. I would use a single 9gram on elevator and leave out rudder at this stage.
    You also want a 2/3AAA battery pack or lipo and voltage reg/ booster.

    My first DF plane flew fine, but glided like a manhole cover. This was because I was not really careful about weight, and it ended up heavy, and I would hate for yours to end up the same.

    J.M

  9. #34
    gkamysz's Avatar
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    RE: Mini F-16 vintage project consideration

    I've made fan shrouds all sorts of ways. One I thought was easy and inexpensive was a glass balsa glass sandwich on a mandrel, not even vacuum bagged or anything. Carbon does look cool, but expensive and it's easy to blow the looks with air bubbles.
    Greg

  10. #35
    RickP's Avatar
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    RE: Mini F-16 vintage project consideration

    ummm,
    This may be a question I should have asked a long time ago. What type of fuel should I be using with the Tee Dee .090? I assume buying COX fuel by the can is no longer possible?
    RP

  11. #36
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    RE: Mini F-16 vintage project consideration

    SIG 25 or 35% Add a little more Castor.
    Real Airplanes have Round Engines and Two Wings.

  12. #37
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    RE: Mini F-16 vintage project consideration

    I've never built a fan shroud, especially one that needed to be perfect to close tolerances and light as a feather.

    Quite a challenge.
    Since the shroud is tied into the model's structure tightly, it needs to have a memory of it's original shape to withstand the bumps and bruises of the Real World without distortion.

    As far as fuel is concerned, maintain an oil % close to 25% and 15% nitro is a nice compromise.
    WHO GUNNA FEED MAW KEEEIDS..???

  13. #38
    gkamysz's Avatar
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    RE: Mini F-16 vintage project consideration

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

  14. #39
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    RE: Mini F-16 vintage project consideration

    I would lay down 1 layer of 2 oz cloth with epoxy over the mandrel and let it cure.
    Next step would be to wind fine music wire over the layer of cloth, possibly using an entire length of it. The trick would be to keep it tight and to solder both ends. Then I would glass over the wire with 4 or 6 oz cloth and call it good.
    A solid, 1 piece mandrel might not want to cooperate with releasing the part, so I would make the mandrel out of 2 pieces of wood with a pair of shims at the parting line that are easily removed.
    If this idea didn't pan out, at least you would still have a reusable mandrel to try different layup schemes with.
    WHO GUNNA FEED MAW KEEEIDS..???

  15. #40
    RickP's Avatar
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    RE: Mini F-16 vintage project consideration

    Wait a second. didn't the RK-049 kit come with 1/32 plywood bent into a circle and held with the plywood rings? Mandrel? That would be no problem. I have help for that...
    RP

  16. #41
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    RE: Mini F-16 vintage project consideration

    ORIGINAL: skaliwag

    SIG 25 or 35% Add a little more Castor.
    Ugh,
    Are you telling me I have to mix my own fuel? can't I just buy something off the shelf?

    is this any good?

    http://www3.towerhobbies.com/cgi-bin...?&I=LXEPD2&P=8

    RP

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    RE: Mini F-16 vintage project consideration

    The first DF unit I got was a wemotec 709 which had a thin glass/ carbon shroud. It was a bit on the flexi side as it was so thin-
    I think it would be just as good made of of a single, thin layer of glass with some ribs of carbon tow wrapped around.
    Glass would be almost as well- the key with the ribs is to make them a narrow ridge that runs around the circumference

  18. #43
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    RE: Mini F-16 vintage project consideration

    You just have to add oil.. Get it at the drug store.. Part of doing something different. ARFers don't even get to build. AND the slaves in China that built it will never be able to afford one in 3 lifetimes.
    Real Airplanes have Round Engines and Two Wings.

  19. #44

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    RE: Mini F-16 vintage project consideration

    Just a thought. For the fan shroud, look at spray can lids. Paint, hairspray, anything in an aresol can with a snap down lid. They are usually plastic so easy to cut with a dremel, and they are light as a feather, and come in tons of sizes!

  20. #45
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    RE: Mini F-16 vintage project consideration


    ORIGINAL: RickP

    Do we know what the power output of the .090 is at 18.5K RPM? I see the problem. If Kress did his homework on the RK-709 the output of the fan should be matched to the output of the .090 at 18.5K
    Yes we do, see test report below for instance...

    I don't think that the problem is simply matching the load of the fan to engine, most fans also seem to work best at very high revs. I don't know much about fans but I believe the operation is quite different from a prop where we think about pitch and pitch speed etc., with the blades digging trough the air. In a fan you develop thrust by ejecting air out through the outlet, it's a different process and they develop more thrust when you go faster. I have only seen a few data sheets for comersial EDF units and they all need very high revs to deliver thrust, I don't think that it is only due to the number of blade and their pitch.
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  21. #46

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    RE: Mini F-16 vintage project consideration


    ORIGINAL: RickP

    ORIGINAL: skaliwag

    SIG 25 or 35% Add a little more Castor.
    Ugh,
    Are you telling me I have to mix my own fuel? can't I just buy something off the shelf?

    is this any good?

    http://www3.towerhobbies.com/cgi-bin...?&I=LXEPD2&P=8

    RP
    Sig makes good 1/2A fuels(but I have yet to investigate), glowplugboy does too from what I have heard. I always add some castorto the fuel I buy from the LHS because its not enough castor for 1/2A, evenglowplugboy fuel is at the 17% castor mark,I prefer at least 20% castor and normally add to my fuels to bring thom up to 25% total lube from the 17% that the norvels require si my engines live long lives.
    I have used that hobbico 1/2A fuel years ago, but I spiked it with some castor just because it does not specify how much of the lube is castor oil and at 18%lube it is a little lower than I prefer. So if you add about 1/2-3/4 oz castorto that hobbico 8oz bottle you should be well lubed for a cox to live a long life. Using it straight may shorten engine life some,but there have been fuel discussions before regarding this matter too. I prefer to get my molneys worth from my engines as much as possible and like the peace of mind that I tried to do so.
    Your preferences are up to you, it should be ok as is to run hobbico 1/2A,fuel but the old cox fuel had more lube than that.
    I try to get as many years as possible out of my engines.

  22. #47
    gkamysz's Avatar
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    RE: Mini F-16 vintage project consideration


    ORIGINAL: Mr Cox
    I don't think that the problem is simply matching the load of the fan to engine, most fans also seem to work best at very high revs. I don't know much about fans but I believe the operation is quite different from a prop where we think about pitch and pitch speed etc., with the blades digging trough the air. In a fan you develop thrust by ejecting air out through the outlet, it's a different process and they develop more thrust when you go faster. I have only seen a few data sheets for comersial EDF units and they all need very high revs to deliver thrust, I don't think that it is only due to the number of blade and their pitch.

    If you are to do a very good fan design you consider inlet and exhaust conditions and optimize the design. Fans only "need" very RPM if they are designed for it. There is a limit to how much power can be absorbed at any given RPM, but this isn't a concern with this project. To get anything beyond a basic fan design take considerable study and understanding of what's happening in a fan. Since we are using a premade rotor here, all that's last is making sure the chosen engine is near it's peak performance. In this case this engine was already used with this fan rotor so it should work well. it's a common misconception that fans make more thrust as airspeed increases. This is true of turbojet engines, but not true of props or fans. A fan can be considered a ducted prop, but as loading increases the theory shifts from prop blade design to close proximity blading formula.

    If we were designing a complete fan from scratch, the method to arrive at best performance would be quite different and include and evaluation of the airframe.

    Greg
    Greg

  23. #48

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    RE: Mini F-16 vintage project consideration

    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

  24. #49
    skaliwag's Avatar
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    RE: Mini F-16 vintage project consideration

    Is there some formula to negate the spinning? ( not to in depth I hope )
    Real Airplanes have Round Engines and Two Wings.

  25. #50
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    RE: Mini F-16 vintage project consideration

    Figure that the first guys to develope the stators had no Divine inspiration or formulas, they just had diplomas that got them well paid jobs to run relentless experiments one after the other, after the other.
    Experimentation that had as much to do with intuition and common sense as it had to do with any existing knowledge.
    The best minds in the World that found jobs developing that new technology were the same ones who were responsible for some the most horrific crashes, burns and epic failures known to man.
    WHO GUNNA FEED MAW KEEEIDS..???


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