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  1. #326

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    RE: Northstar mods - Tell me what you think

    Hi Cougar,  thanks foir humoring my ramblings. The explaination of the tuned pipe was better than anything ~I found on internet but to be super clear bhp suffers at all rpm (compared to non tuned pipe) at all rpm other that what tuned for? So fuel economy would suffer because one would have to cruise at a relatively higher throttle setting? Trade off  os better top if end if tuned for it?

    I am still undecided re pump (not that I doubt your input I would just like wider input). Jen will tap the engine for me and they have the best customer care of any company (RC or not) that I know of. They make the engine and wouldnt tap if unwise.

    I really want reliability (will fit an on board glow, possibly excessive but the engine nacelle can house perry and onboard glow as tank is in fuse) as I am making this my flagship

    VIBRATION or TAP?

    Thanks again
    Happy Landings

  2. #327
    Cougar429's Avatar
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    RE: Northstar mods - Tell me what you think

    Thanks for the reply.

    If you have ever played a musical instrument the idea of tuning, and especially resonance, should be more easily understood. Every structure has a natural frequency it will vibrate at. Resonance is the effect an outside force will impart to cause that vibration if at the correct frequency, (or a fraction or multiple of it). Anything away from those will actually be dampened out and is frequently engineered in to prevent exactly that from happening. If unchecked, resonance from even a very small input source can build to destruction. In fact helicopters are designed so that much of the structure resonates at DIFFERENT frequencies so that anything hitting a natural resonant frequency of one part of the structure would be dampened out somewhere else.

    This is exactly what happens inside the tuned pipe when the engine pulses, (RPM) are NOT at the natural frequency inside the tube. Instead of a smooth flow they will bunch and bounce around inside and partially block the charge transition inside the cylinder. This is where you will notice a very large drop in power. Tuned pipes are very "Peaky", meaning they have an extremely narrow peak power band. Inside that band they scream. Anywhere else and they are dogs.

    That peak can be dramatic and can stress a poorly designed or manufactured engine. In the case of the Northstar I would not think it needed at all. If the plane is built to spec or not anvil heavy then anything in the 1.4hp range and up should fly it fine. In any case, that power really only translates to top speed and expecially vertical performance. Unless your eyes are exceptionally good at long distances I doubt either would be necessary as I find planes get small VERY fast, (and I spot for my friends turbine, clocked at 237MPH!). You also would want a very smooth and reliable power band where the engine gives good performance all the way from idle to WOT. Unless racing very rarely would you run the engine start to shut down "Balls to the Wall".

    Yes, it can honk you out of the water on engine power alone, but a properly designed hull is more effective at that. In some cases any amount of power would not get a plane out of displacement and was akin to towing a dead elephant. This is definitely not the case with the Northstar.

    If the engine maker is installing the tap then I would say there is no better way. It would also mean you can effectively run the pulse type pump. I found them easier to tweak than the shaker type, but that might just be me.

    If your motor is tuned correctly and with good fuel I don't think an onboard glow would be a good installation. If anything affects the plug to the point it cools off and won't promote ignition then adding glow will simply slow the process. You have to hunt down the cause first and foremost for reliability.

    On that note there are some pointers. For any mount orientation tank height is key to reliability. In your case with the pump then getting the setting right through the power band may take some work. I would not fly and definitely not go floating away unless I am confident it will idle reliably.

    Along with seasonal plug changes, (I use OS #8 for warm weather and switch to #3 for cold) anything beyond 90 degree side mount and you should be looking at a 4-stroke plug as they tolerate the heavy dose of fuel and oil better. You should also flip the motor over by hand first and avoid whacking it with a starter as fuel can pool in the cylinder and lock the piston. This is bad if you force things as components can bend or be damaged.
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  3. #328

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    RE: Northstar mods - Tell me what you think

    Thanks Cougar, I gottcha- first, second third etc harmonic envelopes!

    My build is actually getting cheaper now (no tuned pipe, no on board glow system). Re: the glow system I was going for belt and braces i.e. making a reliable engine even more so, not trying to make an unreliable engine reliable......

    As for glow plugs I tend to use OS 8, an infrequent but nice flying temp would be 16 deg C (61F). A more common temperature would be 10deg c (50F). Max temp recorded at my field would have been 26c (79F) about 5yrs ago. I use 5-10% nitro with min 18% oil.

    What do you think of the plug?

    The J'en 56 puts out 1.9bhp- a very handy engine for its weight. I hope tuning with a perry pump is not too difficult as the tank will be going on the CoG- a reasonable distance infront and below the carb. I have no experience with them- do they seem to operate at a specific rpm that they are "tuned" for?

    Your experience is much valued.

    Thanks

    Happy Landings

  4. #329
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    RE: Northstar mods - Tell me what you think

    Once set the Perry pump should work through the entire engine RPM range. The faster the pulses, the more fuel, etc.

    My old style shaker had a return that meant a second line back to the tank. I see the new versions are identical to the pulse in that there are only inlet and outlet fuel lines, (the pulse type has a feed line alone at the opposite end). With the pulse type you want to use the line material supplied as it is relatively stiff and won't absorb pulse energy like regular silicone. This keeps your settings more accurate. Try to keep that line as short as possible and keeping the pulse inlet at the bottom with a slight downward slope to the case as it helps any oil residue return to the motor and not clog the pump. Not absolutely necessary, but especially in cold weather oil can congeal in the line and pump body and resist a proper pulse pattern.

    Except for the inverted engine requiring the 4-stroke plug all year I run #8 on all my 2-strokes down to approx 40F. The switch to the #3 helps retain the heat for better reliability as the #8 can cool down too much at extended idle and when rapidly reducing the power. In warmer weather that #3 can heat too much and burn out, so keep track and change them when necessary.

    NOTE: Don't be too concerned on a new engine to see plugs wipe out. Small amounts of material created as the motor wears in can damage the coil.

    Don't forget, you want to let the motor warm up after starting for a few minutes to allow everything to fit. The colder the weather the more important this is. Your case and piston are alloy and the cylinder barrel made out of steel. When cold the piston shrinks more than the barrel and can slap around, causing scuffing. Once started the opposite happens and the piston expands much faster than the barrel and can bind up, again causing scuffing. On a bearing engine the crank fit to the case is not as critical, but in a bushing motor the same thing occurs as in the piston/barrel fit. A cold motor causes the case to tighten against the crank, reducing or completely removing the lube boundary layer. This can occur between the bearings where the crank needs a relatively tight fit to the case anyway to develop good fuel/air feed into the case. A dose of fuel and hand spinning may help prevent that scuffing.

    I see entirely too many fliers start, quickly set their mixture and go fly full bore. Other than ingesting dirt or dust, (or not using a good after run procedure by treating the motor with oil) nothing harder on a motor. With the Northstar or any other water-craft moisture or a good dose of the wet stuff into a motor has to be dealt with immediately. Even a good flying session should see treatment with after run oil, (I make my own from a 50/50 mix of ATF and air tool oil) before packing things away. As mentioned, a cold engine can wear quickly and that oil will help until up to temp and the oil in the fuel starts to work. It's a bit messy. Still, clean up is a cost I put up with compared to buying a new motor.

    I think with many of my motors now more than 20 years old and still strong performers gives credence to my treatment of them.

    However, we're getting a bit off topic here. I would love to see pics of the installation and perhaps some vids of engine runs and flight. If you need more info give me a PM and I'll try to help.
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  5. #330

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    RE: Northstar mods - Tell me what you think

    Should be getting a big box of wood this Monday/Tuesday, very excited.

    Haven't bought my engine yet but am using a perry pump so weight not a big a problem as could be as fuel tank will be on C of G.

    Anyhow, found a J'en 56 weighing 420g with muffler, rated at 1.8bhp.

    Even the O.S 55ax is heavier (525g) with only 1.7bhp.

    I could go to a .60 but then more power with more weight requires more power etc etc.

    Also did some rough calculations.... the Northstar should have startling performance and be able to prop hang...doesn't seem right....any comments?

    Can post some pics of the UK wooden kit if anyone likes.

    cheers
    Happy Landings

  6. #331

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    RE: Northstar mods - Tell me what you think

    you won't be able to prop hang, because you will not get anything bigger than 11 inch on there (with a bit chopped out of the wing for clearance)

  7. #332

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    RE: Northstar mods - Tell me what you think

    My .02 is build it with the AX .46. My northstar hails the mail. Keep it simple. No pumps, glow drivers needed.

  8. #333

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    RE: Northstar mods - Tell me what you think

    I agree 100%. The 46AX is a great choice for the Northstar. The perfect compromise of weight, simplicity and horsepower. Especially with a Macs pipe. (My 2 cents) A seven pound Northstar looks exactly like a six pound Northstar when it is going by you 10 feet off the water at 90 mph.
    Jim

  9. #334

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    RE: Northstar mods - Tell me what you think

    fair comments, i have found the jen 57 to be the same  weight but putting out 1.8bhp.........

    Cheers
    Happy Landings

  10. #335
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    RE: Northstar mods - Tell me what you think

    Goldenduff,
    Where are you going to fly this beast? Will you be at the Loch Insh event?

  11. #336
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    RE: Northstar mods - Tell me what you think

    ORIGINAL: LADISLAV
    Third scan is showing me digging out what left of my NS. The middle picture is showing 200% NS built by the club member Peter Baab and my 100% un-covered NS and my 50% NS sitting on the top. The bottom picture is from England. I think it is 150% NS.
    Actually that photo in post #320 is of a 200% Northstar built in Northern Ireland by Ian Robb and photographed here on a visit to Scotland (Kilbirnie Loch) in 1996.
    It was powered by a 45 cc Super Tigre glow engine I think.

  12. #337

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    RE: Northstar mods - Tell me what you think

    Hi Alasdair,
    i live near huntly (inbetween aberdeen and inverness)- there is an insch nearby me.....is it the same? When is it? I sent my kit back because the belt was slipping so some parts misshapped. From falcon aviation- did you get his other kit?

    Hope to hear from you
    Happy Landings

  13. #338
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    RE: Northstar mods - Tell me what you think

    ORIGINAL: Goldenduff

    Hi Alasdair,
    i live near huntly (inbetween aberdeen and inverness)- there is an insch nearby me.....is it the same? When is it? I sent my kit back because the belt was slipping so some parts misshapped. From Falcon Aviation- did you get his other kit?

    Hope to hear from you
    Loch Insh is just south of Aviemore, and the Highland Splashin is on September 10/11

    I did not realise that Falcon Aviation could laser cut a Northstar kit.
    I have had 3 NS, but didn't build any of them. The first was built from the kit or (more likely) plan and I acquired it third or fourth hand.
    The second was built by a friend using a foam wing cut by Ric Lorente of Forfar
    The third was built for me using a foam wing again by another friend, John Campbell of Keith. He is up your way and used to fly at Dallachy. Do you know him? John has built a dozen or more Northstars, including a twin and a 150% jet powered one. Three of John's below

    The foam winged versions are good as they are less likely to get hangar rash when hauled in and out of cars, boats etc. And you can pile other models on top.
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  14. #339
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    RE: Northstar mods - Tell me what you think

    On my latest model, based on the Northstar but so much modified that I renamed it the Lochstar, I started with a foam wing core, sheeted it only back to max thickness, and added cap strips on the foam from there to the TE . Then I cut away the uncovered foam leaving what looks like a built up wing, but with the solid leading edge that stands up to rough handling.

    This one is electric, powered by a brushless outrunner and 5S lipo (about 750 watts). photos at the Loch Tay Splash-in near Kenmore, which this year is on June18/19.
    A previous Lochstar had an Irvine 53 with standard silencer.
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  15. #340

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    RE: Northstar mods - Tell me what you think

    My home town is Keith! I live 10miles from there now. Will pm you so as not to bore the others. Loving the pics.
    Happy Landings

  16. #341

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    RE: Northstar mods - Tell me what you think

    Hello again and sorry if I am prolonging this thread. Basically I was not impressed with my CNC kit- accuracy way wrong. Anyhow I'm persuing two options- a scratch build AND the balsa USA. Anyhow I'm going to use a perry pump so engine weight not much of a worry ...I've got a Jen 57 (1.8bhp 480g all up) should I date to use a .60?!(with 3 or 4 blade prop) With perry pump won't have to use weight in nose so could prob still manage 6lb auw. Cheers, Any thoughts?
    Happy Landings

  17. #342
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    RE: Northstar mods - Tell me what you think

    If possible, I'd like to hear some specifics on the discrepancies with the laser cut kit. Perhaps pics of the offending areas would help.

    As I mentioned before I have never had a lot of luck with 3-blade props on 2-strokes. Even with the 1 number reduction in diameter or pitch static thrust drops to approx 2/3 of what you would achieve with a 2-blade. Even with that reduction the motors frequently never get up into the power band and if they do that loss of thrust is immediately and depressingly apparant. For some reason this is not the case with 4-strokes and I am running one on my Saito 91 with very good results.

    On that note you should be aware that the typical rule of thumb with the Northstar is for every gram you add to the tail you will need 3 in the nose. The other issue is prop clearance with the stock pod height. On mine I used the same trick needed for the Seamaster, where I cut down and rebalanced an 11" prop. Some have modified the design to move the pod and attendant motor mount position both upwards and forwards. This seems to be successful and I wish I had known of it when I built my last pair. At this point I am waiting for a MACS muffler for the OS 55AX mounted on mine as it is slightly lighter and a bit better performing than stock. It will also get the exhaust further aft where it won't impinge on the tail surfaces as much.
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  18. #343

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    RE: Northstar mods - Tell me what you think

    Hello cougar, I am on holiday for a week so away from my shed. Basically the guy bosted 0.02mm accuracy (I think!) and this was not reflected in the kit. It should have fitted together with notches and recesses however some notches were missing, some of the ribs broken at the TE and some "mirror" parts were not mirrors of each other. I could have resolved many of the issues but it was an expensive pack of wood so i felt I shouldnt need to. A friend is making me foam veneered wings and I have the plans to scratch build the rest for half the price (will take 10 times longer but i dont mind that). I can also increase prop' clearance.
    Regarding engine choice I am going to use a perry pump so shouldnt have to add nose ballast as the tank will be on the CoG which should help balance. I am hoping that radio and 5000mah 2cell lipo with an 8Amp BEC put up front will negate the need for any additional nose weight thereby offsetting the weight of the perry pump (whilst giving the advantage of constant balance when tank is full/empty).

    Regarding the engine (i have been forced to research this to excess because of sending the kit back and awaiting the wings).
    Jen 57  1.85bhp and 480g
    Irvnine 53 about 1.7bhp and 480g
    or an os 55ax  about 1.6bhp and 500g

    I think a .60 would be overkill especially due to prop clearance? (weight not too much of an issue due to fuel tank/perrypump?)

    Cheers
    Happy Landings

  19. #344
    Cougar429's Avatar
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    RE: Northstar mods - Tell me what you think

    I think you are in for a bit of a shock as most planes specify balance with an EMPTY TANK! ANY weight growth in the back will need to be countered in the nose, so the fact you are moving the tank to the CofG point will simply minimize weight shift from a full to empty tank, not counter permanent weight aft of the CofG.
    Club Saito Member # 787
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  20. #345

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    RE: Northstar mods - Tell me what you think

    Fair point Cougar but......

    On the plans the CoG is set with the tank empty. So acceptable flight will be from this point (tank empty) to slightly rearwards (when tank full).  I would assume the optimum CoG will be between these values. A few folk have been saying the best CoG for a lot of folk is just rearward of that marked on the plans.

    With the tank at the CoG I am hoping (!!) to shift the CoG slightly rearwards again because some (most) say its better rearwards and this new rearwards position will not be exaggerated when the tank is full- something the origonal set up has to compensate for by having the CoG a little far forward to start with?

    I hope that makes sense and is accurate! With the scratch build I may actually shorten the distance from TE to engine pod and maybe elongate the nose by a couple of inches.....

    Cheers 
    Happy Landings

  21. #346

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    RE: Northstar mods - Tell me what you think

    Here's a short test run video of my Northstar with the tank mounted in the wing on c.g using the Y.S 45 for power

    http://www.youtube.com/watch?v=3IOlPk7l25U
    Revver Bro #233

  22. #347
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    RE: Northstar mods - Tell me what you think

    Don't get me wrong. I love the idea of moving the tank to the CofG and did that with my first Northstar and am currently working on the same rig for my NP Seawind for exactly the same reason. Mind you, there is a lot more happening in the mod department on that one than I had intended to start with and likely the list will grow.
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  23. #348

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    RE: Northstar mods - Tell me what you think

    My friend just finished a turbined powered Northstar. First flight was good, haven't flown it off the water yet. Here's the Link to Rc groups

    http://www.rcgroups.com/forums/showthread.php?t=1439516
    Revver Bro #233

  24. #349
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    RE: Northstar mods - Tell me what you think

    Still waiting for some vids.

    We had to cancel our local jet rally last weekend due to conflicts and some fun with the local airport. Would have been cool to include the NS with all the other heavy iron.
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  25. #350

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    RE: Northstar mods - Tell me what you think

    So did mounting the tank on CoG reduce weight needed in the nose? Also what do you think about making the nose longer for leverage if any weight is needed? Anything to go wrong with that idea?!
    Happy Landings


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