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  1. #251

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    RE: Seagull Spacewalker II 120 Arf

    Wow... I should have gone with a G-20 or DLE-20 rather than the G-26 but I had the G-26 on hand. Or... I had an MLD-28 on hand, that is lighter than a G-20 but I thought it might be too much power and wanted to save it for another project.

    Eight ounces is a huge amount of tail weight to add as it means the front end is much heavier than it needs to be. It would mean that the plane could be a pound and half heavier than it needs to be.

    You have me prepared to move the flight batteries aft of the servos.

    The stock Zenoah muffler is fitted and actually looks good as it is black and protrudes about the same distance out and similar location as the dummy engine on the starboard side. It likely will get the exhaust pipe from the dummy engine beneath and aft of the muffler. If I'd known how well it looks, the pitts would not have been considered. A pic to come later.

  2. #252

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    RE: Seagull Spacewalker II 120 Arf

    With the muffler changed to the stock Zenoah and the batteries all moved aft of the servos, the plan is to do another balance check in the morning and if still significantly nose heavy do away with the 3/4" standoffs and mount the engine directly to the firewall. That of course will require cutting a similar amount off the aft end of the cowl.

  3. #253

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    RE: Seagull Spacewalker II 120 Arf

    Yep, that's the same issue Iwas faced with but, I decided to add the weight instead. My carb is 1/2" forward of the firewall on the back of the engine. If you're carb is side mounted you might be OK ...or at least better off.

    We'll see if 2.6hp does the job. It's supposed to be good up to about 12 lbs but, I surely hope it's not that heavy. I may need to get a bigger "fish"scale to weigh it with. My current scale only goes up to 11 lbs.
    Iplan to use a 16X6 wooden prop at first to see how she performs. A fellow club member has the same bird with a different brand of 26cc gas engine. He's using a Master Airscrew plastic prop and Ithink he said it was a 16 incher but, I don't remember the pitch. He also mentioned not being very happy with that prop ...said it was noisy. It's probably flexing a good bit too.

    Find a way to measure the thrust and compare it to the weight of the plane. It will give you a good idea of the power to weight ratio. I'm told you need about 1.5 to 1 for 3D.

    BTW .... my suspicions about prop size and pitch were confirmed Wed. I had been running a 22"X10" Zinger Pro on my MX2 (with 55cc DLE) and was pretty happy with the performance but, I had been wanting to try a larger prop. So, Ibought a 23"X10" Xoar and it hit the power band right square in the bullseye. That bird will now go straight up out of sight and will get small in a hurry. I've found the propeller sweet spot for my bird and will probably order 2 or 3 spares. I also love the way the wood props look. Compared to the composite props, the wood props are cheap but, they still put a dent in my hobby budget at near $40 each after tax and/or shipping.

    I know I'm preaching to the choir about props. You have way more experience than Ihave but, just wanted to pass on my success at finding the right prop for one of my birds. Trial and error isn't cheap but, it will get you there fairly quickly if you have a method and know what you're looking for.

    RJ
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  4. #254

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    RE: Seagull Spacewalker II 120 Arf

    I've a very heavy Phaeton 90 bipe at 13lbs 6oz and fly it with a G-20 (20cc) and it does fine on that engine for general aerobatics that don't require great vertical. On the G-20 I generally use an APC 16x6 and have three of those, the other two being the Ultrastick Lite 120 at a hair under 10lbs and the Seagull AT-6 at 12lbs 8oz.

    The Spacewalker has slightly more wing area than the AT-6 so I've no issues with it flying even if the heavy muffler would have been used... the issue is that planes just fly better when kept as light as possible.

    If I'd not had the G-26, a 20cc would have been used on the Spacewalker. I personally believe that between the G-20 and the G-26 that the performance gain of the G-26 is mostly lost by the additional weight so the only benefit is if the nose weight is needed anyhow. For example, I've been told that an Ultra Stick Lite does not have unlimited vertical with a G-26 whereas it does with the G-20 because its simply lighter. For those building the Seagull Spacewalker and who don't all ready have an intended engine... if going gas, a 20cc looks to be the best choice given that the plane doesn't require any nose weight.

    The G-26 will be propped by a Vess 18x6 or 18x8. Your comments about props fits my own conclusions... that trial in flight is the only sure way of finding exactly the sweet one that matches an air frames speed, drag, and power.

    I've a 72" Yak that flies very differently between an APC 18x6 wide and an 18x8 sport. The sport just doesn't give much braking in the down lines or when landing and it really doesn't start developing power until 3/4 throttle whereas the 18x6 wide provides good pull at half throttle and provides a great cruising range with far less noise. With the sport, even though higher pitch, it wants higher rpms for most of the flight window though admittedly full power with the sport is slightly stronger than with the wide. With the sport, if coming in a little strong, there is no prop braking and its going to land long. The 18x6 wide is preferred.

  5. #255

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    RE: Seagull Spacewalker II 120 Arf

    Second effort at balancing is done with the following results. Zenoah G-26 with after market RCXL ignition under the tank, stock muffler, Vess 18x6 wood prop and supplied spinner. Two 1100mah 6v flight batteries and one 1100 mah ignition battery all located aft of the servos.

    Total weight is 11lbs 15oz. The only thing left to complete is gluing the stabs in place and the flying wires on the stab and the rudder to wheel steering hookups.

    One ounce was needed on the tail to balance. The epoxy to mount the stab, the tail wheel hookups and flying wires will probably amount to that.

    Dry weight of the plane then will be twelve pounds even.

    I'm relieved that there's no need then to readjust the engine aft and that no weighting will be needed.

  6. #256

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    RE: Seagull Spacewalker II 120 Arf

    That's great news. I'll bet the worry wrinkles disappeared when it balanced out for you.

    RJ
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  7. #257

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    RE: Seagull Spacewalker II 120 Arf

    Some time today spent on reinforcement. The firewall got a strip of tri stock across the bottom inside and four small segments on the forward turtle deck. I might come back and fiberglass cloth the two existing triangle side pieces as I don't trust their glue there.

    The gear support is a horse of another color as I consider it wholly inadequate and in need of a multiprong effort to beef it up. Specifically I think it needs three adjustments.

    1. Additional ply forward and external to bridge the gear support area into the firewall belly pan.

    2. Ply piece aft of gear support to spread the strain over a greater area of the longerons.

    3. Ply double on the gear mount, marrying it to a wider area of the longerons and bulkheads.

    #1 is fairly easy. A single piece ply cut between the longerons and glued forward of F2 with tri stock on three sides. The purpose of this piece is to add strength to the lower section of F2 and tie it strongly to the fuel compartment belly pan as well as get more glue area into the longerons. The ply I used here was 3/16 light ply from the craft store. It is light but is five ply and will support some screws from the front going back into the gear mount. Will include a pic of this. The others to come later.

    #2 if also easy. It will simply be a piece of light ply about three inches wide between the longerons and up against F3 that lies aft of the gear support block. I will probably shoulder it up the longerons about two inches before laying in the bottom piece... so it will be a three piece effort.

    #3 is the harder of the three efforts but the most important of the three. The gear support block is not plywood and a hard landing will split it releasing the tee nuts. Needed here is a piece of 1/4 aircraft ply to form a doubler to the gear block. Aircraft grade is needed because the tee nuts will be removed and added above and to this ply. The gear bolts are long enough for this doubler.

    The problem is, the two sq stocks that exist to support the gear block need to come out. The glue on them can't be trusted to hold much and they interfere with what needs to happen. My plan is to use a multi tool and remove them. Ounce out of the way, I will wrap the gear area with a longeron and bulkhead doubler all around to spread the load of the gear support to a greater area of the longeron and bulkhead formers. This wrap will come up perhaps slightly less than two inches. Inside of these doublers will be fitted the 1/4 gear support doubler.

    To finish, drill the four holes through the doubler from the bottom and reinstall tee nuts. Then add several small screws from the front of the F2 doubler into the gear support block.

    That should do it. These steps should provide trouble free gear support and are far easier to do now than after the gear might be ripped out.

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  8. #258

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    RE: Seagull Spacewalker II 120 Arf


    ORIGINAL: rowdyjoe

    That's great news.Β* I'll bet the worry wrinkles disappeared when it balanced out for you.Β*

    RJ

    Hey RJ...

    Yeah I admit relief.

  9. #259

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    RE: Seagull Spacewalker II 120 Arf

    The little sq blocking wasn't much fun to get out but I think the results will be worth the effort. I've the reinforcing parts fitted and ready for glue up.

    I did note that the gear block looks to be plywood, probably two layers of light ply.

    The step that involved removing the blind nuts (that part was easy) and the sq blocking (kinda tough) might be modified to leave the sq blocking and notch around it to make it a lot easier. Just use the heat gun on the tee nuts to release the glue and they come out fairly simply. I made a small puller in a couple of minutes.

    I've seen too many gear ripped out of arfs to trust them.

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  10. #260

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    RE: Seagull Spacewalker II 120 Arf

    Final pic of the gear reinforcements.

    If the gear should get ripped out now... it will be due to a crash... not a hard landing.

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  11. #261

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    RE: Seagull Spacewalker II 120 Arf

    If that gear comes out it'll be the only thing left!
    I don't want to be a "stick in the mud" but sometimes the gear ripping off is a good thing.
    On a landing approach with my Cub; a wheel decided it wasn’t ready to come down and left the axle about one second from touchdown.
    It’s amazing how fast a 30 yard cart wheel can flash before your eyes. Anyway, someone was watching over because the gear ripped out and she slid in on her belly picture perfect.
    It was nothing a little ply and new blind nuts couldn’t fix.

  12. #262

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    RE: Seagull Spacewalker II 120 Arf

    I agree that there are sometimes benefits to having a weak link but my observation has been that the gear support on a great many arfs is far too weak. The greatest cause of this is hot melt glue on light ply. It shows up on both gear supports and firewalls. Another current thread on the Seagull AT-6 describes a pilot who got two flights from his AT-6 when the firewall came loose and the plane was destroyed.

    I've noted the much higher incident of gear failures of ARFs compared to kit builds.... many of which simply didn't hit hard enough that the gear should have ripped out.

    Fair enough... if I do a lot of plane damage because the gear didn't rip out easily... I'll post here and say it was a bad decision to reinforce it. In trade, will you if you have the Seagull Spacewalker, post here if you rip the gear out on a landing that probably shouldn't have done so and it was a headache to repair?

  13. #263

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    RE: Seagull Spacewalker II 120 Arf

    RJ... my Spacewalker is nearing completion. Barring any problems with the engine running ok, it will be ready for maiden soon.

    Will try to get some engine run time a couple afternoons this week and maybe maiden next weekend if the weather gods offer something suitable.

  14. #264

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    RE: Seagull Spacewalker II 120 Arf

    Great. I'm anxously awaiting the report. You've certainly prepared it well and that helps ensure success. Hope you can find someone to record a flight or two. I would love to see it.

    Ordered the new carb for mine yesterday and I'm nearing completion of the Yak. All electrical is installed. Just need one more short extension. Also need a bit more fuel tubing and a "T" fitting, then mount and secure the tank. Getting very close and I'm excited.

    Good luck and God Bless,
    RJ

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  15. #265

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    RE: Seagull Spacewalker II 120 Arf

    Always something needed, eh.

    Hope the new carb solves the running problems of the engine on your Spacewalker.

    My building area is not large and constrains me to usually one project. I do have two small boards, so sometimes can mix a minor repair but can't recall ever doing two build projects together at the same time.


  16. #266

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    RE: Seagull Spacewalker II 120 Arf

    My build are is small too. I have a 10'x10' room on the back of the house that was supposed to be a "breakfast nook" or some such. Needless to say, I turned it in to a radio shack and RC build area.
    The SW is out in the garage sitting on my HOtrain layout (another hobby I'm neglecting for airplanes ...my first love).
    My wife won't let me bring the plane it in the house because it smells like gas. She hates odors.

    I just completed the fuel system installation and mounted the wings on the Yak for the first time. Found out Ihad the fuel DOTtoo close to the wing so, had to relocate it higher up on the fuselage. Gotta patch the first hole too. She'll be ready to run tomorrow. Haven't decided whether to do first flight with or without the cowl. I'll make time tomorrow to cut the holes in the cowl and get it fitted. She's a real beauty and I'm anxious to get her in the air. Conditions look favorable for Wed. this week.

    Yep, I'm hoping the new carb for the Spacewalker will solve the problem. If it doesn't, I'll start shopping for another engine.

    RJ
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  17. #267

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    RE: Seagull Spacewalker II 120 Arf

    Your comment about your building room shared with radio... is my situation as well. I still have all my radio and test gear in my building room. I'm an inactive Ham however, and should clear out the radio stuff but I'm loath to part with what was once important I guess but I have given thought to selling the stuff and making more room. I guess what holds me back is that I've been forced a couple of times to change gears hobby wise so with an awareness that nothing in life can be certain, I might one day want to reactivate as a Ham so why sell out for peanuts.

    And... I've got one bench with test gear; a scope, poor mans spectrum analyzer, sweep generator, and various other test gear.

    I hear you about the fumes. My radio/airplane room is in the house but behind the garage with three doors, to the garage, back yard and living area. I can close that door and otherwise ventilate fumes between the garage and back yard. It works most of the time but have been fussed at a time or two. I do have a very nice setup for modeling with a back yard shop only a few steps from the back door of the building room and storage for planes on garage walls and ceilings.

    It is very nice to have a heated/cooled building room and such is a worthy trade for more size.

    btw, last night was spent buttoning up a few odds n ends on the SW. The cowl was left off for now and probably through the maiden and all is ready for firing the engine and getting idle and failsafe set. Might get that done this evening if not too tired. I started a construction project yesterday so will have less time and energy for modeling for a while.

  18. #268

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    RE: Seagull Spacewalker II 120 Arf

    Your comments about radio in general mirror mine. I operate once in a blue moon to talk to my old buddies on 75 meter but, we email much more than we talk these days.
    A stong wind and a weak guy-wire took my beam down so, all Ihave left is a 75 mtr double bazooka and I'm not motivated to install any more.
    It's hard to get motivated for radio since my brother passed away a year ago. We both got our tickets back in the mid 70's so we could stay in touch while Imoved around the country ...and the world (USAFRet.).
    I don't have much of a radio collection but, it does the job adequately. FT2K, Drake L75, LDG AT 1000 for HF and an FT7800 for UHF/VHF. Ihaven't turned any of it on in over a month and have been considering selling it all but, think I should hang on to it in case of emergency.

    I'm anxious to hear the flight report on your SW. Maybe we'll have "first fight" stories to tell on Thursday if Iget off my duff and get the Yak ready. It's a bit chilly to work outside but, it could be a lot worse. After all, it's Jan. in North Texas.

    Good luck with the first flight. Got my fingers crossed for you.

    RJ
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  19. #269

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    RE: Seagull Spacewalker II 120 Arf

    I've run the engine. The idle position at 1800 hit right in the middle of the trim tab and the engine kills fine going low trim. Top rpms were 7800 (Zenoah G-26) with a Vess 18x6 and they were reduced to 7600 by tweaking just a little richer. Ran a half tank and pronounced it ready to fly. In fact, things went so smooth, I'd not be hesitant to put the cowl on for the maiden.

    The failsafe position was a few rpms above idle and got reset to the idle position.

    Throttle stick linearity seams ok. Gassers require a lot more movement on the top half of the stick and as my radio JR 7202 doesn't have throttle curve or expo for the throttle, it gets a work around by setting the high travel to 100% or more and the low travel to 50% or less. That gives the low half of the stick a lot less movement and its easier to jockey the power setting on landings.

    It is ready for flight. I've got to go to the job site and collect tools... but after that as it's nice out this PM....might go to the field and do the maiden... we will see.

  20. #270

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    RE: Seagull Spacewalker II 120 Arf

    Maiden didn't happen... not enough time left and didn't want to get in any hurry and miss something... it'l wait.

  21. #271

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    RE: Seagull Spacewalker II 120 Arf

    A wise decision. WX looks good here for the next couple of days. Hope it's flyable for you too.

    Ifinally got the Yak engine starting and running OK but, the lowest idle I can maintain is 2200 rpm. Lower than that and she dies after about a minute. I think she's loading up at idle.
    The high speed RPMis about 8650 with a 15x8 wood prop and the needle set almost 1.5 turns out. Low end needle is set about 1.3 turns out and Ithink it needs to be leaned out more. The plug still looks black when I pull it to check and she's still 4 stroking at the low end. However, without a temp gauge, I'm afraid to lean it out more.
    This is the darndest thing I've run in to so far with these gassers. Maybe this one needs a new carb too? Hopefully it just needs a needle adjustment but, Ineed to get the gauge to set it with.
    As the old saying goes ...you get what you pay for. I don't think I'll be looking at any "bargain" engines in the future.

    RJ
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  22. #272

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    RE: Seagull Spacewalker II 120 Arf

    RJ... if it is a new engine, it might need a little time to loosen slightly. Also, a super slow idler may not be needed on the Yak during landing. They are not floaters. Mine almost always requires a few rpms to keep it coming in nicely so if you can get the idle down to where the plane doesn't move on the ground at idle... your good. With my Yak, it was helpful (if not necessary) to expand the low stick throttle rather than have most of the power curve in the firsts half of the throttle... that helped a lot in being able to keep the right amount of power on for the desired glide slope.

    The low end needle is generally the more sensitive of the two and getting it dialed in sometimes is like leaning on the needle. Generally as lean as the low end needle will go without creating a spool up sag.

    Gassers are a bit more of a pain to initially set the needles in part because each adjustment is usually made with the engine stopped. That requires a tack and as you suggest, a heat sensor. I've never used a heat sensor and have relied on the tach method. Most gas engines will tolerate the high end going right to the edge of max upper rpms but careful not to go over that edge. I like to come back just a few to have a little overhead for temperature and humidity changes.

    I adjust the top end rich, and then start running and taching, stopping between each adjustment until the rpms show no further gain or even fall off and then simply back the needle to the previous point if there was no rpm gain or the second previous point if there was an rpm drop.

    If the cowl has inadequate outflow... all bets are off as the pressure changes in the cowl make setting a carb with a tach very difficult.

    Yes... weather looks good for a couple of days.

    Arlyn

  23. #273

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    RE: Seagull Spacewalker II 120 Arf

    Probably both needles are rich. With that 15" prop, you should be seeing 9K plus. Good luck.
    Sometimes, things are exactly as they appear to be.

  24. #274

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    RE: Seagull Spacewalker II 120 Arf

    Thanks for the tips fellas.

    The engine is "fairly"new. I bought it new but, it's been run a few hours in a plane and on the test stand. Of course, it ran terrific in all modes on the test stand and initially on the airframe but, when Itook it to the field it ran for a couple of minutes, died, became very hard to start, and wouldn't run more than a few seconds. I have no idea what changed between my garage and the field.

    Airflow should not be an issue with this one as Iopened up a large area on the underside of the cowl to make room for the cylinder head and exhaust stack (one big 5" wide smile) ...and I'm sure you know how large the cowl opening is in the front. I've also reinstalled the velocity stack which appears to have made a positive difference.

    Before I dropped my tach and broke it yesterday, the lowest reliable idle I could get was 2200 rpm. I can lower the idle through the throttle adjustment in my DX7 but, when I drop it to around 2000 rpm it will idle for about a minute and then die ...and that's what's driving me nuts. At 2200 rpm I know it's going to roll on the ground.

    Grrrrrrrrr !

    About the 9K plus ....I've got the high end adjusted a tad rich to allow for unloading and lean-out in flight so, it should reach very close to that (Ithink) in flight at WOT.

    RJ


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  25. #275

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    RE: Seagull Spacewalker II 120 Arf

    RJ... in my opinion the large opening of a Yak cowl needs dampering (others call it baffling). There is so much air moving into the cowl that it would take a huge hole to exceed the intake and that is what is needed for the air exit size to exceed the intake size. Otherwise what happens is a high pressure condition exist within the cowl and that pressure changes depending on rpms. That screws with the metering circuit of the carb, which wants a stable atmospheric pressure reference to wit the needles can be set. If the metering circuit is constantly changing its pressure reference... setting them to suit the whole range of flight is difficult if not impossible.

    For example, lets say the pressure increases in the cowl at full engine power. That pressure pushes on the anvil of the float needle opening it further causing more fuel to flow so to compensate and get a proper top end adjustment at full power, the HS needle is leaned to suit. At mid throttle the pressure in the cowl starts coming down so less fuel flow so the HS needle is now too lean and even worse at idle because the LS needle must have a proper setting of the HS needle and it doesn't have it. At idle what happens is that the LS needle gets set much to rich to compensate for the too lean HS needle at idle rpms so as to avoid spooling up sag. As you discover... the idle is too rich and if you lean it any, it likely won't spool up without sagging.

    Two choices are left... damper the inflow of cowl air or solder a tube to the atmospheric hole and run a line inside the plane to get normal atmospheric pressure. For me, the better is to damper the inflow because that also insures proper engine cooling and no stagnant air pockets in the cowl to over heat.

    Sorry for the long primer on small engine carbs... but hope the info will help. It explains why an engine runs fine on the test stand but not in a cowled plane. I'll enclose a pic of the cowl damper on my Yak. Note that the inflow is just where the cylinder and muffler are... the rest is blocked off. The exit area is about twice the intake area. I used 1/8 light ply and glued it in with silicone adhesive.

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