Questions from a first-time Nobler flier

[Tim Wescott]

Finally had a day where weather & opportunity came together, and my flying ability didn't abandon me.  I got in three flights on the Nobler (flights 3, 4 and 5 for the airframe, landings 2, 3 and 4 for the wheels...).

It flies!  I have no clue how well it is trimmed, but it's a sight better than the 049 powered all-sheet beasties I've been flying!  I have good line tension, even at the top of a poorly executed (my fault) wingover, corners appear to be square and graceful, tra la.

It's running a Fox 35; I've adjusted it for a ragged 4/2 cycle in level flight, which leans out nicely when I go vertical.  But I notice that in the wind it appears to lean out downwind, right where you'd ordinarily be starting your maneuvers -- is this normal?  Other than this unexpected (to me) quirk, the whole "lean out and go faster on the up lines" magic seems to be operating correctly.

My that thing slows down a lot when the engine quits!  The way it goes from flying bomb to floater surprised everyone at my all-RC field the first time it happened.

So, I'm practicing school climbs and (nibble those fingernails) dives, I managed to get in a couple of wingovers although I'm sure they didn't go straight overhead, and the lazy eights looked credible, if not part of any recognized stunt pattern.  Maybe by the end of summer I'll be able to complete the beginner's pattern without crashing...

[Brett Buck]

It's running a Fox 35; I've adjusted it for a ragged 4/2 cycle in level flight, which leans out nicely when I go vertical.  But I notice that in the wind it appears to lean out downwind, right where you'd ordinarily be starting your maneuvers -- is this normal?  Other than this unexpected (to me) quirk, the whole "lean out and go faster on the up lines" magic seems to be operating correctly.

    The lean out downwind, richen up into the wind is pretty typical if you have ram air pressure. David and I were out this morning working on, among other things, his pressure system, because it isolates the tank pressure from the airspeed variation. Thin-wing airplanes like the Nobler are more prone to this issue than others. It should only happen in a pretty stout wind - can you describe your setup a bit (like the tank vents, prop, etc)?

My that thing slows down a lot when the engine quits!  The way it goes from flying bomb to floater surprised everyone at my all-RC field the first time it happened.

      Hmm, might be that you have the CG too far aft. Seems OK until the engine quits, then it noses up and slows down, right?   If so, put on some nose weight.
 
      Brett

[Tim Wescott]

    The lean out downwind, richen up into the wind is pretty typical if you have ram air pressure. David and I were out this morning working on, among other things, his pressure system, because it isolates the tank pressure from the airspeed variation. Thin-wing airplanes like the Nobler are more prone to this issue than others. It should only happen in a pretty stout wind - can you describe your setup a bit (like the tank vents, prop, etc)?

Yes, I have ram pressure -- I'm using a clunk tank with uniflow, the pickup and uniflow lines each go to their own weight with the uniflow going to a ram pressure tube that exits the cowl in line with the engine on the inside-circle side of the airplane.  There's a fill vent that gets blocked with a fuel dot for flight.

At the moment it's not really a problem, as long as it's expected behavior.  Should I actually learn how to fly the pattern I may want something a bit more consistent -- I didn't put muffler pressure on it because there's no tap on the muffler, and I grew up looking at pictures of planes with ram pressure in the magazines.  I could certainly tap the muffler, though.

      Hmm, might be that you have the CG too far aft. Seems OK until the engine quits, then it noses up and slows down, right?   If so, put on some nose weight.

Oh, it's not an "oh my god this thing is gonna crash" sort of thing -- It doesn't really nose up or down, it more just stays where I was pointing it only slows way down then floats around -- with excellent pitch control -- for a while before plane, ground and pilot reach a consensus about landing.  The first time it happened (a week ago) it took me by surprise and I flipped the thing on landing; the next two landings (today) were ignominious skids on the nose, but the last flight actually ended on the level with a real live rollout -- on fairly long grass, none the less.

I used the stock Fox muffler, and needed about 3/4 ounce of weight in the tail to bring the center of gravity back to where the plans indicate.  It seems smooth enough in the air when I concentrate, but what do I know?  When I think "up" or "down" it goes there without any apparent movement of my hand -- I was assuming this was normal, but maybe I need to fiddle the CG forward a bit -- good thing I made that an easy adjustment.

[wwwarbird]

 Sounds like you're having fun Tim, congrats! You'll quickly find how much better, and actually easier, most of the bigger planes are to fly. You'll also get to learn how to LAND while having actual quality control of the airplane instead of just trying to "flare before impact" like the majority of 1/2a sheet jobbies. Along with everything else, it's a lot of fun to work on "greasing" that perfect landing.

[Brett Buck]

Yes, I have ram pressure -- I'm using a clunk tank with uniflow, the pickup and uniflow lines each go to their own weight with the uniflow going to a ram pressure tube that exits the cowl in line with the engine on the inside-circle side of the airplane.  There's a fill vent that gets blocked with a fuel dot for flight.

At the moment it's not really a problem, as long as it's expected behavior.  Should I actually learn how to fly the pattern I may want something a bit more consistent -- I didn't put muffler pressure on it because there's no tap on the muffler, and I grew up looking at pictures of planes with ram pressure in the magazines.  I could certainly tap the muffler, though.

     It's worth a try. The Fox is pretty sensitive to the fuel pressure since in stock form it has a pretty big venturi for the power level to compensate for the almost absurdly low compression. I think it's pretty straighforward to deal with but as long as the engine is running consistently and putting out enough to do maneuvers I would not recommend fixing it.

  What prop and fuel are you running?

Oh, it's not an "oh my god this thing is gonna crash" sort of thing -- It doesn't really nose up or down, it more just stays where I was pointing it only slows way down then floats around -- with excellent pitch control -- for a while before plane, ground and pilot reach a consensus about landing.  The first time it happened (a week ago) it took me by surprise and I flipped the thing on landing; the next two landings (today) were ignominious skids on the nose, but the last flight actually ended on the level with a real live rollout -- on fairly long grass, none the less.

I used the stock Fox muffler, and needed about 3/4 ounce of weight in the tail to bring the center of gravity back to where the plans indicate.  It seems smooth enough in the air when I concentrate, but what do I know?  When I think "up" or "down" it goes there without any apparent movement of my hand -- I was assuming this was normal, but maybe I need to fiddle the CG forward a bit -- good thing I made that an easy adjustment.

      I think it would be worth experimenting with. The plans CG is a little aft of where I have run them in the past. But these sorts of "teeny tail" models are really sensitive to CG movement. 1/8" either way makes a BIG difference in the way it flies. It's quite a hair-trigger sort of thing - too far forward and the turn goes into the dumper , and too far aft and it does more-or-less what you seem to be describing (and has other ill effect in maneuvers you are currently doing). One of the reasons planes like the Nobler aren't competitive any more is that the performance changes so much from start to end from the CG shifting as the fuel runs out. It shouldn't noticeably or surprisingly slow itself up when the engine quits, and correctly-trimmed it shouldn't have much if any tendency to "float" - the really thin wing tends to make the Nobler and similar airplanes pretty much keep flying once the engine quits, far more than a more modern airplane with a much higher ratio of parasitic drag to weight.

    For your current skill level, you are going to better off with the CG forward of ideal. It will give you decent line tension and control load/feedback in the round maneuvers and reduce the tendency to over-control in the few square corners you have to do. And it won't get jumpy at the end of flights when the fuel load has gone down. The CG *must* be forward of where we normally run on current designs you might see discussed here - put it where it is on my airplane and the Nobler will be grossly unstable.

   If  you have experienced modelers to help you set it up, it would be very helpful. As you aren't too experienced with these type of models, it will not only be difficult to fix on your own, it will also be pretty difficult to describe it fully enough to get help over the internet.

   Brett

   Oregon City, eh?  Lots of experience people in Portland, and Salem!  Even more at the Northwest Regionals over the Memorial Day weekend. Bring it down and I will be happy to look it over and fly it, presuming the weather is cooperative.

[Tim Wescott]

What prop and fuel are you running?

I have a handful of old and new 10-6 and 10-5 props that I'm going to go through to find the best fit -- Master Airscrew, Graupner, and APC, plus some 10-6 Top Flight woods.  I can't really tell the difference between a Top-Flight 10-6 nylon (yes, nylon) that I was running for the first two flights yesterday and the APC 10-5 I ran for the last one.

So I think that at this point I'm just not a good enough flier to tell if the prop is right.

Fuel is what I win at club raffles (10 or 15% nitro to start) with about 6oz/gallon castor added so that I'll still have an engine at the end of the flying season.  When I get better enough to warrant actually spending money on fuel, I'll start thinking about what I need to get.

I think it would be worth experimenting with. The plans CG is a little aft of where I have run them in the past.

I will do so -- I'm regretting not making the tip weight adjustable, but the tail weight is, the leadouts are, and if the tip weight seems to be off far enough to warrant cutting the plane up I'll put in a box.

While it seems to maneuver very nicely, this whole business of having it move while I'm still thinking of moving but haven't gotten around to actually moving my hand makes me think that the CG is a bit too far back.  I was thinking that it was too far back, except that I know it's dead on to where the plans told me to put it.

But if that's known to be further back than optimal, it certainly agrees with what I was thinking.

(sigh) -- had I known the thing was too small in the tail I would have added some extra area in the back, and to heck with nostalga!  Oh well -- next plane.

If  you have experienced modelers to help you set it up, it would be very helpful. As you aren't too experienced with these type of models, it will not only be difficult to fix on your own, it will also be pretty difficult to describe it fully enough to get help over the internet.

I know.  I've got a lot of mileage with radio control models, which does help quite a bit.  But I'm new to this (other than a very short-lived Ringmaster over 25 years ago)

Oregon City, eh?  Lots of experience people in Portland, and Salem!  Even more at the Northwest Regionals over the Memorial Day weekend. Bring it down and I will be happy to look it over and fly it, presuming the weather is cooperative.

If I can make it down at all it'll only be for one day -- I can't decide if I want to go down on Saturday & fly for whatever points I can get with the maneuvers I can do (right now I'm good for crappy takeoff, crappy wingover, crappy inside loop, and crappy landing -- at least I'm consistent!), or if I want to go down Sunday and see the real competition flying.

If I'm able, I won't know until the last minute -- are there any good or bad times for you, and should I just ask for you?

I'm thinking that once I get some basic competence with the thing I should show up at Delta park.  I'm pretty time constrained, though, and that hike takes almost an hour and a half more out of my day than going to my local flying field -- and anyway, I'm trying to convert them to CL!  So while I'll probably go down there from time to time, it can't be an every weekend thing until my kids get older.

[Jim Thomerson]

The whole point of uniflow is to give uniform fuel feed pressure throughout the flight. I don't understand why people run ram air which assures that the pressure will change during flight.  I run a one way valve in my open uniflows.  I'd suggest you make a uniflow plug with a tiny hole in it and give that a try.  Put a piece of .010 or thereabouts wire in an aluminum tube and crimp it down good, then pull the wire out.  The air inlet can be a tiny hole and plenty of air will go in.

[Garf]

On my Nobler, I don't use uniflo, and my vent is 90* to the airstream. I have no mixture change problem.

[Tim Wescott]

The whole point of uniflow is to give uniform fuel feed pressure throughout the flight. I don't understand why people run ram air which assures that the pressure will change during flight.  I run a one way valve in my open uniflows.  I'd suggest you make a uniflow plug with a tiny hole in it and give that a try.  Put a piece of .010 or thereabouts wire in an aluminum tube and crimp it down good, then pull the wire out.  The air inlet can be a tiny hole and plenty of air will go in.

But it's so purdy.

Seriously -- I did it because that's what I recalled seeing, assuming if that's what was done, it must be right.  I see I need to mess with it.

[Mark Scarborough]

Tim,
Brett has given you some GOLDEN advice.
Sunday is the day the big boys fly off, ( well and us advanced dudes too) Its great to watch them fly, but I would bet that weather permiting, you will see them fly saturday as well after officials are done.
The way your uniflow is set up is pretty normal, and likely not anything to worry about right now, keeping the plane in one piece is the real secret
Look forward to seeing you if you make Eugene.

[Garf]

I have a handful of old and new 10-6 and 10-5 props that I'm going to go through to find the best fit -- Master Airscrew, Graupner, and APC, plus some 10-6 Top Flight woods.  I can't really tell the difference between a Top-Flight 10-6 nylon (yes, nylon) that I was running for the first two flights yesterday and the APC 10-5 I ran for the last one.

So I think that at this point I'm just not a good enough flier to tell if the prop is right.
ry weekend thing until my kids get older.

The best prop for this combo is the Top Flite Super M 10-6 wood. Make sure that they are balanced. 

[Brett Buck]

The whole point of uniflow is to give uniform fuel feed pressure throughout the flight. I don't understand why people run ram air which assures that the pressure will change during flight.

   That's what I do. There are two reasons - First, if you have it at 90 degrees, it will frequently siphon off the fuel as air goes in one side of the tube while fuel flows out the other side. You small-diameter inlet would hypothetically solve that issue. The second is that putting it to ram pressure makes it a regulator WRT airspeed - more airspeed, more pressure, engine goes rich, minimizing increase of airspeed. If you get whipped up, you may *want* the fuel pressure to respond to the airspeed to make it go richer  and enhance the braking. How much you want is determined by how the engine/prop/pipe respond to load.

      In dead air to pretty strong wind, my engine/prop/pipe is set up for best response on an open ram air vent. It catastrophic high winds (i.e. the kind we now suspend flying for at the NATs), I will switch to pipe pressure or my trick plug to isolate it so the airplane doesn't load up coming around into the wind in level flight. The transition point is where the wind increases to the point that instead of slowing it down (to mitigate the maneuvering speeds) you have to start speeding it up (to get through the level flight and wingover/overhead . With current piped planes thats about as much wind as you can stand up in.

    People may recall that I got caught out on this exact issue at the 2003 NATs - airplane bogged down so much coming into the wind that eventually I didn't whip it enough to get around upwind, skipped off the ground dead upwind, buzzed the prop, and got a 238 (and I might add, finished 10th in Open anyway). The problem was that I had run it that way the previous 6 months developing the RO-Jett setup, which was based on ram air pressure. I had to switch to my PA61 the day before the Finals when a ball bearing in the Jett (original teeny 3-gram-saver bearings) chipped. I had just plunked it in there with no changes, and had no time to work through the problem. Unlike the Jett it was set to use *pipe pressure* in the wind. Without it, it punched through exceptionally well with incredible 16 or 32-stroking at the bottom of the round loops and I was able to do the maneuvers with essentially no compensation for the wind. Worked great in the first round when it was <20 mph, and also helped pick it up in the intersection of the vertical 8 (which of course might have benefitted from some whip-up). It darn near killed me in the overheads, where my airplane tends to float  coming into the wind at the best of times. So I figured I would go with it the second time (since I was first on my circle in the first round). Unfortunately right as the flier before me (Bear) took off, the speed picked up dramatically and got gusty. It's 5 minutes before I have to be ready, no time to switch then. So I went out with the determination to put as much arm into it as I could, fudge everything to get through, and hope for the best. Right before I signalled for start, we got the high gust recorded for the day of about 32 mph. I start it, get ready, and then lean over to Ted and said "I give this about a 50/50 to stay together for a whole flight". I took off with no issues, but on the first level lap my estimate went down to about 5% because the combination of very low airspeed, loading up into the wind, and extreme turbulence coming of the judges made it just about impossible to fly level. And sure enough, that's where it crashed.

   That's when I developed a uniflow cover for extreme conditions. Its a bit of fuel tubing with a brass plug. The brass plug has a blind 1/16" hole down the middle, cross-drilled with a #60. So I get a capillary tube AND a pressure-neutral vent direction. But with the rest of the setup, the way it is on the Jett,  most contests will be suspended before it's windy enough to need it. If I know it's going to be like that I will switch to pressure but if I don't have time I will use this.

   Note that with a Fox on a Nobler it will have the potentially very desirable effect of backing off the engine to mitigate whip-up. This is pretty critical to the wind performance as the wing is famously skinny, and there's essentially nothing but the vaunted Fox 4-2 break and a positive mental outlook to prevent furious whipping up that these airplane were notorious for. The entire design is based on the concept that you need "penetration" - meaning relatively poor airspeed control - to get through the wind, and will have to live whatever you get from the whip-up. The only thing in the design that mitigates the whip-up is the relatively low aspect ratio. That's probably why many of GMA later designs (like the Magnum, with even thinner wings and of relatively high aspect ratio) were less successful.  Anything you can do to mitigate it in addition to the regular load-based misfiring is beneficial. Of course like most classic airplane with small tail volumes, it's also prone to opening up the corners or running out of control when it whips up. That's one reason they fly so tremendously better with modern engines.

      Brett

[Scott B. Riese]

Tim...If you need help I'm close by. I fly at Delta Park. Just let me know!

[Brett Buck]

I have a handful of old and new 10-6 and 10-5 props that I'm going to go through to find the best fit -- Master Airscrew, Graupner, and APC, plus some 10-6 Top Flight woods.  I can't really tell the difference between a Top-Flight 10-6 nylon (yes, nylon) that I was running for the first two flights yesterday and the APC 10-5 I ran for the last one.

So I think that at this point I'm just not a good enough flier to tell if the prop is right.


Fuel is what I win at club raffles (10 or 15% nitro to start) with about 6oz/gallon castor added so that I'll still have an engine at the end of the flying season.  When I get better enough to warrant actually spending money on fuel, I'll start thinking about what I need to get.I will do so

If you are running 15%, it would be worth considering going to a ST51 spraybar assy. It will improve the fuel suction, be more consistent, reduce the tendency to break back and forth,  and you are already ahead of the game on power. 5" of pitch is probably OK as long as it's reasonably cool, and at sea level, but in general I had a lot better luck with 6". I am a little nervous about the nylon prop - they haven't been made in a LONG time and they have a notorious reputation for shedding blades. It could be a safety hazard, but it's certain to completely destroy the airplane in seconds.

I'm regretting not making the tip weight adjustable, but the tail weight is, the leadouts are, and if the tip weight seems to be off far enough to warrant cutting the plane up I'll put in a box.

  D'OH!

While it seems to maneuver very nicely, this whole business of having it move while I'm still thinking of moving but haven't gotten around to actually moving my hand makes me think that the CG is a bit too far back.  I was thinking that it was too far back, except that I know it's dead on to where the plans told me to put it.

But if that's known to be further back than optimal, it certainly agrees with what I was thinking.

If I'm able, I won't know until the last minute -- are there any good or bad times for you, and should I just ask for you?

I'm thinking that once I get some basic competence with the thing I should show up at Delta park. 

    I'm thinking you should head down there at every opportunity!  There are so many small details that matter, and you (or I, from an internet post) wouldn't consider asking about.

   But far more importantly, this event is not really about the contests. Even if you win the biggest contests in the world, the only real reward for it is *recognition from your fellow fliers*. Take my word for it, even winning the NATs means essentially nothing once you drive off the property. If there are no fellow fliers, the whole thing becomes pretty pointless.

     Barring the unforeseen, I will be in town about 3:00 pm on Friday. I probably won't have much if anything to do most of the day on Saturday, we can go in the practice circle and play around with it. I would suggest entering the contest and doing what you can.

     Brett

[Tim Wescott]

I am a little nervous about the nylon prop - they haven't been made in a LONG time and they have a notorious reputation for shedding blades. It could be a safety hazard, but it's certain to completely destroy the airplane in seconds.

It was probably stupid to use it.  It went onto the plane because flight #1 ended immediately after a major brain fart ("I'll practice roller-coaster!"  Up, down, up, down, up, down, down "damn").  The crash broke my only balanced prop, and did minor damage to the front of the plane -- fortunately I hadn't been running the cowl, as I wanted to make sure that all else as sorted out before I found out if a well-baffled cowl with a scary-small inlet cooled the engine well enough (it does). 

Two days later a flying buddy was encouraging me to come out and fly, and I still didn't have any props balanced other than the nylon one, so I used it.  I probably shouldn't have, and now that it's off I think I won't put it back on.

I'll just nail it to the wall so I don't forget that resolution, eh?

[Bill Heher]

Hi Tim,

Make the effort to get to Delta Park and hang with the gang. They are the most friendly and helpful bunch of guys you will run across. They can give you honest and direct feedback on how your plane is set-up and your flying.
 
Don't let the fact that you are inexpierenced deter you from hanging out with the more advanced fliers- they can help you make more progress in a few flights than you will make flying alone and repeating the same mistakes over and over agian.

They guys are usually there Mon / Wed / Fri mornings.  I have been known to take a long lunch to get in a few flights, and even a "Mental Health Day" to get some free time in my work schedule.