The Osprey in its native habitat - Trim and fuel tank questions

Firstly the plane looks great Rusty. Beautiful work.

I am glad you got use to her flying. Sound like you had a blast.

I do not have any experience with clunk tanks, but I am with Cribbs on this one, if it is easy to do, just raise it and see what happens.

Theo

It's not terribly easy but doable. When I built it I assumed a clunk tank should be centered as was my other Skyray. I copied everything about that good working setup. I can remove the rubber band hooks and make a sliding plate. I was really proud of my neat plumbing job too so I wasn't expecting trouble.

I have the tanks for the Oriental and Shoestring which may work with my current setup. I have plenty of time to fiddle with it before I fly again, probably Thursday next week. I hope to get 3 more outings before Huntersville. I'm not going to be as polished as I would like to be unless I just suddenly get good like a switch was flipped. It's late to be changing planes, but that's typical me, so I'm going with the flow.
Rusty

Well, it doesn't sound like you have "uniflow" in the current setup. The idea with uniflow is that the pressure at the fuel pickup should always be the same, independent of the fuel level in the tank. The exit of the uniflow line from the muffler should therefore always be right next to the intake clunk, and so it also has to move with the clunk.

I understand that you have the uniflow at the bottom of the tank when plane is upright, and that the needle tuning is done with the plane upright. When you then invert the plane you will have the uniflow exit above the fuel level, thus giving you a higher pressure at the clunk position and a richer running engine.

Rusty.
Is it possible that the pressurized line, running so close to the clunk, is causing some aeration of the fuel in the vicinity of the clunk when upright?  Maybe this gives it a "false" lean situation when the clunk is close to the airflow, but when inverted the vent is at the top of the tank above the fuel surface & well away from the clunk which has now moved to the "other" bottom of the tank.  Now it's getting a clean flow of fuel with less air in the mixture, causing it to richen up.  I see no advantage in having the pressure line anywhere near the clunk as pressure should be even throughout the tank.
Well, it sounds feasible to me.  Sometimes I surprise myself.
(Shoot me down in you must ).

Rod.

EDIT:
O.K. someone got in ahead of me after I wrote this, but I'll stick with the aeration theory. I don't see the pressure being any different with the line above or below the fuel level.

Rusty, move your tank higher.Your uniflow pipe dictates your tank height in this situation.  the other option is to loosen the stopper just enough and grab the cap flexing the top so that the uniflow pipe moves higher in the rear. Another option is to take out the hard pipe all together. Run your uniflow pipe just like your pickup in which you will need another clunk and a piece of tubing. The two will work together inside the tank and won't get all twisted up as you might think. When I build my plastic tanks, I use a piggyback clunk. I insert 1/8" tubing and solder into the clunk and I use a tightly shaped Z pipe wrapped and soldered onto the clunk. The Z pipe ends approx 5/16" from the end of the clunk and I have 2 pieces of tubing going to my clunk, one to the actual clunk and one is the uniflow. If I encounter similar problems, I just rotate the stopper slightly in the direction needed. Ken

Oldenginerod wrote:

EDIT:
O.K. someone got in ahead of me after I wrote this, but I'll stick with the aeration theory.  I don't see the pressure being any different with the line above or below the fuel level.

From gravity the pressure is higher at the bottom of the fuel compared to above the fuel surface. The whole prupose of uniflow is to make sure that the pressure at the clunk is independent on the amount of fuel in the tank. This is done by having the pressure feed opening (delivering a constant pressure) right next to the clunk.

In an RC tank with a clunk line one would normally tie a second clunk (with pressure feed) to the regular clunk. Such that these two move together. If the pressure feed cannot move with the intake clunk, as in Rusty's set-up, I think it is better to have it in the center of the tank.

Ken Cook wrote:Rusty, move your tank higher.Your uniflow pipe dictates your tank height in this situation.  

Yes, raising the uniflow outlet to the centerline of the engine would make it symmetric in terms of regular or inverted flying. But there would still be changes with the amount of fuel changes. So even better is to have the uniflow outlet at the same position as the clunk. That is afterall the whole idea behind "uniflow".

On my RC aerobatic ships, the tank is set up directly in-line with the engine so the ease of fuel flow is the same upright or at any angle. The pressure line from my muffler goes into the tank at the same point as the fuel line, but on the inside the pressure line immediately curves up to very near the top, or, on some of the more expensive tanks, a bubble in the ceiling of the tank. I don't have any problems running my tanks like this, it is the "standard" method for setting up a fuel tank in any RC plane. My engines never seem to have issues because or orientation. I don't know what your problem is, though. Maybe its different on CL.

Moving the tank up fill get you a stronger gravity feed when upright, but going inverted will have the opposite effect and weaken the fuel flow.

Waffleman wrote:On my RC aerobatic ships, the tank is set up directly in-line with the engine so the ease of fuel flow is the same upright or at any angle. The pressure line from my muffler goes into the tank at the same point as the fuel line, but on the inside the pressure line immediately curves up to very near the top, or, on some of the more expensive tanks, a bubble in the ceiling of the tank. I don't have any problems running my tanks like this, it is the "standard" method for setting up a fuel tank in any RC plane.

Yes, that is fine in most cases. You do get a different fuel delivery though dependant on the fuel level in the tank. To get rid of that you can use a "Uniflow" setup. In Rusty's case the Uniflow has not been set up correctly and that gives him a different pressure, at the clunk, depending on the orientation of the plane (inverted or not).

I've only set up two uniflow tanks. They both use the two lines attached to one clunk Ken described, they both work great. I would try that before you cut into the tank mount on that beautiful airplane.

Jim

Hey guys, thanks for all the replies and advice. I guess my mistake was assuming the plumbing on my old Skyray was correct, since for whatever mysterious reason it ran perfectly throughout the pattern. That's the only clunk tank I had ever used at the time. I do recall reading about having the uniflow outlet follow the clunk, so I'll redo it that way and see how she runs.

I'm on the move right now, so tonight I will re-read your posts more closely and write my replies. Or questions
Thanks again.
Rusty

Kris of course is right, there's no "Uni" about my flow. That'll teach me about blindly copying something that I should know doesn't make sense. I'll figure out some way to have my uniflow follow the clunk. I'm trying to picture Ken's description of the 1/8" tube and z-bend and have pretty much figured out what to do. I'll let y'all know how it works out.

Rod, your theory makes plenty of sense. I'm pretty sure it's not my problem, but somewhere some time someone may read it and fix theirs. Thanks.

Rusty

RknRusty wrote:Kris of course is right, there's no "Uni" about my flow. That'll teach me about blindly copying something that I should know doesn't make sense. I'll figure out some way to have my uniflow follow the clunk. I'm trying to picture Ken's description of the 1/8" tube and z-bend and have pretty much figured out what to do. I'll let y'all know how it works out.

Rod, your theory makes plenty of sense. I'm pretty sure it's not my problem, but somewhere some time someone may read it and fix theirs. Thanks.

Rusty

Rusty, this is fascinating to me.. given my recent research into uni-flow design for my speed model's tank. Do you have any thin-wall silicone fuel tubing having the same inside diameter as your feed-line? Maybe try cutting a length 1/4"-3/8" shorter than your feed-line.. which would serve as your "static" uni-flow vent line.. and clip it to your feed-line? This would be very flexible.. and follow your clunk/feed-line anywhere it goes within the tank. Do some reading on the uni-flow's external "exit" tube placement as well.. in regards to airstream/prop-blast. There's so many variables.. you just have to experiment to find what works the best.

Very glad to know that you're back in action!!!

\"RknRusty wrote:"I'll figure out some way to have my uniflow follow the clunk.

Rusty

Rusty ,
I use fuel line for my uniflow and zip tie it to the pickup line. A sintered bronze clunk is heavy enough to swing both tubes.

Jim

I'll post this flight report here since the discussion is already relevant.
I took the Osprey out for a romp today and tried out the new tank plumbing. Or more accurately, the de-plumbing. I spent an hour Saturday night fiddling with the uniflow tubing, trying to get it to follow the clunk in various ways discussed above. I just couldn't get it to work in a way that suited me, so I said to hell with it and yanked everything out and stuck a short tube in the stopper for filling, which is capped during use. I flew it with the top vent open and could detect no significant change in the engine run until the last few laps before cutoff. I flew about six flights like that, all consistent. So standard venting works fine, and that's the way it will stay. That was a relief. The only thing I don't like is flying over grass with an open vent sucking in grass seeds. I wonder what would happen if I connected the muffler line to the top vent. It would probably be unacceptable during inverted, but I'll try it next time. Or I could make a pantyhose filter.

It was very turbulent today, especially up high making troubleshooting trim issues difficult. I kept losing line tension in the overhead maneuvers. Not so bad on a wingover or OH8, but the top of the hourglass and cloverleaf are the worst. I moved the leadouts back and it helped, but not completely. I made some impressive saves, which I really don't like doing on a regular basis. I wonder if going from a Topflite 9x4 to a 10x4 might give it more authority up there. Would it give me more thrust in the climbs so I have some extra energy on hand to make the turns and stay tight?

Rusty

Rusty,
How is the silver rustoleum/lustercoat combo holding up to fuel?

Jim

Rusty,

First off I am glad you were able to have a good day with it after waiting so long. Now that you have a good run I wouldn't change anything due to the off chance you suck up a grass seed or two. Run a filter and press.

Some days are just too windy, trim on a calmer day and see if you need a prop change. The plane may fly perfect in 5-10mph winds. If you are regularly flying in higher winds then trim for that, although there is not much you can do to compensate for acts of God.

Just my thoughts, you have been doing this longer, just what I see from the outside looking in.

Ron

If you moving your leadout guide forward for line tension in the overheads, your moving them incorrectly. Sweeping the leadouts back will give you more line tension in level flight and less overhead. You want to sweep them forward 1/8" at a time. This can easily be overcompensated so you need to be careful due to launching. This can make the plane come into the circle. When the leadouts are swept back, the plane yaws outboard. This causes excessive drag and really handicaps the plane where speed is needed up top. You need to be positive that your plane is flying level to the lines and not tip high or even slightly tip high. This means flying the plane inverted making sure the plane isn't flying tip low. This is the real issue and making sure you don't have a warp or even a slight twist in the wing which can happen from just covering. Sight down both trailing edges to be certain and have someone hold the plane while you sight it from the rear.

As for the overhead maneuvers, the OH8 is the maneuver that typically crashes the model due to the one circle being into the wind and not opposing. This is usually where warps and planes that have a tendency to fly inboard fly clear across the circle and out to the other side. Seeing that you manage this well, it certainly could've been funny winds on this day or your plane is slowing down. This tells me on the cloverleaf according to what your describing that your prop is working and that possibly your placing the inside and outside loops to close together which is slowing the plane down immensely. Of course this is all speculation, but as a newer intermediate pilot I can say from my own experience is that we tend to try and group things together too close. This may look good from your standpoint within the circle but not from a judges point of view. Try and fly your intersections of the maneuvers out longer as this will tend to allow the model to fly back up to speed . As for the hourglass, fly the vertical leg of the hourglass and enter into it more like a wingover and spread the top level portion out using more real estate. The maneuver is allowed to be big, don't jam the handle when turning but rather nurse it into downleg and fly it out to the bottom. Turn smoothly at the bottom and not a abrupt transition from vertical to horizontal. Ken

Ken Cook wrote:If you moving your leadout guide forward for line tension in the overheads, your moving them incorrectly. Sweeping the leadouts back will give you more line tension in level flight and less overhead. You want to sweep them forward 1/8" at a time. This can easily be overcompensated so you need to be careful due to launching. This can make the plane come into the circle. When the leadouts are swept back, the plane yaws outboard. This causes excessive drag and really handicaps the plane where speed is needed up top.

I started out with the leadouts all the way forward at the position recommended by Brett Buck for his Skyray. In this pic, you can see where I moved them to first. I later moved them even farther back, so they are now 1 full inch aft of the starting position. It's still forward of the Skyray plan's location.
click to enlarge


If I'm clear on what you're saying, I should have been better off with them forward?

Ken Cook wrote:You need to be positive that your plane is flying level to the lines and not tip high or even slightly tip high. This means flying the plane inverted making sure the plane isn't flying tip low. This is the real issue and making sure you don't have a warp or even a slight twist in the wing which can happen from just covering. Sight down both trailing edges to be certain and have someone hold the plane while you sight it from the rear.

This is the first trim issue we addressed. The wings are straight inline with the lines, no tip up or down, flying upright and inverted. Nor does either wing dip when I pull out of a dive or turn a tight loop.

Ken Cook wrote:As for the overhead maneuvers, the OH8 is the maneuver that typically crashes the model due to the one circle being into the wind and not opposing. This is usually where warps and planes that have a tendency to fly inboard fly clear across the circle and out to the other side. Seeing that you manage this well, it certainly could've been funny winds on this day or your plane is slowing down. This tells me on the cloverleaf according to what your describing that your prop is working and that possibly your placing the inside and outside loops to close together which is slowing the plane down immensely. Of course this is all speculation, but as a newer intermediate pilot I can say from my own experience is that we tend to try and group things together too close. This may look good from your standpoint within the circle but not from a judges point of view. Try and fly your intersections of the maneuvers out longer as this will tend to allow the model to fly back up to speed . As for the hourglass, fly the vertical leg of the hourglass and enter into it more like a wingover and spread the top level portion out using more real estate. The maneuver is allowed to be big, don't jam the handle when turning but rather nurse it into downleg and fly it out to the bottom. Turn smoothly at the bottom and not a abrupt transition from vertical to horizontal. Ken

Maybe it is just me draining it. This plane is too sensitive for me. The old Skyray had a much longer elevator horn, and though not docile, much less twitchy to my inputs. I could stand and plant and fly big high quality loops and H8s, whereas I'm winding up like a beginner again with the Osprey. I'm going to put a longer horn on it in hopes it smoothes me out. I've gotten way to close to contest time to be working out problems like this. Yesterday was only my second time flying this plane, but live or die, I'm going to stay with it. But the old one will be making the trip to Huntersville too.

Thanks.
Rusty

JPvelo wrote:Rusty,
How is the silver rustoleum/lustercoat combo holding up to fuel?

Jim

The aluminum paint is Krylon. It's fine now, but its first visit into the 107 degree sun bubbled the paint around the bird on the nose. And the Lustrekote didn't stick well to the aluminum and came off on the tank pad. And now it has a minor case of acne. In my irritation at all that, I painted some clear fingernail polish over the tank area and a couple of other places I wanted to protect, like the top of the nose that got a big thumbprint, and now it's hard as a rock. Would I use it again??? No. But now I expect it to be trouble free, I just took it outside into the elements too soon.
Rusty

Cribbs74 wrote:Rusty,

First off I am glad you were able to have a good day with it after waiting so long.  Now that you have a good run I wouldn't change anything due to the off chance you suck up a grass seed or two. Run a filter and press.

Some days are just too windy, trim on a calmer day and see if you need a prop change. The plane may fly perfect in 5-10mph winds. If you are regularly flying in higher winds then trim for that, although there is not much you can do to compensate for acts of God.

Just my thoughts, you have been doing this longer, just what I see from the outside looking in.

Ron

Well, there were about a thousand little black grass seeds on the greasy wing. And good point about the wind. I'm well known for over thinking. On the other hand, this field is always very windy. I'm used to that but yesterday it was a crosswind over the trees on both sides of the runway, kept reversing 180, and at 45 degrees elevation looked like the plane was being shot at. Wayne's Smoothie looked like that too. He didn't want to fly a pattern with his. That might tell me something, but it really is too squirrelly for me. And it's not tail heavy. When the engine cuts it continues a flat glide.
Rusty

Rusty, after re reading my post, I noted I made a big error in my typing. Excuse me as my day starts very early and this typing is generally on the fly. I meant to state, if your looking for line tension, move your leadouts forward in the overhead maneuvers. There however will be a point of no gain and it will almost do the opposite. Generally looking for a good place to start is per the plans as this usually has the leading line exiting in or around the spar. Work from there and move forward.  All the way forward could wreck the model on launch. Always hang the model like a plumb bob and note the horizontal reference of the fuse to the floor. There's nothing incorrect about having the plane yawed out on the initial flights.

I'm not a Brett "Follower" so I can't comment on his success. I can only say what I've found to be true in regards of line tension and this is true of all planes. If a plane is getting light on the lines, I look for warps first. I hardly ever use rudder offset and the only thing I will do is to use engine offset with the offset engine shims on top of aluminum pads to the tune of 1-2 deg.

Truth is, sometimes you may have a plane that's just a bit too light. This is something Aldrich also stated in regards to the Nobler. While 38 oz's is a beautiful target weight he said his best ones flew at 44 oz's due to not getting bounced around by the wind. You certainly could've chosen a bad day for flying. I think we've all been there and done that.

If your plane is twitchy and your controls are essentially slowed down as much as possible, I would narrow the spacing of your handle. Adding nose weight would also help and this isn't a penalty. Add as much needed until the plane feels correct. I'm sorry if I was misleading. I know my ramblings can carry on like a run on sentence. Ken

Ken Cook wrote:...If your plane is twitchy and your controls are essentially slowed down as much as possible, I would narrow the spacing of your handle. Adding nose weight would also help and this isn't a penalty. Add as much needed until the plane feels correct. I'm sorry if I was misleading. I know my ramblings can carry on like a run on sentence. Ken

Adding nose weight is something I have neglected to consider, and definitely better to try before replacing the elevator horn. My handle is set somewhere between 3 and 3.5". After you wrote this I went to the shop to take a look at the Osprey and also the old Skyray just out of curiosity. Both balance about 1/2" in front of the spar. Maybe a tiny shift forward is all I need. I'll take some weights and try it next time I fly. I know comparisons don't mean much, especially with two different engines, a 25 and a 35, but I weighed them both. The old Skyray is 38.5 ounces and the Osprey is 35.5 ounces. Elevator deflections look about the same.

Don't worry about rambling on, I always hope you'll toss in whenever I'm figuring something out. I had guessed I was catching you at morning coffee time. Thanks for the help.
Rusty