Author Topic: Why die when I fly high? (Read 5572 times)

Tim Wescott · « **on:** March 25, 2013, 06:29:42 PM »

By and by?

Airplane: more or less Fancherized Twister
Motor: Tower 40
Prop: various
Tank: hand-hewn uniflow, mounted in the usual spot outboard. It's 3.5" x 1.25" x 2", the 2" dimension is inboard-to-outboard.

When I fly overhead, the engine leans and in at least one case has cut out (very exciting, that). Once I'm flying level it's OK again.

This has happened on several different props, each giving its own sort of motor run.

I'm using the uniflow tank because on a previous plane with this engine, and a Hayes 4-ounce tank, the engine would run leaner and leaner as the flight progressed. It was bearable, but I wanted to do better.

Now, with the uniflow, I seem to have this problem...

My testing time has been limited so far, so I have not yet had a flight where I've done the obvious thing and richened it out and tried overheads -- with the first prop I tried on this engine I could either get it too rich to do an overhead maneuver with consistent safety, or I could get it lean enough to fly nicely level, but not both. Since then I've found that flatter (11.5x4 and 12.5x3.75 props) seem to give me plenty of power without seeming to run away, but I have not yet investigated the rich end of the flight envelope (again, due to lack of time).

In the absence of guidance from the group, I'm planning on trying three things before Easter: (1) looking to see if the tank has any obvious leaks (I always leak test, but I'll do it again), (2) finding a needle setting that's at the rich end of comfortable for level flight, and see how it does in the overheads, and (3) flying the damn thing with a Hayes 4-ounce tank.

I have noodled with the idea of building a wide flat tank with a baffle, on the theory that the G-forces in a sustained overhead are causing a change in head to the engine. I'm trying not to seriously consider that option.

Any other suggestions?

Mark Scarborough · « **Reply #1 on:** March 25, 2013, 07:18:38 PM »

where in the fuel level are you trying overheads? if it is in their proper place in the pattern, then I suggest you check your airplane for excessive yaw,,
if you have a substantial amount of yaw ( like nose out 1/4 to 1/2) then you could be uncovering your fuel pickup. I have had this happen before. Us less skilled trim adjusting persons sometimes think we have the leadouts right, but ,, maybe not so much,,

My Gee Bee was prone to this,, and I finally figured out that it was yawed out,, between adjusting the lead-outs, and them shimming the back of the tank out I eliminated the problem....

are you using muffler pressure? if not, is your uniflow pickup on the inboard side of the fuse?

simple troubleshooting,, IF your gear is uniform right to left,, can you see the outboard wheel behind the inboard wheel while flying? can you see straight down the trailing edge of the wing ( or leading edge since this is a straight wing),, if so, adjust leadouts to correct this
then try shimming the back of the tank out if the problem persists

Steve Helmick · « **Reply #2 on:** March 25, 2013, 07:28:02 PM »

I was gonna suggest a new tank, made from a different flavor of soup. However...it also sounds like the engine maybe needs more running, or more oil. I don't recall Mike flying a T.40 very much, + they're really chrome, not ABN. You might axe him, tho.

Steve

Mark Scarborough · « **Reply #3 on:** March 25, 2013, 07:50:40 PM »

Quote from: Steve Helmick on March 25, 2013, 07:28:02 PM

I was gonna suggest a new tank, made from a different flavor of soup. However...it also sounds like the engine maybe needs more running, or more oil. I don't recall Mike flying a T.40 very much, + they're really chrome, not ABN. You might axe him, tho. Steve

Tim, do NOT listen to Steve,, Mike is a pretty nice guy,, I would hate to see him Axed,,,

Tim Wescott · « **Reply #4 on:** March 25, 2013, 08:10:26 PM »

Mark: yes it's in the normal part of the pattern. In fact, on one of the test flights today I did a nice set of overhead eights before the wingover, then had the airplane nearly die in the overhead eights. I bailed out at that point, and it put in another twenty laps before it stopped, so there was plenty of fuel left.

I'll check yaw. Even if the wheels aren't lined up perfectly now I can certainly tweak them into line and then go flying. (And I can double check leadout vs. CG.) The tank is built with the rear 1/4" taller than the front to give it a built-in "back shim", but that doesn't mean that I don't have a yaw problem that I'm not seeing.

I've got a flying buddy now that's willing to look for things like yaw and wing level, so I'll have him look for it, too.

I would love for the problem to be so simple. This plane seems to be shaping up to be a winner for me, and such a simple fix would mean all that much more practice between now and the Tune Up.

Steve, I'm with Mark. Moreover, if I see you get close to Mike with an ax, I'm speaking out.

Jim Thomerson · « **Reply #5 on:** March 25, 2013, 09:06:17 PM »

I was very happy with my Tower 40 on Sig Champion 10% nitro, 20% oil, half castor, half synthetic. Fox two volt long plug. Best prop was Australian made Supercool 11 x 5 carbon petal blade. A Zinger wide 11 x 5 was OK. APC 11 x 5 bad windup and no grunt upstairs, an APC 11 x 4 flyable. Did not try the 11 x 5 Taipan my Fox stunt 35 likes. I ran muffler pressure to uniflow. This was on a profile #7 Easy OTS.

Mark Scarborough · « **Reply #6 on:** March 25, 2013, 09:34:42 PM »

You know Tim, as I think about this,, lets do some bench talk too,, can you snap a picture or two of your whole setup, from a couple angles,, then fill us in again on where you are currently, as to fuel, prop, launch rpm there could be other factors here as well.

one thing hard to communicate,, you say it "leans out" , assuming you are either running on the rich side of a 2 stroke mode, leaning out would speed up the prop and accelerate the plane, starving for fuel would cause it to misfire or quit cold, one other thing,, and this will seem silly maybe, but the tank you build, did it still have the "corrigations" from the can, or am I misremembering

Tim Wescott · « **Reply #7 on:** March 25, 2013, 10:40:59 PM »

I'll post pictures later, when I'm out in my building building.

Fuel is home-brew, 20% castor, 6% nitro, about 3.6% synthetic and the rest methanol.

Yes, the tank is decorated with the corrugations, but I did smooth them out a bit with a body hammer and a flat dolly.

Flights so far have been:

Several flights on a ThunderTiger 11 x 4.5. Launch RPM between 8500 and 8750.
- Launching at 8750 gives me a run in level flight where it's mostly a wet 2-stroke but occasionally blipping down to four. At me enough grunt to safely do a wingover, but it fades in the overheads with that "thin" sound that you get when you're lean, not an onset of a heavier 4-stroke
- Launching at 8500 gives me just enough power to think that I can do a reverse wingover. I got through the first wingover, and the plane did speed up. In the second half of the wingover it went slack and I damn near crashed the plane, only saving it with a mad backwards dash that left me with pulled muscles in my foot and a bent line clip. Even the cheers from the peanut gallery aren't worth a repeat
One flight on an APC 11.5 x 4, saved from the trash after some tip strikes by cutting it down to 11 x 4. It's what I had. I can't remember the launch RPM, but I had enough power to do the pattern -- and enough fuel to maybe do it again. It definitely ran away on me; I was hanging onto the handle with both hands
Two flights on an APC 12.5x3.75
- One flight with a launch at 9500 (fueled by paranoia of launching too slow). Lots of power, 4.65 second laps at first, the engine cut out in the overhead eight, about 20 laps after I bailed from that, with the last few laps at 4.2 seconds
- One flight with a launch at 9200. Plenty of power, more controlled flight than launching at 9500, and the thing at least lived through the overheads. That was the flight that I started with overheads, then did the pattern and had some slowdown in the overheads. I don't think my flying buddy timed those laps, or maybe I forgot

That's the sum total of the flights on the plane so far.

John Sunderland · « **Reply #8 on:** March 25, 2013, 11:00:17 PM »

I had a Tower 40. Flew with it at the '96 Nats. It had the same problem. Get an LA46 and solve a lot of problems in a hurry. Same weight, cheap price, functions well out of the box.

Mark Scarborough · « **Reply #9 on:** March 25, 2013, 11:19:07 PM »

ok Tim, first remember I am NOT the expert,, but only relating personal experience here, there are much more qualified than I however, you could do well to also search for threads on the 40 FP,,

I still dont know, what venturi and needle assembly are you using, and what muffler as well,, ( I could have told from the picture pretty much,, which is why I asked,, ) but if you can tell me it would help..

Bill Little · « **Reply #10 on:** March 26, 2013, 09:47:12 AM »

Hi Tim,

I agree with John S. Get an LA .46, set it up like Pat and Mark run it and have fun flying your model. Why mess with things that are giving you problems at this stage? And the .46 will probably come in handy in the future on another model.

BIG Bear
RNMM/AMM

Tim Wescott · « **Reply #11 on:** March 26, 2013, 10:20:52 AM »

Hey Bill:

That would be good advice overall, except that thanks to 2008 the modeling budget is teeny at the moment. If I could afford it, I'd just go electric. Maybe next year...

Joseph Lijoi · « **Reply #12 on:** March 26, 2013, 11:13:12 AM »

Quote from: Tim Wescott on March 26, 2013, 10:20:52 AM

Hey Bill:

That would be good advice overall, except that thanks to 2008 the modeling budget is teeny at the moment. If I could afford it, I'd just go electric. Maybe next year...

I can relate to budgets. Try some head gaskets. They are cheap. You might be able to get the thing to run at a consistent fast four cycle. Try blocking the third port with JB weld. This would give you the same type of port arrangement as the LA46.

Brett Buck · « **Reply #13 on:** March 26, 2013, 11:17:01 AM »

Quote from: Tim Wescott on March 25, 2013, 10:40:59 PM

I'll post pictures later, when I'm out in my building building.

Fuel is home-brew, 20% castor, 6% nitro, about 3.6% synthetic and the rest methanol.

Yes, the tank is decorated with the corrugations, but I did smooth them out a bit with a body hammer and a flat dolly.

Flights so far have been:

Several flights on a ThunderTiger 11 x 4.5. Launch RPM between 8500 and 8750.
Launching at 8750 gives me a run in level flight where it's mostly a wet 2-stroke but occasionally blipping down to four. At me enough grunt to safely do a wingover, but it fades in the overheads with that "thin" sound that you get when you're lean, not an onset of a heavier 4-stroke
Launching at 8500 gives me just enough power to think that I can do a reverse wingover. I got through the first wingover, and the plane did speed up. In the second half of the wingover it went slack and I damn near crashed the plane, only saving it with a mad backwards dash that left me with pulled muscles in my foot and a bent line clip. Even the cheers from the peanut gallery aren't worth a repeat
One flight on an APC 11.5 x 4, saved from the trash after some tip strikes by cutting it down to 11 x 4. It's what I had. I can't remember the launch RPM, but I had enough power to do the pattern -- and enough fuel to maybe do it again. It definitely ran away on me; I was hanging onto the handle with both hands
Two flights on an APC 12.5x3.75
One flight with a launch at 9500 (fueled by paranoia of launching too slow). Lots of power, 4.65 second laps at first, the engine cut out in the overhead eight, about 20 laps after I bailed from that, with the last few laps at 4.2 seconds
One flight with a launch at 9200. Plenty of power, more controlled flight than launching at 9500, and the thing at least lived through the overheads. That was the flight that I started with overheads, then did the pattern and had some slowdown in the overheads. I don't think my flying buddy timed those laps, or maybe I forgot

That's the sum total of the flights on the plane so far.

Several things to try (aside from getting a 46LA like everybody else):

switch to suction, try with and without pressure. You will have to set it richer at the beginning
try uniflow with and without pressure
use a smaller venturi, a filter, or multiple layers of pantyhose over the venturi. Use more pitch if necessary
use less diameter and more nitro to get the RPM up (9000 is about 6000 below the peak RPM of a stock engine) Less diameter will be required to inhibit the speed without being able to reduce the pitch and improve the fuel draw)
use a narrower tank (like a Sullivan SS-4 with the flat side up against the fuse)

Brett

bob whitney · « **Reply #14 on:** March 26, 2013, 12:47:04 PM »

remember he said it would do overheads at the beginning of the flight, , will it get through the clover i think the tank should be the first thing looked at, try another stock tank
yaw would need to be great for it to completly quit.

Mark Scarborough · « **Reply #15 on:** March 26, 2013, 12:50:55 PM »

Quote from: bob whitney on March 26, 2013, 12:47:04 PM

remember he said it would do overheads at the beginning of the flight, , will it get through the clover i think the tank should be the first thing looked at, try another stock tank
yaw would need to be great for it to completly quit.

I hear what you are saying, and common logic would agree, but from personal experience ( I remember exactly the day I discovered it on my airplane) I have seen small yaw componants cause this..

I do think Brett has some good suggestions his suggestions about props and rpm are another good consideration.
especially with concern to fuel draw and venturi,,

(Tim thats why I want to see your setup where are the pictures dude!)

Tim Wescott · « **Reply #16 on:** March 26, 2013, 01:57:46 PM »

Pitchers.

Two of the whole engine mounting as-is. One of the tank looking in from the back showing the tubing arrangement (which I double-checked because it occurred to me that I may have had the vent and pickup reversed -- I didn't, thankfully). It doesn't show well, but the vent tube is about 3/8" forward of the pickup.

Edit:

I got in touch with Mike, who got me up to speed on what props, etc., he was using on this. It came to me without a spraybar, so I'll double-check dimensions and correct as necessary.

Mark Scarborough · « **Reply #17 on:** March 26, 2013, 02:08:13 PM »

Nothing horribly obvious, you are going to measure the choke area ( inside diameter), is that what Mike was flying it with?
from my experience,, the 12.25 x 3.75 while perfect on the LA 46 is to much prop for the FP,,
I had great luck with the 11x4 APC

Brett Buck · « **Reply #18 on:** March 26, 2013, 02:12:08 PM »

Quote from: Tim Wescott on March 26, 2013, 01:57:46 PM

Pitchers.

Two of the whole engine mounting as-is. One of the tank looking in from the back showing the tubing arrangement (which I double-checked because it occurred to me that I may have had the vent and pickup reversed -- I didn't, thankfully). It doesn't show well, but the vent tube is about 3/8" forward of the pickup.

Edit:

I got in touch with Mike, who got me up to speed on what props, etc., he was using on this. It came to me without a spraybar, so I'll double-check dimensions and correct as necessary.

It hardly makes any difference if you get the pickup and uniflow reversed.

Brett

Tim Wescott · « **Reply #19 on:** March 26, 2013, 02:15:50 PM »

Quote from: Brett Buck on March 26, 2013, 02:12:08 PM

It hardly makes any difference if you get the pickup and uniflow reversed.

On at least one of the uniflow tanks that I've built reversing pickup and uniflow would send bubbles straight from the pickup into the uniflow and thence to the engine. It created absolutely impossible engine runs (on an FP20). Correcting the tubing fixed all (well, except for the fact that that particular tank was only big enough for the beginner pattern. But I was flying beginner at that point so it was OK).

Tim Wescott · « **Reply #20 on:** March 26, 2013, 02:32:39 PM »

Quote from: Mark Scarborough on March 26, 2013, 02:08:13 PM

Nothing horribly obvious, you are going to measure the choke area ( inside diameter), is that what Mike was flying it with?
from my experience,, the 12.25 x 3.75 while perfect on the LA 46 is to much prop for the FP,,
I had great luck with the 11x4 APC

I have the two venturis that Mike was using, and I just verified that my spraybar is the right size. I think I'm using the slightly larger venturi, so I'll try the other one this weekend.

I thought the 12.25 x 3.75 might be too much prop, but I also thought that I should try it. I'll be experimenting, but I'd like to get this "die in the overheads" fixed first (unless the board of experts thinks that it's part and parcel of the whole thing, and cannot be separated out).

Actually, if I nail the "die in the overheads" problem without otherwise changing the run, going back to the 11 x 4.5 prop that I started with may be best -- time will tell.

Mark Scarborough · « **Reply #21 on:** March 26, 2013, 04:53:13 PM »

what rpm was that 11 x 4.5 turning at launch,, I am if I recall saying I liked the 11x4 better on my FP Twister,,

Tim Wescott · « **Reply #22 on:** March 26, 2013, 05:03:20 PM »

Quote from: Mark Scarborough on March 26, 2013, 04:53:13 PM

what rpm was that 11 x 4.5 turning at launch,, I am if I recall saying I liked the 11x4 better on my FP Twister,,

Well, I don't know that the 11x4.5 will be better -- I'm just keeping an open mind. I'm definitely going to test the 11x4 and a real 11.5x4.

Somewhere between 8500 and 8750 seems to be the sweet spot for that particular prop.

Mark Scarborough · « **Reply #23 on:** March 26, 2013, 05:19:37 PM »

Quote from: Tim Wescott on March 26, 2013, 05:03:20 PM

Well, I don't know that the 11x4.5 will be better -- I'm just keeping an open mind. I'm definitely going to test the 11x4 and a real 11.5x4.

Somewhere between 8500 and 8750 seems to be the sweet spot for that particular prop.

.
that sounds really really slow to be running a true 4 pitch at close to 5 second laps,, I would think thats barely going to fly the plane, I was launching much closer to 9600 I think,,
I do not beleive that the tower/FP will be at all happy running those rpms,, IMHO
do you have a pitch gauge to check the pitch on the prop?

Tim Wescott · « **Reply #24 on:** March 26, 2013, 05:23:32 PM »

Quote from: Mark Scarborough on March 26, 2013, 05:19:37 PM

.
that sounds really really slow to be running a true 4 pitch at close to 5 second laps,, I would think thats barely going to fly the plane, I was launching much closer to 9600 I think,,
I do not beleive that the tower/FP will be at all happy running those rpms,, IMHO
do you have a pitch gauge to check the pitch on the prop?

I was unclear -- the 8500 figure is for the 4.5 pitch prop. I'm definitely going to be trying it out with the 4-pitch props.

Mark Scarborough · « **Reply #25 on:** March 26, 2013, 05:43:47 PM »

and my comment remains valid,, that is territory for a 6 pitch prop,

with the 4.5,, a true 4.5, I would expect much closer to the same 9500 range,,,, my LA 46 using the 3.75 pitch APC turns 9800 at launch,,

Hopefully Brett will step in and correct me, but I wonder just what that prop is,, what are your lap times when you launch that slow,, and does it unload more than with the other props?

Tim Wescott · « **Reply #26 on:** March 26, 2013, 06:00:06 PM »

It's a Thunder Tiger 11x4.5. I'm sure the engine is unloading in flight.

Chris Wilson · « **Reply #27 on:** March 26, 2013, 06:31:49 PM »

Just wondering if canting the rear of the tank a bit outboard may help here, and why exit the fuel feed pipe from the top of the tank, make it go through a large 'S' bend around the cylinder to finally reach the fuel nipple on the spray bar?

Seems like a good way to increase fuel draw resistance and perhaps you could temporarily invert the spray bar to negate this and see if it makes much of a difference.

Good luck.

Jim Thomerson · « **Reply #28 on:** March 26, 2013, 07:43:15 PM »

I think Tower 40s are a really good stunt engine. If you can't get yours to work, offer it to me at a reasonable cheap price and I'll take it off your hands.

I forgot to mention that I have a Jim Lee venturi with an ST NVA. I broke four cranks on the engine running it as a diesel before I switched back to glow. I was running a heavy hub which may have contributed to the cranks breaking.

Tim Wescott · « **Reply #29 on:** March 26, 2013, 11:05:10 PM »

Quote from: Chris Wilson on March 26, 2013, 06:31:49 PM

Just wondering if canting the rear of the tank a bit outboard may help here, and why exit the fuel feed pipe from the top of the tank, make it go through a large 'S' bend around the cylinder to finally reach the fuel nipple on the spray bar?

Seems like a good way to increase fuel draw resistance and perhaps you could temporarily invert the spray bar to negate this and see if it makes much of a difference.

Good luck.

Part of home-building a tank is making it tapered so that the outboard side is tilted correctly while the inboard side is flat to the fuselage.

I don't think the resistance of that tubing comes close to the resistance of the itty bitty hole in the needle valve.

Steve Fitton · « **Reply #30 on:** March 27, 2013, 05:55:51 AM »

Have you recently checked the tank for leaks?

Dennis Moritz · « **Reply #31 on:** March 27, 2013, 07:33:45 AM »

Too much prop. 10.5x4.5 APC. You're running too low an rpm. Trying to make the engine run where it doesn't want to. Try a .272 or smaller venturi, if you're getting too much air speed. If the cut off is happening at the end of the pattern, could be the tank is too small, exaggerating any issues that are slightly off. It's hard to tell precisely from the picture, but your pickup might be too close to the back wall. When you're sucking the last bit of fuel out of the tank any foaming or bubbling will kill the engine. Adding some extra capacity, increasing the amount of fuel in the tank available for the overhead maneuvers, will lesson the issue. I've been running profile tanks from RSM 4.5 ounces. Uniflo. You can put in an extra head gasket or two if the 2x2 break is too hard. Engine needs to 2-stroke. Trying to get these engines to 4-stroke (possible to run LA46s sloppy rich) means endless frustration. I prefer Tower 40s and FP40s over LA46s on Twister sized planes. LA46s like props of 12" plus diameter. The prop wash can be problematic in lighter 40 sized stunters. RSM Tank: HF 450U. The stock muffler could be a complication. I never use those. Try a tongue muffler with a lot of holes. You want a free flowing exhaust. A stock exhaust will interfere with the engine's ability to shed heat. Also a hefty weight.

bob whitney · « **Reply #32 on:** March 27, 2013, 08:50:10 AM »

from looking at the tank ,the feed tube is coming in at an angle rather then following the outer wedge and the una flow tube seems to be maybe 1/4 in inboard of that. . combined that could put the uni flow tube out of the fuel on the over heads.

Tim Wescott · « **Reply #33 on:** March 27, 2013, 08:59:58 AM »

Steve: Checking the tank for leaks is on my list.

Dennis: The pickup does come quite close to the rear wall of the tank. That issue is now on my list of things to check.

Steve Helmick · « **Reply #34 on:** March 27, 2013, 11:41:46 AM »

Quote from: bob whitney on March 27, 2013, 08:50:10 AM

from looking at the tank ,the feed tube is coming in at an angle rather then following the outer wedge and the una flow tube seems to be maybe 1/4 in inboard of that. . combined that could put the uni flow tube out of the fuel on the over heads.

I'll side with Bob on this. I would remove the fuel pickup tube and make it come out the bottom of the wedge, not the top, to make a nice & neat run to the spraybar. Then, I would put the uniflow tube against the outboard wall of the wedge, about 3/4" ahead of the aft wall, and either on CL of the > or above it, but definitely not inboard of the pickup tube. Another thing I see that is weird about your tank plumbing, is the uniflow tube not being inboard of the fuel...I'm thinking that it would tend to push fuel into the muffler, but maybe not. Muffler pressure is said to be about +.25 psi, and I'm pretty sure centrifugal force would tend to overcome that when the tank is full.

In short...put the 4 oz Hayes tank on it and see what happens. If you're using the 11x4.5 TT prop, I'd still expect to see 9.5 to 9.7k at launch. The soup can tank is your problem! Try a thinner can next time, and locate the tubes in the conventional places....

Steve

Andrew Hathaway · « **Reply #35 on:** March 27, 2013, 12:20:24 PM »

Chris Wilson touched on this a few replies ago, but who runs the pickup tube out of the top of the tank and through a 7" silly straw of fuel tubing? Isn't standard practice to mount the tank close to the engine, and keep the fuel tubing as short as possible? By building the tank with the fuel pickup exiting in the logical, normal place (front, or bottom of the tank) you can use half as much fuel tubing.

The other thing that sticks out, if this setup worked fair on another plane, with the only change being the tank, I'd swap back to the Hayes tank just to see if it effects the symptoms. If nothing else, a Hayes tank is really basic, and while it's not uniflow and it'll run leaner into the flight, it should at least be consistent.

The last thing that comes to mind, is that engine may never run right. It's just an FP clone, and it clones all of the FP issues. There are more adjustable variables for those engines than the average Rubik's Cube, you're much better off to copy someone's setup that you know works, or run an engine with a commonly accepted standard setup. The time you save with an engine that doesn't require fiddling, is time that can be spent building, practicing, or reading the forum.

Brett Buck · « **Reply #36 on:** March 27, 2013, 01:52:53 PM »

Quote from: Andrew Hathaway on March 27, 2013, 12:20:24 PM

Chris Wilson touched on this a few replies ago, but who runs the pickup tube out of the top of the tank and through a 7" silly straw of fuel tubing? Isn't standard practice to mount the tank close to the engine, and keep the fuel tubing as short as possible? By building the tank with the fuel pickup exiting in the logical, normal place (front, or bottom of the tank) you can use half as much fuel tubing.

I don't see any significant problem with the fuel tube routing. You should see some of the stuff I tried in the "small engine" experiments, particularly trying to get my read-needle engines plumbed up with the same stuff I used for the front-needle types. At times I was looping the tubing around the front of the cylinder with a brass-tube joiner. Never noticed any significant problems with it that way, aside from starting. And that's with no pressure and with some small engines with relatively large venturis. I probably wouldn't do it that way from scratch but I doubt that this is the problem in this case.

Brett

Tim Wescott · « **Reply #37 on:** March 27, 2013, 02:03:16 PM »

Quote from: Brett Buck on March 27, 2013, 01:52:53 PM

I don't see any significant problem with the fuel tube routing. You should see some of the stuff I tried in the "small engine" experiments, particularly trying to get my read-needle engines plumbed up with the same stuff I used for the front-needle types. At times I was looping the tubing around the front of the cylinder with a brass-tube joiner. Never noticed any significant problems with it that way, aside from starting. And that's with no pressure and with some small engines with relatively large venturis. I probably wouldn't do it that way from scratch but I doubt that this is the problem in this case.

Two comments that I've gotten on that tank were that (a) the pickup looks like it's close to the rear of the tank (it is), and that the uniflow vent should be against the outer wall and about an inch forward of the pickup (it is neither). Both sound reasonable, so I'm going to move things around.

Mark Scarborough · « **Reply #38 on:** March 27, 2013, 02:54:54 PM »

Quote from: Tim Wescott on March 27, 2013, 02:03:16 PM

Two comments that I've gotten on that tank were that (a) the pickup looks like it's close to the rear of the tank (it is), and that the uniflow vent should be against the outer wall and about an inch forward of the pickup (it is neither). Both sound reasonable, so I'm going to move things around.

Tim,
seriously doubt that this will be the solution,, but it may be,, have you flown it and checked the yaw yet? I was pooo poooed when I posted about having this same problem and how I fixed it,, but,, that is the only thing I changed, and the problem went away,, do what you want to,, but remember, a GOOD engineer will change the simple stuff first,, oh wait, that's not an engineer, that's the technician who does that,, never mind

as to the recomendation that the tower/FP is a bad deal, it was pretty much the defacto go to for awhile for smaller inexpensive engines. I ran mine for several years and after I settled on a setup, it was very reliable,, that said, the LA 46 was even better,, ( once the 12.25 x3.75 propbecame part of my setup) but comments are correct, the LA wants a bigger prop load,,

Tim Wescott · « **Reply #39 on:** March 27, 2013, 03:06:50 PM »

Mark: no flying until Saturday, but I do want to show up at the field as ready as I can. At this rate I should have an action-item list as long as my arm. I've got some evenings to spend between now and then, and no other model airplane work in the pipeline.

I am going to try the yaw, because it's easy.
I am going to try the Hayes tank, because it is known to work well on another model.
I am going to try all the candidate props that I have (APC 11x4, APC 11.5x4, ThunderTiger 11x4.5, and APC 12.25x3.75), unless one happens to be so astonishingly good that I would die if the run got any better.

Whether I have enough evenings to get the tank modded (a mounting plate for the Hayes tank comes first) is left to tell. It sounds like the tank will just be better with the vent moved, whether it's causing the problem or not, so I think that's gonna happen no matter what if I keep that tank.

Dick Pacini · « **Reply #40 on:** March 27, 2013, 04:02:59 PM »

I am no tank expert, but way back when, the purchased tanks had baffles in them, which helped to keep fuel in the corner when overhead. We always used to remove the back of a new tank to clean it make sure the pickup was in the center of the wedge and securely soldered. We also used to nip a little triangle out of the end of the baffle.

Steve Fitton · « **Reply #41 on:** March 27, 2013, 07:13:55 PM »

Just leak check it first before you move the vents/pickup around. Its always nice to be sure there were no simple issues present before moving on to the interesting ones.

Dennis Moritz · « **Reply #42 on:** March 27, 2013, 10:41:57 PM »

Reading your description again I had this following thought. It is typical and desirable in many ways for a UC plane to lean out in overheads. Overhead, gravity is pulling the fuel away from the pickup creating a leaner mixture. Desirable since more power is needed to keep the plane out there on the lines when airplane speed alone is counteracting the pull of gravity. In level flight, the weight of the plane is supported by wing lift. As we get further and further above level flight, airplane speed and the centrifugal force created by an airplane flying on a tether, keeps the lines taught, while overcoming gravity. Most engines noticeably lean out in the overhead maneuvers. In moderation it is considered an element of a good stunt run. If you think the airplane is speeding up too much add a head gasket, and/or go to a smaller venturi. I would use a smaller prop. The 10.5x4.5. sport APC works for me. A larger prop might complicate finding a happy needle setting, a setting where the engine pulls well throughout the pattern, without over speeding. It is possible that your tank is too fat, hard to tell without seeing the tank in person. I notice that the sides are belled. A flatter tank might reduce the transition changes as fuel is consumed (and fuel head is reduced) during the flight. I have had chicken hopper tanks work well on stunt profiles when space is an issue. The hopper seems to reduce the effects of fuel head change. Also, if cutting out is a problem, a chicken hopper might provide a better and more consistent feed. I usually run these and other tanks on muffler pressure and uniflo. On occasion vibrations issues, common on profiles, create problems, uniflo bubbling can exacerbate vibration induced foaming. Running without uniflo has helped in cases like this. If you suspect fuel foaming might be part of the problem, try running pressure to the overflow and cap the uniflo. Or cap the uniflo and vent with the overflow.

Tim Wescott · « **Reply #43 on:** March 30, 2013, 04:58:51 PM »

Thank you all. I did a bunch of flights, and I now have a combination that works. I'm still going to try changing things around a bit to see if I can do better, but a smaller venturi with a slightly cut-down APC 11.5 x 4 is working OK.

I did switch to a Hayes tank, but that didn't fix the problem -- changing from an 11 x 4.5 to the 11.5 x 4, with the smaller venturi installed, did. I ran out of time today to swap the metal tank back in (it was time to mow), but I'll try that the next time I fly just to see if it'll work like the Hayes.

The prop is not not the one that the original owner was using - but I'm using way different fuel (more castor, less synthetic) than he was, and the plane is a bit (cough cough) porky and may need more power than the svelt things that he builds.

The plane still sounds different in the overheads, and was still going slack on the lines, but moving the leadouts back about 1/4" (yes!) fixed that. That wasn't all that was going on overhead -- the plane was frankly dying at first -- but it was one problem on top of another that was compounding everything.

I'm sure there's more tuning to do -- but at least now I can do a whole pattern with it, where before I was too skeert.

Brett Buck · « **Reply #44 on:** March 30, 2013, 07:38:14 PM »

Quote from: Tim Wescott on March 30, 2013, 04:58:51 PM

The prop is not not the one that the original owner was using - but I'm using way different fuel (more castor, less synthetic) than he was,

Ah so. Might want to try less castor and more synthetic instead. The viscosity of the fuel makes a big difference in how easy it is to draw, and it's clear that the problem is fuel draw.

Brett

Tim Wescott · « **Reply #45 on:** March 30, 2013, 07:55:10 PM »

Quote from: Brett Buck on March 30, 2013, 07:38:14 PM

Ah so. Might want to try less castor and more synthetic instead. The viscosity of the fuel makes a big difference in how easy it is to draw, and it's clear that the problem is fuel draw.

I agree. Yet perfection is the enemy of good enough. I'm kinda torn between just running what I have now (which is good, and matches some of the recommendations I've gotten) and getting on with trimming out the airframe, vs. fiddling forever with the motor and neglecting the airframe trim.

Mark Scarborough · « **Reply #46 on:** March 30, 2013, 07:56:22 PM »

Quote from: Brett Buck on March 30, 2013, 07:38:14 PM

Ah so. Might want to try less castor and more synthetic instead. The viscosity of the fuel makes a big difference in how easy it is to draw, and it's clear that the problem is fuel draw.

Brett

what he said^^

Mark Scarborough · « **Reply #47 on:** March 30, 2013, 08:09:08 PM »

Quote from: Tim Wescott on March 30, 2013, 07:55:10 PM

I agree. Yet perfection is the enemy of good enough. I'm kinda torn between just running what I have now (which is good, and matches some of the recommendations I've gotten) and getting on with trimming out the airframe, vs. fiddling forever with the motor and neglecting the airframe trim.

Tim,,,, there is a reason the "set ups " are there man,, because someone before you tried all the stuff you are,, and found "x + y + z " works,, and ( ok, so I take that back, I am sure you could come up with something no one has tried,,)
cut to the chase,, there are KNown engine setups for that engine, and airframe,, here is my opinion,, if you continue flying with the setup you have, you are not accomplishing anything except burning up that fuel.
from experience,, it may work now,, what is the relative altitude you are flying at and what will it be in July,, ? I experienced on my twister, with a .40FP, just what you are.
real world, to show you how important castor percentage can be, I would tune my FP by adding an another 2% when it got hot, otherwise it would pick up quite a few rpm after the midpoint of the pattern, ( right or wrong that is what I ended up doing) If you can, go flying with someone, borrow a couple tanks of 10% 22 ( 50 castor, 50 synth) and fly a couple flights,, I would use the apc 11x4 to start and it should be I recall 9600 rpm at launch, but you can alter that for whatever your tank config works out to be.
are you really trimming the airframe flying it with a setup that responds differently? Will the airframe trim you are setting up now really be the same when you do "go to the right setup"
I am also extremely jealous, it is just this weekend getting almost ok to fly,,, but the feild is like alabama clay right now, the sod is just a big sponge

Ok ,, I reread what I typed,, It came across pointed, not meant that way,,,, Tim, take it constructivly,, as if we were standing in Salem talking ,,

Brett Buck · « **Reply #48 on:** March 30, 2013, 09:45:46 PM »

Quote from: Tim Wescott on March 30, 2013, 07:55:10 PM

I agree. Yet perfection is the enemy of good enough. I'm kinda torn between just running what I have now (which is good, and matches some of the recommendations I've gotten) and getting on with trimming out the airframe, vs. fiddling forever with the motor and neglecting the airframe trim.

That's why I always suggest some known good engine setup that is repeatable over many different examples.

Brett

Mike Haverly · « **Reply #49 on:** March 30, 2013, 10:22:02 PM »

Quote from: Brett Buck on March 30, 2013, 07:38:14 PM

Ah so. Might want to try less castor and more synthetic instead. The viscosity of the fuel makes a big difference in how easy it is to draw, and it's clear that the problem is fuel draw.

Brett

Since I use mostly electric these days I seldom visit this part of SH. That is my old engine. The best it ran, or at least the most consistant was on a Macs pipe and 10/22 Powermaster and 11 x 4 APC at high RPM. Even with a tongue muffler it needs RPM's at least 9800 to 10000 to get a consistant run, and no muffler pressure. I agree with Brett, more castor only made a bigger mess and I think made the engine run to cool. It is a true ABC and needs to get up to operating temp to be efficient. Wildcat 10/18 would be a good choice for fuel. Of the 18% oil, 80% is Synthetic and 20% castor. 10/18 Powermaster would be good also.