HOURGLASS HELP

Help needed: Trying to learn how to " correctly" do the hourglass. Do not have any local help. I can make the first turn upward OK, but when I try the inverted part on top, the plane comes across the circle, toward the center, and the lines go slack. What am I doing wrong, or is it a trim problem? ( flying Pathfinder with ST 46 )
Plane flies level upright and inverted, and the rest of the pattern is OK, sorta!

does the plane hinge(roll in or out) alot in inside and outside square corners? This trim problem could lead to dangerous loss of tension overhead.

The other likely culprit could be that you are just applying too much control at that corner--bleeding off energy, loss of flying speed, plane comes in.

What happens if you simply pull to vertical like starting a square and keep going to intersect the semicircle passing thru the overhead point, then outside square corner to finish like a wingover? Its like flying a Z

If the plane wont do this, it wont do the hourglass. Preserving energy at the second corner is very important.

FWIW

LAST EDITED ON Feb-20-04 AT 01:12 PM (CDT)
 
No disagreement with Capt Curt.
I would add a suggestion: fly it as "skinny" as possible to start with.
If you lay it too far back going up, then hit that top corner hard, you will have problems now. Go up just off vertical maybe 20* then do the rest of it, and keep opening it up gradually. A lot of folks, when they first start out, fly the hourglass too wide. By that I mean they have too acute an angle to start with which gives too much corner to try and make on the 2nd turn which really kills the airspeed, then the third corner is mushy, and forget trying to get a good last corner.
Quite by accident (read that "scared of the manuever") I started this way. Jim P. remarked about my hourglass at Brodak's being real good. Now if I could just get the rest of them that way! LOL!!
HTH
Bill <><

I would try alittle more tip weight. Make sure the hinge lines are sealed. This should help on the top of the hourglass.

Gordy

I am a 50 year old "beginner" trying to move up to intermediate.
Explain how to seal hinge lines. Thanks, DRM

LAST EDITED ON Feb-20-04 AT 06:51 PM (CDT)
 
I'll let the others tell you how to seal the hinge. What I need to know, what they need to know, is the hinging and what YOU think the hourglass is supposed to look like, from your perspective. It could be you're perception of it is wrong and you are flying it incorrectly.

I know the rulebook says two equal triangles point to point, but think about it, if you fly a hemisphere up to 45 degrees where the intersection is supposed to be, you will quickly realize that there isn't the same amount of room up top. The top triangle cannot be the same size and shape as the bottom. Also, often missed, the top of the hourglass is at 90 degrees and is really a wingover from your right shoulder to the left.

Now I'm really out on the edge here, cuzz there be pros about and I'z just an amatuer. I stop rotating with my back to the wind, and that's not really right to, I usually am leading the plane to this point and step to the downwind position, whip the plane past downwind and make the first corner so that my corner is made even with my hand being even with my shoulder, the two points making a line parallel with the myself and the wind direction. I stop the corner and aim for a point directly downwind and 45 degrees on the way to the next corner. It is important to picture the upper line of the hourglass as going directly across my shoulders. I make the turn accordingly so that the farthest part of the corner is maybe 5 degrees past the top of my shoulder, but the path on top goes over my right shoulder, over my head and over my left shoulder. Now comes the hard part, turning down and pointing it to the correct place on the ground past my right shoulder. It doesn't take long before it gets down to pull on the 4th corner there and thank goodness we only have to do one of them. Aim high initially.

Now if your bird is halfway trimmed you should be able to make this pattern. As said, narrow to a point is easier than wider. With wider you have to make tighter corners and you bleed off way too much power. But too narrow is bad to as you end up trying to basically do a wingover from the wrong side and then reverse it at the top. That doesn't work either. Don't be afraide to initally make good 1st and 2nd corners, then underturn the 3rd and come more straight down. It's esay to make the slightly over square corner there where you have enough energy. Pull through the first corner to help add energy, you are going to loose a chunk from level flight putting your plane over on it's back, but let the plane pull your arm back out on the way up, you'll need energy again at the top so turn and pull gently up there on both corners. A hard, oversharp corner directly over your head will bleed all your energy and you will be in the 'Catching Mode'

Alright, now that I've told you how to do it WRONG, lets here how it really is done. Go ahead, I've no ego left anyways.

At least my Viper is slated for Wednesday delivery!

>I know the rulebook says two equal triangles point to point,
>but think about it, if you fly a hemisphere up to 45 degrees
>where the intersection is supposed to be, you will quickly
>realize that there isn't the same amount of room up top.
>The top triangle cannot be the same size and shape as the
>bottom. Also, often missed, the top of the hourglass is at
>90 degrees and is really a wingover from your right shoulder
>to the left. (snip)

>
>From somewhere near Parkville, Mo.
>William Crane
>AMA 6733

OK, enlighten me, why sin't there the same room on top? If 45 degrees is equidistant, and we follow level flight at the bottom and the wingover path at the top, doesn't that leave the same amount of space on both segments. I suppose we can argue angles, etc., but space and shape should be equal top and bottom (Am I missing something?)

http://www.clstunt.com/pattern.htm

LAST EDITED ON Feb-21-04 AT 01:35 AM (CDT)
 
The last part of this response has little to do with the original post/question. Regarding the line tension problem at the top of the hourglass: There are several suggestion already posted that will help with the line tension on the top leg of the hourglass. If the airplane is properly trimmed with no problems in any other maneuvers with the wing being level in level flight and no hinging, there should not be too much problem with the hourglass. More power helps, good wing loading helps, good power loading helps, play with leadout positions and tip weights to see if improvements can be made, conserve energy by not hitting either of the first two corners corners too hard including the initial approximately 120-degree turn for the slightly inverted climb towards the upper portion of the hemisphere, and do not hit that second corner too hard so that the model still has plenty of speed to go across the top of the circle (as in the top portion of the wing over), make the hourglass shaped properly which means the climb and dive portions are more vertical than they are horizontal (this makes it easier to fly and is also more what the rulebook specifies, the climb and dive are about 60-degrees to the ground, not approaching 45-degrees that many less experienced pilots do). Learn to "fly" the airplane through the corners instead of jerking the airplane through the corners. And to top it all off, the Rabe rudder is a tremendous tool to have because where it really helps is the outside turns of all of the vertical or high maneuvers when line tension can often become a problem. This is particularly so with the outside turns of the hourglass. The Rabe rudder also helps with the outside loops of the overheads and vertical eights and the top outside loop of the hourglass.

Now for another issue regarding Post #5 above:

Snip
>I know the rulebook says two equal triangles point to point,
>but think about it, if you fly a hemisphere up to 45 degrees
>where the intersection is supposed to be, you will quickly
>realize that there isn't the same amount of room up top.
>The top triangle cannot be the same size and shape as the
>bottom. Also, often missed, the top of the hourglass is at
>90 degrees and is really a wingover from your right shoulder
>to the left.
> (snip)
>>From somewhere near Parkville, Mo.
>William Crane
>AMA 6733

Both triangle shapes of a properly flown hourglass are equal in size and shape. The intersection is to be at 45-degrees elevation. The top leg of the hourglass is the upper portion of a wing over directly above the pilot's head. The length of that leg is the same length as the bottom leg at the base of the hourglass. If these legs are of different length and/or the intersection is not at 45-degrees, the hourglass is not being properly flown. Unlike the square loops and the square eights, the triangle and the hourglass figures on our hemisphere can be very precisely described. The current rulebook does a fair job describing the hourglass.

See there, Told ya there'd be experts. Alright, next time I'm out at the field, I think I'm opening the top of my hourglass just a wee bit more.

But I'm a bit confused. If I read your response correctly and there is low tension up top but no hinging, he should add more tip weight and work with the leadout position? Wouldn't adding tip weight make it hinge? Cuzz my Stang is light at the tops, really light and I'd like ta fix it but haven't had a chance yet. Fact is, I think I'll go down and check the alignement on it right now even though it's just past midnight and I've been up since 1 yesterday. Supposed to go flying today at noon and I have to do some more test flights on my ARF Nobler as well as this plane. Oooo so much to do.

>But I'm a bit confused. If I read your response correctly
>and there is low tension up top but no hinging, he should
>add more tip weight and work with the leadout position?
>Wouldn't adding tip weight make it hinge? Cuzz my Stang is
>light at the tops, really light and I'd like ta fix it but
>haven't had a chance yet.
snip
>From somewhere near Parkville, Mo.
>William Crane
>AMA 6733

I did not say just add more tip weight. What I was suggesting is that there may be other trim problems. Even if the airplane is behaving "satisfactorily", it might be possible to improve the way it flies overall. Changing tip weight suggests that more or less might help, or changing tip weight while at the same time trying different leadout positions, either more forward or more rearward might help. It is almost universal that some line tension will be lost at the top of the hourglass. The good airplanes are trimmed to minimize this to acceptable levels. Technique on the handle can also be a factor. There is a big difference in what can be described as "flying through the corners" rather than just pulling hard on the handle to get the airplane to turn.

Though it does not help Dale (Spitfire in the original post) with his current airplane, the Rabe Rudder can really make a difference when properly employed. However, like anything we do with these toys, an improperly adjusted/trimmed Rabe Rudder can create other problems.

>I am a 50 year old "beginner" trying to move up to
>intermediate.
>Explain how to seal hinge lines. Thanks, DRM

I copied the following off of Stuka Stunt Forum in Nov. '02. Note the diagram attached, drawn by Brett Buck. I hope this is ok to do this. I would send it by private message, but can't attach the diagram that helps so much. Steve

http://www.nwskyraiders.com/index.html

>10. "RE: Flap Sealing Tape"
>Len and Warren: What is better:
>3/4" width, or 2"? Inquiring
>minds want to know.

The 3/4" width is just perfect for me. By the time you fold it down into the gap to the hinge pivot line, and then back out, it leaves a little over a 1/4" on each surface, so it doesn't look conspicuous. You certainly wouldn't want to use the full 2" width on your plane, or you might have to put some postage on it !! <g> And trimming down the 2" width to something less, would be tricky.

You'll notice on the package, that the roll is 650" long, so you can get 8-10 planes out of one roll.

>Do you deflect the flaps in
>one direction to the max,
>and then apply the stuff?

Here is a sketch that Brett Buck sent me one time. It shows the procedure clearly. Thanks Brett.

I only apply the tape *between the hinges*. So I cut each piece to the
correct length, then stick half of it (length wise) to a piece of "release paper"....the backing for Ultracote/Monokote works nicely for this. Then you can position the tape on one surface and gently rub it down. Then I use a thin, plastic squeege to force the tape down to the pivot point, and up the opposite side. Then remove the release paper and rub the tape down on the second surface.

Someone (I think it was TF) once suggested that after you do each
section, check the control surface to make sure that you did not increase the stiffness. If you did, remove the tape and do it over again.

You do have to use care, because over 60-65" of hinge line (wing and
stab) you can introduce considerable stiffness to your control system,
which of course you don't want.

Have fun. Cheers, Warren W

You can try to learn the maneuvers by "installments"..

I started, for example, to do square loops by goin' up (first corner), puttin' the plane inverted (second corner) and bailing out like a regular, round inside loop.

Then I added the third corner (nose down) and bailed quickly back to level flight.

After feeling kinda confident I did the last corner (all this on 10' bottoms).

Now, think of a "breed" betweem the hourglass and the vertical eight.

Do the first corner, treat the top part (second and third corners) like a vertical eight and then do the last corner.

Do the oposite too, start as an eight and do the second corner. Skip the third corner if you don't feel confident.

You'll end up gettin' so bored that the third corner wil come inevitably at some point.

Then you can do the first and second corners.

The idea is to be able to do each corner with the plane not being *upset*, because that's where you loose tension.

Instead of trying to do the whole maneuver at once you keep "adding" the corners.

Might be a good idea to start with some extra power (shorter lap time) to insure the tension.

Don't be in a hurry and if you're concerned with who's watching you practice alone or with a close buddy.

God bless ya!

In Christ,

I had exactly the same problem (free flighting over the top) plus being extremely difficult to get the turn up in the reverse wing over. Adding half an ounce of tip weight totally cured it.

Dale, Mike Scott told me to fly level from my right foot to the left foot, climb past my right shoulder to the top of the hourglass,then fly level across the top, descend through my left shoulder toward my right foot again. First time I tried it was the closest I ever came to pranging my SVII- I fixated on my right foot! Afterwards, it helped a lot. I'm trying to break the habit of flattened hourglasses, standing them more "upright". But I see a lot of the experts flying the high level segment much more abbreviated than the low level segment, as though there was no room at the top for the high level segment. (Like Leonard asked about). Once again, I think this has to do with connecting lat/lons on a hemisphere instead of just painting a two dimensional shape on the easel (sp). If your plane has marginal power, just put a lot of arm into the entry and "fly" the corners to conserve energy. Whew! I'm starting to sound like a retired aviator! PS- Prez Don has mailed your key. Best regards,

One thing I would try is more pitch at the tip of you prop,
OR try a BROD Prop like a BY&O or and EW. If that doesn't work try moving your leadouts back 1/8".

Thanks for the help. I "think" my biggest problem is that I was trying to fly it wrong in the first place. I was trying to make the
2nd. turn on top, and keep the plane in line with the "circle", and not a partial wing over across my shoulders. If the wind stays calm, I am going to go practice today, will try different leadout positions, etc. Thanks again, DRM
DALE G., THANKS FOR KEY

Same here Dale. not only that, but I checked my Mustang and found that the engine had about 1.5 degrees of inset as the Fox slowly settles through the 5 ply. So Hopefully I've found MY tension problem.

Good luck.

Dale,
What Keith said is correct. I designed the pathfinder and with a tigre 46 it should have lots of power and line tension. I fly mine with an 0S 40fp. I`d try alittle more tip weight and work with the leadouts. Get the plane trimed before trying to master the pattern. A good flying plane helps you learn the pattern easier. You`ll know when you have too much tip weight.Don`t be afraid too try moving the leadsout forward or back. Make one ajustment at a time.

Gordy

GORDON, how much offset should I have in the engine? Could the ST 46 be too much. I run an APC 11/4. Seems I have to tame it down a little too much, and might be loosing rpm on top??? I have a strong FP 40 I could try. Also, are the leadout location on the brodak plans close to right? Thanks, DRM

Here are the specs.for my pathfinder. The ones we had in my area are trimed almost the same. So this should get you in the ball park
CG. 2 3/4 to 2 7/8 inches from the leading edge.
Leadout front=3inches
flaps at 24degrees has 30degrees at elev.
weight=45 oz.
Handle spacing is 3 5/8 inches.
tip weight 1/2oz.
This is all I have.Hope this is enough. What does yours weigh?Were is the c/g and leadout position.

Gordy

G: weight- 51 oz., a little chunky cause of my "lack of" painting skill. leadouts set per plans, CG as plans suggest. How about out-trust on engine ? Plane flies great, till I get to overheads, and hourglass???????????? Wind did not help my attemp to trim today, gusty, and changed direction several times per flight. DRM

I don`t have the kit plans here so could you give me the measurements from you plane. CG,Leadout,Tip weight. I need these measured as close as possible.

Gordy

>GORDON, how much offset should I have in the engine? Could
>the ST 46 be too much. I run an APC 11/4. Seems I have to
>tame it down a little too much, and might be loosing rpm on
>top??? I have a strong FP 40 I could try. Also, are the
>leadout location on the brodak plans close to right? Thanks,
>DRM

DRM,

This post just jumped out at me!

I flew Tiger .46s for many years and would never have considered a four pitch prop on this engine. The Tiger is sort of like a bored out Fox .35. Its a cross scavenged engine that preferes moderate RPMs and more pitch on the prop than the modern schnerle ported engines. First thing I'd do is find a 12 X 5 or even a narrow blade 12 X 6 prop and give them a try. The hourglass is the ultimate horsepower maneuver and loss of tension up top is exactly what will happen if you aren't utilizing the energy of the engine in the proper way.

I'm curious what length lines you fly on (either eyelet to eyelet or handle to the center of the airplane...just be sure to tell us which) and what your lap times are. I'll just be more pitch and a bit more diameter will make your problems go away. 51 oz on an airframe as large as the Pathfinder is not out of the realm of reason. You do have to get the machine moving however and the four pitch probably just isn't doing the job.

>GORDON, how much offset should I have in the engine? Could
>the ST 46 be too much. I run an APC 11/4. Seems I have to
>tame it down a little too much, and might be loosing rpm on
>top???

EEK! 11-4? I agree completely with Ted - I had one of the worlds strongest 46's, but no way would it have worked with an 11-4! I flew with one once, and it was really, really, gutless. It was great for reseating the ring, but not for flying.

You want something like a 11.5-6 or 12-6. I flew with as much as a 13-6 at times with very strong rings. The best all-around prop I ever used on the 46 was a 12-6 Rev-Up Special Pro3, greatly cleaned up, with 5.8 basic pitch heading towards 6.3 at the tips. I could get away with 13-5's cut down to 12 and cleaned up in cool conditions at sea level, but it was not enough pitch in the summer or away from sea level.

Modern engines are great and allow good performance with small diameters and low pitch at high revs. The ST46 is not one of these engines, and the old standards still apply - 5 or 6" of pitch, and as much diameter as can reasonably be accomodated.

By the way, the ST really responds well to nitro.

Here's my baseline setup for the ST46 (unchanged since I stopped flying them in 87):
STOCK engine with STOCK COMPRESSION and STOCK HEAD
STOCK sprinkler venturi ( see other post ) with .173 diameter
Tongue muffler with 12 1/8 holes.
Rev-Up Special Pro 2 12-6 with 5.8 and washing in to 6.3 at the tips
SIG 15% nitro fuel (Omega or even Cool Power with a bit of castor will also work)
Uniflow with vent open to air
K&B Long R/C or Glo Devil #300 plug

If the engine has poor compression, you need a new ring.
If the engine had decent compression, but runs unevenly, disassemble the engine, and take a small brake cylinder hone and run it very slowly with lot of oil up and down for a few seconds until the entire bore has a cross-hatch. Too long, and you'll ruin it. Clean an reassemble, and it should run evenly.

This is very conservative and will almost certainly work, assuming you have a good ring. If you don't have a good ring, there are people who make them, or, if you are serious about running the engine for a while, the Tony Cincotta ceramic-coated piston/liner is a good alternative. Ted and I were talking about that last night - we would have given our eye teeth for something like that 20 years ago. Would have saved many hours of ring fiddling. NOTHING, I repeat, NOTHING else needs to be altered on the engine.

Brett.

THANKS GUYS! The 11/4 prop was recommended when I first flew the plane.I should have known better! Will try correct prop first, wing tip weight second, more out-thrust third if needed.
LEONARD, THIS FORUM IS GREAT!
DRM

Don`t know how I missed that 4 inch.pitch on a tigre 46.But Ted is right on the money. I ran a 11.5-5in. on my 46.Thanks Ted for jumping in on that.I missed it completely.

Gordy

UPDATE: Found a new REV-UP 12/6 in shop, put it on and went to fly.
"thought" I had needle adjusted correctly. Take off was good, line tension good, etc. Made it through wing over, and it LEANED out, big time. (9 minutes later it quit running) BLACK oil all over the plane.
MY FAULT: in too big a hurrrrrry, and did not pay attention to engine.
Have not gone into engine yet, took muffler off and piston is dark brown, but it still has good compression. Hope I can just clean it up, if not, good thing I have another one!
What rpm do ya'll suggest with 12/6?
Also Gordon, this thing seems to want to sit on tail instead of tricycle gear, even though it is balanced. Have you tried converting to taildragger?
I'm learning guys, and not ready to give up yet. Thanks to all, DRM

>UPDATE: Found a new REV-UP 12/6 in shop, put it on and went
>to fly.
>"thought" I had needle adjusted correctly. Take off was
>good, line tension good, etc. Made it through wing over, and
>it LEANED out, big time. (9 minutes later it quit running)
>BLACK oil all over the plane.
>MY FAULT: in too big a hurrrrrry, and did not pay attention
>to engine.
>Have not gone into engine yet, took muffler off and piston
>is dark brown, but it still has good compression. Hope I can
>just clean it up, if not, good thing I have another one!
>What rpm do ya'll suggest with 12/6?

I want to say somewhere around 8500, but it's been a long time. I usually set mine by ear, and not a lot different from a Fox - just a little to the lean side of the 4-2 break point. 75% "2" 25% "4". If the engine is a little weak, then it will have to be set slower to get the same lap time compared to a strong motor, because a weak engine will unload more than a strong engine.

The black stuff, however, concerns me.

Lots of great help offered here! A good topic. I want to echo Bretts concerns with the engine. It kind of sounds like it may be a bit tired. If the rings are worn and it heats up, and goes full lean half way through the pattern, swinging a 12/6 prop, which loads the motor up pretty good, and you have black in the exhaust residue you may have a problem.

I am curious what fuel mixture you are using? A short term fix might be related to oil content.

John S.

LAST EDITED ON Feb-22-04 AT 11:34 AM (CDT)
 
The landing gear for tricycle gear the mains should be angling back.If they are I would chech c/g. If thats OK then bend the gear back a little more.We`ve flown it both ways. You can swap the mains and remove the nose gear and install a tail wheel. Just about that easy.Might try cutting your prop down to 11.5.Might help the needle setting.

Gordy

Great thread guys, Gordy, it's good to see you getting more involved, we all can use some of your insights.

Gordy mentioned that several PF's have been set up as tail draggers. It's rather easy to do, and the plans mention the method, at least the first ones did. Basically just swap sides, the gear will now be angled forward. You might need to adjust the forward sweep a bit for best handling.

What he didn't mention, is the reason Trike gear is used in the first place. Easier takeoffs, and landings for lower timed pilots. No nose overs in the grass. Less chance of broken props. It's possible that learning to use the advantages of trike gear can mean anywhere from 10 to 30 points in the average, up into Advanced class, pilots, final score.

The design intentionally places the mains close to the CG. Mine, Gordies, and Petes PathFinders will set on the tail easily without a fuel load. This setup minimilizes the force necessary to rotate smoothly for takeoff. If the gear is further back, It requires more pressure to rotate, and the plane will often jump into the air, rather than rise smoothly. My PF will easily rotate and smoothly climb, almost without visibly rotating. So will Gordy's and Pete's. It usually scores pretty good for takeoffs. There are also good things that happen during landings with this setup, but we'll save that for another discussion.

I'm wondering why everything is spinning around?

NOW I AM CONFUSED*!#!!**??!
Was getting perfect engine runs with 11/4. Put on 12/6, ran lean, etc.
Checked engine, cleaned spraybar, filter, new fuel line. Engine still has great compression. Went back to fly. Started with 11/6, then 12/6, then 11/5, engine leaned out on all. ( never had any more black oil ) Same tank(clunk tank with pressure), same fuel, P/M 10-22. I even started once so rich it barely took off, but after 4-5 laps, it leaned out again. Did the first lean run ruin the engine even though it still has good compression?

>NOW I AM CONFUSED*!#!!**??!
>Was getting perfect engine runs with 11/4. Put on 12/6, ran
>lean, etc.
>Checked engine, cleaned spraybar, filter, new fuel line.
>Engine still has great compression. Went back to fly.
>Started with 11/6, then 12/6, then 11/5, engine leaned out
>on all. ( never had any more black oil ) Same tank(clunk
>tank with pressure), same fuel, P/M 10-22. I even started
>once so rich it barely took off, but after 4-5 laps, it
>leaned out again. Did the first lean run ruin the engine
>even though it still has good compression?

I doubt it. Of course an 11-4 runs well- that's a break-in prop for the 46. But it's not going to fly the airplane very well.

I'm not sure what the problem might be. What venturi are you running?

As Brett says, hard to tell what is wrong. I would go back to the basics, something changed to cause the lean runs. Check tank and fuel lines for leaks, clean filter, check back plate screws, check head screws.

The prop didn't cause this problem something else changed...

Spitfire1,
I run 22% oil in my ST 46. This is what has been working for me.

>As Brett says, hard to tell what is wrong. I would go back
>to the basics, something changed to cause the lean runs.
>Check tank and fuel lines for leaks, clean filter, check
>back plate screws, check head screws.
>
>The prop didn't cause this problem something else changed...

But it could easily have allowed a previously latent problem to surface. They suck fuel a whole lot better at 10500 than they do at 8500!

Assuming the setup is reasonable, I would first remove the pressure and run open vents. It's possible that the engine is over the hill.

I would suggest locating an expert to look over the whole thing. It's really difficult to diagnose this over the internet.

Hi,

I think the engine is hitting an RPM/ frequency causing the fuel in the tank to foam. Lower revs might cause a shakier nose..
Did you check for bubbles in the feedline between tank and engine?

fwiw

Paul

Hi,

I was told to squirt one squirt of armourall in a gallon of fuel to break the surface tension. This stopped fuel foaming and bubbles in the fuel line and tank on profile setups and the engine ran true for the full flight and not wind up and runaway in the middle of the flight. Lighter power loadings ie smaller props and easy maneuvers did not do this but once the engine started working under a load such as a larger prop the problem manifested itself as the engine got hotter from the load.

Bob Smiley
A Lancair 360 builder/pilot trying to be a modeler

Cleaned up engine, checked tank, put on new filter and fuel line.
When it stops raining, will try one more time. Will open new can of fuel ( P/M 10-22 ), go back to 11/4, if it runs OK, will try 11/5, 11/6, 12/5, etc. If problem continues, I will change engines.
Thanks to all for info. DRM

You've got tons of good advice here but here. Make good use of it all but here's one more thought: Most beginners get carried away with tight corners at the expense of the rest of the manuever. As you learn, try to "fly the Lines"--in other words on anything with a straight line in it, even the center of the clover, first get the lines/sides straight and precise. Keep trimming and improving those lines, then work the corners tighter as you and the model improve capability. A square, triangle or hourglass with great "sides" and slightly wide corners will get more points than one with tight, jerky corners and lots of twitches going in and out. Funny thing, when I practice enough to get the sides right, my corner problems usually get better on their own. Magic???

One thing I noticed, is that there has not been an answer to Brett's question about venturi size. It got me wondering if maybe the bore isn't too small, making the engine weak with the bigger props. Never having had a ST G.21 .46, I would still make a wild guess that a full 12-6 is just too much load for anything less than a really strong engine with maximumized venturi size, and maybe more nitro.

Also, while I'm personally ok with PM 10-22, I just got two Tom Lay engines (ST .60bb and G.51), and he very emphatically suggested 25% all castor. I agreed on using all castor for breakin, and asked about maybe mixing 10-22/10-29 50-50, yeilding 25.5% oil (which would be more than half castor), explaining that my local fuel options were limited (and I like Powermaster). Strongly discouraged. Steve

>One thing I noticed, is that there has not been an answer to
>Brett's question about venturi size. It got me wondering if
>maybe the bore isn't too small, making the engine weak with
>the bigger props. Never having had a ST G.21 .46, I would
>still make a wild guess that a full 12-6 is just too much
>load for anything less than a really strong engine with
>maximumized venturi size, and maybe more nitro.

Well. maybe, but I ran 13-6's on stockers with .157 venturis and 5% nitro. It wasn't optimum, but it worked OK.It had no problem getting through maneuvers that way - although getting through was about all I could manage at the time as a pilot, too.

Actually, my idea was that the venturi was too large, not too small. If it runs steadily with a 11-4, but goes lean with a 12-6 (and obviously much lower revs, maybe 1500 rpm less), I would guess that suction may be an issue.

In any case, if there's any question, it's easy to try an 11-6. If it won't turn an 11-6, there's something very seriously wrong with it.

It would be great if we could get an expert to look at it.

LAST EDITED ON Feb-28-04 AT 01:56 AM (CDT)
 
Like Brett, I'm reluctant to try and fix an engine run via e-mail.

However, the inconsistent runs were a problem for me over the years and a couple of things seemed to be the culprit for many of the problems.

If you're running the stock ST needle valve and spray bar make sure that, #1 the needle itself is straight, and; #2. that the jam collet nut is tightened down enough to make the needle almost hard to turn.

The Tigre needle when in good condition does a nice job of regulating fuel. It does, however, have some weak areas mechanically. Because it is only a single shaft of fairly soft steel and is supported in only one place, it is susceptible to bending. If it is bent at all ... repeat, at all ... it is all but worthless for fuel regulation. Take it out of the spraybar and make certain that it is straight. If not, find a straight replacement.

There is a tendency for most of us to not tighten the collet enough. Like all cross scavenged engines, the ST vibrates more than the modern schnerle stuff. Because the needle is only supported in that tiny area where the threads are compressed by the collet, that vibration can cause the tip of the needle to vibrate and destroy its value for fuel regulation.

I got a good tip from Big Jim Greenaway a hundred or so years ago at a nats when I was having nightmares trying to get a decent run. Mike Rogers was nice enough to call Jim and ask him what he thought might be the trouble. Jim suggested a big wrench and a bit of muscle. Instant cure!

The third fix I suggest with some trepidition. Brett mentioned this earlier and in my opinion if the engine shows any evidence of significant use during its lifetime, it is very likely the run problem is caused by a bad ring/liner fit.

Take the head off and shine a light into the top end with the piston all the way down. What would be perfect would be to see a dull consistent roughness everywhere except maybe right at to dead center. If you see lots of shiny areas or if the whole thing looks polished you are likely experiencing what I called hydroplaning of the ring. The ideal situation for a ring/liner fit is for a uniform cross hatch sort of pattern caused by honing of the sleeve. When this happy circumstance exists the tiny grooves in the cross hatching both carry oil for lubricating during the cycle and also give the oil some place to go when the ring moves up and down. If the surface of the ring and liner are totally smooth the ring will "ride" up on the oil rather than seating against the liner. This allows the combustion gases to blow by the ring and reduces cylinder pressure and power. When the power goes away turning a big prop becomes a problem.

Unless you've some experience with taking engines apart and putting them back together again you might want to find someone who is knowledgable to do this sort of refit to the engine. The tigers are a bit of a bother to take apart unless you know what you're doing and you do not want to try to force them apart with hammers and chisels or whatnot.

The actual honing is not rocket science. Go to a auto parts dealer and get a brake cylinder hone (spring loaded, one size fits all!) and chuck it up in a variable speed drill. Squirt some cutting oil or any reasonable lubricant into the liner and with the hone turning at a modest speed move the hone up and down the sleeve uniformly. Do it five to ten seconds at a time and wipe out the oil and inspect the surface with a light. What you want is to achieve that uniform cross hatch pattern throughout. You're not looking to remove a lot of metal, only to break the surface of the chrome uniformly from top to bottom.

It shouldn't take more that 30 seconds to a minute total to achieve this. If you've done a minute or more and you still have shiny areas the sleeve might be out of round or just flat worn out.

While the engine is apart check the condition of the ring as well. It should show some uniform machining marks around the mating surface. If it has shiny spots that have worn through the maching grooves the ring is shot and you'll have to track down another one. While not easy to find they are still around and I expect you'll be able to con one out of someone right here at Leonard's Bar and Grill.

Cap'n Fancher- if you ever have difficulty with the hourglass maneouver-just take a look at posting #9 made in this thread by myself! Just so everyone knows- the tip therein from Mike Scott seems to have originated from the fecund mind of Ted. Having re-read his flying the maneouvers guide, I was startled to see it there, word for word. So if both these gentlemen use this method, it must work well! Best regards,

>Cap'n Fancher- if you ever have difficulty with the
>hourglass maneouver-just take a look at posting #9 made in
>this thread by myself! Just so everyone knows- the tip
>therein from Mike Scott seems to have originated from the
>fecund mind of Ted. Having re-read his flying the maneouvers
>guide, I was startled to see it there, word for word. So if
>both these gentlemen use this method, it must work well!
>Best regards,

Fecund! fecund! You can't say "fecund" on SSW!

Ted

p.s. what does fecund mean?

p.p.s. Just kidding. Everyone knows what fecund means, right? Right? Shoot.