Extreme Speed Prop Planes Discuss the need for speed with fast prop planes (Screamin Demon, Diamond Dust, Shrikes or any REAL sound breakin'''' plane)

Going lean at high 'G'.

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Old 11-10-2004, 07:19 AM
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Barfly
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Default Going lean at high 'G'.

I'm finding it a bit tedious to search out info on this. I have a Lanier Shrike running a TT Pro .46 and the engine goes real lean in high 'G' maneuvers and verticals. Tank is centered inside the nose and the engine is upright (no choice, it's a belly lander) so the carb is almost the same hight as the top of the tank (not ideal, I know). In level flight it goes a little lean towards empty but when I yank the stick it goes real lean and loses power. If I set it rich it's weak on launch and strong when I pull. I'm sure I'm not the first to experience this, so what do you all do to solve it?

I'm thinking a/ Uniflow tank set-up, b/ Crankcase pressure to tank, or c/ Option a/ or b/ with a regulator. Uniflow is easy, will it be enough? Case pressure is easy, but will the engine tune correctly. Regulator is expensive, can I avoid it?

I want (need ) to go flat out the whole tank so please share your experience. Tx.

Cheers from the Barfly.
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Old 11-10-2004, 08:00 AM
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daven
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Default RE: Going lean at high 'G'.

Get a bladder tank and your problems will be solved.

www.pspec.com for the Tetra tank, or www.jettengineering.com for the Jett bladder tank
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Old 11-10-2004, 12:45 PM
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Default RE: Going lean at high 'G'.

You will be much better off with a bubble-free tank as Dave mentioned. Jett and Tetra had a number of sizes available. Check the web site for the one you feel will fit best.

The bubble free tanks avoid any air being mixed with the fuel resulting no lean run at the end of the tank, or in hard manuves. A bonus is that you can run 'flat out' to the very last drop of fuel without concern of the engine going lean, so it effectively extends your flying time. The biggest benifit is it minimizes/eliminates the chance of creating fuel foam.

Installing a bubble-jett tank or tetra tank will instantly correct the conditions you noted.

Other approach...

From what you described, there is a very good chance you are developing fuel foam. You should be able to adjust the needle on an TT46 so the engine is about 500-600 rpm down from peak at launch, and it should not go lean at any point in flight. The fact that you noted the leaning tendency....and that making the engine 'rich enough' resulted in it being so rich there was not enough power for launch.... leads me to surmise you have a foam problem and/or other fuel system issues. What is happening, is that in the air, the engine/prop/airframe are vibrating, creating air/fuel foam within the tank. After a brief while, this foam will be all the engine is drinking. The pre-mixed air/fuel foam will cause your engine to go lean.....and the resulting over-heat will eventually damage the engine. In many cases, you will not see the foam effect on the ground.... it happens in the air when the engine unloads.

Many have sucessfully flown a Shrike with a standard tank, even using high-output engines. It can be done.

If you choose to continue with the standard fuel tank, ensure that:

1) the tank is completely isolated from the airframe stucture with foam rubber - no part of the fuel tank can touch wood

2) double check your fuel tank clunk line and metal clunk. Make sure there are no cuts or holes in the line, and that the clunk is attached and moves freely at all aircraft angles

3) make sure the fuel line and vent line have no holes or kinks, and that they are not pinched in the installation. Make sure the vent/pressure line is properly connected and that the pressure fitting on the muffler is clear of dirt and obstructions.

4) make sure the prop is balanced - I'd recommend a stock C series APC 9x7 or 9x8 for the Shrike with the TT46. The engine will turn either of these props around 15-16K rpm. APCs are generally good from the bag.....but always check and balance them anyway.

5) Always back the engine off 400-600 rpm rich from peak rpm on the ground, prior to launch. The shrike is quick. In the air, the engine will unload a great deal, and it will need the additional fuel.

I hope this is helpful. Any questions, feel free to post here, pm or email.

Bob
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Old 11-10-2004, 02:17 PM
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Default RE: Going lean at high 'G'.

bob27s and daven, that's something I hadn't considered. A bladder tank! Option 4/? My friend Iskander uses them but I thought it would not solve the high 'G' problem. Bob, I'm a little bit proud of this plane (it's scratch built and modified, not kit) and I've been carefull to make sure everything is sweet. Also, this is my first speed model so I expected the unexpected. During the early flights I didn't push it and had no problems, but now I'm getting the hang of it I get this leaning whenever I pull hard on elevator. Going lean towards empty is not a biggy, but the high 'G' issue is much more significant. I've noted your suggestions 1) to 5) and all is cool, just one thing. I run an APC 10 x 8, and I have no issues at all. Haven't tached it though. It unloads coming out of a shallow dive, otherwise sounds great. I have a 10 x 7 on hand, worth a try?

If you guys can confirm a bubbleless tank will solve the high 'G' problem I'll try to get one in there. Thanks for the advice.

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Old 11-10-2004, 02:44 PM
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Default RE: Going lean at high 'G'.

The bladder solves two of the problems you are encountering:

1). Like Bob mentioned, the High G maneuvers at High speed is causing some fuel foaming. When using a bladder, you remove all air from the bladder before filling up the tank with fuel. This lack of air, solves 99% of all fuel foaming issues.

2). I don't want to say that a bladder tank is pressurized, but to some extent they are. When using bladder tanks I am able to run my fuel tanks back on the C.G. of my racing planes, and still have good fuel flow to the engine without a pump.

I've been starting to use bladder tanks on some of my sport planes because they really help an engine run consistently throughout the tankfull of fuel.
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Old 11-10-2004, 02:59 PM
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Default RE: Going lean at high 'G'.

barfly,

when you have a chance, post a photo or two of the plane. Sounds like a nice bird. We often get questions about the shrike on here...... always helps to have more photos to point to

Either of the 10" props will work......but both of those are a little bit big for that engine, especially in this application.

I'd say at least drop back to the 10x7. If the opportunity presents itself...... try out the 9" diameter props I suggested. You will get much better top end speed.

That 10x8 may be part of the problem in the first place... its a lot of load. If you have a tachometer, check and see what the engine is turning. The TT40 and 46 both prefer to have top end RPM above 14,500. Prop selection should be made accordingly. Either engine is happy with up to about 16.5K peak RPM on the ground.... try to limit to no more than that.

As Dave noted, the bubble-free type tanks are not traditional 'pressureized' bladder tanks. They vent to atmostphere and use muffler pressure, however the seperate the fuel from the air. Very easy to use.

Just as with Dave, I use them in a number of sport planes. Some of those ARF's are terrible on fuel tank installations.....no room or accomodations for padding.... fuel foam can be a big issue.
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Old 11-12-2004, 08:23 AM
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Default RE: Going lean at high 'G'.

Okay, I've had another look over it and, well, small mistake. The prop is, and always was, an APC 10 x 7! So I guess I'm okay with that. I noticed on Dubb Jett's site he says the bubble less tank may still go lean in turns, and this is my primary issue. I've never seen pylon racing so I don't know how aggressive the turns are, but with the Shrike I'm pulling full elevator at full speed, sometimes inverted and sometimes in vertical maneuvers. If I just fly like a sport plane it's a little lean at the end but this is not a problem. The real issue is the high 'G's.

I've read here on RCU that some are using higher tank pressure and a regulator, can anyone offer any comments on that idea?

I've contacted a shop in Singapore, they don't have the Tettra in the smaller sizes so I've asked them to get me one, but it may take a while. In the meantime, I think I'll just try the Uniflow to see if it helps, easy to do (and undo) and can't hurt.

Bob, I took a few photos today but it's a new roll of film and I'd like to use most of the roll before I get 'em developed and digitised. Hope you can wait a little while.

Cheers from the Barfly.
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Old 11-12-2004, 10:28 AM
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Default RE: Going lean at high 'G'.

Tetra makes a 4 oz, a 5.25 oz, and a 6 oz tank. I would think the 4 oz would work well for short flights.
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Old 11-12-2004, 12:57 PM
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Default RE: Going lean at high 'G'.

If your tank is too far off in regard to the carb you are always going to get fuel flow problems during hing G maneuvers. A bladder tank may solve part of it because it ensure your engine is always fed with fuel instead of foam... but the problem is still there. There's only one real fix: line your tank up with the carb.

Pylon planes can make insane turns. A Q500 can make incredibly tight turns without loosing much energy. Smaller sleeker pylon types can be yanked into a high speed stall. One can clearly hear this when standing under the #1 pylon. You hear this "whooshing" sound... that is actually flow separation.
Anyway, during these turns the plane is subjected to very high accelerations. I don't think 25-30 G is uncommon... probably even more sometimes.
When subjected to this kind of punishment you just need proper tank alignment.

Since you can not align your tank... you may just have to go easy on the stick...
But get the bladder tank anyway.

If you have the room to fit a Cline regulator: that wil solve you problem pronto.
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Old 11-12-2004, 01:01 PM
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Default RE: Going lean at high 'G'.

I also run a TT46pro with a 9/7apc and Ultra thrust muffler with no problems. Is your engine dialed in right? Meaning removing or pinching off the fuel line and listening to the sound of the engine when it quits?

I see many engines every week that seem tuned in but they are not even close. They dial in the low end and thenthehigh and assume its okay and it's not.
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Old 11-12-2004, 07:44 PM
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Default RE: Going lean at high 'G'.

I'm using a 240cc tank and getting about 10 min. flights, just about right for me. That's about 8oz. I've asked the shop to get a 6oz. and an 8oz. for me.

Rudeboy, I reckon I'm not even close to that sort of 'G' loading. 25 -30G.... wow! Go easy on the stick? Seriously! Unfortunately, there is no option to reposition the tank, have to live with it. The regulator option is interesting, but no-one I know here has any experience with them.

Snoop Doggy Bag, I do the pinch test when I tune and I run a few clicks rich on the high end. Engine stays cool and seems to run great. I use the stock muffler. CoolPower 15% nitro heli fuel 'cos it's got more oil. Any other fine tuning tips are welcome.

I'll report back after this weekend's flying. Thanks for your help here.

Cheers from the Barfly.
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Old 11-20-2004, 12:04 AM
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Default RE: Going lean at high 'G'.

Well, it was a long weekend here and, due to the monsoons, I only got four more flights in. I changed the tank to a Uniflow set-up and was a little dissappointed. More consistant in level flight but seems to lose fuel pressure in a steep climb or vertical.

The shop in Singapore has confirmed my order for two Tettra bubble less tanks, one for the Shrike and one for a Diamond Dust (future project). But I have to wait 'till end of December.

Some pictures here for ya Bob, 'cos you asked! The shot with the hatch off is a bit blurred, sorry, but you get the general idea. These are digitised from 35mm film negatives.



Cheers from the Barfly.
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Old 11-20-2004, 12:22 AM
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Default RE: Going lean at high 'G'.

Rudeboy, I thought you were exagerating a tad when you said "25-30 G" but you're serious, aren't you? [:-]

Have you used regulators on your planes? Would I need to tap the crankcase, or is muffler pressure enough?

Cheers from the Barfly.
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