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*Help*Pusher Prop changed Tuning & will not run right-Is it a venturi sucking issue?

Old 09-07-2009, 08:50 PM
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GizmoMadMax
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Default *Help*Pusher Prop changed Tuning & will not run right-Is it a venturi sucking issue?

I am just back from our club field, and I am puzzled and frustrated... especially beigs I claimed my new Super Tiger G-61 ABC was broke-in and Tuned PERFECTLY at home, then went to the field after changing from a std prop to a pusher prop, and I had 15 guys eyeballing a totally new aircraft for our club, with this supposedly perfectly tuned engine from an hour before in my driveway, go figure...

YES the motor was taken through the OEM break-in routine, yes by the book, and yes with a standard 11x7.5 prop, yes as the book states, 5 minutes full throttle and tuning high speed needle to not be too rich and not too lean for the ABC engine break-in, than after 5 mins, did the low speed, midrange, PERFECT PERFECT and ran it for 20 minutes on and off for an hour with 2 tanks fuel. NEW gallon of Omega 15% pink half and half synthetic and castor. IT was flawless, perfect with std prop 11x7.5

I tuned it with a standard 11x7.5 prop.

Then I put on the APC 11x7P pusher prop and headed for the field, then guess what, the midrange is too rich and the stupid thing would NOT tune. IT was hard getting to full throttle past the rich mid-range, then would stahl and shut down, what the HECK???


OK, here is the story:
==============
I have a Bobcat 50 setup with a new ST G-61 ABC, which is a pusher prop Jet.

Similar to this, but not a 75
http://www.rcdon.com/html/the_bobcat-75_project.html

So what happened between the standard prop vs the pusher prop???

Yes, I used a standard 11x7.5 prop to break in the engine BECUASE the pusher prop (11x7P) will NOT cool the einge sitting on the ground, because the airflow cooling on a pusher is about 80% to 90% less cooling due to the air going the opposite direction.

So, one of the seasoned guys is thinking the pusher maybe setting up a different draft and maybe causing some suction out of the carb or some strange dynamic??? He is thinking I need to make a snout or tubing to connect to the carb and route it back some to get the suction from the pusher out of the carbs face????
What do you all think or know about pusher prop and engine tuning issues?

Would a hotter plug make a difference, becuase I did notice, that with this being my first super tiger, I need to leave the hotshot starter on the glow plug for 30 to 60 seconds and fun the motor to full then back down before I can take the glowstarter off the glow plug, or the engine will slow down and sometimes act too rich, then stahl???

I've been using this same fuel in my two OS engines and thunder tiger engine, no issues, could this fuel not be best for ST G-61 ABC ???


I did Not change the plug, still the OEM plug...
What is the recommened plug for a Super Tiger G-61 ABC here in the North East USE (S.E. PA corner)
I have a stack of NEW OS #8's, some Fox short and fox long standards, then HOT OS LC3 long and a Fox miracle plug?

** Also, on a jet, does the exhause head-wind matter at all once in the air, will this be another tuning crisis and flameouts?


Thank you in advance for any help!!!!
Please post any tech help, this has me frustrated thinking my new Super Tiger was perfect, then change prop and BAM, stupid thing is terrible...
Old 09-07-2009, 09:16 PM
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Randy M.
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Default RE: *Help*Pusher Prop changed Tuning & will not run right-Is it a venturi sucking issue?

Going to pusher will change things a little. os 8 plug is fine. Just tune it where it will fly without quiting and tweek it a little at a time. Just don't get it too lean, it may be good on the ground but they tend to lean out more it the air so leave a little room on the needle. If you have to leave the glow driver on as you said, it's too rich on the low end. the pinch test works well on the low end as it does on the high end.
Old 09-08-2009, 10:04 AM
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Default RE: *Help*Pusher Prop changed Tuning & will not run right-Is it a venturi sucking issue?

I've done a couple of pusher jets and I've found you really need a fuel pump. The best engine I've used is the old YS .45 with the built in pump. This engine with a 10 inch prop will out fly a 60 size engine plus it is lighter than most 60s. Most pusher designs require you to put the fuel tank at or foward of the CG and that makes a really long fuel line. A fuel pump goes a long way to helping get fuel to the engine. If you can't do a pump, use a header tank just foward of the engine. Don't take this wrong, but another common mistake is putting the fuel tank in backwards. I've done it myself. We are so used to the fuel lines point at the engine when mounted in the conventional cofiguration, that we don't think about pointing the tank to the front of the plane. If you got it right, I apoligize for the suggestion. An exhaust deflector will help with engine tuning. Forward flight will increase the exhaust back pressure and without one, your engine tuning will change. Lastly, avoid long idle time on the ground. Pushers aren't cooled as well as tractor setups so get in the air to keep the engine cool.

Hope this has been helpful.
Old 09-09-2009, 10:38 PM
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GizmoMadMax
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Default RE: *Help*Pusher Prop changed Tuning & will not run right-Is it a venturi sucking issue?

Your the first person to mention the fuel tank!!!! cheers to you!!!!
I asked this in some other forums with NOT a reply, go figure.
So I went ahead and put my fuel tank in as you stated, the tank pointing forward so that the pickup tube could actually stay in fuel and work at all times, but my fuel line is long...

How will i tell if I have a pumping problem???

Do they make tiny fuel pumps for 40 to 60 size r/c planes?

Can I move the fuel tank even futher up to be over the CG pointso that I can decasue the extra 5.5 ounces of lead in the nose of this Bobcat; but then my lines will be longer, just lovely??


Thanks again
Old 09-10-2009, 03:15 PM
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Default RE: *Help*Pusher Prop changed Tuning & will not run right-Is it a venturi sucking issue?

Lots of questions...I'll try my best.

In my opinion, if the tank is not right next to the engine, you need a pump. The further the engine has to pull the fuel the more twitchy the engine will be when it is not flying straight and level, which is almost never.

I've done two pushers and both of them had the fuel tank at the CG location and both used pumps. I did not want the tail heavy condition when I had a full tank. I used the YS engine on the first plane and it had the built in pump. For the second plane, I used a Perry pump. Perry makes several models of fuel pumps that are mechanically operated so you don't need batteries, switches,etc. They only work when the engine is running. On the plane with the Perry pump, I had to change the engine orientation. The engine was mounted inverted and I had all kinds of starting problems. Once I switch the engine to an upright orientation, all that went away. Do a search on Tower's website for Perry pumps and pick the one that fits your engine. As far as the long lines go, don't worry about them when using a pump. I never had problems.

OH! Instead of running silicone tubing through the fueslage up to the tanks when mounted at the CG, use antenna tube. Then run a short piece of silicone fuel line from the tube to the tank and the tube to the engine. When Combat Models was selling their pusher F-16, that is how they suggested to run the fuel line.

Let me know if you need any more help

Good luck.
Old 09-12-2009, 01:23 AM
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GizmoMadMax
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Default RE: *Help*Pusher Prop changed Tuning & will not run right-Is it a venturi sucking issue?

Well, I fabricated an exhaust pipe to keep head wind from messing with the tuning

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Old 09-12-2009, 12:46 PM
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GizmoMadMax
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Default RE: *Help*Pusher Prop changed Tuning & will not run right-Is it a venturi sucking issue?

OK, here are some more pictures of the Exhaust re-routing.

Do you think it will hold, or will the vibration cause it to come off? [X(]

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Old 09-13-2009, 01:06 AM
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littlepiston
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Default RE: *Help*Pusher Prop changed Tuning & will not run right-Is it a venturi sucking issue?

change the plug and try difrent fuel.
Old 09-13-2009, 08:48 AM
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Default RE: *Help*Pusher Prop changed Tuning & will not run right-Is it a venturi sucking issue?

I have the same plane. I don't use a perry pump or a header tank. I use a simple setup as I do in every other plane I fly. Yes the tank needs to go with the connections forward. If you went with the factory settings on the engine then your probably not setup correctly. Those settings are made for a specific altitude which you are probably not at. Sounds to me like all you need to do is tune the engine with the prop on it you are going to use. Yes, long run times on a pusher will result in problems, they don't get the air flow from the prop as a pull type does. I use F plugs in mine because they are hotter. I've run two engines on this plane. An OS55AX, runs awesome, great performance. The other is a Dubb Jett 50. Definately goes faster with the Dubb.

Dale
Old 09-15-2009, 11:05 PM
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Default RE: *Help*Pusher Prop changed Tuning & will not run right-Is it a venturi sucking issue?

Couple questions??

I am on my fifth tank of fuel on the ground(no flights yet) and it runs great with fox long or the new OOS #8 I stuck in it this eve for grins

I solved on ground heat issues by using my air compressor blow gun and keeping steady to heavy air on it as in the air!!!!

This baby runs PERFECT on the ground, although the 13" fuel line scares me, but all ranges of throttle seem to be perfect and a little rich so that the pusher with less prop wash wind does NOT get too hot on the ground or in the sky.


Question, I have threads out there, but the fuel tank is 3/4 forward of CG and empty tank I have it balanced, but 1/2 to full tank she is a little to medium nose heavy, it would NEED a lot of weight by the engine to balance it, or 1/4 of that on the rear horizontal stab to balance with full tank, unless I remove the 5.5 oz in the nose I had to use to balance it?
Some guys on RCU say balance with no fuel, others say with fuel, so I am confused????

>So for the moment, I will maiden it like this, unless someone would please give me solid evidence that they have crashed due to this or some expert review or article, because folks are saying both ways in different threads, yiks, confused

I hope for a maiden tomorrow.
Please reply with any tips or help or articles
Thanks in advance again, great forums here!
Old 09-16-2009, 11:45 PM
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GizmoMadMax
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Default RE: *Help*Pusher Prop changed Tuning & will not run right-Is it a venturi sucking issue?

No maiden today because my buddy and club member (and windy weather ) kept him from making it out.
So I ran her up and down the runway 2 or 3 times then shut her down to cool and keep from overheating. Did that 3 times, 1/2 tank fuel, she is running perfect through-out all throttle ranges, so lets see what happens in the sky, hopefully this friday eve...

BUT,
now I am questioning the prop direction, which way should it face? I notice today with the color of grass on it, that the semitar tips that are sweeping back are going in the spin direction, counter clockwise, BUT get this, that is the thicker edged side of the blade, whereas the sharp opposite side that is trailing in the rotation is fricken sharp and cut me while I was messing around??? so it seems to me the sharp edge should spin into the wind, but I am not sure???? HELP

thanks
Old 09-16-2009, 11:54 PM
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GizmoMadMax
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Default RE: *Help*Pusher Prop changed Tuning & will not run right-Is it a venturi sucking issue?

GREAT NEWS,

My heli friend from our club sent this over on the Carb Check, awesome setup.
I automatically measures the head heat and riches the carb mixture to keep engine cool!!!



The CarbSmart is typically sold for helis, but should work on any engine. ReadyHeli sells it, but it's also carried by a number of other online shops. It's made by "CSM" (Colin S. Mills), a small company in the UK. To make use of this you also need a small servo. Any micro-servo should work. I'm using a Futaba S3107 micro-servo on my heli.

http://www.readyheli.com/CSM_CarbSmart_p/csm0050.htm

The header tank that I'm running is a 2oz. Hayes tank. For non-heli use, you probably just need the tank. It's pretty cheap and available from Tower:

http://www3.towerhobbies.com/cgi-bin...?&I=LXK828&P=0

The heli version includes a mounting bracket. That adds another $15 or so to the price. For aircraft use you don't need the mounting bracket as it's pretty easy to mount in the model or tie-wrap it to the model.

Old 09-19-2009, 04:17 AM
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Default RE: *Help*Pusher Prop changed Tuning & will not run right-Is it a venturi sucking issue?


P.S. My fellow club member who flies 5 different jet types (from ducted to .91 nitro) took the first attempted maiden flight of my Bobcat.... BUT, about 20 feet off of take off and the engine shutoff, crap.... so she came in for a fairly good landing at fast high AOA landing and bent the landing gear and broke one of those cheap THIN china plastic screws. So, I am frustrated that it shut down, what the heck????
Old 09-19-2009, 08:50 AM
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Randy M.
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Default RE: *Help*Pusher Prop changed Tuning & will not run right-Is it a venturi sucking issue?


ORIGINAL: Fledgling

No maiden today because my buddy and club member (and windy weather ) kept him from making it out.
So I ran her up and down the runway 2 or 3 times then shut her down to cool and keep from overheating. Did that 3 times, 1/2 tank fuel, she is running perfect through-out all throttle ranges, so lets see what happens in the sky, hopefully this friday eve...

BUT,
now I am questioning the prop direction, which way should it face? I notice today with the color of grass on it, that the semitar tips that are sweeping back are going in the spin direction, counter clockwise, BUT get this, that is the thicker edged side of the blade, whereas the sharp opposite side that is trailing in the rotation is fricken sharp and cut me while I was messing around??? so it seems to me the sharp edge should spin into the wind, but I am not sure???? HELP

thanks

Just a note about the prop- be sure to have it on right. I saw a guy flying a bobcat with it on backwards. It will run like crap and fly even worse. After convincing the guy it was on wrong, he finally turned it around and it ran like a scalded dog. The apc 11x7p is about the best prop. at least for my os61.
Old 09-21-2009, 09:45 PM
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Default RE: *Help*Pusher Prop changed Tuning & will not run right-Is it a venturi sucking issue?

I tuned this and ran it for a week or so every other day and it was tuned to idle, slam the throttle with no hesitation, and come down fine, run at all throttle positions and no issues, UNITL it was 20 feet off the ground at maiden, and just shut off, crap.....

any thoughts...
I guess all those that said I needed a pump or header tank are right .....

We messed up the landing gear with a helicopter type hard but flat landing.... bent landing gear and broke that tiny junk boom plastic screw... but at least it is still in great shape...
so once again, I am NOT going to fly it until I get a header tank or pump

any thoughts...

thanks in advance!
Old 10-10-2009, 11:49 PM
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Default RE: *Help*Pusher Prop changed Tuning & will not run right-Is it a venturi sucking issue?

A Few weeks ago, I ended up cutting in a custom window to install a 2oz header tank, and it seems to have solved the problem!!!

Then finally this latest news!!!!
Finally, after weeks of one issue after another(stahlled on take off and broke nylon screws and bent landing gear, then wind storm last week and afraid to maiden, then my only Jet flier not able to make it), But we finally got it into the air for the first time this eve, my 3D buddy did the maiden for me. we did very well. He took off and flew and did some stunts which had me a wreck...because I don't trust those 4 little nylon screws, but afraid to use metal screws because if there is a hard hit incident like the flame out last time, the only thing that broke was the nylon screws....

So anyway, he gave it to me and it seems more touchy to me than my other planes??? the 5 to 10 mph wind seems to make it subbenly lift or fall or seemingly cause a quick 1/4 roll sort of like I just hit the ailerons, but I didn't, so i have to fight her back, then landing was scary, it seems 20 times more touchy that my other planes, it will jump up real quick on up elevator on low rates, yuk... so it seems to take some real perfect fingers to not glich and over steer....

My third low pass at high speed caught some wind and it flipped up to a 1/4 left roll and drove it down at same time and my left wing tip just touched the top of the grass and scared us all at the same time... wow, they all thought there were seeing a discentegrated plane, but thank God it didn't catch and destroy it... man, that made me shake....

Then on my second landing, I got a slight down draft and I pulled back on the stick a little too much and it seemly caused it to drive harder in the grass landing strip and broke both rear landing gear wheels off, crap.... BUT at least the plane survived... so I am heading out to garage right now to bend new matching landing gear from the 3 foot spring steel rod I bought from the hobby shop this eve, I think it is 3/32" spring rod...

I also bought the hobby radius bending dies to put in vise, so they said heat red hot and bend, then heat and put into cold water asap to reharden it...?

NOTE: when it flamed out a few weeks back, the dead stick landing did bend the landing gear back about half way, so bending them back plus the other guy who owned it for years bending them, they seemed to break right off clean on my landing this eve, they seemed to break right off very easily...

My buddy said forget flaps and just use elevator, but DANG, that thing is hot and touchy, so scary for me still....

I wonder if I can use flaps to slow this hot plane down so I can land it slower and easier? OR will it stahl and roll and crash on me?

Thanks to all for the input thus far, keep it coming
Thank you
Old 10-11-2009, 10:56 AM
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Default RE: *Help*Pusher Prop changed Tuning & will not run right-Is it a venturi sucking issue?

another thing to think about.....

silcon EXHAUST extension...... it will push back in flight and restrict your exhaust flow.

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