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General control line discussion => Open Forum => Topic started by: bob whitney on October 23, 2014, 10:23:19 AM
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has anyone tried turning the tank vent tube to the rear to prevent wind windup.
in speed a jet on suction runs much steadier with the tube turned to the rear .they also like the vent tube to the inside like the older stunt tanks, on unaflo they go rich .i had to turn my vent to the back to get it a complete steady flight ,i have not tried this on a stunt ship yet.
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Well, that's one of the reasons to use uniflow and muffler (or pipe) pressure. To regulate the pressure in the tank and prevent windup.
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I put the vent foward to prevent siphoning. If I notice a tendency for the engine to go rich the second half of the flight with outside uniflow pressure I put a restrictor over the uniflow tube. This decreases the amount of air that goes into the tank through the uniflow vent. It usually works. As far as uniflow over muffler pressure, some engines run better one way over the other. On a new plane/engine combo I try both and use what works the best. 8)
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I think you'll find it will go less than a lap and quit. I tried it on my slow rat to keep from going rich in the air and that's what happened. Of course a stunt engine has a stronger fuel signal than a slow rat so, what do I know try it. Also trying various angles I found the vent tube is subject to the wild variations around 90 degrees from straight ahead especially in stronger winds.
MM
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Some guys put the uniflo vent opening inside the cowl....
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I do like Pete does. If I'm having a serious problem with rich upwind/lean downwind I just slip a smaller diameter tube into the uniflow vent. I keep a 1/16" aluminum tube with one end pinched down in my box for just such an occasion. Turning the vent around might cause some fuel loss.
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I do like Pete does. If I'm having a serious problem with rich upwind/lean downwind I just slip a smaller diameter tube into the uniflow vent. I keep a 1/16" aluminum tube with one end pinched down in my box for just such an occasion. Turning the vent around might cause some fuel loss.
Well this just sounds like something a guy who is NOT a modeler would say! 8)
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Variations on a theme: some of them have already been mentioned.
1. If there is a cowl around the engine, figure out a way to have the vent opening inside the cowl. It seems there is a more constant pressure inside the cowl because of the prop blast regardless of the orientation to the wind. I know this has helped in "some" cases.
2. Place a restrictor in the vent tube. This was successful, to a degree, on my Gulfhawk Bearcat. On that, the 3/32" i.d. uniflow vent was directly in the prop blast. The restrictor was two tube to get an inside diameter of 1/32". That mostly solved the problem unless there was a lot of wind.
3. The best solution was to just hook muffler pressure onto the uniflow vent and the problem goes away.
Just a note - you could play with having the vent face different directions relative to the prop blast. However, my experience in dong this has not always given positive results. However, with a rearward facing vent and if the engine is running, there is little chance that the fuel will be siphoned as the vent will always be venting air into the tank. The siphoning action will be much smaller than the suction by the engine drawing fuel from the tank.
My thoughts based on a bit of experience.
Keith
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Some guys put the uniflo vent opening inside the cowl....
This is what I do, I make a little tube fitting that I can bridge with a piece of fuel line. I fill, the start and then reconnect the line pulling air from inside the tank bay.
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Well this just sounds like something a guy who is NOT a modeler would say! 8)
I know, huh. I'm surprised I didn't just jump on the guy for not already knowing how to solve the problem. LL~
(For those thinking "what is this nonsense?" It's from a different thread)
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With open uniflow vent, I have used one way valves. I have not found them necessary with muffler pressure, but have used them with crankcase pressure on TD engines.
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The simplest method and the most effective for me has been the one Randy Ryan suggested above.
Just use a short stub outside the fuselage for the uniflo vent and another short stub of tubing that goes back into the tank compartment and connect the two with a short piece of silicone tubing.
I've never had an issue with this problem on piped engines (some may have) but my PA's never seem to be bothered by it when running on a pipe.
Randy Cuberly
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If you've seen Bruce Perry's first (yellow) "Jester", the uniflow tube faces straight down. I couldn't find a close-up, but this Jester. I asked why, and he said it was to prevent that rich/lean stuff from upwind/downwind. I asked why he tried that, and I believe he said "Randy said to", meaning Randy Smith. I also noticed that his second "Jester" (white'un) has a normal forward facing uniflow vent.
Personally, I am fond of muffler pressure, but Randy (Smith) doesn't like it. There are some negatives, such as when your muffler is getting loose, the pressure is reduced and the engine goes very lean. I haven't tried it on a piped setup, but might. Like Randy Cuberly wrote, I have not noticed a wind related speed change with either my PA .51 or my Randy Smith AAC OS .46VF. This may have something to do with the pipe or Randy's venturi design? But if that's it, then why did Bruce have the problem with his piped PA .75?
The plane I'm flying now (the .46VF) has a Randy Aero pipe and it had a pressure tap added by Norm Whittle...I should give it a try. It won't happen this week! Raining like the bejeebers here right now. H^^ Steve
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Interesting bit of trivia. I face my uniflow vent forward but file the tube to an angle. (like a hypo needle) I ran a test some time ago and found that filing the tube to a 45 degree angle reduced the pressure to about .7 that of a squared off end and filing further to a 30 degree angle reduced it to about .5. Check your sine tables and pick your pressure??
Don
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If you've seen Bruce Perry's first (yellow) "Jester", the uniflow tube faces straight down. I couldn't find a close-up, but this Jester. I asked why, and he said it was to prevent that rich/lean stuff from upwind/downwind. I asked why he tried that, and I believe he said "Randy said to", meaning Randy Smith. I also noticed that his second "Jester" (white'un) has a normal forward facing uniflow vent.
Personally, I am fond of muffler pressure, but Randy (Smith) doesn't like it. There are some negatives, such as when your muffler is getting loose, the pressure is reduced and the engine goes very lean. I haven't tried it on a piped setup, but might. Like Randy Cuberly wrote, I have not noticed a wind related speed change with either my PA .51 or my Randy Smith AAC OS .46VF. This may have something to do with the pipe or Randy's venturi design? But if that's it, then why did Bruce have the problem with his piped PA .75?
The plane I'm flying now (the .46VF) has a Randy Aero pipe and it had a pressure tap added by Norm Whittle...I should give it a try. It won't happen this week! Raining like the bejeebers here right now. H^^ Steve
Hmmm....
I find it very interesting about Bruces' vent pointed straight down. It is possible that with a squared off tube at right angles to the airstream you could get a suction in the tube that would tend to siphon fuel and air from the tank. That's a simple fact of physics. I'm not doubting that it worked in this case...just that it's strange...it would seem to be non-intuitive that it could happen that way!
I ran pressure off of two different pipe setups in the early days of pipe applications. One on a VF40 and Smith/Werwage pipe setup, and the other on a PA51 and Smith/Werwage pipe setup. They both worked but seemed to be more critical to get the pipe length and needle setting right, so I eventually abandoned that and now just use a pipe with the uniflo vent faced into the airstream. On a non-piped PA61 that I have I have found that the rich lean situation in wind is very real but the engine produces enough power in the 54 oz, 688 Sq in, airplane it's in that it doesn't seem to matter.
I always think about that airplane, when I hear someone talking about the posibility of overpowering a stunter and have to smile...Nothing in my opinion is better than a grossley overpowered airplane!!! y1 <=
Randy Cuberly
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If you've seen Bruce Perry's first (yellow) "Jester", the uniflow tube faces straight down. I couldn't find a close-up, but this Jester. I asked why, and he said it was to prevent that rich/lean stuff from upwind/downwind. I asked why he tried that, and I believe he said "Randy said to", meaning Randy Smith. I also noticed that his second "Jester" (white'un) has a normal forward facing uniflow vent.
The same effect was instrumental in my problems on Top 20 day in 2003. During the week I had to switch from the Jett to the PA61 due to a chipped bearing. The Jett is very insensitive to ram air pressure, so that's what I had set up. No problem in good air with the PA. Big problem in a 30 mph wind - it helped in the maneuvers but hurt in level flight. I could have connected the ram-air uniflow to the "unconnected" pressure fitting, but I left it open, and then I just didn't have enough speed to get around the upwind side of the circle. David was running pipe pressure to combat the same issue, and our set-up for the PA were much less sensitive than the stock setup, in particular, the stock venturi greatly enhances the speed differences.
Some engines are very sensitive to the ram air pressure and some are not, so you should experiment to find out what works.
Brett
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Randy Cuberly wrote: "Hmmm....I find it very interesting about Bruces' vent pointed straight down. It is possible that with a squared off tube at right angles to the airstream you could get a suction in the tube that would tend to siphon fuel and air from the tank. That's a simple fact of physics. I'm not doubting that it worked in this case...just that it's strange...it would seem to be non-intuitive that it could happen that way!"
Yup, that's exactly what I thought would happen also. But apparently not!
Thanks for your (and Brett's) comments about tapping into the pipe for tank pressure. I seem to recall that Brett or somebody tapped right into the 'luminum header, but this (Randy Aero) pipe is tapped right at the max diameter. I'd have to run an aluminum tube, because that much silicone tubing would be a lot of weight, plus it would be floppy and too ugly to consider. Thought about CF, but probably not practical from a leakage standpoint. D>K Steve
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I questioned this some time ago when I had my ARF Nobler flying with a Fox .35 Stunt. During the flight I would have the engine suddenly go rich. So rich I could not do any maneuvers. After landing would find the tube for my unit-flo dangling in the air. It was on a peice of silicon tubing to attach to the vent on the tank in side the airplane. The screw would not stay in after a couple of flights until I finally epoxied it in place.
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Raining like the bejeebers here right now. H^^ Steve
It's been raining since last Sunday. So there's only a maximum of 32 more days to go.
(It's supposed to clear up on Monday down here, then start raining again).
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You should have been here with me yesterday at the new field. The was hardly enough wind to blow the dust away while mowing. Temps were in the 70'sF. I managed to destroy two sets of lines. Did get three flights on the latest Ringmaster. Also am going to change out engine on the Super Ringmaster.
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You should have been here with me yesterday at the new field. The was hardly enough wind to blow the dust away while mowing. Temps were in the 70'sF. I managed to destroy two sets of lines. Did get three flights on the latest Ringmaster. Also am going to change out engine on the Super Ringmaster.
Hey Doc...did you run over the lines with the mower or what??? n~ %^@ LL~
Randy Cuberly
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If I told you the story you wouldn't beleive it. But, here goes.
When I rolled out the first set of lines they were quite a bit longer than my stooge line. So I thought with this feeble brain I had gotten the lines for the bigger planes which are about 65 foot. So I grab another reel and roll it out. Aha same length. So like a dummy I switched handles and layed them down side by side. Walked out to the planes and pulled the second plane to the outer portion of the circle. Fired the engine on the new plane and launched. Immediately thing went wrong as the plane started to climb into a loop and I seen something move in the grass. Thought it was my stooge handle and gave full down. Not so good as the plane went into another loop. After about five loops the plane finally pancaked killing the engine and breaking a prop. Had to rebend the landing gear. Once on the ground that is when I seen the other handle about half way out on my up line. So scratch two sets of lines and the plane did not show any damage other than the gear being spread a little bit. Rolled up the lines and found another set in the box. Got three more flights on the new RSM Ringmaster. Using Bigirons E-Z Just style handle the plane flew great. Was rock solid and did every thing I told it too. Does get a little light on insides loops. Lines may be a little long as it is has a Brodak .25 for power that is still breaking in. 9-5 Top Flite prop for starters. Needs a lot more flying. Also need to get the canard finished.
This old age sucks when a person starts thinging too much and gets in a hurry. Also flying alone. All I could think of was keep the plane from hitting me and getting it down in one peice. Thank the good LORD not more happened.
Sorry I got off track as Randy asked for it. The tank I used is a modified Perfect 2.5 ounce for uni-flo. Works great. Pictures to come when and if I can get them downloaded.
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Hi many things will help with your problem, I use a 90 degree angled piece of plastic molded tube made by Formost for our use, or I just bend a small piece of aluminum tubing into a sharp 90 degree bend and connect it to the end of the open uniflow vent tube, it can point up or down, this will stop the wind from making the tank charged more and less with air pressure... and making the engine go lean and rich. note.. I used this for decades on many types of engines, it works on all of them, and they all do this. note I also used this in the very high wind NATs, it works very well. There are many dozens, maybe 100s of flyers who use this trick, I have tried a restrictive opening. I personally do not like that and it does not work for me nearly as well. Try them all and see for your self.
Randy