Rebel Hot by Comp Arf
12-30-2021, 02:10 PM
#1001
Last edited by retiringforgood; 12-30-2021 at 02:12 PM.
01-06-2022, 06:18 PM
#1004
Critique my fuel setup
So I'm done with plumbing finally, only missing step is installing electronics, programming radio, and CG.
Tried to keep it as simple and clean as possible. I modified a 3D printed valve holder STL with an angled base, which came out great, though not as perfectly aligned as I had hoped.
Anybody have any objections on my setup? In hindsight I have 2: Should've mounted the UAT with the ports vertically to facilitate bubble elimination (meh I can always just tilt the model around). And I know Tygon on festo connectors is controversial, but many people swear by it and I have a CM jets tank on the way so it can be festo connectors on 4mm PU hoses all throughout the system.
And no I didn't forget the filter, my fueling cans have felt clunks and a final 2 micron industrial filter before the nipple to the fill line, and this DIgitech UAT itself is a very fine filter (supposedly).
Nice job looks tidy
Tried to keep it as simple and clean as possible. I modified a 3D printed valve holder STL with an angled base, which came out great, though not as perfectly aligned as I had hoped.
Anybody have any objections on my setup? In hindsight I have 2: Should've mounted the UAT with the ports vertically to facilitate bubble elimination (meh I can always just tilt the model around). And I know Tygon on festo connectors is controversial, but many people swear by it and I have a CM jets tank on the way so it can be festo connectors on 4mm PU hoses all throughout the system.
And no I didn't forget the filter, my fueling cans have felt clunks and a final 2 micron industrial filter before the nipple to the fill line, and this DIgitech UAT itself is a very fine filter (supposedly).
Nice job looks tidy
Last edited by retiringforgood; 01-06-2022 at 06:27 PM.
01-06-2022, 10:12 PM
#1005
Tygon on Festo is a 100% No No and people who swear by it fools.
I know it’s a small turbine, but 4mm od (2.5mm I’d) tube on the suction side gives the pump a hard time. The difference in area between 3.2mm Id Tygon and 2.5mm tube is huge as a percentage.
I know it’s a small turbine, but 4mm od (2.5mm I’d) tube on the suction side gives the pump a hard time. The difference in area between 3.2mm Id Tygon and 2.5mm tube is huge as a percentage.
01-07-2022, 05:49 AM
#1006
As for the rest I don't really have a choice the X90 is designed for 4mm all around on the pump and engine sides.
01-07-2022, 07:20 AM
#1008
I Figured since it's just for the fill line it may be less risky. For ground testing I'll just leave it as it's for now but I'm trying to source nipples with a suitable tygon size.
As for the rest I don't really have a choice the X90 is designed for 4mm all around on the pump and engine sides.
As for the rest I don't really have a choice the X90 is designed for 4mm all around on the pump and engine sides.
The turbine plumbing is fine in 4mm like 95% of turbines, it’s the tank to hopper tank line that is the issue. I guess the fault is the hopper tank fitting if that is what was supplied.
01-07-2022, 07:35 AM
#1009
My Feedback: (1)
Hi,
I installed the same Digitech header tank in my K70 Rebel Hot. You can see it in post #891.
I suggest you rotate the tank 90-deg so the line to the tank is at the highest point, keeping as high as possible above the fuel inlet to the pump.
It seems you have the fittings installed wrongly. Swap the barbed fittings to the fill line and use the Fesco fitting between the tank and header tank inlet. Use 6mm between the tank and header tank. 4mm between the header tank & pump and between the pump and the turbine inlet.
As Dave W. pointed out, it is better to use larger tubing on the suction side of the system so that the pressure drop is minimized. But since the clunk line is smaller than 6mm, this is only a very minor improvement.
I like to put the pump close to the turbine to keep the discharge line short. The pump is positive displacement type and cavitation is not an issue, so as long as your set up is leak-free the pump will deliver the fuel.
I installed the same Digitech header tank in my K70 Rebel Hot. You can see it in post #891.
I suggest you rotate the tank 90-deg so the line to the tank is at the highest point, keeping as high as possible above the fuel inlet to the pump.
It seems you have the fittings installed wrongly. Swap the barbed fittings to the fill line and use the Fesco fitting between the tank and header tank inlet. Use 6mm between the tank and header tank. 4mm between the header tank & pump and between the pump and the turbine inlet.
As Dave W. pointed out, it is better to use larger tubing on the suction side of the system so that the pressure drop is minimized. But since the clunk line is smaller than 6mm, this is only a very minor improvement.
I like to put the pump close to the turbine to keep the discharge line short. The pump is positive displacement type and cavitation is not an issue, so as long as your set up is leak-free the pump will deliver the fuel.
01-07-2022, 08:51 AM
#1010
Fill line is as (or more) important than all the rest…if it allows air in the UAT will drain during the run-that’s in flight so you will get an unexpected flame out sometime during the flight when the Hopper tank is below the tube.
The turbine plumbing is fine in 4mm like 95% of turbines, it’s the tank to hopper tank line that is the issue. I guess the fault is the hopper tank fitting if that is what was supplied.
The turbine plumbing is fine in 4mm like 95% of turbines, it’s the tank to hopper tank line that is the issue. I guess the fault is the hopper tank fitting if that is what was supplied.
Hi,
I installed the same Digitech header tank in my K70 Rebel Hot. You can see it in post #891.
I suggest you rotate the tank 90-deg so the line to the tank is at the highest point, keeping as high as possible above the fuel inlet to the pump.
It seems you have the fittings installed wrongly. Swap the barbed fittings to the fill line and use the Fesco fitting between the tank and header tank inlet. Use 6mm between the tank and header tank. 4mm between the header tank & pump and between the pump and the turbine inlet.
As Dave W. pointed out, it is better to use larger tubing on the suction side of the system so that the pressure drop is minimized. But since the clunk line is smaller than 6mm, this is only a very minor improvement.
I like to put the pump close to the turbine to keep the discharge line short. The pump is positive displacement type and cavitation is not an issue, so as long as your set up is leak-free the pump will deliver the fuel.
I installed the same Digitech header tank in my K70 Rebel Hot. You can see it in post #891.
I suggest you rotate the tank 90-deg so the line to the tank is at the highest point, keeping as high as possible above the fuel inlet to the pump.
It seems you have the fittings installed wrongly. Swap the barbed fittings to the fill line and use the Fesco fitting between the tank and header tank inlet. Use 6mm between the tank and header tank. 4mm between the header tank & pump and between the pump and the turbine inlet.
As Dave W. pointed out, it is better to use larger tubing on the suction side of the system so that the pressure drop is minimized. But since the clunk line is smaller than 6mm, this is only a very minor improvement.
I like to put the pump close to the turbine to keep the discharge line short. The pump is positive displacement type and cavitation is not an issue, so as long as your set up is leak-free the pump will deliver the fuel.
I considered putting the pump on the engine mounts but was concerned with CG being too far aft since it's a bigger engine. Won't really know until I put it in the balancer, I may relocate it.
After much sleuthing I think I found a place to get these nipples locally, Festo part N-M5-PK-3, for 3mm ID with M5 thread, I'll get one for the tank port and one for the fill port.
Last edited by retiringforgood; 01-07-2022 at 09:09 AM.
01-07-2022, 11:32 AM
#1011
@retiringforgood,
I agree with all the recommendations regarding not using tygon on a Festo connector. This is especially important for a fill line since tygon can change shape over time (harden/deform) and will develop a leak. This will eventually cause a flameout. It seems the connectors on the UAT need to be swapped. I would put the 4mm for the fill line and Festo on the "Tank" side. If you want to use 6mm polyurethane lines you can slide a short 4mm polyurethane line over the nipples, then a 6mm over that. This is how it was done for years with the jetcat pump setups. Otherwise, it looks good.
"V"
I agree with all the recommendations regarding not using tygon on a Festo connector. This is especially important for a fill line since tygon can change shape over time (harden/deform) and will develop a leak. This will eventually cause a flameout. It seems the connectors on the UAT need to be swapped. I would put the 4mm for the fill line and Festo on the "Tank" side. If you want to use 6mm polyurethane lines you can slide a short 4mm polyurethane line over the nipples, then a 6mm over that. This is how it was done for years with the jetcat pump setups. Otherwise, it looks good.
"V"
The following users liked this post:
retiringforgood (01-07-2022)
01-08-2022, 08:40 AM
#1013
You need to turn the hopper 90 degrees. At the moment you will only get the hopper tank half full. Follow the process, fuel goes in, hopper fills till it starts to feed to main tank.
01-08-2022, 08:50 AM
#1015
Dammit I have to redo almost everything mounting wise then
01-08-2022, 11:48 AM
#1016
Wouldn’t touch them with a long pole! Loads of leak points, no warning of cavitation, difficult to purge all the air filling, heavy…this one is even worse as it was designed with a different pick up that was complicated, so now has a tube rapped in fibre…🙄
01-08-2022, 02:21 PM
#1017
Well before I tore everything apart I decided to test the thing for grins with my new RC fueling systems can with the graylor pump and long story short as far as I can tell the way it's mounted should be a non issue. When filling up it does go up to 99% with the tiniest bubble left over at the top. When emptying with my pump at full speed, there's a lot of cavitation bubbles but even then if I run it in reverse until the main tank is dry, the UAT never seems to go less than 80% full. And the turbine's pump is nowhere nearly as powerful as this so as to cause the bubbles. I plugged off the vent to pressurize the whole system a tiny bit and everything seems tight no leaks whatsoever. I guess this fueling pump is powerful enough that the orientation doesn't really matter and the bubbles just get pushed out to the main tank vent no matter what. I tried filling and emptying while tilting the plane around and the results were pretty consistent. I'll obviously do one final test on the ground with the engine itself and shaking the crap out of the plane in the process but I have no reason to believe it will be any worse. Dunno if it makes sense but if you guys really want I could take a video.
About the average size bubble I saw. Worse case was not a whole much more than this.
About the average size bubble I saw. Worse case was not a whole much more than this.
01-09-2022, 12:36 AM
#1018
When you did the filling the fuselage was flat like it would be on the wheels? I know the hopper is angled, but still does not look like it would fill completely sitting still. Yes you can manoeuvre the airframe around while filling just about any set up-but that is not always practical.
Your other points make sense, though flight operation is different.
Dave
Your other points make sense, though flight operation is different.
Dave
01-09-2022, 01:11 AM
#1019
I can't see a bubble or two in the air trap mmaking any difference.
01-09-2022, 03:30 AM
#1021
My Feedback: (53)
Well before I tore everything apart I decided to test the thing for grins with my new RC fueling systems can with the graylor pump and long story short as far as I can tell the way it's mounted should be a non issue. When filling up it does go up to 99% with the tiniest bubble left over at the top. When emptying with my pump at full speed, there's a lot of cavitation bubbles but even then if I run it in reverse until the main tank is dry, the UAT never seems to go less than 80% full. And the turbine's pump is nowhere nearly as powerful as this so as to cause the bubbles. I plugged off the vent to pressurize the whole system a tiny bit and everything seems tight no leaks whatsoever. I guess this fueling pump is powerful enough that the orientation doesn't really matter and the bubbles just get pushed out to the main tank vent no matter what. I tried filling and emptying while tilting the plane around and the results were pretty consistent. I'll obviously do one final test on the ground with the engine itself and shaking the crap out of the plane in the process but I have no reason to believe it will be any worse. Dunno if it makes sense but if you guys really want I could take a video.
About the average size bubble I saw. Worse case was not a whole much more than this.
About the average size bubble I saw. Worse case was not a whole much more than this.
I just don’t understand……you buy an expensive UAT, and then decide the design is not good for you installation…so you change the way it’s suppose to be used….then once you get a flame out….your most likely going to say the UAT wasn’t good…..well good luck 🤞
01-09-2022, 07:19 AM
#1022
Alright I was going to reply individually to everyone but here's videos in glorious 4k 60FPS to appease the skeptics. For what it's worth I accidentally pressurized the bejesus out of the whole system when I fueled it until the pump stalled because I forgot to unplug the vent. Pump can pressurize to 20psi and I didn't hear any fizzing or see any leaks anywhere so I think it's very safe to say after that accidental stress test that the plumbing is sound, leak-wise at least.
Filling:
Emptying:
On the emptying one I start off slow to what I estimate is a consumption equivalent to full throttle, then gradually increase. At the 30s mark, it's not until what I estimate to be 3x the consumption of the turbine pump at full chooch that you see a tiny amount of fizzing bubbles. At full chooch its easily about 6 to 8x the rate of the turbine's pump and the bubbles appear to be due to cavitation at the tank inlet itself as the hose shows no bubbles. At the end you see that even in this completely unrealistic scenario the inner wick isn't even exposed to air at all, and these UATs are known to work fine with 50% air or more.
I'm planning eventually on actually bench testing it with the engine itself and simulating a long nose dive to see how long it takes for it to flame out with the main tanks clunk exposed. As it stands right now I don't see why it shouldn't work normally.
Let's not be drastic here. I won't. I am capable of learning from my mistakes. Should it work flawlessly, and I don't see why it wouldn't so far, what are you going to learn from that then? Furthermore, at least I'm getting CNC machined parts and industrial grade connectors. Overkill? Perhaps, but I'd say that's far more for my money than paying $50 for a glorified $2 nalgene bottle with a $2 lawnmower filter with some holes poked through it. Those gave me far more flameouts.
Filling:
Emptying:
On the emptying one I start off slow to what I estimate is a consumption equivalent to full throttle, then gradually increase. At the 30s mark, it's not until what I estimate to be 3x the consumption of the turbine pump at full chooch that you see a tiny amount of fizzing bubbles. At full chooch its easily about 6 to 8x the rate of the turbine's pump and the bubbles appear to be due to cavitation at the tank inlet itself as the hose shows no bubbles. At the end you see that even in this completely unrealistic scenario the inner wick isn't even exposed to air at all, and these UATs are known to work fine with 50% air or more.
I'm planning eventually on actually bench testing it with the engine itself and simulating a long nose dive to see how long it takes for it to flame out with the main tanks clunk exposed. As it stands right now I don't see why it shouldn't work normally.
Let's not be drastic here. I won't. I am capable of learning from my mistakes. Should it work flawlessly, and I don't see why it wouldn't so far, what are you going to learn from that then? Furthermore, at least I'm getting CNC machined parts and industrial grade connectors. Overkill? Perhaps, but I'd say that's far more for my money than paying $50 for a glorified $2 nalgene bottle with a $2 lawnmower filter with some holes poked through it. Those gave me far more flameouts.
Last edited by retiringforgood; 01-09-2022 at 07:55 AM.
01-09-2022, 08:30 AM
#1024
Bob
Yes. But all tubes are a tight fit over the tube/barbs, plus our hottest days are mid 30’s so the tube does not soften.
RFG Draining from the filler does not replicate the turbine pump drawing through the pickup. At this life of a fuel system I would not expect a problem-it was over a season before the Intairco traps started causing flame outs.
Yes. But all tubes are a tight fit over the tube/barbs, plus our hottest days are mid 30’s so the tube does not soften.
RFG Draining from the filler does not replicate the turbine pump drawing through the pickup. At this life of a fuel system I would not expect a problem-it was over a season before the Intairco traps started causing flame outs.
01-09-2022, 08:35 AM
#1025
I was considering connecting my fueler pump directly to the pickup but that seems more of a hassle than it's worth with adapter and what not. Anywho may as well fire up the engine for real.
