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Fluid Pressure - 4/23/2003 12:32:30 AM   
PJ_TankPilot



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From: Phoenix, AZ, USA
Status: offline 		The bends may affect flow but not pressure. The pressure of fluid caused by gravity is simply the height of the fluid above the exit point. When you change the height or the gravity, you change the pressure.

Just keep in mind the old water tower. The water pressure is a function on how high the tower is. The gravity for a water tower is fixed so you don’t have that problem. It’s simply the weight of the water above the exit point that causes the pressure. The higher the tower, the higher the weight of the column of water. The diameter of the water tower does not affect the pressure.

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Mr. Smoothie for Q-40 - 4/23/2003 12:44:00 AM   
matchlessaero



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From: Cordova, TN, USA
Status: offline 		Good points Kane (didn't take it as smarta$$, I am trying to understand too). As for my experience, I have flown 428-424 and half-A for too many years. I think the Half-A's are the most applicable to the Q-40s(which I do not claim to have run) though, as I am running piped half-a's on pressure spinning between 26k and 28k and flying in the 110-120mph zone. While the volumetric differences are obvious between the two, the forces are somewhat similar. Even when running engines on suction, the forces and issues are the same. Running pressure just serves to minimize the effects of g-loads on the engine run.

IMO, I believe what you have to look at is the general flow direction of the fuel. If the tank(centerline or avg height of tank) is higher than the spraybar center, you will get a positive fuel pressure (above and beyond regular running pressure) at the spraybar, ( from 30lbs to 30.75lbs) and induce a richened state. The opposite would be a tank with its center lower than the spraybar center. Pulling through the turn induces a negative force on the fuel flow, (maybe from 30lbs to 29.25lbs of pressure).

The extreme version of all this is the 4-2-4 run of a properly tuned CL Stunt engine. The key thing to note is that stunt engines achieve the 4-2-4 in both g-loads (inverted and regular g-loads) and with engines in all attitudes.

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Mr. Smoothie for Q-40 - 4/23/2003 12:52:17 AM   
PylonWorld



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Status: offline 		From Duane's explanation, and thinking about it in the following terms, I think I'm starting to understand why tank location would matter.

For a pilot in an aerobatic airplane, two different situation with the same effective end results can happen. A blackout occurs when the pilot pulls too many positive G's, and a redout occurs when the pilot pushes too many negative G's. Even though the pilot's body is a closed system, the blood rushes from the head in positive G's, and to the head with negative G's. So ... the effect of the G's on the fluid, which has weight, overcomes the pressure from the heart.

This would be consistant with an engine going rich when the tank is more inside the turn than the engine, and going lean when the tank is outside the turn. It would depend on the fuel draw of the engine. If the force of the draw is less than the force on the fluid, that would cause a lean condition. If the tank is inside the turn, then additional pressure would increase the fuel flow into the engine.

The real question is how critical is tank location. Today's flat screen CRT's look flat, but in reality they are curved, typically to a 50 meter radius. Our perception is that they are flat, though.

Aren't F3D's still allowed to use crankcase pressure? If so, they are running with more pressure than the muffler pressure of the Q-500/Q-40's. If tank location matters in an F3D, then it probably matters for us as well.

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Mr. Smoothie for Q-40 - 4/23/2003 1:20:09 AM   
kane


 

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From: Arlington Heights, IL, USA
Status: offline 		This is a subject I hadn't really thought about. It makes sense, I understand the rich condition with a high tank. I was trying to break it up into all its little sub parts to see if they adversly affected the outcome. Barry said it best in his last reply, whatever the reasons, this is what it does. Sometimes, I need to be hit in the head with a rock to understand something.

I would still be interested to hear feedback on if anyone has tried to change the tank location in their current QM. My airplanes don't last long enough to experiment. Plus, I don't know if there is much room in any of the current designs to move the tanks around???

Barry, I had one of the first sidewinders with the changed fuselage. (As a matter of fact Tim Lime flew it at Lyle's race) I did not notch the wing. I never did anything different from any of the Dago's I had. I must have been lucky or stupid when I set mine up. I never had this issue (that I know of). That is why I asked so many questions about this subject. I remember when those guys had all the problems. I just never did.



WE TODD DID

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Mr. Smoothie for Q-40 - 4/23/2003 2:51:45 AM   
PylonWorld



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Status: offline 		[QUOTE]Originally posted by kane
...
WE TODD DID [/QUOTE]

WE KID KNOT

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Mr. Smoothie for Q-40 - 4/23/2003 3:18:03 AM   
bl10


 

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From: Chatsworth, CA,
Status: offline 		F3Ds are allowed to use any fuel feed method but every one I’ve seen, including the 2001 F3D worlds in Australia, used pipe pressure. Dan you are correct in that most Q40 designs don’t have room to move the tank much. The exception to this might be the Sidewinder with notched wing. I think the long and short of it is the Mustang type fuse with the engine rotated down to center the muffler seems about right for the current Q40 setup. Keep in mind even though Lyle’s F3D Vendetta is a Mustang type the engine is mounted inverted. Again we get back to the spray bar / cylinder along with any difference between pipe and tuned muffler pressure (a new one) as the difference in the setup. Probably the only way to determine what is actually going on would be with an on board data logging system. Fred Burgdorf is the only one I know of who has tried a board data logging but as far as I know was fairly unsuccessful at it. The thing that’s most frustrating about all this knows which direction we are going in. We all should remember that Rusty’s Ashly, designed and built without the benefit of today’s technology remains the plane of choice for many top pilots and one of the fastest and best flying Q40’s around.


Barry

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Mr. Smoothie for Q-40 - 4/23/2003 5:41:23 PM   
kane


 

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Status: offline 		I was looking at this year's AMA mag (Nats issue) and there is a great picture of Travis's Ashley while he is fueling it. To me it looks as if the tank is high in comparison to the engine. Especially with the engine over rotated to center the muffler. I don't have one of Rusty's airplane's to take measurements. Can anyone take a good picture of this with some legends (center of tank, vs center of engine)? The reason I am asking is because as Barry has pointed out so nicely Rusty's is the BEST. And since it is working, then this is an acceptable dimension to use.

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D'oh! - 4/23/2003 10:31:04 PM   
DHG


 

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Status: offline 		Of course it's the spray bar. It [COLOR=crimson]has[/COLOR] to be the spray bar, because that's where the mixing of fuel and air takes place. Raise the tank, increase the fuel pressure at the spray bar and you'll squirt more fuel into the carb throat. That means a richer mixture going into the engine. It doesn't matter where the needle valve is, or for that matter where the carb is. You could have a 2-foot-long extension between the carb and the crankcase, and the mixture would still be determined by the amount of fuel coming out of the spray bar.

Dan, all I can tell you about the Pole Cat is that the front-end layout looks identical to the Stinger, and on the Stinger I put the tank as high as I could, right behind the firewall. It works fine. I haven't tried moving the tank back to the CG (even though that seems to be what they're all wearing in Paris this year) because:

(a) It's not broken & I have other fish to fry;

(b) Moving it back would mean moving it below the spray bar, and I've seen at least one very similar airplane (a Nemesis) that went lean in the turns using that setup;

(c) I'm not a good enough pilot to worry about the difference in elevator response between a full tank and an empty tank; and

(d) Anyway, the thing goes so darn fast I finish my 10 laps before the fuel gets from the tank to the engine! So there!!

M.R. Turkeys

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Re: D'oh! - 4/23/2003 10:39:48 PM   
PylonWorld



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Status: offline 		[QUOTE]Originally posted by DHG
...
M.R. Turkeys [/QUOTE]

M.R. NOT

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Mr. Smoothie for Q-40 - 4/23/2003 11:50:57 PM   
daven



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Status: online 		Now,

What if, one happened to mount their fuel tank backward (not to mention any names) ???

How would this add to the equation.

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knaT - 4/24/2003 12:20:45 AM   
PJ_TankPilot



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Status: offline 		>>What if, one happened to mount their fuel tank backward

I think you then have to contend with Reverse Osmosis

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Mr. Smoothie for Q-40 - 4/24/2003 1:20:25 AM   
splatt



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Status: offline 		is that like watching the Osborn's in reverse?

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Mr. Smoothie for Q-40 - 4/24/2003 8:22:16 AM   
PylonWorld



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Status: offline 		With the comments (and conclusions ???) that have been discussed here, it would seem that an upright engine for Mr. Smoothie may not be such a good idea. The tank would have to be at the very top of the fuselage to even come close to being centered on the spraybar vertically, and even with the spraybar in a turn.

I measured a CSP Dago and the tank centerline is at least 1/2" above the spraybar outlet minimum, and of course 1/2" inside the spraybar in a turn.

I'm really confusing myself now ... because the significant mass of fluid in the tank has effectively the same pressure exerted on it whether it is inside or outside of the engine in a turn. Using 25 feet as the radius for a turn means that the change in radius with 1" of difference in tank height is only a factor of .0033 or 0.33% ... that shouldn't be enough to matter. The G's on the significant mass are effectively the same. The weight of the fuel in the fuel line is miniscule, so that shouldn't be a factor. Yet evidence seems to prove otherwise.

Maybe 0.33% is enough to matter.

M.R. Tanked

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Mr. Smoothie for Q-40 - 4/24/2003 11:48:06 AM   
Bill Vargas



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Status: offline 		[QUOTE]Originally posted by kane
Can anyone take a good picture of this,,, [/QUOTE]

Ashley pic


BV

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< Message edited by Bill Vargas -- Apr 24 2003 7:07AM >

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Mr. Smoothie for Q-40 - 4/24/2003 4:38:48 PM   
kane


 

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Status: offline 		Bill,

Where the heck are my reference lines?

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