Cross-country flight

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GrizzlyAir
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Cross-country flight

Post by GrizzlyAir » 27 Aug 2018, 14:32

On my twitch stream yesterday I made a cross-country flight that Transcontinental and Western used to make from Port Columbus KCMH to Indianapolis KIND. I used a map and followed the interstate which is sort of cheating because there were to interstates back then. But it was a fun flight.

During the crossing, I tried to roll the Vega inverted and much to my delight, the engine nearly quit as they were starved for fuel. Since this plane has gravity fed fuel and no fuel pump at all, I guess any inverted flight was not going to happen.

Love the plane. Can’t wait to see what’s coming in the future.

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Vitus
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Re: Cross-country flight

Post by Vitus » 27 Aug 2018, 14:51

Didn't you read the pilot's instructions? No aerobatics allowed! :lol:

I find this form of flying a lot of fun too.

Btw. the Vega does have a fuel pump installed. I am just reading up on the exact type of carburetor and it is my current understanding that the behavior of the simulation is not accurate. The NA-Y7B Stromberg carburetor has two barrels and a float in each of them. The float regulates the quantity of fuel that is discharged in the nozzle. So when the barrel empties, the float goes down, the needle lifts up and more fuel is supplied to the nozzle. If you invert the aircraft, the floats will fall "down", permanently lifting the needle. As a result, the mixture will be super rich, ignoring the mixture lever setting. I'm not quite done with the Stromberg manual, but when I am, this sort of behavior will be included in the aircraft as well.
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triflyman
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Re: Cross-country flight

Post by triflyman » 27 Aug 2018, 15:57

Actually you may be accurate...in addition to the issue of the carburetor floats you would have the fuel pickup tubes in the tanks, which would be pointing up with the fuel level below their opening...result...fuel starvation.

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Vitus
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Re: Cross-country flight

Post by Vitus » 27 Aug 2018, 16:57

oh, excellent point! But there's still some fuel in the lines when you invert the aircraft. So starvation wouldn't immediately occur, but set in after flying inverted for a bit... :geek:
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triflyman
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Re: Cross-country flight

Post by triflyman » 27 Aug 2018, 19:45

I remember my Dad telling me that during his primary training he and another cadet dared each other to fly upside down under a bridge in the PT-19. He went first...got under the bridge and just as he was rolling out the engine quit and he landed on the beach. It was Florida so hard sand...got it started and flew back. His friend decided better not to temp fate twice and just flew back with him.

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Vitus
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Re: Cross-country flight

Post by Vitus » 27 Aug 2018, 19:57

Wow, that's quite a scary situation to be in.
Do you know what carburetor the PT-19 used? I tried to find information on it, but didn't find anything specific.
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triflyman
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Re: Cross-country flight

Post by triflyman » 29 Aug 2018, 15:00

Sorry no...I looked also but could find nothing specific. I did find a picture but was unable to copy it. Looked like a single barrel downdraft. This would make sense since the engine was 200hp or less.

Jarek
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Re: Cross-country flight

Post by Jarek » 30 Aug 2018, 15:22

Generally NAY7B is ready for inverted flight, as long as fuel is supplied to the float chamber. Low pressure created by moving pistons and supercharger will draw fuel from there, through discharge nozzle. With gravity feed, engine will quit, with mechanical pump it should not. You can rotate this carb and valve in the chamber float will invert it's operation. However we don't know much about fuel tanks design, it can be assumed that it was some simple system and Vega was not designed for any aerobatic maneuvers.

Two simple drawings to illustrate some effects, for normal operation:
ftank_normal.jpg
ftank_normal.jpg (21.99 KiB) Viewed 295 times
And for inverted. Float chamber is probably big enough to provide fuel for one roll, but engine will quit if flown inverted for longer period. (if the construction itself will survive this experiment - as entire fuselage hangs on 16 tiny bolts)
ftank_inverted.jpg
ftank_inverted.jpg (32.56 KiB) Viewed 295 times

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Vitus
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Re: Cross-country flight

Post by Vitus » 30 Aug 2018, 15:59

Hey Jarek,

yes, I agree with your assessment on the fuel tanks. The common setup for those type of tanks would be a small sump on the bottom of it with one feed to supply fuel to the carburetor. So once you invert your aircraft, the sump is dry and once the fuel has been sucked out of the lines, the carburetor would run dry. I haven't precisely worked out the math, but I'd expect that there's about one liter of fuel in those lines? That alone would supply the engine with fuel for about half a minute. On top of that you have some fuel in the two barrels.

Buuuut, considering the build of the float-type carburetors, the mixture would be super-rich, so fuel consumption would go up significantly and if you're flying high up, where you'd need to lean your mixture, your manifold pressure would drop as well.

Here's my source for the operation of the NA-Y7B, there's a section on inverted flight as well:
http://n2999c.com/N2999C-info/aircraft/ ... omberg.pdf
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Jarek
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Re: Cross-country flight

Post by Jarek » 30 Aug 2018, 17:18

I believe 1 liter is a good estimation for now.

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