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90L - 90LX fuel consumption

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Old 10-09-2012, 04:02 PM
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Rudeboy
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Default 90L - 90LX fuel consumption

Hey Bob,

is there any data available on the fuel consumption rates for these engines, using standard 15% fuel, in general sport flying?

The reason I ask is, I managed to get my hands on a Midwest Super Hots kit a while ago and I'm planning to build it during the winter. Now, I remember from the previous 2 kits I built many years ago that tank space is at a premium in these things. The plans mention a 12 oz Sullivan flex tank, and that's just about all you can fit due to the shape of the fuselage, while still keeping the tank at the correct height.
12 oz worth of fuel on a 90 size engine turning 15-16K isn't going to last all that long I can imagine.

I realize it is a bit of a silly question, but if the fuel burn rate is too high, I'd like to be able to plan a bigger tank into the construction before I actually start it.


Thanks in advance,
Winibald
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Old 10-10-2012, 12:32 PM
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Default RE: 90L - 90LX fuel consumption

Thanks for writing.........

Well best I can tell you is figure on 2oz per minute at FULL throttle on an SJ-90 engine.

However... that is at full throttle. And most likely you will not be flying flat out full throttle the whole time. Even with some of the propjet aircraft, if you consider takeoff, landing, throttled back a bit now and then ..... it all does add up quite a lot. So averages to about 1.5oz per min in application.

What I might recommend, for a number of reasons Consider one (or more!) of the Bubble-Jett fuel tanks or alternately go to Central Hobbies website and look up the Tetra bubble tanks they have a 14oz size I believe. Or some others might fit the aircraft better.

The BubbleJett tanks can be connected in parallel (not series). We have found in some installations that a couple of 6oz tanks fit better than one big one.

Will eliminte any fuel foam and fuel delivery issues. No need to pad all the sides and completely isolate it so you can install a tight fitting larger tank if needed (Within reaosn of course). Most importantly you can use ALL of the fuel in the tank.

A regular tank has about 15-20% of unusable fuel. So a 12oz tank only really can deliver (consistantly) about 10oz under flying conditions. Yes, you can run the tank dry, but there is risk of picking up an air bubble or foam at any capacity much below the thickness of the clunk and clunk tube.

I hope this is helpful!

Bob
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Old 10-10-2012, 05:59 PM
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Default RE: 90L - 90LX fuel consumption

Hello,

and thanks, it is helpful.

I was already looking into a bladder tank (mainly because stuff just runs that much better with them), but I hadn't considered running two of them. That just might do the trick.
The Super Hots fuselage has a triangular shape from the centerline on up, that's the main reason for the tank fitting problem...so two tanks stacked might just work for a little extra juice.

Perhaps I can look around for a triangular plastic bottle that fits the bill, send it to Dub, and have him convert it to a tank? I don't suppose he is in the habit of sending latex bladders out to people for them to build their own tanks...haha

But anyway, thanks man, I think you just about solved my worries.

Regards,
Winibald
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Old 10-14-2012, 04:12 PM
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Default RE: 90L - 90LX fuel consumption


I have a Super Hots mostly framed up and have contemplated a few options for fuel tanks, and decided to go with the 12oz Jett. The tank compartment is very short, a Tettra 14 or 10.5 ounce will definitely not fit. Tettra has nice line of tanks, but Jett has something they do not have, a short high capacity tank - that nice relatively chubby 12oz.

It doesn't quite fit though - the tank itself is equal in length to the distance between the front of the former at the wing LE, and the front of the firewall, give or take 1/8". So it needs relief either with a hole in the firewall for the neck, or a cutout in the former and wing LE for the butt end. I think I will go with the LE cutout option, the Hangar 9 Pizazz wing is built this way to create more room up front for the tank, and I haven't ripped the wings off mine yet, though I've tried. The LE doesn't take much load I guess. I'll have to open up the former in situ and reinforce the opening, but that's why they make Dremel tools and CA.



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