Fuel Weights & Airfoil Questions Answered

Before I begin spewing numbers out (again! lol) I learned some valuable and interesting information such as succeptibility to fuel flow failures, causes, effects and so on. I also learned that the mass of virtually every fuel I ran across can and do vary by temperature. Some fuels are specifically blended for high altitude flight while others are not intended for extreme heights.

Another fact I learned, which I was not aware of, was that jet engines will burn nearly any type of fuel. Now, whether it will turn over the same performance or cause fuel blockages is another story - though I didn't find any mention of the use of off-hand fuels and failures. Mention of, the now no longer used, JP-4 having a totally different consistency and smell from modern JP-8 which is now burned in its stead in aircraft that previously employed it. (JP-4 was a blend of 50-60% Gasoline to a 50-40% ratio of kerosene, while JP-8 is a kerosene blend developed to be less volatile and includes an additive package including a corrosion inhibitor/lubricity enhancer, anti-icing and anti-static compounds. Optional additives are an anti-oxidant and a metal deactivator. Jet A-1 is basically JP-8 but does not require the additives.)

I also learned that the movement to recycle cooking oil was not limited to a few cars on the road but some jets have been used to test the feasibility of this with promising results. In the past few years the US Department of Defense has been experimenting with a 50/50 mixture of conventional JP-8 and Biofuels for certification for use. Due to its widespread success in US Military Jets and Helicopters, including the famous Mach 1.7 flight of an F/A-18E Super Hornet, coined "The Green Hornet," it is hoped to employ this widely by the year 2020.

Not surprisingly I was reminded of the fact that typically fuel in aircraft is described by pounds (or kilograms) rather than gallons (or liters.) This is an essential point in both aircraft design and in operations as aircraft often have more than one fuel tank and, unlike our aircraft here in SimplePlanes, prior to the age of computers, you would have to manually switch between them to keep a proper balance and performance by remaining mindful of how much weight remained in each fuel tank, switching from one to another, adjusting trim to compensate for slight imbalances, etc.

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Here are some fuel weights for comparison.

• Heating Oil (Fuel Oil); 8.2 Lb/gal.

• Diesel Fuel; 6.943 Lb/gal. (Varies by temperature; up to 7.5 Lb/gal., some truckers estimate weight by 8 Lb/gal.)

• Jet Fuel (JP-5); 6.79 Lb/gal.

• Jet Fuel (JP-8); 6.67 Lb/gal. (Several sources round this to 6.7 Lb/gal.; Military grade modern jet fuel.)

• Jet Fuel (Jet A-1); 6.66 Lb/gal. (Most common civil/commercial aviation jet fuel.)

• Jet Fuel (JP-6); 6.55 Lb/gal. (Developed for the supersonic XB-70 Valkyrie with a lowered freezing point.)

• Ethanol-Free Gasoline; 6.217 Lb/gal.

• Gasoline (w/Addatives); Varies; 6.3 Lb/gal. (Most common answer.)

• Avgas (Aviation Gas/Aviation Spirits); 6.01 Lb/gal.

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Sources;

• Diesel & Ethanol-Free Gasoline; Loring Chien, 54+ yrs in the Oil/Gas exploration/production industry.
• Diesel, Ethanol-Free Gasoline & Jet A-1; www.reference.com
• Diesel Temp. Variation; www.truckingtruth.com
• Jet Fuel (JP-8); "Memorandum of Understanding Between the Department of Defense," Aug. 16, 2007, Def. Energy Support Center.
• Jet Fuel (JP-6); B-70 Aircraft Study Final Report, Vol. III, by Taube, L.J. Apr. 1972.
• Gasoline (w/Addatives); US Department of Energy.
• Avgas; Pilot's Handbook of Aeronautical Knowledge, FAA-H-8083-25A, FAA. pp. section 9-7.
  

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Summary: The fuel our aircraft in SimplePlanes amounts to 6.65 Lb/gal, according to the statistics of the fuel block which is 177 Lb loaded and 44 Lb empty. I am guessing they decided to go with a figure likely based upon Jet A-1 ... Or is it?

One 1x1x1 fuselage block weighs 27 Lb by itself and holds an estimated 9 gal at 6.88 Lb/Gal, While a 2x2x2 fuselage block weighs 135 Lb by itself and holds an estimated 100 gal of fuel at a rate of 6.78 Lb/Gal. Going all the way up to the standard maximum of a 5x5x5 fuselage block, it weighs a whopping 1,246 Lb empty but full, it can contain a maximum of an estimated 1,862 gal at a rate of 6.71 Lb/Gal.

(Note, I did test different fuselage block shapes to see if there was any perceivable changes but none were noted during testing.)

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Request for the Developers;

I would like it greatly if you would provide us with variable size drop tanks, each would have an AG which would allow the aircraft to draw exclusively from one or more drop tank at the same time and to monitor that, to either bring up a second fuel gauge, or change the background color of the fuel gauge and show how quickly that fuel specifically is being expended so that when used up, we can deactivate the drop tank AG to begin drawing from the aircraft's internal stores and can opt to jettison them normally from a pylon via the selected pylon's AG.

As it is at present, when we jettison a "drop tank" of our own creation we are losing precious fuel. In the alternative if an AG for the drop tank isn't selected I would suggest it goes to the default "feeds from all tanks," for wingtip tanks.

Secondly, a minor update needs to address various weights indicated under part properties. Under Fuselage Blocks, originally a 1x1x1 Fuselage block weighed 11 Lb, if I'm not mistaken? Now that the minimum part size has been reduced to 0.25 - this is now the base 11 Lb. weight which I think has increased the weight of aircraft produced between the advent of the fuselage blocks and the so-called "SimpleCars" update. I was shocked to learn that the original blocks from version 1 now weigh less than our sophisticated Fuselage Blocks of precisely the same dimensions by 5 Lbs! I'm beginning to understand why the standard turbojets we were provided with back when can't quite muster the power we had once upon a time.

Thirdly and finally, can we get a set figure for fuel that can be contained within parts, such as 1 gallon exactly in a 0.5x0.5x0.5 block, 8 gallons for 1x1x1, since you can fit exactly 8 of the former into that space, 64 gallons for 2x2x2, since you can fit exactly 8 of the former into that space and possibly give us a decimal figure for odd sized/shaped parts, with the set standard fuel weight of exactly 6.65 Lb/Gal? This last portion is not a stretch of the imagination or would be limited in terms of volume. According to Rectangular Tank Calculator A 1x1x1 block, which amounts to 19.2 inches, according to the width of the standard cockpit, if used as a tank of fuel could contain up to 30.64 gallons! Meaning that even our 20 gallon tank is a little underrated in terms of dimensions.

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Airfoils

In a recent conversation with a friend this question came up. We knew that Semi-Symmetrical Wings provided better lift than Symmetrical surfaces. Most of us use Symmetrical airfoil types for our horizontal stabilizers and vertical stabilizers but I'm sure few of us knew this airfoil actually is a superior type for high speed aircraft. However; We wondered what Flat Bottomed Wings were good for? I found a perfect graphic that explains it here.

Now we have a better understanding for what the three airfoil types excel at. Symmetrical is for high speed aircraft, Semi-Symmetrical is for mid range speed offering more lift while Flat Bottom offers more lift benefit than it provides for speed. However, you'll note that there is a fourth in this list not presently represented in SimplePlanes, the undercambered airfoil. This is the type of wing surface many WW1 aircraft, STOL Army Co-Op Aircraft, Gliders and several small and low horsepower civil/ultralight aircraft have used in the past. (Many modern designs don't typically have a full undercamber but have a cusp at the back of the wing that allows the airflow to be directed as though it does. Others such as the famous Fieseler Fi-156 Storch used a flat bottom wing in conjunction with flaps and leading edge slats that remarkably looks like an undercambered airfoil when deployed, which allowed for excellent STOL capabilities.)

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Summary: This data has been most informative, I was amazed to find a graphic that depicted the strengths of each wing type in SimplePlanes and to see that there are still other important airfoil types that are not currently represented in our game. While I say this, in the modern age of CAD software nearly every mass produced aircraft receives its own unique airfoil but are generally derived of these types.

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Request for the Developers;

Could we possibly see undercamber or perhaps lamilar flow airfoil wing surface appear in the future? Secondly, are we ever going to see the wing surfaces look more like airfoils and less like slab sided lego pieces? I think that'd look a LOT better on our 3D Printed Planes, to be honest . . .

D.A.