Hi, this is my first post and it's a long one, sorry, hope it's interesting to some though. The question I have (and speculative answer): Does HondaJet have a fuel capacity larger than 1,300 Liters? I examined the reported fuel capacity and implied fuel burn rate and IFR range of the HondaJet, in comparison to the Cessna Citation M2, and the Cessna Mustang, using available manufacturer data and specs. The available data is more or less available or derivable for both Cessna's, but in the case of the HondaJet that level of basic performance, weight and volume data remains sparse, or ill-defined. What information is available is mostly relevant to the early developmental prototype(s), not to a production HondaJet. Nevertheless I modeled the jets for a ball-park comparison within a spreadsheet, to reveal the key differences, similarities, performance trends, and likely fuel costs over time. I used available HondaJet prototype based figures from earlier industry articles initially, and more recent Honda supplied basic specs and claims, though it fairly quickly became clear within the spreadsheet that these are very unlikely to reflect real performance, or real dimensions, weights and volumes for the HondaJet. This required a lot of reading, sometimes between the lines, working out what was clearly not true, or possible, then working out what was then likely to be true or possible. As far as I can determine, Honda itself has never made clear what the real fuel capacity of the production HondaJet will be, but I've come to the view that the actual fuel capacity is going to be much larger than the 2,300 lbs = 1,300 liters = 343.3 US gallons claimed for the early prototype (about 9 years ago). When I first read the 1,300 liter figure I immediately thought it odd that Honda would bother to develop a new jet with such a tiny fuel load. The shape of the jet suggested it had plenty of room to carry much more than 1,300 liters. But when thrust rose from 3,340 lb to 4,100 lb I wondered more about the fuel load and range, because the picture that was emerging didn't 'gel'. But if fuel load were higher this would imply MTOW significantly more than 9,200 lbs (4173 kg), and the available payload also higher. There are in fact a few implicit hints that the production version is going to have a much higher fuel load than the mere 1,300 liters of the early prototypes. Here are some of them; Firstly; the available (Honda supplied) Garmin G3000 screenshots of the fuel flow within their 2012 PDF brochure called, "hondajet-brochure.pdf", showing the displayed fuel load is much larger than the prototype's 2,300 lbs (1,300 liters). When screen-captured and zoomed at higher-resolution then filtered with a histogram tool to clarify the numbers it makes the numbers much more legible and revealed the following Honda fuel-load figures: L WING QTY = 960 LBS R WING QTY = 940 LBS CENTER QTY = 1,760 LBS TOTAL QTY = 3,660 LBS And between the nacelle icons below that we see the words, "TOTAL USED" = 270 LBS , while the EMS RPM indicators show engines near idle. So by adding that TOTAL QTY figure, i.e. that currently held within tanks, to the TOTAL USED, i.e. burned in the engines so far, the total amount of fuel in the tanks before the engines were started up comes to 3,930 lbs of fuel. 3,930 lbs = 2,079 liters = 549 US Gals The prototype in 2005 had a reported fuel capacity of just 2,300 lbs = 1,300 liters = 343.3 US Gals A small (OK, large) volume difference is seen within the G3000 screen-shots, which represents a large fuel increase. i.e. 1,630 lbs = 768.3 liters = 203 US Gal ... of extra fuel capacity. Honda's screen-shots seem to be indicating that the correct fuel capacity of the production version has increased to 170.9% of the 2005 prototype's reported fuel load. If so, the HondaJet will comfortably (OK, greatly) exceed its claimed IFR range figure of 1,180 nm with four P.O.B. Any estimate of the actual range would be ball-park given the lack of fuel-burn with RPM or payload data, but a conservative estimate has the range significantly exceeding all similar small jets by a wide margin. You have to ask if it is physically possible for a HondaJet to structurally accommodate 3,930 lbs, or 2,220 liters of fuel? Has Honda been leading people think it would only accommodate 1,300 liters to spring a larger figure on competitors at time of certification? Hey, that's business. It just indicates Honda was always intending to manufacture the jet it developed. It seems they down-played the potential range so major competitors would remain complacent for longer. For some comparison, the shorter-range, 20% slower Cessna Mustang, holds 1457.5 liters of fuel, while the Citation M2 holds 1,870 liters. I've come to the view that it is indeed physically possible for the HondaJet to hold the 2,220 liters of fuel, which the G3000 screens claim. Firstly; given the early PROTOTYPE'S MTOW (~9,200 lbs), and the more recent excellent thrust to weight ratio, due to 4,100 lbs of available thrust making for a T:W of 1 : 0.446 (carrying only 1,300 liters of fuel that is), then there's more than enough thrust overhead in this design for it to carry much more fuel than that. Some comparative thrust : weight ratios and maximum cruise speed figures; Mustang T:W ratio = 1 : 0.338 Max Cruise 340 kt, ceiling FL410 Citation CJ1 = 1 : 0.355 = Max Cruise 389 kt, ceiling FL410 Citation M2 T:W = 1 : 0.367 = Max Cruise 400 kt, ceiling FL410 Beech Premier 1A = 1 : 0.416 = Max Cruise 454 kt, ceiling FL410 Hawker 200 Prototype = 1 : 0.435 = Max Cruise 473 kt, ceiling FL450 HondaJet T : W = 1 : 0.446 = Max Cruise 420 kt, ceiling FL430 Can you tell me which one of these things is not like the others? Clearly the HondaJet (with 1,300 liters of fuel in the above) has more than enough thrust, to lift a much larger fuel load to FL430. This combined with the much lower max cruise speed for that superior thrust to weight is more than reason enough to suspect the payload and fuel load of the production version will be increased substantially, to well above 1,300 liters fuel, in order to extend the HondaJet's range to well beyond what any of its potential competitors could achieve. Why wouldn't you? If you had both high thrust, low weight, high laminar-flow efficiency, and a clean-sheet design with innovative structures, to work with as you pleased, why wouldn't you turn the clearly excess thrust capacity into a higher fuel load and higher payload, to achieve a waaay longer range than any competitor? Seems a no-brainer. For comparison of what can occur even with a supposedly light-weight carbon-fiber fuselage's MTOW, notice that the Beechcraft Premier IA holds 2,073 liters of fuel, within highly-swept wings and a large ventral fuel tank structure. It's also a much heavier composite design than Honda's, plus cruises faster, at 453 kts, but it needs a much more thirsty engine to do it, for an MTOW of 12,500lbs. Yet the jet itself has comparable cardinal dimensions to those of the HondaJet, they're about the same size! The HondaJet just has a lower-profile undercarriage. So we know it's possible for such a small jet to hold well over 2,000 liters of fuel, if the wet-wing thickness is thick enough to do it, plus the ventral fuel tank is bulky enough, and strong enough, to accommodate high volume loads. And we do know from the HondaJet prototype that the wing thickness was 15% of the wing chord, which means it does indeed have a thick wing section, to accommodate a high-volume of fuel within it. The G3000 MFD fuel system screen showed the HondaJet wings may have a combined capacity of at least 1,084.6 liters (1,920 lbs). Yes, we can say the HondaJet wet-wing can physically accommodate this sort of fuel capacity. In which case the ventral fuel tank structure would then only have to accommodate the remaining 215 liters, in order to reach the prototype's claimed petite fuel capacity of only 1,300 liters. Now take a look at several images of the shape and size of the ventral fuel tank's structure under the HondaJet cabin. It is in fact a very large fuel tank in volume, for such a small jet. It clearly can accommodate far more than a mere 215 liters. Only the Beechcraft Premier IA has a similarly large ventral fuel tank (and a similar total fuel capacity, at 2,073 liters), but the HondaJet's ventral tank is even deeper under the wings than with the Premier 1A's huge fuel tank structure. It's also a wider fairing when viewed from the front, plus more 'squared-off', i.e. it has 'corners', rather than being fully rounded, which also increases its fuel capacity further. Have a look at its shape from these angles: [I was going to post some image links here but I notice the forum rules frown on that, so I deleted them from the post] As you see, HondaJet's designers clearly went to great lengths to equip the HondaJet with both high-volume wet-wings, and a high-volume ventral fuel tank that's as large as they could make it. Much larger in capacity than what's on the Mustang or M2 Cessna's (at 1,457 L and 1,870 L, respectively). Given the wing goes under the cabin's cylindrical shell, so that other than the wing spar and fuselage attachment and cables in there, plus the very short undercarriage folds into the exterior wings, so around 80% of the structure's internal volume will be available for fuel tanks. The G3000 MFD indicates the ventral fuel tank will hold at least 994 liters. So I have no problem accepting this as physically doable. In which case it's then reasonable to conclude that the wings and the ventral tanks, combined, can indeed physically contain at least: Combined Wing Tanks ~1048.6 liters Ventral Tanks ~994 liters Thus, at least 2042.6 liters The G3000 MFD shows it may actually hold 2,220 liters, which is 920 liters more than we've been lead to expect. As a result I think the promo G3000 MFD screens may be telling us the truth, that the real fuel capacity of the HondaJet is going to be around 3,930 lbs, or 170.9% higher. Thus the production HondaJet MTOW would necessarily be higher, and Thrust to Weight ratio at MTOW lower, and the claimed climb rate possibly lower at MTOW also, but the claimed 4 person IFR range would be very much exceeded, out to well beyond what the HondaJet website currently reports. But does anything else support this view of reality? We know the PROTOTYPE MTOW was reported as ~9,200 lb, but that of course doesn't mean it's an accurate measured weight. Rather, it may just be a design weight target, for that PROTOTYPE alone. And Honda are hardly going to tell the competition the truth about such numbers. But we can be fairly sure a fully-equipped production HondaJet will be much heavier than an early 9,200 lb prototype. Furthermore, look at the Beach Premier 1A to see what a similar size jet of similar construction and materials can weigh, as in certified production form it's 12,500 lbs, and the proposed Hawker 200 prototype (its update) is given as 13,800 lbs! Pressurized carbon-fiber aircraft can be a surprisingly heavy aircraft (depending on the construction technique used So a higher intended MTOW HondaJet might also account for the early heavy-duty undercarriage of the early prototypes (as seen in the first link above). The undercarriage has since been re-designed but it remains chunky and clearly intended to absorb a high max-landing payload. Which would be required if the real maximum fuel capacity was about a tonne heavier. Another significant hint of a much higher fuel load capacity to come for the HondaJet was cryptically contained within this 2005 AOPA magazine article: "... Slightly smaller overall than the Cessna CJ1+, the HondaJet cruises 10 percent faster, has a cabin that is 30 percent larger, and has a range about 40 percent greater on about 14 percent less thrust. ... " - Source: AOPA Pilot Magazine, August 2005 Volume 48 / Number 8; "HondaJet: Behind the Curtain - An exclusive first look at a most unusual airplane", By Thomas B. Haines. But in August 2005 (when the quote was published) the jet still had not gone 10% faster than a CJ1+ yet, nor anywhere near it. Even now it's only gone 9.3% faster (425 kt), but at max-sustained throttle when using a 2,195 lb rated thrust engine. So the article's claim is of course referring to the Honda designer's simulated projection of the aircraft design goal, i.e. ~10% faster than a CJ1+ with 14% lower thrust, but at some undisclosed lower economical-cruising airspeed. Thus when Honda modeled it, at that airspeed, the design simulation showed that it should possess approximately 40% greater range than the 1,300 nm range CJ1+. Which was quite a startling claim for the HondaJet designers to make to the article's author, right? It was such a huge range claim that it was apparently discounted. But what if it's more or less accurate? What it means is that in 2005 Honda was telling that author that it expected the fully developed version of HondaJet to eventually achieve an economical cruising range of up to 1,820 nm (3,370 km), thus enough range to fly right across the USA or Australia, from east coast to west coast, without even needing to refuel. Would, or could, Honda expect anyone who's aware of such range factors to take such a projected range target seriously, if a CJ1+ has 1,870 liters of fuel, while the HondaJet would only have a measly 1,300 liters, but needed to move 10% faster, for 40% longer! That's not possible, so that claim was discounted, almost immediately. In order to achieve that sort of range the HondaJet's designers would need to accommodate a fuel load that's significantly larger than that of a CJ1+, in order to reach 1,820 nm radius. You'd need something more like about 2,220 liters (3,930 lbs) of fuel to do that ... as reported by the G3000's MFD screen. The more I've looked at this the more I've come to think that perhaps Honda already let the answer slip. What do you think?