Spin a KR2? Hasn't at least one life been lost from spin testing a KR2?
jg On Tue, Jan 10, 2023, 05:36 victor taylor via KRnet <krnet@list.krnet.org> wrote: > I wouldn’t spin a KR at all. It may not come out. > > In regards to the Blue foam we still slurry it on all composite airplanes > to prevent delamination. > > CH you are so right about just adding too much fuel. You only have so much > power and so much wing area. Also consider the consequences if you have an > engine failure with a very high wing loading. > > Make sure that if you do put fuel in the wings that you have two fuel > pumps that can move fuel from both tanks. I would reserve at least four > gallons for the header tank in case of an electrical failure. > > Fly safe! > > > Victor Taylor > > On Jan 10, 2023, at 07:04, colin hales via KRnet <krnet@list.krnet.org> > wrote: > > > Hi there, > > I've been reading the "How much fuel" issue for a few days now. There are > a few factors I think are missing that might need to be added into the > stirring pot. > > First some necessary background information. My KR2 is just a standard KR2 > and certainly not specifically designed for long distance flights more than > 400 NM. Because we use blue foam in the wings, which melts if you get fuel > on it, there can be no fuel in the wings, in case of a fuel leak. Blue foam > is closed cell and therefore you don't need to spread a micro balloon > slurry into the surface before glassing, so the benefit of blue foam is > keeping the weight down and with the Jabiru engine, my empty weight is 560 > lb. We are limited to 900 lb which is the original build MAUW, but > strangely only in the UK? When I take a UK plane out of the UK, I am no > longer limited as such, the MAUW is then at the discretion of the country > you fly in, but I digress. > > The Jabiru engine is 140 lb all up with Prop and has to be placed on a > long engine frame to place the C of G as far forward as possible for one > pilot. This creates a long nose. We did some wind tunnel testing to see > what this did to stability, seemingly not a lot. I got the Empty C of G so > far forward I had to move the main wheels forward 2 inches to place any > weight back on the tailwheel with a full main tank. But then I can fly 'two > up' or dual, with no C of G issues at all. If I fly solo, I have to put the > spare passengers parachute on the parcel shelf behind me to make the plane > fly nicely or the C of G is too far forward. I'm 175 Lb. > > Because we can not put fuel in the wings, all we can do is fit a fuel tank > above your feet. The biggest fuel tank I could fit in this space and still > get my feet in past the bottom of the tank to the rudder pedals was 25 US > gallons. Fuel burn of the Jabiru is 5US Gallons per hour giving 4 hours > plus an hour of reserve. I cruise at 120 mph. So my endurance is 500 > miles in a standard KR2 that i can fly solo or dual with a climb rate of > 800 ft at MAUW of 900 lb and cruise of 120 mph with the 80hp Jabiru engine > at 5 US gallons on hour. That is fact. > > You want to be careful putting too much fuel in the wings in long tanks. > Why? Well research Aircraft Spinning Characteristics and you will find out. > If you want to make an aircraft spin better, then go put weights on the > wingtips. There is some 'A to B' ratio, 'A' being weight on the > longitudinal Axis and 'B' torque created by weight and moment arm, but it > was a very long time ago. If I remember correctly, the more weight you > place away from the centre axis the more difficult it is to get that weight > to stop spinning. Get into a spin with 50 gallons of fuel in long wing > fuel tanks and I expect it won't come out. With half tanks, role to the > right or left, a bit of side slip and the weight shift could be dramatic. I > read I think from Mike that a guy was building a long range KR2 " For > flights of shorter length he had removable wing extensions. These also > held fuel and the day I was there he was fiddling with the fuel quantity > sensors." The idea of fuel in the outer panels makes my eyes pop out. The > Lear Jets I used to deal with, they could only put fuel in their tip tanks > if the overall fuel weight was above a certain figure due to stability > issues. > > In Russia I had to do 1,000 NM flights between airfields or 1,150 statute > miles, so had to carry 220 litres of fuel or a whole barrel of fuel. 58 US > gallons. This was done by 25 gallons in the main header tank, 15 gallons in > a fiberglass reserve tank that sat on the passenger seat and then 4 fuel > bladders carrying 4.5 gallons in each down by the co pilot rudder pedals. > Feeding the main header tank from the reserve tank sitting next to me meant > the C of G was only going forward. I can fly with a 175 lb passenger with > no problems but this fuel weighed about 200 lb. So the C of G was beyond > the 6 inch aft limit we use here in the UK, but still within the 8 inch > book figure. It was horrible to fly though and had no stability at all, it > was truly not nice. > > "So what!" you may ask? Well all the above is boring. > > The interesting fact and the one you want to know is, that I couldn't > carry efficiently that much fuel in a standard KR2. I took off out of Nome > with full power obviously and was requested to climb to FL100. I couldn't > do it. The plane stayed on full power for two hours trying to lift 58 > gallons up that high and the highest I could get was 8,500 feet and yes > that was cold air. I was burning about 7 US gallons at full power just to > lift the fuel. It took until I got rid of 20 Gallons of fuel to be able to > climb to FL100 and throttle back. The issue is the jabiru's genuine 80 hp > is only at sea level. I bet you are down to 50 HP at 8,000 feet and that's > not enough to lift a heavy aircraft. > > So if you have more power, that will help, except more power means more > fuel burn. Also, a KR2S is relatively much bigger and able to carry a > bigger pay load. For my standard light KR2 with 80HP there is no point > putting more than 40 US gallons onboard, or you end up burning fuel so > inefficiently just trying to lift it up. Yes I did the 1,000 NM flight, but > used 54 us gallons to get there. It was a 9 hour flight so fuel burn > averaged 6 gallons an hour which is 1 gallon an hour more just to carry all > that fuel. > > I'm sure if you drew graphs you could find the ultimate maximum fuel for > the KR2. You can just 'max it out', as I had to do, but I would say > carrying 58 gallons was horrible, something I would never want to do except > for the Russians insisted at the time I could only fly to certain airfields > that were that far apart. Later they dropped all that and allowed you to > fly VFR throughout Russia, so I could have gone back down to my normal nice > 400 NM flights. And now of course Russia has shot themselves in the foot > and closed their borders to VFR flight again. > > So please consider that I don't think you can come up with a nice or > recommended Max Fuel amount for a KR2 or any plane come to think of it... > There comes a point where the more you put in the less efficient the plane > will be until a point where the added fuel is not getting you any further > down the road. Also, the KR2 rudder is not that big. Before you put a lot > of fuel away from the longitudinal axis, I would go and do some spin > testing and then slowly place more fuel in the wings and see what the > difference in spin characteristics are, before loading up max fuel, heavy, > aft C of G with a lot of fuel in long wing tanks... > > CH. > -- > KRnet mailing list > KRnet@list.krnet.org > https://list.krnet.org/mailman/listinfo/krnet > > -- > KRnet mailing list > KRnet@list.krnet.org > https://list.krnet.org/mailman/listinfo/krnet >
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