Guest ozzie Posted December 20, 2007 Share Posted December 20, 2007 Mal, from your question above for suggestions on ali tank cracking is that i assume that it is already built, so i will try and help there, Then a bit from experience. One is that you may be able to make a bladder for it depending on its shape that would be the ultimate but expensive even if you did it yourself. The other is if the tank is in good condition is to coat it with a rubberised coating on the outside. this will help with the vibration and if a crack does develope it will slow down the leak. there are also some systems for coating the inside but not to keen on that personally. Building/repairing a tank, don't weld it. bond the seams (the right glue) and use sealed rivits. Use threaded bulkhead type fittings. to stop any canning and there is room glue stringers to the outside, you may be able to use these for mounting the tank. use an approved method to patch a hole or crack. i don't think mounting the tank on anything that can absorbe the leaking fuel is a good idea. don't mount the tank on anything that can perish and then allow the tank to rub. make sure that the area the tank is mounted in has decent drains holes so it won't flow along the fuse or wing. a tank mounted on a saddle and strapped down seems to be the most widley used method. Make sure that the vent cannot become blocked. other than the obvious engine failure as the fuel pump sucks like crazy to try and keep the engine running the tank will start to collapse and deform and start the cracking process. and i bet the owner will never put two and two together when it comes to quantity (sic) lack of. This happened on the center tank on a beaver (N77WK)that collapsed and cracked on the top. doing only short hops it never carried full tanks until it was to be relocated. we did an annual and filled the tanks. we were sitting in the lunch room and we heard it start and then shut down, the pilot walked in and calmly asked were we kept the extingishers.(he walked past three) we ran out and flames were licking up the sides. put it out defuelled and replaced the tank and polished off the sooty bits. how that did not go woof who knows. Rubber bladders ARE time limited. replace them before they fill your hanger with fuel. A good tank system i worked on was the Nomad main wing tanks. one of the very few no drama parts of it. it is basically a rectangular bay with a carbon lid that is the top skin. held in place by many machine screws. the wing has to be jacked level and never moved with the lid removed. (It is a structual part of the wing). it has a bladder that is held in shape by lacing it to the bay around the top. double gaff tape on the sharp bits and plenty of baby powder to prevent chaffing. piece of cake compared to replacing one in a bonanza with only a hole big enough to stick my skinny arm into. fact of life is that sooner or later a metal tank will crack. attention to design manufacture and fitting. make sure it has baffeling. the continuous slamming from the 'free surface effect' may cause more damage than the wing flexing or vibrating. if i remember rightly i think that on the air crash investigation show about that 747 that blew the centre tank, was that the solution for preventing this happening again was to have a sealed fuel system that uses an inert gas instead of air. would not be that hard to do on any fuel system.' hope this helps to set your gears in motion and thanks for asking for my suggestions ozzie Link to comment Share on other sites More sharing options...
facthunter Posted December 21, 2007 Share Posted December 21, 2007 Fuel Tank Type. I could be wrong here, but I felt that the favoured tank by the EAA (USA) people was welded aluminium. More so lately, with ethanol possibilities looming. Obviously the mount points would have to carry the stresses properly and if the frame to which they are affixed flexes, then the mounts should permit this to happen. Like with a table 3 points is easier to get right, than more. Fuel sloshing is a problem in larger tanks, particularly with aerobatic aircraft. As an example, the Citabria can suffer tank damage if "flick" manoeuvers are performed over a certain speed. Commonsense really, just wave around a 3/4 full Jerrycan of fuel and you can feel the inertia effect of the contents. (Thats how I check the Barbie cylinder too). Getting to the reality of our situation, a good exit strategy is a minimum requirement (At least be able to get the seatbelt undone quickly),and don't wear inflammable clothes. To be seriously aware of the possibility of fire is a good motivator. Nev... Link to comment Share on other sites More sharing options...
Guest ozzie Posted December 21, 2007 Share Posted December 21, 2007 just to clarify the term and effect of 'sloshing'. correct term is 'free surface effect'. it does not matter if the jerry can is 3/4 full 1/2 full or any were in between. it is the surface area of the liquid that is doing the damage. the only difference you will find when swinging your jerry can around is the weight you have to lift swing and stop. the only time there is no effect is when the tank is totally full. as fuel is a fluid it will still be sloshing around but there will be no surface effect because there is no surface but as soon as the level drops and a surface is obtained the effect will be the same until the tank is emptied. assuming that the tanks dimensions are the same top to bottom. baffels or foam to reduce the area will reduce the effect. I don't think i have ever read anything on this in aviation texts. but it was covered in great detail when i studied for my masters ticket. possibly because of the greater tankage. can anyone add to this, most interested to hear other views. welded ali may well be the preferred type. material, welding techniques and equipment have vastly improved over the years. ali is easy to obtain work with and has a long life, FRP is messy hard to work with requires time consuming mould making hard to get consistency in thickness ect. welded may be EAA preferred as it is more a specialist thing so consistincy in manufacture is easier to obtain on the whole. not every homebuilder has the skills or equipment so the fuels tanks are usually made by a professionals. using common sense in your apparell when flying is more an education thing that should be included in your training, the most common mistake is the wearing of makeup in aircraft fitted with drop down oxygen masks. skydivers are possibly the most at risk from hidious burns, everything they have on is synthetic. youse pays your money youse take your chances. why did Big Al's caravan explode on impact even tho the pilot shut down the engine and all elec sytems as soon as the tail got ripped off at hight? most possibly from the heat generated from the fuel impacting with the sides of the tanks as they compresed from impact forces. this is the free surface effect and latent energy. Damm, channel 7 just news flashed another fatal "ultralight" crash near Perth. whether or not they are wrong it's just bad news. please Play Safe least we forget, we are not playing chess ozzie Link to comment Share on other sites More sharing options...
facthunter Posted December 21, 2007 Share Posted December 21, 2007 Inertia. Fuel in tanks. Ozzie, the damage is done to the tank by the MASS of the fuel which impacts the side (or end ) of the tank, and the VELOCITY that it reaches prior to impact. There would be an optimum content for maximum effect for any particular "G" force applied in the opposite sense to the commencement situation, and the quicker the high "G" figure is reached the more the effect. This is why the "flick" manoeuver is the problem. As you point out ,there is no effect when full, and of course there is none when empty. Baffles absorb most of the energy by reducing the velocity of the migrating fuel, as would the fire retardant aluminium mesh mentioned earlier. The U/L crash north of Perth has been mentioned thru the night on ABC radio. Bad News! Does anyone have any details? Nev... Link to comment Share on other sites More sharing options...
BigPete Posted December 21, 2007 Share Posted December 21, 2007 I remember many years ago when atending a promotion course at Balcome Apprentice School - the local fire boys were filling the water tank of the fire engine. ;) They realized that when the tank was only half full that they would miss morning tea at the mess, jumped in the truck and headed off. :;)1: All was fine until they got to the the first corner, a 90 degree decending bend - BANG - one fire truck upside down in an instant - no one badly hurt fortunatley. ;););) The CO was not impressed - regards Link to comment Share on other sites More sharing options...
facthunter Posted December 21, 2007 Share Posted December 21, 2007 Inertia. That is another aspect of all this. On a very smooth day, when your aircraft has settled down, Get your passenger to move back & forth fairly vigorously, and sit still in your seat and feel the effect of his/her movement on the aircraft. the more active the movement , the more pronounced is the effect. Anything moving in the aircraft can have a similar effect ie fuel in an unbaffled tank in rough air. Nev Link to comment Share on other sites More sharing options...
Methusala Posted December 22, 2007 Share Posted December 22, 2007 Newton Nev et al, from high school physics f=ma. Therefore the greater the quantity of fuel (m), and the acceleration (a) is constant then the greater the force exerted on the tank walls, regards Don. Link to comment Share on other sites More sharing options...
Guest Redair Posted December 22, 2007 Share Posted December 22, 2007 Geetings each, just to add fuel to the fire as it were, has anyone else seen the "Fuel tank seats" that are being advertised? I don't think I would want to be sitting on a chair-shaped plastic fuel tank, especially if I was about to hit the ground hard. I assume these things are well tested before being offered for sale, and I'm not making any claims against the manufacturers, (don't sue me!) I just wonder about the logic of being stapped to all that fuel. At the very least, in an impact, there is the potential to get soaked in the stuff, never mind the risks conected with static electricity. Like I say, not having a go at anyone here, just raising the point for debate. Regards, Redair. Link to comment Share on other sites More sharing options...
facthunter Posted December 22, 2007 Share Posted December 22, 2007 Inertia. Methusala, I have constantly refered to INERTIA in all my posts, on this thread. We are talking about different concepts. Nev Link to comment Share on other sites More sharing options...
Guest ozzie Posted December 22, 2007 Share Posted December 22, 2007 OK this is all correct and all linked together. throw in another term. STABILITY. aircraft landing, and moves sideways in relation to centerline. wheel hits ground sideways movement stops. fuel in lge unbaffelled tank keeps moving until it hits the tank sides. fuel wants to keep moving in that direction. if force is great enough aircraft will depart runway. pilot fills in incident report stating that a gust blew the aircraft off the runway ect ect. the "gust" may have started the sideways movement but that is not what made it depart the runway. the large free surface area allowed the mass to accellerate until it hit the wall and took the aircraft with it. the only thing that can be done to stop this happening is to remove the surface area by baffelling the tank. race cars foam filled tanks for fire suppression, maybe, but possibly more so to keep the car on the track. i wonder just how much an aircraft is influenced in flight by this. our local RFB wrote off their tanker last year charging around half full. ozzie Link to comment Share on other sites More sharing options...
facthunter Posted December 22, 2007 Share Posted December 22, 2007 Fuel movement. ozzie, you have put it very well. I was trying to make this point about 6 posts ago. You get CofG movement too but the inertia effect of the moving fuel is of a higher order, and could manifest itself as "wobbles" that might be put down to gusts or overcontrolling. Nev... Link to comment Share on other sites More sharing options...
trevorp Posted December 22, 2007 Share Posted December 22, 2007 As a student pilot learning in a Jabiru 160, I was wondering if someone could inform me, what type the tanks in wing the J160 has, for iv'e noticed theres a lot of sloshing and rocking of plane whilst pushing plane back in hanger. Also , but im sure you's all would know, but just in case, if you ever happen to spill fuel on your clothing make sure you wash down under shower or hose with water before removing clothing. Im sure you've experienced static electricity when removing clothing. Just a quick note on the un-explosive fuel tank, had superviser you told us to use this new 1gal fuel tank to use for re-fueling the generator who then bent down over top off, un screw the lid then lit a match and waved over top of opening,to which i was suprised so many verbal obsinerty's could come out off my mouth while back stepping at incredible rate, and as much suprised at the whole thing not blowing up in his face. Have not and would not show that to any one, but would not have belived it if i had'nt seen it. When i asked a tech'y once why dont aeroplanes have it fitted, the old answer 'profits generally win over saftey' , Cheers and a safe new year to all, Trevor. Link to comment Share on other sites More sharing options...
Guest ozzie Posted December 22, 2007 Share Posted December 22, 2007 to feel the effect for yourself. TRY CATCHING A CANNON BALL drench showers should be near all refuelling points. again attire for flying should be considered. good point Trevor. so Trevor you are in command with your instructor, you are just starting to round out and you have just been gust induced by a bit of crosswind. what you going to do.? seat tanks have been around since the 70's, in a accident you will leak before they do. in theory. i once wittnessed a head on collision between two cars . one car had blown the fuel cap off and caught fire around the filler. i just picked up the cap and refitted it. the tank won't blow up as there is no air in it just fumes. Link to comment Share on other sites More sharing options...
trevorp Posted December 22, 2007 Share Posted December 22, 2007 I guess, small amount off oppisite rudder, but bit hard to say from down here. I kept getting told not to use to much stick and let plane fly itself more. Trevor Link to comment Share on other sites More sharing options...
Guest Flyer40 Posted December 22, 2007 Share Posted December 22, 2007 I hadn't heard of seat fuel tanks before, got a link? From a C of G point of view it seems to make sense. I have to admit the idea of being surrounded by fuel in an impact doesn't really appeal to me, but on the other hand F1 cars do the same thing and they usually survive extreme impacts well. Although they have a lot more crash worthiness designed-in that the average airframe. Trev your story reminded me of an incident that occurred at a petrol station at Lakemba a few years ago. The attendant was paranoid about being ripped off by tanker drivers, so after a delivery he got onto the tanker and opened a top hatch to make sure it was empty. It was dark inside so he decided to illuminate it with a cigarette lighter. He was blown off the tanker and severely burned, but I think he survived. Could have been a candidate for the Darwin awards. Link to comment Share on other sites More sharing options...
BigPete Posted December 22, 2007 Share Posted December 22, 2007 The Gyroplane that crashed recently at Echuca had fuel tank seats....... regards Link to comment Share on other sites More sharing options...
Guest ozzie Posted December 22, 2007 Share Posted December 22, 2007 There has been at least one other fire on impact with seat tank. wonder if there are any statistics on fire with relation to types of tank and location. i think i'll stay with my 10ltr plastic tank and bungy system that will go bush if i thump in. hopefully by the end of next year i will not have to worry about fuel fires, but will have to learn all over with high current high discharge rate batteries. but will have to be definatley safer. ozzie Trevor, there is a easy remedy for that senario, but as you are a student you should discuss it with your instructor. Link to comment Share on other sites More sharing options...
Methusala Posted December 22, 2007 Share Posted December 22, 2007 Nev, we are talking about the same thing. Inertia is a force which reacts to accelaration (either +ve or -ve) as in fuel hitting the side of a tank in a collision. Regards, Don. Link to comment Share on other sites More sharing options...
facthunter Posted December 22, 2007 Share Posted December 22, 2007 Clarity. Don, I have tried to explain it the way I have done, and it is my best effort. I always re-read my posts many times. My main aim is to make the point clear,without overcomplicating it. I have altered my post 01:27 yesterday. Cheers Nev.... Link to comment Share on other sites More sharing options...
blueshed Posted December 30, 2007 Share Posted December 30, 2007 Carbon Fibre Does Carbon fibre conduct electricity? Do you have to bond it? Jet fuel I believe is very much more susceptable to the possibility of creating static electricity whist filling the tanks, although having a higher ignition temperature! Safe Skies, and filling em up! Cheers Guy Link to comment Share on other sites More sharing options...
Guest brentc Posted December 31, 2007 Share Posted December 31, 2007 As a student pilot learning in a Jabiru 160, I was wondering if someone could inform me, what type the tanks in wing the J160 has, for iv'e noticed theres a lot of sloshing and rocking of plane whilst pushing plane back in hanger. Hi Trevor, the J160 has fibreglass tanks within the wing skins. They are a fairly simple and very thin design but seem to do the job well. Link to comment Share on other sites More sharing options...
Flyer Posted December 31, 2007 Share Posted December 31, 2007 hopefully by the end of next year i will not have to worry about fuel fires,but will have to learn all over with high current high discharge rate batteries. but will have to be definatley safer. Dont be so sure on this one Ozzie. We use LiPo (lithium Polymer) batteries in our model aircraft. A 2.2aH 3 cell (11.1v) battery can generate, and has done, a big enough fire to burn a landcruiser flat to the ground.:yuk: Jump onto google and check out lithium fires. :;)2: Not pretty and just as volatile as a fuel fire with the added bonus of being electrocuted as well. DC power takes NO prisoners and nor does AC for that matter but may be more forgiving under certain circumstances. Know the rules of the game that you are playing and exercise caution. If you're building an electric plane though I'm keen to have some involvement perhaps ;);) Regards Phil Link to comment Share on other sites More sharing options...
Guest ozzie Posted December 31, 2007 Share Posted December 31, 2007 Hi Phil, yes the dangers of high rate charge/discharge i am aware of. in many situations they will be safer than fuel. the real danger with LiPo types is poor quality charges and cell assembly. It would be wise to monitor the battery, motor and controller temps during flight and have warning systems similar to conventional petrol engines. battery isolators and circuit breakers and impact cutoffs are a must. as are programable controllers I can do this with the lg scale R/C motors and controllers like the Plentenburg Predator but they are right on the limit for the sustained climb settings. Cooling for motors and controllers will be the biggest problem. So this is what i have set for the converting my Lazair to electric power. retain original twin engine setup use original 32X14 props direct drive 55lbs static thrust @ 5,500rpm each side minimum of 45 minutes duration. this will give me the same performance as the 100cc pioneers. these engines are almost impossible to restart in flight when they are cold and having the ability to have instant restart and full power on command would make for a perfect afternoon. any suggestions, figures constructive debate ect are always welcome. ozzie Link to comment Share on other sites More sharing options...
Guest disperse Posted December 31, 2007 Share Posted December 31, 2007 Inertia switch A ex's father was selling these for car's a few years ago. Basically it's a battery isolation switch that cuts all the power with a impact. Much like the crash bar. A weighted object about the size of a small salt shaker, clips into a socket. Then breaks free with a decent bump. The one I saw was a aftermarket job but I believe some cars are fitted with something similar, Jaguar for one. and emergency canopy release that can be opened from the outside. For easy extraction should you wear a bump to your noggin. But I do think rupture resistant fuel cells, definitely need more consideration.;) Link to comment Share on other sites More sharing options...
Guest disperse Posted December 31, 2007 Share Posted December 31, 2007 Found slight problem with crash resistant tanks: Its is not uncommon for a fuel cell for an Australian touring car to cost over $10,000. Bummer Link to comment Share on other sites More sharing options...
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