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Geoff_H

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Everything posted by Geoff_H

  1. Geoff_H
    Maybe afforfable flying is an oxymoron. I have been trying to make an aircraft design that can be built for under $10k, with access to good metal machines. Not sure that I have enough years left to get it done. I have been using the twin small two strokes a brilliant idea, but as it will never get capable of being RAA it maybe a fruitless effort.
  2. Geoff_H
    Thanks guys now I understand the 95.10 is for very low performance aircraft. I will have to leave my project in VH category I just hope that my medical holds out by the time it's finished.
  3. Geoff_H
    Not limited to one engine but just try to get a two engine light aircraft registered with RAA, eg Cri Cri, just can't happen!
  4. Geoff_H
    I looked into using the jet engines that are used in the cri cri for my cri cri like project. I can't remember the exact endurance either the dual two stroke engine tank. It endurance was less than the monomum. The guy in WA that has put the engines into his cri cri has added significant fuel storage. The engines were designed for model aircraft and had very high fuel consumption.
  5. Geoff_H
    I don't know about this GT, they are not even considered in power generation, but weight is a big factor with recupetators. The bigger they are the less fluid flow penalties, the smaller they are the higher the gas flow, and consequent efficiency loss. Gas and air losses square as the velocity increased. So a designer, I guess, would pictch recupetators size at cruise power.
  6. Geoff_H
    Recupetators duct the exhaust gas over the out of the compressor to heat the air and expand the air. Just like a burner would. Not as much fuel is then required to heat this heated air to get the gas (air plus products of combustion) to the maximum first stage turbine blades. Roughly same turbine power, a slight reduction due to exhaust pressure gain from having to pass through the recupetators. Recupetators usually reasonably heavy having to withstand compressor outlet pressure, they also decrease the gas pressure to the turbine.
  7. Geoff_H
    Cmc coatings of burners have been around over 15 years to my knowledge. I have not seen blading yet ,(retired so out of the loop), but may they have. Both Siemens and GE have ceramic coated burners. Refurbished burners were more expensive than refurbished blades, for 100MW Gt 10M every 3 years of continuous operation (2011 price)
  8. Geoff_H
    GE were experimentimg with ceramics over 10 years ago. Turbine blades are subject to huge radial forces. With no operational GT yet my money would be that a successful product has not yet been developed. First to do it will make a lot of money. In power generation just a few % improvent in efficiency means big bucks.
  9. Geoff_H
    Pt6 is a brilliant design. It was designed many years ago. Has a very high bsfc.
  10. Geoff_H
    What is the weight and bsfc of the RED engine. I can't find a reference to it.
  11. Geoff_H
    What is an "equivalent gas turbine". The BMW B 58 engine gets 340hp out of 300lb weight....the state of the art (Merc get 400hp out of same ).. but there are many gas turbines less and some more. Modern engines, modern gas turbines are similarly developed. We need to compare similar with similar.
  12. Geoff_H
  13. Geoff_H
    Check out the dates of the original manufacture of the engines in the brake specific field consumption. Of GT and piston increase dramatically as date gets more recent. GT low power very low bsfc are a function of air compressor pressures at low speed. Hence low "compression ratio". I always ran my Mooney at full throttle, landing very much excepted.
  14. Geoff_H
    Far too general a statement. Quality gas turbines can get to 40% efficiency with expensive Blade material and multiple compressor stages. Higher than all but the most sophisticated piston engines. Cheap turbines do have poor fuel efficiency.
  15. Geoff_H
    I thought about the comments about the dreaded thirst of gas turbines. I looked at the power increase required to increase the speed of a Mooney 201. Let's look at increasing the speed by 50%, to 300mph. Drag increases by the square of the velocity, horsepower is proportional to the product of the speed and the force. Hence to power a 50% increase in speed I must increase the power of the engine by 1.5 raised to the power of 3, around 3.3 times. The Mooney would need to increase its power from 200hp to 660hp. Plus whatever drag would increase by owing to increasing main spar strength and up isconsequent weight. So apart from finding a 660hp piston engine we would probably need to go to a gas turbine. If it has the same thermal efficiency as the piston engine we are going to burn 3.3 times as much fuel. For the same range we are going to require increased weight for the extra fuel which will incur more drag etc etc. The exercise looks something like a TBM 800, a Mooney designed aircraft. Speed alone I creases required horse power by dramatic amounts, probably why turbines seem to be very thirsty.
  16. Geoff_H
    Actually the aircraft turbine derivatives that I have worked on were more like 93,000hp. The largest non derivative I worked on the desighn was approx 250,000 hp. Stationary turbines are also much more efficient using water injection and evaporative cooling of inlet air.
  17. Geoff_H
    I got a quote 10 years ago for refurbished blades for a 60MW GT of $6M. Cheap blades will not take high temperatures hence low efficiencies high fuel consumption.
  18. Geoff_H
    They are bigger and power big aircraft demanding large power. Low temperature inlet turbines will have significantly less efficiency. We know of no material that can take the temperature of stoichiometric combustion. They would simply melt. So we must cool the gas out of the stoichiometric burners with air that bypasses the burners. A GT compressor must compress much more air that doesn't contribute to power, just cooling. This means that the efficiency drops with lower allowed turbine inlet temperature. High temperature blading is expensive, single crystal, and usually with small holes to the leading edge of the blade to provide a cooling blanket to the blade. Expensive.
  19. Geoff_H
    A quality GT will have a compressor discharge pressure circa 250psi. That is 16:1.
  20. Geoff_H
    A high quality turbine is more efficient than an aircraft piston engine. I think that the turbines usually develop so much more power and capable of higher speeds that have an exponential power demand. The Rolls Royce Trent engine that was powering a generator was around 40% efficiency. GTs are very dependants upon air density so they somewhat in efficiency, from day to day.
  21. Geoff_H
    I think that the dipping in the paint is a great idea. Just be careful that your favourite colour may fail because the paint carrier that disappears on drying is conductive. I would not expect so but I am not really certain what is in the carrier.
  22. Geoff_H
    Yes a good quality Meyer with a very high input resistance would probably indicate a conductive paint. A Fluke or equivalent meter, not a cheap Chinese one. First measure the substrate, without any paint, push the probes as hard as possible into substrate. The resistance should be infinite. Then paint the surface, at dry remeasure in the same spot, if the resistance is less than infinite do not use that paint. I have made a resistor by mixing black carbon ochre with epoxy. When set I could measure resistance across the part. Another was is to download an RF Meter on Apple/android and see the effect of putting the phone in a painted box. Geoff
  23. Geoff_H
    Recupetators weigh! Stationary engines of larger size don't use them because of pressure losses in exhaust gas, pressure loses affect turbine output.
  24. Geoff_H
    I worked in Florida on the design of 185MW gas turbine. The efficiency of a gas turbine depends heavily on the maximum turbine first row of blade temperature. To get high temperatures you need very exotic blade materials, as a rule of thumb the more you pay the better the efficiency. These people are getting better efficiency by using heat from the exhaust to increase the volume of compressed air so not so much fuel is used to get to maximum temperature. It is used by a company called micro turbines, small medium efficiency turbine manufacturer. I hope the guys are a great success.
  25. Geoff_H
    Carbon black paints are offer used as RF absorbers. Other forms of colouring may have been used on your GPS antennas. I would find out what pigments are used in any coloured paint and check the conductivity of the pigment before applying them else you create a Faraday cage.
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