220mph Proximity

[omegooliebird]

Few pics preparing for flight, the 4x unconnected chargers required to get a 14s charge without creating a series connection between them! ..then the damage... Hard to see how bad the airframe was, but cracks all over the back end right up to the hatch on top and bottom skin. The motor mount had broken free and demolished the back end from the inside. You can see where 200a @ 50 odd volts vapourised the motor windings. There was copper balls rattling in the fuselage, wet with battery electrolyte.. A proper job.. haha!

https://photos.google.com/share/AF1QipO3vHXu8to1jlWfQ6ZlGq5_XGR50RGYi-w6T3OPcX2FF3J0e5JqeNGpmkkNCw-sYg?key=RXV6cm14Yl9lWWJSdmJreUdJWExOWmZ1blN6TEdn

[ched]

WOW I am surprised there wasn't more damage!!
Like the van and reg. Bet you have to go slow in the field due to the ground clearance?

[omegooliebird]

More bad news with the jet engine. Just preparing the plane for another run, and the engine is flaming out on fast throttle. It means blocked injectors and an expensive service in Germany...and months of waiting most likely. Still waiting on prop blades for the 14s electric too. So no progress at the moment..

[FPVSteve]

At what point does it become "not fun" any more? I'm all for the sentiment of breaking records etc, but months of waiting to potentially have 3 or 4 minutes in the air doesn't sound like much fun to me, especially when the wait is down to someone else pulling their finger out to fix your engine.

[omegooliebird]

Yeah, I'm struggling to justify it to be honest, but I am also quite determined to see this through! This whole project has fought me so hard at every stage. But that does make the achievement of pushing beyond my previous fastest speed feel all the better! This level doesn't come easy, but I really have been plagued with an unusual amount of issues with the jet project.

In other news on the 14s project, I have a selection of new prop blades coming from the top guy in Germany, designed by Powercrocco and laminated by Marcus Koch. They are really strong! Marcus has been in contact to say they should be ready this week. And the new collet/yoke adapter for the 8mm motor shaft has an M12 nut to hold it on.. so that isn't going anywhere. So that whole arrangement should be more likely to hold together.

[ched]

You really have worked so hard it would be a shame not to have another go :-) but costs are high. I assume no way to replace the injectors yourself is there? Surely they are not in the rotational part so no issues about balancing etc. Don't they just protrude into the combustor cans? Sorry I only know how full size ones go together.

[omegooliebird]

As far as I know they are hypodermic needles, with a tiny bore. I tried to clear them by dismantling the engine as far as possible, I then submerged the whole engine in boiling kerosene with injector cleaner in there (very scary), then pumped fuel backwards through the nozzles. It didn't work.

If you mess with the nozzles, the engine needs to go into a test cell to tune the FAEDC (ECU) to deliver the right amount of fuel related to rpm.. So they cant be replaced easily. And it would be impossible to poke anything in them to clear them, so it has to be stripped, nozzles replaced, then tuned in the test cell. Such is life.

[ched]

Sounds like you have done everything you can. I am amazed that the engine actually has a FADEC, I assume that's what it has ?(Full Authority Digital Engine Control! I assumed it would just be a simple solenoid system based on rpm. Just amazing that the detail they have had to go to to get results. I know how difficult it is designing combustion systems for jets as I was involved in the testing of some of them, in test cells.
Good luck and fingers crossed it all comes together.

[omegooliebird]

I think it is pretty standard for micro turbines to have a FADEC these days. It has RPM and EGT sensors, electric start and cool down. This one has to get up to temp on gas, ignited with a glow plug, before the kerosene is ramped up, but some slightly larger turbines will start on kerosene alone..even do a re-start in the air! Pretty crazy... Bit the sophistication and incredibly tight tolerance engineering does not come cheap! The tail wheel is cast out of inconel in house, which alone must take some gear to get right! The 3d machining on the compressor wheel is incredible, and to such tight tolerances. At full throttle it is at 210,000 Rpm... Going round 3,500 times a second!!

[ched]

It's just amazing what can be produced these days. The technology that goes into the kit we now use is just mind blowing from just 10 years ago.
Good luck.

[omegooliebird]

Jet engine project stalled for the engine service.

So on to the electric project! I have built a new 14s battery pack, New ESC is built up with heatsinks and extra caps, got a couple of different motors to test.. and a selection of some crazy props from another manufacturer in Germany.. they look much stronger than the ones that failed on me last time.

[FPVSteve]

What's the idea behind them only having one blade? Doesn't it cause an imbalance?

[omegooliebird]

They are folding props, I have 3 blades of the two smaller sizes, as I may run a 3 blade.. to increase the thrust volume without the extra tip speed from a bigger diameter. You can run just one blade with a counter weight though if you don't have the torque to pull 2 blades.

[English Turbines]

  The Gas Turbines speed, is largely governed by the rate at which fuel is pumped into it. This is assuming the fuel delivery system is working properly and the injectors are all clean. The ECU governs the engines rotational speed and EGT simultaneously. Excessive ramping up of the fuel delivery for example can cause excessive EGT, but this can also be caused by a bad Combustor or fuel sticks which have drifted due to heat cycling.
  In the early days Gas Turbines did not have exotic ECUs, simply an electric fuel pump and a glorified speed controller with some soft ramping. Engine speed can also be calculated by using case pressure and a gauge rather than a hall effect tacho. They are much simpler to operate than some folk imagine, but the construction, dynamic balancing and setting up isn't. Most problems with commercial model Gas Turbines are related to fuel delivery injectors and or Combustor failures. Jet Cat were notorious at one time for poor quality combustors, not made from Inconel and fuel sticks also. Repeated heat cycling, excessive up ramping causing over_temps and early failure. I would suggest a decent fuel filter downstream of the fuel pump near to the engine to avoid blocked needles.
  The smaller engines running in excess of 200K rpm are a lot more picky regarding combustion, this is because the combustors are relatively short giving less time for effective vapourisation. In turn, this means their combustors are more vunerable to abuse which can cause them to distort or dispace their fuel sticks which in turn can cause hot spots in the NGV area.
  My advise is to keep a modest fuel ramp when accelerating the engine, you can program the ECU to do this. The engine will accelerate slower, but its better for longevity. You just need to think ahead a little more when using the throttle.
 
 

[omegooliebird]

Tomorrow is the day, weather permitting..