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285 vs EXT - what say you?
#1
Hello,

I am a former Brantly, Safari, 162F, and Helicycle owner and am now considering the Mosquito 285 or EXT.  

Looking back the Brantly was probably the smoothest and easiest helicopter to fly.  It just felt "right" in every phase of flight, but unfortunately parts became ridiculous and the rotor blades developed an AD that makes operating one prohibitive.

The Helicycle was an absolute blast.  All the power you wanted, fast, easy to fly, and the engine just purred at a perfect constant RPM all day regardless of how hard you ran it. One of the hangups with it for me was the somewhat short fuel range, the elastomeric bearings that just did not seem like a good idea to me, but the biggest problem I had was the horrible vibration / main rotor shake that pretty much ended my desire to fly the machine anymore.  I was one of the 10 or so people that experienced this problem and do not want to experience it again.  The company was great to work with after the experience, but I was never satisfied that the issue was resolved.

After taking a break from helis for 3 years I am now considering another one and one of the requirements is that it is experimental as I do not intend to pay for 12-year rebuilds or spend $200-500 per hour for parts, fuel, and maintenance.  That really only leaves the Mosquito.  I initially thought the XET would be the choice, but I see that now the 800 is available.  After researching it a bit it appears it is basically the Arctic Cat 800 HO engine that has been re-purposed / re-engineered for the Mosquito.

I would greatly appreciate input from anyone that has owned and flown both power plants and would give an honest opinion of them.  I do not mind burning fuel, but want a minimum of a 2 hour range with a cruise true airspeed of 85 MPH.  While the turbine sound is cool, I really do not place much emphasis of coolness - I just want a *reliable* engine that does not have to be tweaked or torn down every year.  I intend to fly this machine back and forth to work a few days a week which will realistically be about 200 hours per year.  I will be taking off my my home on a large lake and the first 60 seconds of takeoff and landing will be over the water - again reliability is key Smile

Thank you!
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#2
The XE285 is definitely the way to go. Much better fuel burn than a turbine but with a heavily derated engine (160 hp capability at 8300 rpm typically producing 60-70 hp at 6000). Fuel injection with twin fuel pumps means reliable hands off operation and water cooling keeps temps down and tolerances close. Lower initial and operating costs with the same power. I typically cruise at 85-90 mph. Two hours range on the standard tank with an additional hour with the belly tank. If you are flying over water you can order the floats as well.
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#3
Thank you very much for the reply.

Can you please clarify a few things for me:

1.  Am I understanding correctly that the problem with carbed 2-strokes in helicopters is that the engine tends to seize up due to maintaining a high RPM, but low MP while descending which causes too little oil to be drawn in from the oil injection (or too little oil/fuel in non oil injected systems?"  If so, how does fuel injection solve this problem?  I can see how it would solve density altitude variances, but does it correct oil injection rates for RPM separate from MP as well?  I know that the Bombardier engine in the REV uses many sensors and if I recall correctly even flows fuel through the ECU to cool the ECU.  From what I could grasp that engine would have made a great helicopter engine due to it's ability to monitor CHT, EGT, and coolant temps and adjust the fuel, oil, and RAID valves along with direct Injection.  Does the 800 engine you provide adjust fuel and oil to proper levels so normal helicopter descents can be made or do you still have to add collective in the descent to keep temps down?  I ask this because, again, I want to fly it like a normal certified helicopter.  Having to worry about the engine and adjusting descent profiles to do this is not a good practice from a safety standpoint.

2.  As for the floats - how much would they slow down the helicopter in cruise and would they really be any benefit in an autorotation from a boom strike or other perspective I am maybe not understanding?  I would be flying close to shore and am not worried about drowning, but I would like to salvage the machine if the engine failed.
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#4
Let me re-phrase question #2: Would a properly executed auto down to smooth water have a good chance of saving the machine? There would be no torque to deal with, so you would not be spinning on the water leading to a tip over. Mast bumping or a boom strike would also not be a factor, correct? Also still curious about the loss of airspeed with floats vs no floats.
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#5
Two stroke engines by virtue of their simplicity should be more reliable than a 4 stroke which has far more moving parts to fail. But since two strokes can produce so much more power for a given engine size they are always used in roles where light weight for the needed power is the primary goal. So since they are always running at near full capacity they are more likely to fail than a much heavier and over-designed four stroke.

Two strokes rarely fail at low power settings. They typically fail at high power settings where the fuel/air ratio is not set correctly and the lean burn overheats the piston and melts it. With the fuel injection you can set your fuel requirement on the fuel map and then the sensors will maintain that in spite of changing atmospheric conditions.

No engine likes to run at high rpm with no load for extended periods since cylinder pressure keeps the pistons/connecting rod loaded and in alignment so it is always better to keep some load when possible. Long, low power descents are acceptable even with the two stroke, but its best to avoid them if possible.

The floats don't have as big an effect as you might think on cruise speed, about 5 mph. There is no reason you wouldn't be able to do a completely normal auto landing with floats. You would of course have a softer landing but less resistance to rollover so you would want to land as straight as possible with minimal residual speed.
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