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PostPosted: Sun Jul 18, 2004 3:08 pm
by JPXman
Hey lazairheads,

I guess the warm weather is keeping people in their planes than on their computers :) good on ya. However, I need hanger talk to keep me going, so I'll start a thread about interesting things about my lazair, and chime in with your own things.

I have only flown a few hours, but the first thing I noticed was that when the engines were at higher RPM, there wasn't much airflow on my face while flying! When I went in for my first approach and cut the throttles, all of a sudden there was 5 times the air wooshing by. It gave me a false sense of speed. It also taught me that if I'm flying around and getting a bit warm, just chop the power for a few seconds to cool off :)

Tyler
"Lazair by August?"

PostPosted: Mon Jul 19, 2004 4:55 am
by ozzie
hi Tyler, it's winter time here in oz snowing on the hills west of sydney as the cold snap passes thru, at last some rain as well but we need a lot more. (having a bit of trouble getting used to winter after living in the tropics for ten years)
in one of the early updates for the mark 1's it was found that in a dive the tube type airspeed indicator stopped at 55mph (by coincidence the VNE) it was found that the air flow from the props built i little windscreen in front of the pilot, and the faster you went the more the air built up in front of the asi. as a result the asi was put on a stick to put it futher away from this effect i then found that i was decending at over 65mph. i was experiencing some buffet at this speed so when i realized what was happening i eased off a bit. later at an airshow at the local beach i had a smoke cannister fitted halfway up each flying strut when i ignited them i noticed the smoke did not stream straight back but curved inside the tail. so does the effect of the prop wash create an invisible fairing? it would be an interesting exersise to do some smoke tests and see what is going on. ozzie

PostPosted: Wed Aug 18, 2004 2:54 pm
by rayjb60
Hey Ozzie,

Thats an interesting observation, no wonder the install of a fairing adds speed instead of reducing it.

Also makes you wonder about the odd aerodynamics going on.....a smoke test should prove very interesting indeed.

I also wonder about prop rotation....do twins ever use engines with complimentary rotation, so that one engine rotates clockwise, while the other goes counter clockwise to cancel out torque or propwas effects?

Having not flown my Lazair yet Im wondering if the engines perhaps cause a slight roll to one side or the other?

PostPosted: Wed Aug 18, 2004 4:57 pm
by ozzie
hi ray, yes some interesting airflow around the lazair. as both engines turn in the same direction the lazair does have what is known as a critical engine the P factor from the rotation of the prop will allow the aircraft to turn easier in one direction than the other when experiencing an engine out you should be aware of this as if you lose an engine and have to turn going left or right depending what side is still running may mean the difference on getting to a landing site. some GA twins have overcome this by having contrarotating props or one engine that runs backwards(reverse cam grind) so the adverse yaw is the same it has been a while since i have done any "real" twin flying but it is easier to controla twin with contra props than without. i don't know which way the rotaxs turn so you will have to work it out and do some shut downs at hight. idle will do best yet go do some twin time but work up the leg musles first. the last big twin i flew was an otter and had about 80lbs of rudder force to keep it straight.remember dead leg, dead engine. have fun ozzie

PostPosted: Sat Aug 21, 2004 5:03 pm
by Chappy
When Ultraflight's prototype two-place Lazair was upgraded from Rotax 185's to more powerfull NGL Westlake twin cylinder engines, we found that the tail began to shake quite a bit at certain speeds and power settings. Dale moved the engines outboard on each wing about six inches, IIRC, and that got the airflow over the tail cleaned up enough to stop all of the commotion.

Chappy

PostPosted: Tue Sep 21, 2004 9:12 am
by Bill
I find that when the engines are realy in sync that the vibrations increase. It is better to keep the engines slightly out of sync to keep the shaking down.