That was probably EAA Ch 105 = here in=20 Portland, OR. Four of us were trained up by the DSS factory guy = back in=20 November using the DSS Micro unit. It's a basic unit (forget the = model)=20 but all we are going to use it on is an airplane. I forget = exactly what=20 we paid for it but it was about $5600. This chapter has upwards = of 100=20 active members and half of them are building RVs.

If = you're=20 serious about the investment I can get the details for you. A = person=20 could make it back balancing experimentals. Our rules are that = the owner=20 is responsible for adding any weights, we just tell them where to put=20 it. Any certified bird has to come with it's own A&P to do = the=20 wrenching and make the log entries. (Our chapter president is a = lawyer=20 and Das Fed is a member of the chapter. We (ahem) know the rules = rather=20 well.)

So far we have balanced a couple of dozen planes and = it's making=20 a lot of difference here on the local fleet. The challenges are = as you=20 have discovered, gear reductions, getting a good trigger signal, and = realizing=20 that you can't get a good reading because a plane has a bad engine = mount or=20 some such thing. These computer based units are great because = you can=20 even show bad cylinders, frozen harmonic balance weights and similar = problems=20 by looking at the spectrum. On a gear reduction unit like ours = you can=20 look at the spectrum and see the prop side vibes as well as the engine = side=20 vibes. I suspect on a rotary, with some practice, you would be = able to=20 see a bad apex seal. Not to mention on a rotary you will have a = spectrum=20 on the shaft side (6000 rpm) and the rotor side (2000 rpm). If = you put=20 the transducer on the accessory end you can see the vibes from your = alternator=20 and water pump (adjusted for pulley ratio).

My current struggle = is with=20 a guy's Thunder Gull sporting a Hirth 2 banger and a 2.53 gear. = Spent an=20 afternoon with him only to discover a broken motor = mount...(grrrrr..). =20 Since I'm the alternative engine guy in the group I get to deal with = all the=20 "Renaissance Men". The Lycomings are a 20 minute job once the = cowling is=20 off -- too easy.

Mike McGee, RV-4 N996RV, O320-E2G, Hillsboro, OR
13B = in=20 gestation mode, RD-1C, EC-2=20

I am going to bring a copy of this e mail when I = get my=20 prop dynamically balanced, just so the guy can have a better ideal of = what to=20 expect.