cant get RPM readings
well today during lunch hour I decided to pick me up a Tac. I purchased the Hanger 9 Tac/ Volt meter one. This is not really the one I wanted but all they had there. Anyways I just tried to get a reading on it and it did not seem to work to well. I am running the GRRT and using a 7.2 x 8.6 prop on my Diamond Dust. My question is when you go to get a reading does there have to be daylight behind the prop? The way I was trying to get a reading was by having the plane on the stairs with prop over hanging. My concern was that it was a bit shady in that area. I was wondering it daylight needs to be in line with the tac and not the stairs. I was running it this way due to no landing gear.
Anyhow I was only able to get 10,000 rpm to 11,500 at just under half throttle. I could get a reading at idle to under half throttle and that was it. After that the readings showed it was turning 300 to 1300 rpm. It fluctuated back in forth. Any suggestions?