Thanks for the excellent analysis, Claude. I'm sure we all can benefit from your experimentation with the extra airspeed indicator.
Syd Claude Wheelbarger wrote: > > Hi Syd > Yes I replaced the MLG lights and noticed an immediate and drastic speed > difference when running my 7148 prop. Wierd part is when I use the 7150 it > seems > to make no difference. My local AI had a nice toy, an airspeed indicator and > pitot tube with a long hose and a flat mout for attachment to the place with > double sided tape. If you use a alcohol and wait a sec it will let go of the > paint. We mounted it on each mlg and test flew the plane. Also mounted it on > various points under the wings and on top of the tail and used the sticky > tape and anchors to hold the tube back to the cockpit. Surprise surprise... > The 48 had a much much wider propwash at low speeds than the 50! Since both > props have been to Carolina in the last 6 months for non destructive testing > (for cracks etc) and a pitch check (both had one blade slightly out of pitch > from the other) I assume they are within spec. Anyway the big difference was > how much airflow passed over the MLG lights on climb out and at full > throttle cruise. For the 48 prop it was linear and stayed at 45-55 mph above > the indicated airspeed. If I powered back from redline to a 2150 or so slow > cruise It didn't change much. Now the 50 was like a storybook picture. The > airspeed at full throttle climbout or cruise was only 7-10 mph faster and > immediately upon powereing back even slightly was within 2-4 mph of > indicated. The elevator is much more sensitive and the aileron control is > about the same at any cruise speed (supposidly since they are almost > entirely out of the propwash now) So after spending a whole day changing > props and moving the pitot we both came to the conclusion that my 50 kept > the propwash firmly against the plane where it should be and the 48 was a > wide conical pattern propwash that placed more of the plane in the higher > speed higher drag air. By the way the same applied to the nose fork. The top > of the fork where it splits off was right at cruise with no snubber cable on > both props. However with the cable in place it had to fly through 10mph > faster air on the 50, and 40mph air on the 48! End result being the nose > wheel drag almost doubles from 100mph cruise to 148mph propwash and the MLG > lights are also dealing with 145 mph drag versus 100mph clean cruise air. So > even though it was a higher pitch the plane flew and climbed faster with the > higher cruise prop than the climb prop. When I removed that snubber and the > MLG lights in Burlington it's no wonder I flew a different plane. Also as > for the speed I flew the interstate e/w then the powerlines n/s and timed it > in all configurations. With the 48 I averaged almost 8mph faster with the > snubber and lights removed. With the 50 it was only an avg of 4mph > difference but overall the 48 with the lights and cable was 11mph slower > than the 50 with those items removed. I settled for replacing the lights > until i can put in wing lights and the cable is staying gone. He also > produced the sensenich equal to my 50 and I tried that. I was IN LOVE but he > wont part with it. better climb and cruise and all that buffeting I hear > around my canopy was gone gone gone. Seemed to have a really smooooooth flow > past the plane. > > Nuff-fer-now > > Claude Wheelbarger > six-two-zero > Waynesboro, Va. (W13)
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