Formation Flying. Why no vernier throttles

[Bob Redman]

Tried a search on the formation threads for mixture setting and this is the best result.

I fly an RV-7 from the right seat with centre push/pull throttle (friction), prop & mixture (both vernier). The engine is an Aerosport IO-360M, 180hp, parallel valve, 8.5:1. Prop is Hartzell BA CS. Basic weight 1085lb.

I am happy with 2500RPM (and the throttle) but I have been running full rich mixture because I have been chasing two IO-540s, usually below 2000ft MSL.

What mixture setting(s) do you experts use/recommend and why ?

Thanks in anticipation.

[Kahuna]

Well the engine does not know you are in formation. You should operate your engine prop within the manufacturers recommend power range.
If you are looking for best power, you should be leaned for best power. Generally thats in the ~100ROP range. You are C/S prop. Your leaving a lot of power on the table at 2500RPM. A LOT measured in wingman station keeping opportunity. I would know instantly if anyone of my wingman were operating with that low a HP output. Your greatest first opportunity , from your post, for more speed, is a much higher RPM.

[scard]

Twoop! 2500 and full rich would leave me screwed on every flight. You don't want to know what kind of RPM I'm turning in order to make it happen in airshows.

[Bob Redman]

Thank you gentlemen,

2600 (Pmags), and leaned to 100F RofP it is.

First formation for many years - & first using a Lycoming, so I left it rich. Then others noticed deteriorating radio transmission power & readability. Fixed the radio problem by cleaning all the soot off the bent whip on the belly.

Best regards.

[Bob Axsom]

When Jeanine and I built our RV-6A I had no intention of ever flying formation and we installed vernier controls for throttle, prop and mixture. For 8 years I flew it with nothing but smooth dependable performance. Then last year I made a decision to try to fly in the Pylon Racing Seminar and ultimately the Sport Class at Reno. It can be done and slower planes than mine have done it.

I decided to determine the full set of requirements and one was formation flying ability. The formation flying groups I am aware of do not allow vernier throttle controls. A lot of things had to be accomplished in the off season of the Sport Air Racing League to meet the requirements and to improve the performance of the airplane. I flew from northwest Arkansas to northern California to work with Red Hamilton to install high compression pistons and at the same time replace the vernier throttle control with a friction lock throttle control. We had bought the original from Van's but Red offered to buy the new cable from Wicks.

I knew from the part number what length I needed but the exact same length was not available from Wicks. I determined that a slightly different length would work because the cable routing was not direct and slack could be easily added or taken out of the original path. An order was placed for a cable manufactured by the same manufacturer (ACS) with a slightly different length.

When the cable arrived it looked like the same high quality cable but where the original had a threaded termination at the remote end of the cable housing (sheath) upon which nuts could be adjusted to vary the termination support position the new cable had a circumferential grove machined into the end piece of the sheath.

The support bracket that I had made for the adjustable sheath termination on the vernier was not in perfect position for the new cable slot and I had to develop a two piece bracket to mate with the slot on the sheath and a spacer to position the cable end at the correct location and angle to form a straight line connection with the throttle lever on the carburetor.

After a lot of small part detail work I got it rigged for non binding full range of motion throttle control. When we completed the engine work I did a ground test run, thorough inspection and two test flights along the coast around Fort Bragg. Then I flew home via Prescott, AZ and Amarillo, TX.

Back at home I decided to make a test flight of something I was working on but when I started the engine I could not get it back to slow idle. My immediate destination was the self service fuel pump so I started taxiing there at a higher that desired RPM. I could increase the speed of the engine but I could not slow it down to a normal idle on the ramp - I don't remember the number any more but as I recall it was well over 1000 rpm. I thought this was just some minor binding so I really pulled on the control and then it became jammed solid in one position. I knew this was a serious problem so I taxied back to the hangar to start the trouble shooting process.

I pounded on the knob to try to get it back to the panel but it was frozen solid. When I had it disconnected at the carburetor end I pulled on that end of the cable and it came loose but it would always bind at the slow speed (closed throttle) end of the travel. I removed the cable and shipped it to Wicks and asked for failure analysis and told them I would pay a reasonable price for that work. So far as I know no failure analysis was performed. Since I was not the customer that bought it I can see their reluctance to deal with me.

I needed a good friction lock throttle cable so I called Van's and ordered one with the threaded sheath termination and installed it with all of the proper rigging adjustments. It has worked smoothly and correctly for over 250 flight hours but I still had some personal adapting to do.

Where I had three parallel vernier controls I now have one friction lock and two verniers. Not a problem but early on I found myself wanting to turn the throttle control and being reminded of its proper operation when there was no response.

In July I was flying in the Mount Vernon 100 air race the day before the AirVenture Cup Race and on the first leg Gary Wilcox in his RV-7 called to announce he was passing on my right. Well I know Gary is very fast and it is not the first time he has passed me but it was disturbing to see it happening so early. He went by and he was moving. I looked at my GPS ground speed and it was down to 154 kts. How can this be? Then I saw the throttle knob was on the order of 2 inches out of the panel. You really have to lock it down not just position it and forget it like a vernier. I have experience that a couple of times since but my internal reaction to throttle changes is not to passively trust the variable friction drag to hold position - I always give the lock a little twist.

So having flown the same plane with both configurations ... It was a change I had to make to get the experience and I'm glad I did it for that reason only. Either version works fine but neither is worth the trouble of making the change unless you are forced to do it to achieve some other than performance objective.

Bob Axsom

P.S. I am not a formation pilot in spite of my training but because of my personal experience in that training I agree with the wisdom of the formation flight restriction to friction lock throttle control.

B.A.