I am a racer and I like high RPM but I like to have done something to earn it not just see it go up to new heights on two successive flights in trend fashion and at the same time see a speed reduction of the aircraft below the previous top end speed.
I have recently been working on a speed mod involving the gap around the inboard aileron mounts.
I have been flying and racing the RV-6A for several years with a Hartzell C/S prop so I am somewhat familiar with its performance. The most I have ever been able to get out of it is 2730 rpm and that was rare.
On 7-18-13 I made a test flight with the new closure plates and recorded the speed as 182.4 kts and notes the RPM as 2720 (which is common - 2730 is the highest number I have ever seen). This was a failure since my previous speed without the mod was 189.8 kts.
Instead of removing the new plates I had some time ago developed some end plugs of balsa wood for the flaps and ailerons that I decided to reinstall and test in combination. They had failed also but I thought in combination the results might be different. I did my standard USAR handicap procedure triangular pattern run twice at 6,000 ft density altitude on 7-19-13 and post processed the data in the NTPS spread sheet. The speeds were 181.6 and 183 for and average of 182.3 kts. Another not unexpected failure but I noted in my raw data sheet that the RPM was initially 2720 but increased to 2750 and occasionally to 2760.
Even though the experiment was a failure I was pleasantly surprised to see the increase in rpm which for my 72" prop is still below the tip speed problem area. So I finally gave in to the failure and started removing the two mods. This is not an insignificant task. On 7-22-13 I reflew the test with mods removed and the speeds were 183.3 kts and 182.9 kts for an average of 183.1 kts. Verifying that the mods appeared to be no good but the speed was still way off and the RPM this time was up to 2770.
In the past in 2004 I had a prop runaway and engine seizure due to loss of oil so I am sensitive to that possibility. The oil was recently changed and is still at a full 8 quarts.
This weekend is the biggest race of the year - the AirVenture Cup - so there is not a lot of time. I am going to pull the cowl today and see what I can find but this is not normal (over 1,000 hrs flying this plane). It almost seems like the prop can't reach high enough pitch so the oil pressure is compensated with higher RPM.
If you has seen this increasing RPM trend and have some experience to share I would be glad to hear it.
Bob Axsom
I have recently been working on a speed mod involving the gap around the inboard aileron mounts.
I have been flying and racing the RV-6A for several years with a Hartzell C/S prop so I am somewhat familiar with its performance. The most I have ever been able to get out of it is 2730 rpm and that was rare.
On 7-18-13 I made a test flight with the new closure plates and recorded the speed as 182.4 kts and notes the RPM as 2720 (which is common - 2730 is the highest number I have ever seen). This was a failure since my previous speed without the mod was 189.8 kts.
Instead of removing the new plates I had some time ago developed some end plugs of balsa wood for the flaps and ailerons that I decided to reinstall and test in combination. They had failed also but I thought in combination the results might be different. I did my standard USAR handicap procedure triangular pattern run twice at 6,000 ft density altitude on 7-19-13 and post processed the data in the NTPS spread sheet. The speeds were 181.6 and 183 for and average of 182.3 kts. Another not unexpected failure but I noted in my raw data sheet that the RPM was initially 2720 but increased to 2750 and occasionally to 2760.
Even though the experiment was a failure I was pleasantly surprised to see the increase in rpm which for my 72" prop is still below the tip speed problem area. So I finally gave in to the failure and started removing the two mods. This is not an insignificant task. On 7-22-13 I reflew the test with mods removed and the speeds were 183.3 kts and 182.9 kts for an average of 183.1 kts. Verifying that the mods appeared to be no good but the speed was still way off and the RPM this time was up to 2770.
In the past in 2004 I had a prop runaway and engine seizure due to loss of oil so I am sensitive to that possibility. The oil was recently changed and is still at a full 8 quarts.
This weekend is the biggest race of the year - the AirVenture Cup - so there is not a lot of time. I am going to pull the cowl today and see what I can find but this is not normal (over 1,000 hrs flying this plane). It almost seems like the prop can't reach high enough pitch so the oil pressure is compensated with higher RPM.
If you has seen this increasing RPM trend and have some experience to share I would be glad to hear it.
Bob Axsom
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