Air Racing for Rotax 912 Series Engines
The Royal Aero Club 3Rs holds up to 8 air race weekends per year where race pilots pit their skill and aircraft against each other in handicapped air races. The races require pilots to navigate around a defined course running at constant top speed, above 100mph. The winner is the pilot who has maintained the highest navigation standards, flown the tightest line and maintained their speed close to their handicap speed the best.
For aircraft with Lycoming and Continental engines racing means wide open throttle (WOT) for anything up to an hour. For these ‘classic’ engines WOT for long periods is not an issue as they are very low revving, and the difference between cruise and WOT is small. For aircraft with the Rotax 912 series engine air racing is virtually impossible due to the strict 5 minutes at max power limitation.
For aircraft with Lycoming and Continental engines racing means wide open throttle (WOT) for anything up to an hour. For these ‘classic’ engines WOT for long periods is not an issue as they are very low revving, and the difference between cruise and WOT is small. For aircraft with the Rotax 912 series engine air racing is virtually impossible due to the strict 5 minutes at max power limitation.
Rotax 912 Racing
Figure 1 shows the engine performance data for the Rotax 912 series engine. The maximum continuous power can be seen, in the table and text, to be achieved at 5500rpm with a 5 minute limitation.
Figure 1: Rotax 912 series engine performance data
This table shows the power generated by the engine in terms of RPM and manifold pressure. From the information presented it follows that a Rotax 912 series engine can be run continuously at WOT if that achieves 5500rpm, or less, in level flight. If this can be proven and the aircraft achieves at least 100 mph then it would be safe to race, assuming of course that you are happy to run the engine in this configuration for perhaps an hour.
It is common in the UK that aircraft (microlight or Group A) fitted with a Rotax 912 series engine cannot achieve full rpm. This occurs because of the BMAA & LAA airworthiness rules, weight restrictions and airframe restrictions (VNE). To stay within the rules the propeller is set or made very course thus not allowing maximum RPM in level flight. The specific information for each aircraft may be available from the flight test record at initial permit application, should the aircraft be young enough.
It is common in the UK that aircraft (microlight or Group A) fitted with a Rotax 912 series engine cannot achieve full rpm. This occurs because of the BMAA & LAA airworthiness rules, weight restrictions and airframe restrictions (VNE). To stay within the rules the propeller is set or made very course thus not allowing maximum RPM in level flight. The specific information for each aircraft may be available from the flight test record at initial permit application, should the aircraft be young enough.
Questions for Rotax Gmbh.
To confirm the above assertion the following questions should be asked of Rotax Gmbh. or their appointed UK representative;
- Is maximum continuous power for a Rotax 912 series engine always measured from RPM?
- Is running the engine continuously at maximum RPM below 5500 allowed within the performance limitations?
Certifying a Rotax 912 for racing
To allow an aircraft with a Rotax 912 series engine to race in a 3Rs air race an additional set of checks should be undertaken.
Prior to racing;
Prior to racing;
- Provide the pilot with the relevant information
- Review the aircraft ‘flight test record’ (where available) for VNE & Engine speeds
- Record the maximum RPM achieved in level flight with WOT
- Record the airspeed, OAT, QNH
- Ensure the throttle is WOT and has no further travel
- Validate that the aircraft achieved 100mph (87knots)
- The pilot signs a Rotax 912 declaration
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Rotax 912 declaration |
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I confirm that my aircraft, fitted with a Rotax 912 series engine, is not capable of generating more than 5500rpm in level flight. I understand that to compete in a 3Rs air race that I need to run my engine at wide open throttle (WOT) continuously for the whole race. If this operation is outside the limitations of the Rotax 912 series engine (maximum 5500rpm for 5 minutes) then it is likely to damage my engine and I am responsible. |
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Signed |
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Date |
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Race Number |
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Registration |
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Figure 2: Rotax 912 race pilot declaration
Passing these tests should be a pre-requisite to allowing the aircraft to enter a race and ensure that the pilot is clear about the restrictions of their engine operation.
Notes
Notes
- These assumptions are only valid for Fixed pitch propellers. Further thought and procedures will be required for variable pitch or constant speed propellers.