April, 07
Our RV-12 Proof-of-Concept prototype N912VA has flown about sixty hours now. That may not seem like a lot, but when you consider almost all it has been in real-world flight test, you can see that it?s had the opportunity to teach us quite a bit.
Here?s some updates on our progress so far, with notes on various aspects of the airplane:
ROTAX 912S ENGINE-CARE AND FEEDING THEREOF
The RV-12 is our first experience installing, operating, and servicing the 100 hp Rotax 912 engine. Being a liquid cooled, high RPM, geared engine, it is quite different than the Continental and Lycoming engines.
Installation was more challenging than a Lycoming because the engine has two carburetors, a separate oil tank, and two heat exchangers; the coolant radiator and the oil cooler. On the plus side, with liquid cooled cylinder heads, no baffles other than a shroud for the inner fins of the cylinders are needed.
We mounted the heat exchangers vertically in the lower forward cowl, under the spinner, and fed them air through a single horizontal oval inlet. Mounting them to the cowl isolates them from engine vibration and provides an excellent seal, so no air is lost through duct connections or relative motion between the cowl opening and the coolers. There are also two small round inlets near the spinner which provide air to the carburetors and cool the inboard portion of the cylinders. They have worked very well in keeping the cylinder head temperatures cool.
The oil cooler has worked too well in the cool ambient temperatures we?ve experienced testing in autumn and winter. Rotax specifies that engine RPM should not exceed 2500 (the Rotax idles at 1200 rpm and red line is 5800 RPM, so 2500 rpm is still low power) until oil temps reach 120 deg. F. This has caused long run-up times before take-off.
Operating the Rotax is a very pleasant experience. The Bing carbs are equipped with chokes for starting rather than primers (older drivers will remember chokes; they were common way back when cars had carburetors.) They also feature automatic mixture compensation for altitude changes, so there is no mixture control in the cockpit. The engine starts easier than either a carbureted or fuel injected Lycoming. It is smooth and quiet, both on ground and in flight.
Fuel consumption is obviously lower than other RVs because of the low power of the engine. However, despite magazine writers like to rhapsodize about how the Rotax "sips" fuel, its consumption (in our experience and from Rotax charts), is consistent with other aircraft engines of similar power. Its Specific Fuel Consumption (bsfc) is similar to Lycoming and Continental engines, so at rated 75% power, it burns about 5.8 GPH. Figures like "3.5 to 4.5 gph" are often quoted in flight reports, but these can only be achieved by using less than 75% power and should be noted as "economy cruise consumption" figures.
HANDLING QUALITIES
The full span flaperons provide brisk roll control, similar in roll rate to an RV-9. Initially, stick forces required were very light, so we tailored the flaperon trailing edges to provide a pleasant stick force level. During the design phase, we worried about possible adverse yaw when the flaperons were lowered into the flap positions. Testing revealed that adverse yaw is minimal and easily coordinated with light rudder pressure.
The new (to us) stabilator has proven to provide good pitch control, pitch stick force, and damping. The RV-12 has an electric pitch trim which repositions the large anti-servo tab on the stabilator trailing edge. The trim rate is moderately slow, with no tendency for over-control.
Stall characteristics are good. Tail surface buffeting several mph above stall speed provides ample warning. The nose pitches down when the full stall is reached, and flight control is regained almost instantly when stick backforce is released. In an aggravated stall when the stick is held back through out the actual stall, one wing or the other will drop as much as 30 degrees.
We contracted with a professional test pilot to explore the spin characteristics of the RV-12. The results were very encouraging. Spin entry and recovery was found to be normal and predictable. Good rudder control authority was found both during spin entry and recovery. The RV-12 tail configuration, with the vertical surfaces positioned forward of the horizontal surfaces, provides minimal blanking of the rudder in all conceivable pitch attitudes. Recovery from 1-turn spins was achieved in less than ? turn following anti-spin control application.
PERFORMANCE
Strange as it may seem, we have not expended a lot of effort on measuring the RV-12 performance. We measured enough to realize that the performance was "good", and then concentrated on stall speed, stability, controllability, weight and balance, and other such issues. Here are some basic numbers:
Cruise Speed (75% power @8,000?) 118 kts.
Climb rate: 1320 lbs. gross wt. 750 fpm
Climb rate: (solo, 1000 lbs) 1100 fpm
Stall speed: @ 1320 lbs. 50 kts
STALL SPEED
Stall speed has been one of the tougher nuts to crack, and the focus of much of our test flying. Initial testing showed that the RV-12 no-flap stall speed was higher than 45 knots required by the rules of the Light Sport category.
We experimented fairly extensively with corrective measures. We tried vortex generators in many configurations and placements. We even made full-span leading edge cuffs that increased the camber of the wing. Neither improved the stall speed -- and just to make things more frustrating, the cuffs actually reduced the cruise speed.
Airflow tuft testing of the airframe showed undesirable flow under some conditions at the wing root/fuselage intersection -- not unusual for low wing airplanes. We devoted considerable time and effort installing and testing various wing root filets in an attempt to improve lift in this region and thus lower stall speed. The airflow was improved somewhat, but there was no measurable improvement in stall speed.
IN THE (NEAR) FUTURE:
Work is underway to design and build a new KIT PROTOTYPE airframe (as opposed to the PROOF OF CONCEPT PROTOTYPE described above).
Our best projection is that the new Kit Prototype RV-12 should be ready to fly late in the third quarter of 2007. Kit availability will depend upon the test flight findings of that aircraft and on our ability to initiate component production both in-house and from our suppliers. We hope to have at least partial kits available in the fourth quarter of 2007 or the first quarter of 2008.
Our RV-12 Proof-of-Concept prototype N912VA has flown about sixty hours now. That may not seem like a lot, but when you consider almost all it has been in real-world flight test, you can see that it?s had the opportunity to teach us quite a bit.
Here?s some updates on our progress so far, with notes on various aspects of the airplane:
ROTAX 912S ENGINE-CARE AND FEEDING THEREOF
The RV-12 is our first experience installing, operating, and servicing the 100 hp Rotax 912 engine. Being a liquid cooled, high RPM, geared engine, it is quite different than the Continental and Lycoming engines.
Installation was more challenging than a Lycoming because the engine has two carburetors, a separate oil tank, and two heat exchangers; the coolant radiator and the oil cooler. On the plus side, with liquid cooled cylinder heads, no baffles other than a shroud for the inner fins of the cylinders are needed.
We mounted the heat exchangers vertically in the lower forward cowl, under the spinner, and fed them air through a single horizontal oval inlet. Mounting them to the cowl isolates them from engine vibration and provides an excellent seal, so no air is lost through duct connections or relative motion between the cowl opening and the coolers. There are also two small round inlets near the spinner which provide air to the carburetors and cool the inboard portion of the cylinders. They have worked very well in keeping the cylinder head temperatures cool.
The oil cooler has worked too well in the cool ambient temperatures we?ve experienced testing in autumn and winter. Rotax specifies that engine RPM should not exceed 2500 (the Rotax idles at 1200 rpm and red line is 5800 RPM, so 2500 rpm is still low power) until oil temps reach 120 deg. F. This has caused long run-up times before take-off.
Operating the Rotax is a very pleasant experience. The Bing carbs are equipped with chokes for starting rather than primers (older drivers will remember chokes; they were common way back when cars had carburetors.) They also feature automatic mixture compensation for altitude changes, so there is no mixture control in the cockpit. The engine starts easier than either a carbureted or fuel injected Lycoming. It is smooth and quiet, both on ground and in flight.
Fuel consumption is obviously lower than other RVs because of the low power of the engine. However, despite magazine writers like to rhapsodize about how the Rotax "sips" fuel, its consumption (in our experience and from Rotax charts), is consistent with other aircraft engines of similar power. Its Specific Fuel Consumption (bsfc) is similar to Lycoming and Continental engines, so at rated 75% power, it burns about 5.8 GPH. Figures like "3.5 to 4.5 gph" are often quoted in flight reports, but these can only be achieved by using less than 75% power and should be noted as "economy cruise consumption" figures.
HANDLING QUALITIES
The full span flaperons provide brisk roll control, similar in roll rate to an RV-9. Initially, stick forces required were very light, so we tailored the flaperon trailing edges to provide a pleasant stick force level. During the design phase, we worried about possible adverse yaw when the flaperons were lowered into the flap positions. Testing revealed that adverse yaw is minimal and easily coordinated with light rudder pressure.
The new (to us) stabilator has proven to provide good pitch control, pitch stick force, and damping. The RV-12 has an electric pitch trim which repositions the large anti-servo tab on the stabilator trailing edge. The trim rate is moderately slow, with no tendency for over-control.
Stall characteristics are good. Tail surface buffeting several mph above stall speed provides ample warning. The nose pitches down when the full stall is reached, and flight control is regained almost instantly when stick backforce is released. In an aggravated stall when the stick is held back through out the actual stall, one wing or the other will drop as much as 30 degrees.
We contracted with a professional test pilot to explore the spin characteristics of the RV-12. The results were very encouraging. Spin entry and recovery was found to be normal and predictable. Good rudder control authority was found both during spin entry and recovery. The RV-12 tail configuration, with the vertical surfaces positioned forward of the horizontal surfaces, provides minimal blanking of the rudder in all conceivable pitch attitudes. Recovery from 1-turn spins was achieved in less than ? turn following anti-spin control application.
PERFORMANCE
Strange as it may seem, we have not expended a lot of effort on measuring the RV-12 performance. We measured enough to realize that the performance was "good", and then concentrated on stall speed, stability, controllability, weight and balance, and other such issues. Here are some basic numbers:
Cruise Speed (75% power @8,000?) 118 kts.
Climb rate: 1320 lbs. gross wt. 750 fpm
Climb rate: (solo, 1000 lbs) 1100 fpm
Stall speed: @ 1320 lbs. 50 kts
STALL SPEED
Stall speed has been one of the tougher nuts to crack, and the focus of much of our test flying. Initial testing showed that the RV-12 no-flap stall speed was higher than 45 knots required by the rules of the Light Sport category.
We experimented fairly extensively with corrective measures. We tried vortex generators in many configurations and placements. We even made full-span leading edge cuffs that increased the camber of the wing. Neither improved the stall speed -- and just to make things more frustrating, the cuffs actually reduced the cruise speed.
Airflow tuft testing of the airframe showed undesirable flow under some conditions at the wing root/fuselage intersection -- not unusual for low wing airplanes. We devoted considerable time and effort installing and testing various wing root filets in an attempt to improve lift in this region and thus lower stall speed. The airflow was improved somewhat, but there was no measurable improvement in stall speed.
IN THE (NEAR) FUTURE:
Work is underway to design and build a new KIT PROTOTYPE airframe (as opposed to the PROOF OF CONCEPT PROTOTYPE described above).
- It will have an improved wing with a different airfoil and more area.
- We found we could improve the CG by moving the engine forward. At least two good things came out of this: improved access to the back of the engine and about 2 more inches of legroom in the cabin.
- The canopy on N912VA has never been a beauty point. It was built with some plexiglass canopy halves left over from an earlier project. The kit prototype will feature a much more attractive 1-piece blown canopy with additional headroom, designed specifically for the RV-12.
Our best projection is that the new Kit Prototype RV-12 should be ready to fly late in the third quarter of 2007. Kit availability will depend upon the test flight findings of that aircraft and on our ability to initiate component production both in-house and from our suppliers. We hope to have at least partial kits available in the fourth quarter of 2007 or the first quarter of 2008.
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