Old 05-24-2010, 04:52 PM
Join Date: Jun 2009
Location: Caldwell ID
Posts: 214
Default The Vanguard Squadron, 16 plus years of ethanol use
Gary Kuhns, lead pilot of the air show squadron, ?The Vanguards? has info on ethanol use. This is no surprise, they have been practicing and performing in RV-3s all the while running the IO-320 engines on ethanol and all mixtures of ethanol and avgas when flying x-country to and from the show sites. I figure with their 16+ years of ethanol experience, they can provide some insight for my own flex fuel project. In addition, by putting the team?s experiences out here on the board, hopefully it will answer a question that has come up occasionally on the vansairforce boards. What about the Vanguard Squadron? What have they done to the airplanes so they are ethanol compatible?
This posting is based on 3 or 4 conversations I had with Gary during 2010. The last conversation we had, Gary added some clarifications and corrections to the draft I had sent him.
Basics on the Vanguard airplanes
Four similar Rv-3 airplanes, N6GT, N16MR, N19EH, N25RV
IO-320 and wood Sensenich propellors
Fuel system
Like many other early Rv-3s, all four Vanguard airplanes have 24 gallon fuselage tanks. However, two of the four also sport wing tanks giving them impressive fuel capacity. None of the fuel tanks were built using special procedures or unusual materials as the planes were built with avgas in mind. Aerobatics are flown with wing tanks (if present) empty and fuel feeding from a flop tube inside the fuselage tanks. All have a factory type mechanical fuel pump and backup electric pump on the firewall. In order to accommodate the higher fuel flow needed with ethanol, Airflow Performance, Inc has re-calibrated the Bendix fuel injection systems. None of the airplanes have fuel drain sumps or gascolaters, Gary reports they were removed when they realized they weren?t performing any function. There is no separation of water and any particulates are trapped at the screened inlet to the Bendix fuel servo. All four have avgas priming systems for cold starts. They use a small fuel tank, (weed-wacker size) mounted behind the seat to feed the priming system.
I specifically asked Gary if they have had any fuel pump failures or tank sealing problems. He couldn?t recall any, and he asked the rest of the team if they experienced any issues. None. Gary did report Van?s Aircraft advised flop tubes needed inspected for softening/swelling. All four airplanes got the inspection and flop tubes were in good condition.
Engine setup.
All four airplanes now run high compression ratios. Three of the engines had engine work and the 10 to 1 setup by FWF/Demars approximately 20 years ago. Two of those engines are still in use. The third, N16MR got a new engine set up as 10.8 to 1 compression by Central Cylinder, Omaha NE. Gary?s N6GT was for many years just a stock 160 hp 320. The recent rebuild at Central Cylinder utilized the old crankshaft and case, though he reports the case got beefed up. Central Cylinder set his engine up with the custom pistons as well and he is running 10.8 to 1.
All four engines are have inverted oil systems.
Performance.
The team is very happy with the airplanes performance. Gary as formation lead, runs partial throttle throughout the routine, allowing the others to apply power as necessary for positioning. The team appreciates the consistency, smoothness, and reserve power that is available with these airplanes. Gary did not report any detailed performance testing, as they are very happy with how the planes performed, so they haven?t been in a troubleshooting or documentation mode. On Gary?s lead airplane, N6GT, he reported the rebuild shop saw 175 HP on their dyno running avgas. Gary?s estimate of HP while running on ethanol based on climb rates and speed is an additional 10 HP. (probably due to charge cooling, compare the latent heat of ethanol to gasoline, the ethanol is cooling the inlet stream- Stan).
Cold starting on ethanol is a problem. The engines like pre-heaters. The avgas priming system is used when below 50 degrees F. Once the engine is running, the avgas isn?t needed. Gary reported they had trouble finding fuel ethanol near one air show, so they used a local E-85 pump and had no trouble on starting. The 85% ethanol with the 15% gasoline likely provides enough easily vaporizing components for cold starting.
Gary reports no vapor lock issues, though he does caution they don?t have any significant experience at higher altitudes (over 10,000 feet). They don?t spend time up high.
Gary did report that back in 1993, he remembers a short clean out period when the engines were switched from avgas to ethanol. They observed some smoke in the exhaust as the ethanol loosened carbon up and the engine cleaned out.
Fuel composition
Ethanol, but when traveling back and forth to air shows, they will use 100LL as necessary, since that is what is available at fuel stops. Gary suspects they have run on about every possible combination of ethanol and avgas.
**The non-technical, keep it simple folks say, 100% ethanol, but pure ethanol doesn?t exist legally in the US motor fuel market, since gasoline presence is required by law so the liquor taxes continue to flow. The highest ethanol concentration you?ll legally see outside the production plant fence will still have 2 to 5 percent gasoline, and this is what the Vanguard squadron normally consumes, as do folks seeking ethanol out for racing. They find a plant or distributer who will sell the denatured ethanol (Stan?s comment).
Fuel flows
Gary reports approximately 15-20% more fuel flow on ethanol than avgas. The fuel injection system was set up for the higher fuel flow, so when running avgas, operations can easily be over-rich. The pilot compensates with the mixture control but it?s fairly close to the lean edge of the adjustment window. Tractability on avgas is OK if the pilot stays on top of it.
Some comparative fuel burns. Numbers come from the digital flow meter on Gary?s N6GT. Slightly rich of peak at 7500 to 8000 feet 140 to 145 knots, Gary sees about 9.3 gph on ethanol and 8.4-5 on av-gas. Gary?s leaning protocol (fixed pitch), lean until RPM loss, then go rich to gain back RPM, then a touch more rich. Gary observes 350 to 375 F CHT?s in cruise. He is in the cruise ROP camp, so if he observes CHTs approaching 400 F, he adds fuel.
Warning on carbs. Gary reported a carburated engine operator running on ethanol had a fuel stoppage. The operator told him of occasional fuel interruptions as the airplane warmed up (about 20 minutes into operations). The problem was traced to inlet valve seat. Apparently, the fiber seat would swell and cut off fuel flow. The operator reported the seat was replaced with brass and the problem was fixed.
Lastly, I will mention that Poet (previously known as Broin) sponsors the squadron, and if you?ve seen the airplanes or been to their website ethanolairshows.com you?ll already know this. So, the airplanes fly largely because a well known and successful ethanol company has chosen to support their efforts. What that means I don?t know for sure, but given the anti-ethanol aviation landscape, the corporate support is likely the one thing that allowed the ?test? to occur. Who else would have done such a thing? In talking with Gary, it seems pretty simple. I get the sense that they'd been doing this for so long and it has worked so well, that running on ethanol is a non-issue. Interesting, considering all the predictions that have been made on what will happen to gaskets, fuel lines, fuel pumps, and etc.
__________________
Stan
1990 RV-3 (now apart, upgrades in the works)
1959 C172 O-360
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