When to boost?

[GR8 8]

I've just recently bought a nice RV 8 with an IO-360 Lyc. I can't find any proceedural info in the POH or standard proceedures flip charts (that cover every other subject) regarding use of the electric boost pump. Most of my time is in high wing airplanes such as C-210 and C-185 when boost pumps are in the picture. I remember flying A-36s where the take-off proceedure includes use of the boost pump. Some POHs require boost pump when in the pattern for any reason.... take0off or landing.

What is standard proceedure? And why?... ie. why not let the electric boost pump ride along unused until the engine shows the first sign of roughness, and then hit the boost pump as a standard reaction to the emergency as in standard proceedure in a high wing fuel injected Cessna?

Thanks for your thoughts guys. This is a great resource for us new-to-RV guys.

[Don]

In my Cherokee, another low wing plane, the POH says to turn the aux. fuel pump on for take off and landing and when switching tanks. I plan to do the same when I finally finish my 9A.

Now as to the logic that arrived at this conclusion, I was told that the reason to have the aux. fuel pump on for T/O and landing is the event your main fuel pump fails you won't have to deal with an engine out at a potentially busy time. It was never clear to me why you turn it on when switching tanks but I have noticed in really hot weather the fuel pressure has dropped noticably when I turned the aux. pump off after switching tanks. My guess is there must be some vapor lock potential, but I don't know why. One evening when the temps were running about 105 I noticed the pressure stayed down for what seemed like an eternity (probably a minute and maybe more in reality). The engine never hiccuped but I was ready to flip the pump back on if it did.

[westwinds]

Gr8 8, I would suggest you use the boost pump during takeoff and landing phase of flight when you are below an altitude that will allow safe return to the airport. RVs are low wing planes and you will have no gravity fuel feed pressure like you can get with the high wing Cessna aircraft. If you lose an engine driven fuel pump right at take off, will you get fuel pressure back quickly enough when you turn the boost pump on at a first indication of trouble? I fly a Piper Comanche 250 which is a low wing carbureted 0-540. I always use the backup electrical pumps on takeoff and landings. I turn it off at 500' and then watch fuel pressure for a few seconds. Especially so in hot temps. Make sure you remember to turn off the electrical pump as soon as you get to a safe altitude. In my Comanche continued use of the electrical pump in hot weather can actually lead to vapor locking in the mechanical fuel pump because these pumps are not in series as they are in a RV. So the fuel actually gets routed around the engine pump so it no longer gets cooled by fuel. Bottom line, I will use the electrical pump on my RV8 during takeoff and landings. Hope this helps, Tony

[GR8 8]

Thanks guys, This does make sense. I am more familiar with the Continental continuous flow systems than the Bendix system on the Lycs. I had a PA 24-260B for many years, but never looked at a fuel flow schematic. I hadn't considered the cooling effect that flow has on fuel. I'll plan to boost while in the pattern, or when switching tanks. I always ran the tanks dry in the Comanchee, but the engine was not nearly as fast to come back up to power as with a Continental system. It took several seconds to smooth out and be back on line. I switched tanks, hit boost, and reduced throttle in that order until I had smooth power again. The Continental is almost instantly powered up and smooth after running dry.

I am a little surprised that this isn't in my POH, as it is otherwize very complete and well done. THanks for your help.

[RV6_flyer]

Try this link for Lycoming recommendations on boost pump use.

[pierre smith]

Originally Posted by GR8 8

I always ran the tanks dry in the Comanchee, but the engine was not nearly as fast to come back up to power as with a Continental system.

Guys,
It's a bad habit to run the tanks dry for several reasons. At the higher altitudes where these little rockets are so happy, the temps are down. The thermal shock from a sudden shutdown can wreak havoc with your cylinders, especially the front ones when cold air hits them.

A Bonanza swallowed a turbocharger blade over the mountains on the way to Tahoe after the pilot ran it dry in the winter, lunching a cylinder. I can see doing this if fuel is critical to getting to your destination but not under normal circumstances.

Be careful

[wv4i]

The boost pump in my carb RV-6 makes a lot more racket when it cavitates. From that point, you have at least 20-30 seconds to switch tanks without flameout. Obviously n/a for a FI engine. There are various reasons you may want to intentionally let this happen. N/w, the likely detrimental effect of a sudden shutdown, shock cooling, is a point well taken, not to mention having the big fan stop in flight.

[GR8 8]

There are a number of reasons why you would want to be carefull about running a tank dry, but some equally good reasons to do so as well. If you don't have a fuel totalizer you trust, and you have changed power settings numerous times as in when climbing and desscending for Wx, you easily loose track of the fuel used or remaining. If you want to know with certainty how much fuel remains... not how much you calculate is remaining, but to absolutly KNOW.. that is when one tank is full, and one is empty. You have half fuel. This tells you two things you wouldn't know without emptying a tank, (1) what your actual fuel burn has been to this point in the trip (you otherwise only hope you guessed right), and (2) What you can reasonably expect to get out of the other tank. Based on #1, you can make or adjust the flight plan and KNOW you are making a decision based on facts instead of conjecture. I've seen many pilots get well into a flight and then have to change a plan, only to panic because fuel was getting low and they didn;t know exactly how much was left. You can't make a good decision if you don't know how much fuel you have on board. FLy within your limits, and don't push it if you don't feel comfortable. But if you want all the options open to you at the second half of the flight, I think you have to make plans during the first half of the flight.

[johnp]

when i first got my 310 i had both aux tank bladders replaced. in the 310, the tip tanks are the mains (50 gal each) and the wing tanks are the aux's (15 gal each). the continental 470's injection system pumps more fuel than is required by the injectors, and the excess is returned to the main tank (on each side). at 75% power, the 470's burn about 15 gph each, so if you didn't know about the scavenge/return system you would think that you could get about an hour on the aux's. in reality, you would start on the mains, burn at least 45 minutes before switching to the aux's (to allow room in the mains to receive the fuel returned by the injection system.) the aux's would then run dry after about 32 minutes +/- 1 minute (in my plane). i used to offset the switching from mains to aux's by 5-10 minutes (left vs right), so they both wouldn't go off-line at the same time. but i routinely ran the aux's dry and never worried about it. after all, i had new bladders, so the likelihood of trash in the fuel was less.