Hi all.  I was looking through a bunch of plans on the internet and saw that almost all of them have an inverted engine.  Personally I hate inverted engines because of the starting problems, etc.  Why are most planes desighned with the inverted engine instead of the upright?  Is there an advantage other than looks?  And if I wanted to build a plane that is designed with an inverted, but put in an upright, can I just drop the bearers to accomodate it?  Or are there other factors I don't understand?

Huh?  Why is it far easier to start them inverted?  I always have to flip mine over and that can be a problem cause I uauall fly alone.

Huh?  Why is it far easier to start them inverted?  I always have to flip mine over and that can be a problem cause I uauall fly alone.

   Because it's almost impossible to flood them from choking. What happens with uprights, many times, is that if you choke them enough to get fuel into the cylinder, there's too much fuel in the crankcase. When it pops, it sucks all the fuel out of the case, and kills it rich. Inverted, the issue is usually getting enough fuel in them by choking, since it tends to run out on the ground if you remove your finger.

    Technique is everything. You have to work it out for each engine, but it's something along the lines of this:

      1 Fill tank, put finger over venturi, pull through 3-4 times. This gets fuel up to the venturi.
      2 Flip through forward as you remove your finger from the venturi. The idea is to remove your finger as the engine is sucking in air, so it will suck in the fuel now in the venturi
     3 Flip through forward 3-4 times to aerate the charge and get clean fuel and clean air in the cylinder. Once you know what to listen for as you flip it, you will be able to hear whether or not there is sufficient fuel. If not, pull through again, flip forwards some more until it sounds right.
       4 WHILE HOLDING THE PROP, attach the battery.
       5  Back-bump up against compression. Don't flip through backwards, just sling it backwards so it comes up on compression smartly when your finger is off the prop. You don't have to whack it hard, for most current engines just twisting the spinner is sufficient. Repeat if necessary. Your finger should be off the prop when it hits compression.
       6 Engine will likely start
        7 If it doesn't problem is likely not enough fuel, pull it through some more.

     More choking will be required on the first run of the day, or when it is cold. If the engine is still warm from previous flight, it may require no choking depending on which engine it is. It's very hard to over-choke it but if you do, remove battery, pull it up on compression, hold it, then turn the airplane with the exhaust port facing down, and then release the compression and rock it back and forth. This will remove excess fuel. Then put it back on its feet, attach the battery, and back-bump, should take off in a few tries. It takes more fuel to start with a back-bump than it does with a forward flip through.

      If the engine is hot and you over-choke it, it can get "shrinky piston syndrome" when cold fuel sloshes on the back of the piston and shrinks it, but not the cylinder, and the compression goes away.  The solution is to flip it forward through compression many times to distribute the fuel and heat evenly, and the compression will come back.

      Note that someone should hold the airplane ALL THE TIME when the engine is being choked, etc. With any current AAC/ABC engine there is a real chance that it will kick or start without the battery. Particularly if you get your choking technique just right, it will have a perfect mixture and start very easily. I have had them start from merely rocking back on compression from the weight of the piston. It's more prone to happen when it's really hot* but could happen anytime.

     Very occasionally, with low-compression engines and when it is hot, conventional flipping will be required. There's also an advanced technique that involves flipping through compression forward while simultaneously holding your finger over the venturi, and then removing it as the engine starts. I have had to do that occasionally on my tired 40VF on back-to-back runs.

   With piped engines, you have to get the oil that has run down into the engine from the pipe out of them on the first run of the day, and in that case I do usually flip them upside down and *prime* them (not choke).

   Brett

*at the 1993 NATs in Lawrenceville, it was brutally hot all week, and my 40VF started without the battery repeatedly at step 2 or 3 above - I mean just about every time, including my official flights. The first time it happened, Ted was impressed that I was able to get my fingers on the spinner fast enough to stop it before it got to full crank. After that I signalled before I started and got it going while I was on the clock.

I pretty much do what Brett said.  I have been flying a Fox 35 upright and done it enough that I usually got one flip starts.  The last time I flew it at the VSC, early in the morning, I primed it extra heavy because of the cold.  It started backwards three times before it cleared out enough to start forward.  I was running a heavy hub and had a heavy leather starting glove on, so I stopped it by grasping the heavy hub.  I do not advise this practice. 

    The "fist on the spinner" trick I mentioned above is NOT RECOMMENDED, either, because if you wait the 2 seconds it takes to hit full speed and then try it, all you get is your skin ripped/burned off from the friction.

     For inverted Foxes I got dead-nuts reliable starts with a completely different technique than above. For the Fox, it was attach the battery, pull through with finger over venturi until I got one "bump", then remove finger and flip through forward. That worked hot, cold, anytime.

     On upright Foxes I never mastered a one-flip start, but as long as I prime it and then start flipping pretty quickly I can usually get it going in a few flips. Choking more than once seems to be the kiss of death. I have no end of trouble starting engines on the test stand because of the fuel going into the crankcase.

      Brett

On inverted Fox 35's what works for me is to choke and pull the prop to bring the piston to TDC, and then release my finger while pulling the prop on through. About three of these on a cold engine seems to be about right. You can hear the engine suck in fuel when you remove your finger. Pretty much the same as what Brett said. I think Marvin Denny is the one that taught me this trick.

On my upright Anderson Spitfires on ignition, I rock the prop back to where the shaft valve is closed, fill the venture full of fuel, and flip about six times. Turn on the switch and it will generally start on the first flip. When the temp drops below 60 deg. things can change and I usually give an exhaust prime. Ignition engines get a bit fussy when the temps are cool, and it is easy to foul the plug with oil. Mine generally start better on gasoline in cool weather instead of fuel.