Author Topic: Tank size and engine run duration. (Read 3288 times)

the original Steve Smith · « **on:** February 27, 2006, 07:24:22 PM »

After flying in my second contest and still not completing an entire pattern because of engine run duration issues, I got a question.

How do you best determine how much fuel to put in the tank? I have two planes, one is an ARF Oriental with a 6oz uniflow tank, the other is a Twister that I recently finished, also with a 6oz uniflow tank. Both planes have OS LA 40s with tongue mufflers (stock muffler is too heavy). The Oriental has a stock LA but the Twister has an LA I got from Lew Woolard. The Oriental is using muffler pressure but the Twister is on uniflow only.

My first contest I just filled the tank and ran over on all my flights (9 or more minutes on each). At the most recent contest I flew the Twister and short tanked it (4 oz or so) but came up short in the duration on both flights - ran out in the vertical 8 on the first flight, had more fuel load in the second flight but ran out in the overhead 8.

What I really need to learn is a procedure that I can use during practice that will help me zone in on the correct amount of fuel to put in the tank so I don't run under or over during a contest. Also I need to learn what effect temperatures have and how to adjust for either low or high temps.

Anyone care to help this old newbie figure this out?

Thanks in advance.

Crist Rigotti · « **Reply #1 on:** February 27, 2006, 09:29:04 PM »

Steve,
Once you have settled on the prop, venturi and such then you can fill the tank and fly it out timing it with a stopwatch. If the engine runs longer than 6 1/2 minutes then on the next flight fill the tank and then with a syringe suck out some fuel say 1/2 oz. Then with your stopwatch time that tank till the engine quits. Keep doing that till you get a 6 1/2 minute engine run. Depending on the lap speed and such you might want to stretch the engine run to 6 3/4 minutes. Typically a 6 1/2 minute engine run will be plenty. Always be sure to fill the tank then remove the amount of fuel you need. This way you always start with a known amount of fuel.

Bill Little · « **Reply #2 on:** February 27, 2006, 09:37:08 PM »

Hi Steve,
No matter what the size tank, I always fill it up completely then pull a measured amount out. You never know if there is any fuel in a metal tank when you go to fill it up, but if you get it full, you WILL know how much you take out.
If you run 9 min. on 6 oz., that works out to 1 1/2 min. per oz. Pulling out 3/4 oz. will give 8 min. But that doesn't count the time you take to start the engine. I have gotten pretty comfortable in knowing that I can start in one or two flips by practice with that eninge set up beforehand. I also like to be on the ground in 6 :45 or so after I give my hand signal for start. (I just don't like going around in circles at the end! LOL!) Next time you go out to practice, time your flights closely. And make sure you are running out of fuel, and it's not a fuel draw problem that is hitting you near the end of the pattern. That's a whole nother ballgame.

Dennis Pedersen · « **Reply #3 on:** February 27, 2006, 10:20:49 PM »

Do you have a proper syringe to measure the fuel going in and coming out?This is the most important part .Carl Shoup makes a nice set up that is cheap and will last forever .This is his number 970-250-8047

Bill Little · « **Reply #4 on:** February 28, 2006, 06:03:52 AM »

Quote from: Dennis P on February 27, 2006, 10:20:49 PM

Do you have a proper syringe to measure the fuel going in and coming out?This is the most important part .Carl Shoup makes a nice set up that is cheap and will last forever .This is his number 970-250-8047

Ditto on Carl's syringe! I got a full set plus an extra "cone". Now I have two great tools in case someone likes one of mine more than I do! LOL!! (be careful, one might grow legs and walk away!)

the original Steve Smith · « **Reply #5 on:** February 28, 2006, 09:08:49 PM »

Thanks guys! This is all really helpful.

I've heard about the fill then remove procedure but didn't understand till now.

I'll work on this and report back.

Louis Rankin · « **Reply #6 on:** February 28, 2006, 10:24:47 PM »

Yes, get several syringes, and thin some epoxy and smear over the numbers. The numbers are not fuel proof and will wear off very quickly.

L0U CRANE · « **Reply #7 on:** March 13, 2006, 04:08:35 PM »

Louis,

Well, we at least spell it right...

Another way to make the syringe markings last is with clear 'Shipping and Mailing Tape' like Scotch sells on the small red dispenser/handles. Do this before letting a new syringe near fuel...

This tape can be rubbed down real well, leaving very small voids around raised lettering, but is otherwise pretty invisible. It might not be fuelproof to long immersion in fuel, but it is slick enough that fuel can be wiped clean before there's damage.

Btw, anyone who needs to measure ether/kerosene-, or gasoline-containing fuel can adapt a typical 60cc syringe to a red (or black) 4 oz fuel bulb by trimmng the 'ears' on the syringe barrel to fit the bulb's groove, intended for the spout cap. Those fuel ingredients do fairly rapid damage to the usual silicone-type plunger caps.

Mike Clark · « **Reply #8 on:** March 15, 2006, 02:34:12 PM »

Hi Guys,
Wavy the LA40's should be fine on a 4 3/4 ounce tank. I fly both the LA & FP 40's and I use a GRW 4.75 ounce tank. So get yourself a fueler and put 4.5 ounces in the tank or change out the tanks and forget the fueler, it's up to you.

I can usually get my pattern plus 8 to 9 laps extra on a bone stock LA, depending on the wind.

the original Steve Smith · « **Reply #9 on:** March 23, 2006, 06:13:18 PM »

Thanks for all the advice. I've had a chance to test a few things and I found the easiest for me was to just put 4.5 oz in the tank. I tried the fill up and remove method but it was not quite working for me.

Now I have another problem: The LA40 runs great on the first flight - 8100rpm on the ground and a good 2/4 break. Second flight < 5 minutes later, same fuel load, same ground rpm (8100) but it leans out in the air and I over run and it flies way too fast. Tried again < 5 minutes after that and had the same result. 4th flight < 5 minutes after that (yah, I was lucky, no one else at the field and my wife was launching for me!) I backed off the needle valve and it ran so rich once in the air that I could hardly make it through the pattern - had to bail on the clover (flying real slow though).

Any ideas? I am using a uniflow tank, tongue muffler, no pressure.

RC Storick · « **Reply #10 on:** March 23, 2006, 06:40:41 PM »

Yeah heres a thought. Call Randy Smith and order a PA.40 lite with header and a pipe, come and get my Viper and bolt it in and go flying. Problem solved.

Joey Mathison 9806 · « **Reply #11 on:** March 23, 2006, 08:15:42 PM »

this is where a flow-meter comes in handy. if your spray bar is restricted due to built up castor it will tell you. if your needle is bent it will tell you. saves alot greef from bad runs.

john e. holliday · « **Reply #12 on:** March 25, 2006, 07:50:22 AM »

Quote from: wavyhill on March 23, 2006, 06:13:18 PM

Thanks for all the advice. I've had a chance to test a few things and I found the easiest for me was to just put 4.5 oz in the tank. I tried the fill up and remove method but it was not quite working for me.

Now I have another problem: The LA40 runs great on the first flight - 8100rpm on the ground and a good 2/4 break. Second flight < 5 minutes later, same fuel load, same ground rpm (8100) but it leans out in the air and I over run and it flies way too fast. Tried again < 5 minutes after that and had the same result. 4th flight < 5 minutes after that (yah, I was lucky, no one else at the field and my wife was launching for me!) I backed off the needle valve and it ran so rich once in the air that I could hardly make it through the pattern - had to bail on the clover (flying real slow though).

Any ideas? I am using a uniflow tank, tongue muffler, no pressure.

I myself have the same problem. Now I try to warm up engine before flight or after first flight I open needle 1 or 2 clicks. Also temperature changes will affect needle setting also. DOC Holliday

Alan Hahn · « **Reply #13 on:** March 25, 2006, 12:46:41 PM »

Steve,
Assuming those run characteristics are everytime you go out, I might suspect an airleak somewhere. On the first flight, the castor/lube gunk leftover from the previous outing probably is sealing. However the fuel through the first run, coupled with sitting warm after may clean out the old gunk. This lets air into the crankcase, giving you a lean run. Check the backplate.

The other possibility is that the engine is very sensitive to temperature, and the first and following flights warm it up, but I don't think so.

Jim Thomerson · « **Reply #14 on:** March 27, 2006, 06:29:52 PM »

What is the shape of your tank? Are you are running the so-called profile tank, higher than wide? I was never able to get them to work right for stunt. Either die before finishing the pattern or overrun, no happy medium. As to your not run the same from flight to flight, probably an air leak in either the engine or the tank.

the original Steve Smith · « **Reply #15 on:** March 30, 2006, 08:22:14 PM »

Thanks again for the insight. I'll be checking for air leaks.

Jim, interestingly I am using the profile tank shape you mentioned. What did you replace it with that worked better? I am intrigued by the "chicken hopper" tank.

Bill Little · « **Reply #16 on:** April 01, 2006, 04:56:03 PM »

Quote from: wavyhill on March 30, 2006, 08:22:14 PM

Thanks again for the insight. I'll be checking for air leaks.

Jim, interestingly I am using the profile tank shape you mentioned. What did you replace it with that worked better? I am intrigued by the "chicken hopper" tank.

Steve,
Did you replace the backplate on the LA? I saw a guy having a lot of problems with his at our last contest because the backplate wouldn't stay tight.
At least put a *little* silicone sealer on the backplate and let it cure if you can't get a metal (Tower or FP 40 )
backplate.

the original Steve Smith · « **Reply #17 on:** April 03, 2006, 09:19:28 PM »

Update!

Flew again this past Saturday. Getting much more consistant runs. Now using fuel from RSM and I am getting 6 to 6.5 minute runs on a full tank (5oz) and about 4.9 to 5.1 sec laps on 62 ft lines.

Tried different props, boy did that make a difference! I switched from an APC 11x6 to a RevUp 11x5 and things just got a lot better. The LA 40 is 4-2-4 most of the pattern but it does speed up a bit either during the square 8s or right after.

Bill, thanks for the suggestion on the back plate, I'll check that out as well.

So many variables - so little time!

Author Topic: Tank size and engine run duration. (Read 3288 times)

the original Steve Smith

Tank size and engine run duration.

Crist Rigotti

Re: Tank size and engine run duration.

Bill Little

Re: Tank size and engine run duration.

Dennis Pedersen

Re: Tank size and engine run duration.

Bill Little

Re: Tank size and engine run duration.

the original Steve Smith

Re: Tank size and engine run duration.

Louis Rankin

Re: Tank size and engine run duration.

L0U CRANE

Re: Tank size and engine run duration.

Mike Clark

Re: Tank size and engine run duration.

the original Steve Smith

Re: Tank size and engine run duration.

RC Storick

Re: Tank size and engine run duration.

Joey Mathison 9806

Re: Tank size and engine run duration.

john e. holliday

Re: Tank size and engine run duration.

Alan Hahn

Re: Tank size and engine run duration.

Jim Thomerson

Re: Tank size and engine run duration.

the original Steve Smith

Re: Tank size and engine run duration.

Bill Little

Re: Tank size and engine run duration.

the original Steve Smith

Re: Tank size and engine run duration.