fuel economy

Hi gang,
Went out flying my Twister OS 35 FPS (Stock) tonight and had the most unusual run. After the engine started and I walked to the handle I started my wrist stopwatch. I flew the plane for 5 min. doing the usual loops, inverted, eights, etc... I then called my 11 year old son out to the circle so he could get a few minutes in ( his U-key 35 OS25 had engine problems due to crud in the spray bar). I figured he would get a 2-3 min flight before the engine would cut. Well his flight went for 6 min and 3 sec before the engine quit, for a total of 11 min 3 sec!!! not counting the time to walk to the handle. Now this is with a 3.75 oz Acme tank. I had seen runs of 8-9 min before but this was just far longer than I thought possible with a tank this size. I am in Colorado at 6000 ft but regardeless, this is incredible fuel economy (isnt it??). Has anyone out there seen fuel economy like this or am I slated for some sort of world record? BTW my son liked the Twister so much he wants to take it over so I better get my partially finished Oriental completed soon
Brian

I had a similar event once. I don't ordinarily time my engine runs. I usually fly the pattern and the count the laps after I finish. I like about 10 laps. The engine was a K&B 4011 on a 4 oz Fox or Veco flat wedge tank, filled to overflow, on muffler pressure. I put up a flight and it went about 15 laps over after the pattern. I tweaked it a hair richer and flew another pattern. After it finished the pattern it ran an additional 68 laps, not sounding particularly overlean, and was not hot when I got to it. I did not touch the needle and immediately put up another flight. It went 10 laps after I finished the pattern. This was very disturbing, but nothing like it has happened again with that or any other engine.

>I had a similar event once.
> I don't ordinarily time
>my engine runs. I
>usually fly the pattern and
>the count the laps after
>I finish. I like
>about 10 laps. The
>engine was a K&B 4011
>on a 4 oz Fox
>or Veco flat wedge tank,
>filled to overflow, on muffler
>pressure. I put up
>a flight and it went
>about 15 laps over after
>the pattern. I tweaked
>it a hair richer and
>flew another pattern. After
>it finished the pattern it
>ran an additional 68 laps,
>not sounding particularly overlean, and
>was not hot when I
>got to it. I
>did not touch the needle
>and immediately put up another
>flight. It went 10
>laps after I finished the
>pattern. This was very disturbing,
>but nothing like it has
>happened again with that or
>any other engine.
>
>Jim

Where's Rod Serling of Twilight Zone when we really, really need him?

I'm humming the theme song right now. Try as I might, I can't characterize it in print here. Currell

>
>Where's Rod Serling of Twilight Zone
>when we really, really need
>him?
>
>I'm humming the theme song right
>now. Try as I might,
>I can't characterize it in
>print here. Currell

"do-do-do-do, do-do-do-do"

Presented for your approval...

An ordinary man, with an ordinary plane, on an ordinary day. Flying the pattern he knows so well. Which he has flown many, many times before. With this same plane. In this same circle.

Only thing is, he's just flown into, the twilight zone.

Observe his behavior, as he clings to the handle for dear life, as his darling obsession threatens to overtake his very existence. The question is, just who is in control?

I'm Rod Serling. For the next 30 minutes, sit back and relax, as we take you on a journey you've never experienced before. The Twilight Zone (ba-ba-ba-ba....)

THis has been happening here as well with both the .40FP and 25 FP. I had a couple of .40 flights that went 10 minutes on 3.0 oz fo 10%. I chalked it up to the very high humidity and temps.

What size venturi are you using? What fuel are you using? What prop? How are you running the engine (rich 4-cycle, rich 2-cycle, etc?)

The "junk in the needle" syndrome could change things for you and definitely change the run, but then you should, also, notice a difference in lap time, etc.

I once had (still do) a modified Magician with a Fox 40 on it. The plane would normally do 6 minute runs on a 4 ounce tank. I was running muffler pressure and the muffler (stock Fox, not good) broke in mid-air, the engine took off like a banshee (however that is) and ran for 15 minutes. I wasn't as fortunate as you, however, in that it did go overlean and destroyed the rod to pin fit which meant needing a new piston/cylinder/rod assembly.

But it was a wild ride, while it lasted.

I've got a Fox 35 running on a 3.25 OZ chickenhopper tank. In the past a normal 4-2-4 run would go about 5 1/2 minutes running on Fox Superfuel. The other day I noticed the runs getting to around 6 1/2 minutes and the engine didn't seem to be going lean. It has been hot and humid here in NE Okla with the heat index running 106-113.

My blush is that it was hot and humid, too. And that you are running a 6 pitch or so prop?

Fairly common behavior to one that is overpropped.... there are all sorts of guys that can "tame" it, but a 35 responds real well to a 4 pitch X ten prop. (I have 10X3 pitch props in my box, too). When it's cool outside, almost anything runs pretty well.

See Ya

More or less stock 40FP's,.265 venturi, in a wet 2 cycle,11/4 Zinger, 62 ft lines, unmuffled,seem to need about 3.5 oz on a Twister sized ship to do full pattern and 10 laps or so. Leonard's 35FP's need a full 4oz on slightly larger ships,big props and 63 ft but it is a real horse compared to a stock 35FP and not a valid comparison. On the stocker, figure about 5.5 minutes on 3.5oz. A lean 2 cycle can add several minutes and definitely cause an over run. Interesting in that I also have noticed longer runs recently as the temp goes over 100 every day with humidity low to moderately high. Anyone have a theory on fuel consumption vs temp/humidity?

Brian,

A lot of possibilities here that can cause the effect you mention. In general if you set the needle and fly a "normal" flight on a cool day and then fly the next flight on a hot day and leave the needle at the last setting you'll have a rich, slower, flight of shorter duration. Here in Oregon I had been practicing in Salem at 600 feet elevation and 77 degrees and then went to Nils contest in Redmond at 3500 feet and 85 degrees. The first flight there was 1 minute and 30 seconds shorter with 6 second lap times (same 6 oz fuel load) 13X5.5 prop. Had to turn in the needle over a turn and use a 13X6 prop to get back to "normal".

Odd runs can be caused by several things. The one I've been running into more often than the past is due to a lot of flights with high % Castor fuel. The exhaust holes in the tongue muffler build up with "crud" and the back pressure on the engine causes it to get more fuel efficient (and also lose power).

Crud in the fuel builds up in the filter and restricts the fuel flow making for leaner longer flights. Two piece fuel filters leak adding air to mix causing leaner longer flights. Splits/cuts in the fuel line at the tank vent leak adding air to the fuel mix causing leaner longer flights. The needle assembly loosens in some manner causing air leaks (loose nut on assembly, loose keeper nut on needle of ST types) Then there is the crud in the needle. Flying over a grass field in the dust and wind of central Oregon left my model covered with grit. Had to hose down the model to get it clean Hate to think about what the inside of the tank looks like.

In general, keep it clean, keep it tight, filter everything going in and going out if you want to have consistency.

Bruce Hunt
Salem, OR

My thought is that if your boy's NVA was clogged with crud, so was yours. As for Bruce's "Dirty Shark", there were a few dust devils that came through that would make anything pretty dirty. Not a bad idea to flush your tank after a weekend in such an area. Also not a bad idea to keep your model in the pit area as short a length of time as possible, or at least keep the nose wrapped in a plastic bag or towel. Somebody wrote in PAMPA about making sleeves for their models out of the chrome mylar bubble wrap type of insulation. Pretty good idea for protection from sun, heat, dust and hanger rash. You could use "hook & loop" tape to make some of the seams open as needed. Steve

Here are the details I should have included in the first post. (Leonard sorry about the confusion but the crud in the NVA was on my boys plane and thats why he was flying mine (OS35). Yours is a great story though...) Anyway it wasnt hot (we dont get too hot here in the springs) about 70 but it had thunderstormed earlier so it was a bit humid. I run 15% Champion fuel, stock venturi (whatever that diameter is) 11x5 zinger prop on 60 ft eye to eye lines. The engine was running a little lean but it wasnt hot at the end and seemed to have reasonalble power (no 4-2-4, didnt think I was supposed to try for that on a OS Schnurle engine, should I?). My sons plane had stuff in the NVA because of a crash the last time out and our failure to flush the system competely. I am pretty careful about filtering the fuel. Anyway if somebody doesnt post a run longer than 11 min on 3.75 oz I guess I get the Walker Cup for longest flight?
Brian

Sorry, but I claim the title. I once ran over for a total time of 18 minutes. This was with a Twin Flight Streak with a pair of OS 20fp's with a total fuel load of just under 6 ounces.

This flight occurred at the Northwest Regionals about 5 years ago. One of the other contestants asked me if the plane was making it's own fuel while in flight. I was sure embarresed.

B Hadley --

One of the best chapters of any book I ever read was from "Flying the Early Jets", and I can't remember the author. Anyway, the chapter was about how test pilots collect and analyze data. It is a good data collection model for all of us, who are test pilots in some sense.

One of the early tests for the pilots was on the AT-6, which had well documented performance. Flying at 100 feet both upwind and downwind, checking instrument accuracy, and keeping the data on a knee board told a story. Flying at other altitudes and attitudes told more. If the performance recorded by the pilot was off much, the test pilot didn't cut it -- either because of faulty data, or poor analysis of density altitude and dew point adjustments, or inconsistent flying.

We should approach analysis and data recording of models with the same rigor that those pioneers used. If we do, there will be fewer surprises. I suspect that looking at the logs of any of the top stunt guys would cause most of us to blanch, if not vomit.