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[Ty Marcucci]

 

[Howard Rush]

Another lesson is that engine run time is not a function of humidity.

[john e. holliday]

I had that problem with my blue LA 40 & 46.   First flight was great or close after adjusting the needle.   If I didn't adjust the needle the flight was a little lean.   So I learned with those two engine not to touch the needle until the second flight.   Usually by then all was back to normal.   Seldom had that problem with the silver LA's.

[Douglas Ames]

Different location, different Density Altitude for the day.
Wonder if you got a bad spinner? Made on a Monday...

[dennis lipsett]

This thread is mostly for Intermediates and Begginners.   I have a 660 Cavalier that flys very niclely, when I concentrate. But with a T&L ST .46 in it, it tended to use a lot of fuel. So I installed a 5 oz tank and it would use the entire tank for the full pattern and about 7 or so laps after the 4 leaf. So far, so good, but on several occassions the second flight it would go rich and I'd have to fly out the pattern in level flight. Bummer.  I found my engine was just loose enough to set up lots of vibrations. Found one of the "blind nuts" had torn from the mototr mount. Got out the tools, replaced all four "blind nuts", flew a nice pattern. Second flight it got rich again, so I decided, finally, to check the alleged balanced prop.  Seems it had got out of balance, not much, but it does not take much. Rebalanced the prop, then I stared at the true culprit. The long, 2 inch needle nose spinner. I had "assumed" it was balanced as I have never had any, to my knowledge, problems with them other than fitting them. HA, it was so out of balance I'm surprised the engine even ran. Got it, prop and every thing all ship shape, went to Paducah, filled the tank, with 98% humidity, bad move and flew a nice 10:10 flight. No pattern points, no landing points and a great last place finish. Moral. BALANCE everything. Adjust fuel load to humidity. Do more than one test flight. Lesson relearned. 

Ty,
there is another option. Go electric set the timer and that problem is taken care of. Then adjust rpm for what you need at that field. Never mind that I don't fly electric yet but after 60 years I'm going to finally have a clean car.

Dennis

[Hoss Cain]

Another lesson is that engine run time is not a function of humidity.

Mr. Rush, I recognize you as the supreme expert in engine function/s.

OTOH I disagree with you about humidity not effecting engine run time.  Cold Dry days will need adjustment versus a HOT muggy day.
BTDT many times. Even back in my CL days there were slight differences. Especially so now in current RC flying, here in the Houston, TX humidity and hot, versus winter rather cool and sometimes low humid.

[Howard Rush]

OTOH I disagree with you about humidity not effecting engine run time.

Actually, I disagree with myself.  See http://stunthanger.com/smf/index.php/topic,22408.50.html .  I think the main effect you see is from temperature, though.  Humidity does a little, but not much.  Did the tables my homeboys made for you to fly your 727 include humidity?

[bob whitney]

Electric not  cure all  i installed a Brand name electric spinner on my profile and almost shook the motor off, installed a stubby home made carbon spinner and all is good

[Howard Rush]

Howard,  humidity does affect engine run times. I have always had longer runs in high humidity, hot or cold air. Not sure about jets and couldn't care less. I run IC methanol engines.  More water in the air, more oxygen from burning water vapor, leaner runs. It does not take much to extend a flight by one minute. Been there dozens of times. Not in the cooler NW but deep south. Come on down and I'll prove it.

You think that your engine runs longer because it takes oxygen from the water in the air?  I assume you have it fitted with a device from the J. C. Whitney catalog.

[Motorman]

Mr. Rush, I recognize you as the supreme expert in engine function/s.

Or maybe just a guy who wears a clown suit. hmm, then again I fly a clown plane.

Humidity does something but if you crunch the numbers you'll see it's nothing compared with air density.

MM

[Steve Helmick]

Or maybe just a guy who wears a clown suit. hmm, then again I fly a clown plane.

Humidity does something but if you crunch the numbers you'll see it's nothing compared with air density.

MM

Howard only wears the shoes, nowdays. Whatever works! 

I see about 1/4 turn on the (Randy Aero) NV between morning and afternoon. I don't understand how guys can get away with starting the engine, giving it the evil eye and walking out to the handel (sic). It's 200-300 rpm. I've seen a lot of guys start the engine, quickly adjust until it sounds good, and walk to the handle. By the time they're ready to launch, the rpm has dropped 300 rpm because the engine has warmed up.

I get mine warmed up by either blocking the uniflow inlet or pinching off the muffler pressure tube until the engine is (at least) peaked, then let it drop to wherever it's set, and repeat one more time. Helps to heat it up quicker. When I get it to where it drops to the correct launch rpm, I'm off to the pilot's circle.  Steve

[Brett Buck]

You think that your engine runs longer because it takes oxygen from the water in the air?  I assume you have it fitted with a device from the J. C. Whitney catalog.

   I put everything from the JC Whitney catalog on my Volkswagen, but I didn't get 10,060% more horsepower. Why is that?

      Brett

[Howard Rush]

Density altitude I understand.  

Then show us your calculation.  I don't think you do.  I did some work and put it in the reference.  Now you do some work.  Tell us how you get the same benefit of water evaporating with water that's already evaporated. 

[Lauri Malila]

When relative humidity is high, the engine gives less power and to be able to fly fast enough you've got to run it leaner (with same venturi) which explains your longer running time. In a foggy morning, or after a rain shower on a warm summer day, relative humidity is low and air density is high. Then you get more power.
L

[Paul Smith]

All this scientific theory comes down to an analog needle valve with no calibration whatsoever.

I'm tweaking the needle all day and always have.  I think the fuel jug sitting in the sun, warming up, and reducing the viscosity of the oil is somehow involved, but I do not have a doctorate from Stanford to back it up.

I have few years experience with jet engines.  Unlike piston engines, jets do not operate on a precise air/fuel mixture.  Rather, they always run massively over lean, so additional fuel is able to combine with a small part at the exess air and make more power, heat, and pressure and maybe blow the thing up if you're not careful.  Water turns to steam and boosts jet thrust.

[Ward Van Duzer]

Howard, Ty is right (at least about Huntersville, NC). That place caused me more over-run grief during my competitive days than any place I've ever flown!

W.   

[Hoss Cain]

Actually, I disagree with myself.  See http://stunthanger.com/smf/index.php/topic,22408.50.html .  I think the main effect you see is from temperature, though.  Humidity does a little, but not much.  Did the tables my homeboys made for you to fly your 727 include humidity?

HA HA, good one.    Not to my knowledge. No knowledge of such in either of 727, 737, DC-8, DC-10. However some bird strikes, freezing rain,
lightening strikes, ETC, did get my attention during the total 15 years military (included reserve) and 28 years civil. Military, T-29, T-33 (not much in the T-33, beautiful slow machine) C-123 ( but that was P&W R-2800 and some humidity at times kept the pilots a tad busy) B-47 (NO PROBLEMS)
T-37 was no problem, but when I was an instructor in the T-38, all one had to do  on ground with canopy open, just whisper
ICE and it foundered big time.     One day went through some low rain showers to try to get a student qualified solo. (Bad Choice)
Called the operators of the practice field and they were getting ready to close shop. Made a traffic pattern, but told "No Touchdowns" so student made a low go and started a go-around. Then BAM, on #1, compressor stall, fire about 10 feet out, and #2 shut down. Probably had a bit of ice on the inlets. I took control and got a restart on #2. Went to home field and landed. So humidity of some kind did something. HA!