First Flight Since Rebuild

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myles-dean

Well-Known Member
Joined
Mar 18, 2013
Messages
101
Location
Stonewall, Manitoba, Canada
Well after what seems like years and years of slow progress, there was finally a first flight!
https://cloud.macdon.com/index.php/s/KshCyvPqHu8Mq9f (Video is too large to upload - please let me know if the link doesn't work for you).


Overall it was a success as it took off and landed in one piece but I am looking for some feedback regarding performance as the flight only lasted one circuit.
Could not get over 70 mph and most of the circuit was done at 65 mph.... way too slow!

Conditions:
Sunny, approx. 80° F, slight wind 020° (1-2 kts maybe).
Runway altitude: 780 ft.
Pressure altitude: 2500 ft.
Runway: 2300 ft. long grass (approx. 5-7" deep - really needing a cut!) running 090-270°
Engine: 1835cc Aero-Vee - no starter, hand-prop only
Static RPM: 3100 with Slick mag
Prop: 53x42 wooden
Fuel: 100LL (no fuel pump)
Pre-rebuild hours on engine/prop/airframe: 69.7
Pilot flying: 22,000+ hours (retired airline, actively flies Ag spray aircraft, Harvard & RV-8)

I will start at the beginning of the evening:
After the new Aeroinjector was installed a couple of weeks ago, the engine would always start on the 3rd pull.
Have started it a dozen times and always starts on 3rd pull when cold.
Fuel level was a little low for a test flight, so I filled the fuel tank right full.
I actually over-filled, as there was some fuel coming out the overflow tube which goes in front of the landing gear.
This time when I went to cold start the engine, I propped and propped and propped until I literally had blisters.... not even a pop or backfire.
Tried multiple things but nothing worked.
I then wondered about the fuel tank, so I opened the fuel cap and instantly heard a suction release.
I kept the cap off and flipped the propeller and it instantly fired! Thankfully it didn't run long as fuel started spraying back toward my friend who was sitting in the seat.

I then had a young guy stand close to the wing on the right side, holding the fuel cap just slightly about the fill neck (to stop any fuel spray).
Completed a normal cold start prime and it fired on the 3rd pull.
Put the cap on and engine continued to run with no problems.

I offered to drain a bit of fuel but my friend planned to taxi down the runway a couple of times to burn off some fuel instead.
I followed along with a quad and he taxied with no hesitations.
I'm guessing he figured that everything was ok, so when he turned around, he went full throttle and departed on 090.

He used up about 2/3 of the runway before getting off the ground in around 65 mph.
From that point he climbed as best as he could but the airspeed never increased.
On downwind he stated that airspeed went up to around 70 but never beyond.
RPM's were around 3100 the whole time.
From the ground I could see that he plane was plowing through the air.
He landed and was quite shaken by the fact it wouldn't build speed.
Once he taxied in and shutdown, I opened the fuel cap but there was no suction.

I have since triple checked the engine over.
Compression: 115-120 psi on all cylinders.
Spark plugs are tan after 3 minutes full rich full throttle static run.

I have 2 thoughts about what happened:
1) fuel starvation due to fuel being in the overflow with a full tank (similar to when it wouldn't start)
2) he was behind the power curve the whole time

After checking the engine and confirming everything is good and watching some YouTube videos, I am thinking that he should have sped up in ground effect before climbing.

Has anyone experienced issues with density altitude, too full of a fuel tank?
Any suggestions before we try to take it up again?

Thinking of taking it to a close long hard-top runway or a wider longer grass strip.

Sorry for the long message but just trying to make sure I have all the facts.

Regards,
Myles
 

ThePipster

New Member
Joined
Oct 21, 2016
Messages
2
Hello Myles,

Just some thoughts which may help.

From the video the exhaust note sounds like the engine is being a bit choked, what is the air filter / exhaust setup?

Whilst the climb out was a bit anemic, it didn’t look to be a very high angle of attack, are you sure the pitot / static system is working properly or could the asi be lying?

What was / is the elevator trim situation? Is it possible that the tailplane is out of trim / incorrect incidence and the drag is adding to other performance problems?

Sadly fuel system issues are a factor in a number of serious and fatal homebuilt aircraft crashes, even if this isn’t the cause of the poor performance, it needs to be fixed before further flight.

Best regards

Phil
 

eschrom

Well-Known Member
Joined
Jan 18, 2006
Messages
799
Location
Manchester, PA
I don't see how there can be any fuel starvation if the engine is making 3100 rpm and by the time he turned downwind the speed appeared to be higher than 70 (just a guess). Are you sure the ASI is functioning correctly?

Ed
 

myles-dean

Well-Known Member
Joined
Mar 18, 2013
Messages
101
Location
Stonewall, Manitoba, Canada
Hi Phil,

The air inlet side of things is an automotive K&N air filter with a carb heat option.
This picture shows the original POSA carb but the air system hasn't changed.

1593345950398.png


I am not positive about the ASI readings but from watching the flying attitude, I think it is close to correct.
It seemed like it was tail low the whole flight.

I have made up an adjustable trim for the horizontal stabilizer and had it set in a neutral position.
From what my friend said, he wasn't fighting the stick for pitch.... but he could have adjusted it if he was fighting it.

My game plan going forward is to replace all fuel lines.
I really don't think they are an issue but for what they're worth... best take them out of the equation.

Thanks for your thoughts on this!

Myles
 

myles-dean

Well-Known Member
Joined
Mar 18, 2013
Messages
101
Location
Stonewall, Manitoba, Canada
It is a strange scenario where the engine has good rpm's but no apparent power.
I have an article on how to calibrate the ASI.... I will plan to verify soon, just for piece of mind.

I don't see how there can be any fuel starvation if the engine is making 3100 rpm and by the time he turned downwind the speed appeared to be higher than 70 (just a guess). Are you sure the ASI is functioning correctly?

Ed
 

eschrom

Well-Known Member
Joined
Jan 18, 2006
Messages
799
Location
Manchester, PA
The prop determines how much power the engine is making. To turn it 3100 rpm requires a certain amount of power and either the engine can make that much or not. If not, it won't turn at 3100. But maybe your 53 x 42 requires more than 3100 to make enough thrust to pull the airplane. I don't know the prop equations that tie prop diameter and pitch together with power, speed and thrust but I'll bet someone on this site does.

Ed
 

myles-dean

Well-Known Member
Joined
Mar 18, 2013
Messages
101
Location
Stonewall, Manitoba, Canada
I was trying to verify the rpm using a digital tach but they weren't working (likely due to the polished spinner). I might have to pull the spinner of and retest.

By ear, the engine and rpm do sound close.
Would be nice to verify though.

Couldn't load the video but I question the rpm gauge. That's the only thing that makes sense to me.
 

myles-dean

Well-Known Member
Joined
Mar 18, 2013
Messages
101
Location
Stonewall, Manitoba, Canada
As far as I'm aware, this is the original prop which the previous owner flew almost 70 hours on.

The engine rpm/prop should be compatible.

This is a head scratcher....

I had a friend with a performance chart, he said a 53x42 prop at 3100 should do 125mph. Never have me any other specs.



The prop determines how much power the engine is making. To turn it 3100 rpm requires a certain amount of power and either the engine can make that much or not. If not, it won't turn at 3100. But maybe your 53 x 42 requires more than 3100 to make enough thrust to pull the airplane. I don't know the prop equations that tie prop diameter and pitch together with power, speed and thrust but I'll bet someone on this site does.

Ed
 

eschrom

Well-Known Member
Joined
Jan 18, 2006
Messages
799
Location
Manchester, PA
This web site has a free spectrum analyzer for audio signals and when I upload your video to it the strongest frequency at the fly-by is 80 Hz, or 4800 cpm. It's a bit grainy but that's what I make of it. For a four cylinder engine that corresponds to 2400 rpm, which would explain a lot. Good idea to check the tach and then of course the question is, why is the engine only turning that fast?
 

myles-dean

Well-Known Member
Joined
Mar 18, 2013
Messages
101
Location
Stonewall, Manitoba, Canada
That is an awesome tool!

I will definitely find a way to test the tech/engine rpm.
I'm planning on going this afternoon after work to take the spinner off and try again with the digital tach.
Will post results.

Thank you very much for your help!


This web site has a free spectrum analyzer for audio signals and when I upload your video to it the strongest frequency at the fly-by is 80 Hz, or 4800 cpm. It's a bit grainy but that's what I make of it. For a four cylinder engine that corresponds to 2400 rpm, which would explain a lot. Good idea to check the tach and then of course the question is, why is the engine only turning that fast?
 

danman

Member
Joined
Jun 20, 2019
Messages
14
Location
Ohio
As far as I'm aware, this is the original prop which the previous owner flew almost 70 hours on.

The engine rpm/prop should be compatible.

This is a head scratcher....

I had a friend with a performance chart, he said a 53x42 prop at 3100 should do 125mph. Never have me any other specs.
If the rpm is low then probably a mixture issue as the rpm should have increased in flight. Probably lean? EGTs?
 

kennyw

2nd and current "Caretaker" N994SP
Joined
Aug 27, 2017
Messages
160
Location
Mount Vernon, WA
That is an awesome tool!

I will definitely find a way to test the tech/engine rpm.
I'm planning on going this afternoon after work to take the spinner off and try again with the digital tach.
Will post results.

Thank you very much for your help!
Put a light coat of polish on the spinner and don't buff it out (leave a light haze on it). Point the spinner into the sun. Then try that optical tach again, from the pilot seat.

Also, if you haven't checked that optical tach against some flourescent lights, you should do that. The instructions that came with it should have instructions on how to do this.
 
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myles-dean

Well-Known Member
Joined
Mar 18, 2013
Messages
101
Location
Stonewall, Manitoba, Canada
Tonight's update:

Tied plane down securely and started the engine.
Was able to verify tach with 2 different optical tachs..... only about 20-40 rpm out from displayed!
Checked at 1000, 2000 and then full throttle. (Thanks for the tips Kenny!)

It still bothers me that the gas tank took suction once the tank was over-full before the flight and would not start.
Once again (as always when cold) it started on the 3rd pull today.
I keep wondering what happened with the fuel when he went full throttle and the fuel in the tank went back towards the vent line.
Due to the carb using some fuel and not a lot of room in the top of the tank for head pressure....just don't know if fuel would plug the overflow and cause some issues.....

So the tach is ruled out..... still going to plan on trying to calibrate the ASI, going to measure fuel flow rate (when emptying the tank anyways).
Thinking of replacing the fuel lines... just to rule them out.

To reply to Danman,
During full throttle extended static runs, EGT was 1100, CHT was 300.
After the last full rich static run for 3 minutes, shutdown and pulled the plugs and they were the correct tan colour.
It doesn't seem to be too lean... or rich.

I wish I had set up a gopro or something like that to monitor the instrument panel during the flight.
It sure could tell a lot right about now!!
 

kennyw

2nd and current "Caretaker" N994SP
Joined
Aug 27, 2017
Messages
160
Location
Mount Vernon, WA
I'd be really curious to see if he couldn't push the nose over to stay in ground-effect and see airspeed doesn't build to 80-90mph before trying to climb. I'd also compare IAS to GPS ground-speed, just for ballpark figures.
 
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myles-dean

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Joined
Mar 18, 2013
Messages
101
Location
Stonewall, Manitoba, Canada
He is away for a few weeks crop spraying, will be asking him when he's back.
Really thinking that not staying in ground-effect and getting to 80-90 was the main problem but I need to check and double-check all other possibilities.

I'd be really curious to see if he couldn't push the nose over to stay in ground-effect and see airspeed doesn't build to 80-90 before trying to climb. I'd also compare IAS to GPS ground-speed, just for ballpark figures.
 

Bil438

Well-Known Member
Joined
Oct 17, 2007
Messages
802
There are no absolutes in fuel and air. ...In my J3300 I had a cobrahead duct between the K&N and the Aeroinjector. It would not get to Takeoff RPM. I had to run a straight pipe to the filter and an airbox to provide ram air. T/0 rpm is 2850 but in fast cruise full power is 3300 rpm and 180 kts. Wonderful to fly an S2 at 180 kts.
With that engine prop combination 3300 rpm is 127 HP. That's 100% of the power available.
In my experience ASI is a bit tolerant of pitot leaks. There is so much excess capacity in pitot air, that tiny air losses don't indicate.
In your application I'd run the filter straight into the carb then use a Tee to provide Carb Heat.
Bill

I don't see how there can be any fuel starvation if the engine is making 3100 rpm and by the time he turned downwind the speed appeared to be higher than 70 (just a guess). Are you sure the ASI is functioning correctly?

Ed
 

tloes

Member
Joined
Feb 18, 2013
Messages
6
Location
Waterloo, IA
There's a quirk to the slide-plate, non-venturi, no-float carburetor. They can be set up to regulate fuel/air mixture just fine yet if the slide plate is not controlling the amount of air, the fuel delivery will not be appropriate. Basically at full-throttle while lugging the engine, you can be air-limited by the "lugging" instead of by the throttle plate restriction. Full throttle climb doesn't produce the same rpm as full throttle cruise therefore the airflow isn't comparable in these two situations yet the fuel flow will be identical (because the needle and jet are in the same relative position).

You might have to fiddle with the throttle position on climb to find out how much to "pull back" from full throttle to get the mixture back under control. You could fiddle with the mixture lever too but I think you are better off to find the throttle position that works best.

AeroCarb even has a note about this in their manual. They stopped making carbs under 32 mm diameter and suggest that when their 32 mm is used on smaller engines, a throttle stop will need to be implemented to prevent the wide-open bog.
 

myles-dean

Well-Known Member
Joined
Mar 18, 2013
Messages
101
Location
Stonewall, Manitoba, Canada
I'll look at the carb heat and air filter configuration to see if it can be changed.... there definitely isn't much room!

There are no absolutes in fuel and air. ...In my J3300 I had a cobrahead duct between the K&N and the Aeroinjector. It would not get to Takeoff RPM. I had to run a straight pipe to the filter and an airbox to provide ram air. T/0 rpm is 2850 but in fast cruise full power is 3300 rpm and 180 kts. Wonderful to fly an S2 at 180 kts.
With that engine prop combination 3300 rpm is 127 HP. That's 100% of the power available.
In my experience ASI is a bit tolerant of pitot leaks. There is so much excess capacity in pitot air, that tiny air losses don't indicate.
In your application I'd run the filter straight into the carb then use a Tee to provide Carb Heat.
Bill
 
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