First Flight Since Rebuild

[mhflyit]

Myles - three things:
1. do you still have the carb heat attached to the Aeroinjector?
2. have you checked the vent line for a blockage?
3. check the mixture controls on the carb are tight and the idle adjustment screw

Use half a tank of gas for the next flight.

Matt

 

[myles-dean]

I did notice a difference between WOT and slight back from WOT.
Statically was getting 2900 rpm WOT and if I pulled back slightly, would get 3100 rpm.
My friend did mention that he tried to pull back slightly but at that time he didn't see any difference.

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.

 

[mhflyit]

OK, so you have carb heat - the Aeroinjector doesn't require carb heat. Could this be 'opening' un-commanded? Maybe not if your RPM is 3100 throughout the pattern.

As asked by Xsonerai - what is you CofG.

Also, have you verified your propeller pitch?

 

[myles-dean]

Total weight for the flight was ~776 which put the CG at 9.71"

What is the weight and CG?

 

[myles-dean]

I was thinking of taking the carb heat off but figured it fit and is nice to have the backup.
There shouldn't be any way that it could partially open as it is a solid wire control.

I have triple checked the vent line, no blockage.
That is most definitely my plan to run half a tank next time!
I regret filling it right full for this run... thinking things may have turned out differently.

Myles - three things:
1. do you still have the carb heat attached to the Aeroinjector?
2. have you checked the vent line for a blockage?
3. check the mixture controls on the carb are tight and the idle adjustment screw

Use half a tank of gas for the next flight.

Matt

 

[Chucker]

Fuel syphoning in the vent system with an over-full tank is a known issue with the Sonerai aircraft. If fuel enters the vent line once the cap is installed (typically during takeoff acceleration) and is not allowed to flow back into the tank it can become trapped in the vent line. Suction in the tank holds the fuel up while gravity is pulling it down. The early vent configuration did not have this problem because the vent line ran along the top of the tank to the front before going down to the exterior vent. The Stretch plans changed that configuration with the vent line running straight down without traveling forward along the tank centerline. The early configuration prevented trapped fuel. The Stretch configuration did not. This issue only presents itself when the tank has enough fuel to fill the vent line during acceleration. I believe that common practice is to leave enough space above the fuel to avoid this. Old issues of the newsletter address the issue. Dave Wilcox designed a very effective system to preclude this problem even with a completely full tank. To my knowledge, the Stretch plans were never modified.

From the sound of the video there was no change in performance after the initial acceleration. that would lead me to believe that this was not your issue during the flight. However, since you mentioned the syphon problem, I wanted to make sure you were aware of this issue.

ATB,
Chucker

 

[mhflyit]

The 3100 rpm around the pattern suggests a prop pitch issue, RPM gauge issue (which you've verified is reading OK), WandB issue or...?

 

[myles-dean]

Thank you very much for this Chucker!

That is exactly the theory that I had in my head.... I will be very aware of how full I will be filling the tank.
I'll also do some digging into what Dave did.

Fuel syphoning in the vent system with an over-full tank is a known issue with the Sonerai aircraft. If fuel enters the vent line once the cap is installed (typically during takeoff acceleration) and is not allowed to flow back into the tank it can become trapped in the vent line. Suction in the tank holds the fuel up while gravity is pulling it down. The early vent configuration did not have this problem because the vent line ran along the top of the tank to the front before going down to the exterior vent. The Stretch plans changed that configuration with the vent line running straight down without traveling forward along the tank centerline. The early configuration prevented trapped fuel. The Stretch configuration did not. This issue only presents itself when the tank has enough fuel to fill the vent line during acceleration. I believe that common practice is to leave enough space above the fuel to avoid this. Old issues of the newsletter address the issue. Dave Wilcox designed a very effective system to preclude this problem even with a completely full tank. To my knowledge, the Stretch plans were never modified.

From the sound of the video there was no change in performance after the initial acceleration. that would lead me to believe that this was not your issue during the flight. However, since you mentioned the syphon problem, I wanted to make sure you were aware of this issue.

ATB,
Chucker

 

[myles-dean]

As far as I am aware, this is the original prop (so pitch shouldn't be an issue).
Everything else checks out and W&B was good.

Really thinking he needed to hit 80 before climbing.......

The 3100 rpm around the pattern suggests a prop pitch issue, RPM gauge issue (which you've verified is reading OK), WandB issue or...?

 

[Chucker]

Dave mounted a chamber on the aft side of the firewall at its highest point. The fuel tank vent line runs to the top of that chamber. The exterior (ram air) vent line also runs to the top of that chamber. The bottom of the chamber has a drain line which exits the aircraft just behind the ram air vent. Positive pressure on the tank is maintained because the drain line is smaller than the ram air line. Dave actually tested the system pressure by connecting an airspeed indicator to the chamber. There was no loss of ram air head pressure on the tank compared to the standard system. The beauty of this system is that (as long as the ram air line is not obstructed) it is physically impossible to create a syphon. The chamber weighs 3.65oz. Cheap insurance.

 

[myles-dean]

Thanks for the description.

When I initially installed the fuel tank, I didn't realize that the vent line went down in front of the landing gear (I reworked it after everything was completed).
I had installed a PCV valve to act as a vent.... that way it would allow suction but prevent fuel from splashing out.

Thinking of reincorporating it into the current system:


Normal venting can occur using the drain line - green line but if it ever gets plugged and a suction starts, the PCV would take over and allow air to enter through the top - orange arrows (under the cowling).

I think it would be a simple fix with parts I already have.
Thoughts?

Dave mounted a chamber on the aft side of the firewall at its highest point. The fuel tank vent line runs to the top of that chamber. The exterior (ram air) vent line also runs to the top of that chamber. The bottom of the chamber has a drain line which exits the aircraft just behind the ram air vent. Positive pressure on the tank is maintained because the drain line is smaller than the ram air line. Dave actually tested the system pressure by connecting an airspeed indicator to the chamber. There was no loss of ram air head pressure on the tank compared to the standard system. The beauty of this system is that (as long as the ram air line is not obstructed) it is physically impossible to create a syphon. The chamber weighs 3.65oz. Cheap insurance.

 

[poormansairforce]

Thanks for the update. One other clue you gave us was you said the plane was plowing. Is the incidence of the wings correct? Grasping at straws...

 

[myles-dean]

Off the top of my head, I believe it was neutral or 1° (whatever was written in the assembly instructions).
I do recall actually measuring it and it was correct.

I never changed the AOI and the plane had flown 70 hours as configured.
The crazy part that I found was that he had flown for that long without any rear spar bolts and no aileron safety pins.
All it would have taken was for someone to bump the back of the wing and the ailerons could have completely disenaged!

Thanks for the update. One other clue you gave us was you said the plane was plowing. Is the incidence of the wings correct? Grasping at straws...

 

[poormansairforce]

An 1835 VW is good for about 60 up but my prop calculator says you need about 67 hp to match your results. Don't know how accurate it is but you may be right about the power curve. 80 mph may have put him over the hump. Maybe a prop adjustment is in order.

 

[kennyw]

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'm guessing here. But, even if he never accelerated "in-ground-effect", holding the nose up at that airspeed and wide-open-throttle, should have eventually led to the problem fixing itself somewhat, assuming the engine is developing something close to full power (fixed pitch: power=RPM).

That being the case, your 22,000+ hr pilot is not likely gonna want to take that aircraft in the air till you have some idea of the problem and the solution (although, as I said, "I'd be really curious to see....").

While you're waiting for him. You might confirm all your rigging; i.e. wing incidence, control throws and control surface deflection, just to rule that out.

I agree with you that continued flight testing should be from a hard-surfaced runway till you get a little more confidence in the bird. Maybe some high-speed taxi testing is in order, just to see how quick the tail comes alive. The 1835cc isn't a rocket motor. But, it should still get things flying pretty quickly.

 

[kennyw]

... Maybe a prop adjustment is in order.

on 4SP's 1835, the 52/42 Sterba IS the sweet spot. I can't imagine a 53" would make THAT much difference.

 

[poormansairforce]

on 4SP's 1835, the 52/42 Sterba IS the sweet spot. I can't imagine a 53" would make THAT much difference.

A 52" brings the hp down from 67 to 62. Again I don't know how accurate that really is but just trying to find an explanation.

 

[myles-dean]

Thank you for all the assistance on this, it is greatly appreciated!
I just wish I had an "ah ha!!" moment and could tell my friend that this or that was the problem.

If nothing else, it is good piece of mind knowing that everything is being checked.

I will be sure to post an update as things progress.

 

[kennyw]

A 52" brings the hp down from 67 to 62. Again I don't know how accurate that really is but just trying to find an explanation.

I got about the same calculation from http://www.godolloairport.hu/calc/strc_eng/index.htm .

I'd be curious to know how that reconciles with this table from Great Plains. Do we have any engineers here that can enlighten us?

 

[kennyw]

Has anyone here attempted a "static thrust" test with a direct reading scale, like one of the large spring type fish scales?

In theory, he should be developing around 200lbs of static thrust with that prop @3,100rpm.