Engine Lost Power on Outside Part of a Horizontal Eight?

[Kafin Noe’man]

Guys,

I just finished my flying session this morning. I had like 6-7 flights today.

The first 3 flights were mostly about perfecting the engine run with some inside loops and wing over — MISSION ACCOMPLISHED, no issues.

Having the confidence that the plane was gonna do well, I added horizontal eight to my practice set for the last 4 flights, BUT THEN, I found out the plane was losing its tension when I was doing the Outside Loop part of the Horizotal Eight.

At first I thought it had to do with my leadout position, so I tried to move the leadout forward (2 flights) and to move leadout back (2 flights) both were by 1/8” from the initial position. NO LUCK AT ALL. The problems were still there regardless my leadout position.

Then, I thought something else. I somehow felt the power was dropping but I wasn’t 100% sure if the sound was changing or dropping as well since I got so focused on recovery. Could this be the issue?

Engine is set wet-2, tank height is already 1/8” higher from the engine center line. Should I raise the fuel tanl further more?


Best,
Kafin

[Lauri Malila]

Kafin,

In your story it's unclear if the problem has occurred before, have you done the horizontal 8 earlier?
Anyway, getting that rich burp in outside part of 8 is quite normal for side mounted engines (Profile model, right?). The main reason is oil accumulation somewhere in the bottom of crankcase. So it's not really a tank issue, even though you can try to compensate it with tank height. But then you compromise other parts of flight, like level/inverted lap times.
What's funny is that the engine can run just fine and very same (I can measure & record engine rpm at any point of flight if I want.) when doing just inside or outside loops, but what triggers the burp is the sudden direction change in the 8 intersection.
It's very difficult to get completely rid of the problem without changing the engine mounting orientation, but you can try to reduce it with higher rpm, less load, hotter glow plug or lower viscosity/less oil. L

[Kafin Noe’man]

Hi Lauri, thank you for responding my post.

Yes, it is on my Profile Brodak P40 with an OS LA 46.
And yes I have done horizontal 8 without any problems with my other plane.

It felt the plane was like floating when the plane was at the bottom part of the outside loop and when it was going up it didn’t get any better and it left me with a ‘kite’ when it reached the top. I gained back the power when the plane was back level upright.

Higher RPM : It pulled my arm really strong
Hotter Glow Plug: it already had a hot glow plug (ENYA No. 3)
Lower Oil: Something that I can try - my current fuel is 5% Nitro 22% Oil


Thanks for your advice Lauri!


Best,
Kafin

[Lauri Malila]

Higher RPM, > less pitch.
Maybe you just run the thing too rich?
If it’s been ok before, then change the plug first.
Also, if the same setup works well in another model, maybe check the nose stifness.

[Ken Culbertson]

Every plane and motor is in some way different so I would suggest first trying Lauri's approach.  If that fails, and only if it fails:

All of this assumes they were AMA not "Lazy" eights. I ran a stock (except for a ST needle valve) LA46 on both profile and PA planes from my reentry into stunt in 2018 till I went electric in 2020.  My configuration was a 6oz clunk tank 10-15% nitro and an 11-6 prop running a fast 4 cycle on muffler pressure.  The motor never lost power anywhere in the pattern.  I reviewed a couple of videos to confirm that before posting this.  Other than a few very quick breaks into 2 cycle there was very little difference anywhere in the pattern.  I am only offering this as an alternative.  I am from the 4-2-4 Fox 35 generation, so the high RPM low pitch approach is not something I have ever been comfortable with.  Others have, quite successfully so there is nothing wrong with it.  I am not a motor person, so I am not sure which of the elements in my setup make it respond differently from yours.  It may be the tank.  Maybe taking off just over half full has something to do with it.  Our weather goes from too cold to too hot sometimes in the same day and fuel required to do a pattern can vary by almost 1 oz.  A big clunk tank accommodated that.  Another factor may have been the noses I use on profiles.  They are very thick and I use large fillets, especially at the wing LE.  Very little vibration.

Good luck, let us know what works.  - Ken

Something hit me as I reread your original post.  Where do you start the horizontal eight relative to the wind?  It should be 22.5 degrees to your right if you are facing directly down wind.  One of the most difficult lessons learning the pattern is that the loops of the 8 have their backsides biased into the wind where the normal loops have their front sides.  Getting this wrong can cause drastic differences in line tension between the inside and outside segments.  This may be what you are feeling and not be the motor at all.  Just a random thought - Ken

[Dave_Trible]

I'd think a minor shift in tank position would solve most of any power issue if that's what's going on but what you describe to me sounds like an airplane trim issue.   I'd suspect a little wing warp or build anomaly or perhaps a crooked stabilizer.   Perhaps a flap tweak or trim tab would help.  As Lauri says maybe just going faster would help you get the plane through it if it was too slow but it should behave about the same going both directions.

Dave

[Jim Svitko]

I am with Dave on this.  The first thing I would do is to make sure that alignment/trim is not the problem here.  Are the hinge lines are parallel?  Is the stab tilted when viewed from the front?    Does the stab have any incidence?  Are you sure both flaps and both elevators are at zero with the handle neutral?  Alignment is critical and if it is off even a slight amount, it will cause problems.

Regarding engine run--have you gone inverted with this plane/engine?  If the engine goes leaner or richer when inverted, then a tank adjustment is needed.

[Colin McRae]

A few suggestions/notes:

I have a P40 ARF, but run an Evolution 36 with 11-4 MAS prop at around 11,300 rpm on the ground. But I do run a few OS LA's on other models, both profile and cylinder down arrangement. I do not notice any power issues with my LA's.

1. On your 46LA, are you running muffler pressure? I run muffler pressure on all my LA's. All run fine even in maneuvers.

2. Maybe you are running your engine a bit too rich. The LA engines like to run fast. When setting the needle on the ground, I look for peak rpm, then open the needle maybe 20-30 degrees and look for the engine rpm to droop a little. (Basically, just like the OS owner's manual says.) I run the engine like this and try different props and pitch to manage model speed in the air.

3. When putting together the ARF kit, did you use the kit provided flap and elevator joiner wires. The Chinese kit wires are undersized (and maybe not even stiff music wire) and produce a 'significant' amount of differential flex. This causes the model to roll in maneuvers, and the roll can be quite severe under hard control inputs. Actually, I'm in the process of a repair on my P40 ARF to stiffen the joiners to eliminate or greatly reduce the differential flex.

4. I also run 10% nitro/18% oil VP fuel, but I add a bit of castor to boost the total oil to 20% per the OS manual. Maybe try 20% oil vs the 22% you are running.

[Steve Helmick]

Uniflow tank? Uniflow tanks require being mounted higher than a non-uniflow tank. If you didn't put the stopper on the overflow tube in the tank, it becomes a non-uniflow.

Otherwise, I'd ask if the wing is level both upright and inverted, but I'm not sure how your inverted flying skills are progressing.

Not enough tip weight might also be a problem. Too much will make some maneuvers a little ugly, but not enough can cause the dreaded sudden silence...  Steve

[Kafin Noe’man]

Thanks guys for all your inputs.

After thorough inspection, my wing and elevator are straight and parallel to each other. Flaps-Elevator are also neutral and no warps or whatsoever. But both are not perfectly square to the fuselage. In upright level flight, the plane can fly straight, meanwhile it's kinda hard to tell when it's inverted since I still don't have the confidence to fly inverted at around 5ft height.

Having read all your comments, my next plan would be:
- Try to fly inverted at lower height and see how the wing position if it's level or not on both upright or inverted.
- I was thinking about adding more tip weight.
- I also felt that my current spectra lines is too long at 62.5 ft, so I've been thinking to switch back from Spectra (62.5 ft) into my steel lines (61.5 ft) so I can have more tension when flying.
- The other reason of switching back to steel lines is I think I might have some 'room' to add more tip weight since I couldn't add more my current tip weight at 4 gram with my spectra lines setup since the outboard wing will drop instantly when gliding to land if I add more weight. My notes from previous flights tell me that a total of 7-10 grams of tip weight will be fine with the steel lines when landing.

I think those are few changes that I will try first. I'm not really sure if it was a power lost or just simply lost of tension when I was doing the outside loop.
If after those changes I still have the problem and can indicate any signs of power loss, I might also try to raise the fuel tank a bit.

I hope it has nothing to do with the assembly error, if it is, I will have to ground this plane for quite some time since I'm expecting another baby boy next month.
So any work that requires me to spend some time in the workshop would be impossible to do until everything is settled, or otherwise my license to this hobby will be stripped off completely by my wife 


Best,
Kafin

[Ken Culbertson]

Thanks guys for all your inputs.

After thorough inspection, my wing and elevator are straight and parallel to each other. Flaps-Elevator are also neutral and no warps or whatsoever. But both are not perfectly square to the fuselage. This is not much of a problem.  As long as the wing and stab are in perfect alignment, how they sit on the fuselage is relatively unimportant.  In upright level flight, the plane can fly straight, meanwhile it's kinda hard to tell when it's inverted since I still don't have the confidence to fly inverted at around 5ft height. It will show regardless of the angle.  Just watch it relative to the lines.  Level Upright but not level inverted is a tough fix.

Having read all your comments, my next plan would be:
- Try to fly inverted at lower height and see how the wing position if it's level or not on both upright or inverted.
- I was thinking about adding more tip weight.
- I also felt that my current spectra lines is too long at 62.5 ft, so I've been thinking to switch back from Spectra (62.5 ft) into my steel lines (61.5 ft) so I can have more tension when flying. Spectra lines are lighter and less resistance than Steel if you get the right weight.  I use 80-100 depending on weight.  Under 65oz I use 80, 100 over.  Shortening the lines may help but it is not going to give you more line tension.  Actually it should be less.
- The other reason of switching back to steel lines is I think I might have some 'room' to add more tip weight since I couldn't add more my current tip weight at 4 gram with my spectra lines setup since the outboard wing will drop instantly when gliding to land if I add more weight. My notes from previous flights tell me that a total of 7-10 grams of tip weight will be fine with the steel lines when landing.

I think those are few changes that I will try first. I'm not really sure if it was a power lost or just simply lost of tension when I was doing the outside loop.
If after those changes I still have the problem and can indicate any signs of power loss, I might also try to raise the fuel tank a bit. If you can't tell if it was poser loss on an IC it probably isn't. You didn't respond to my comment on positioning so I will  bring it up again.  Everybody tells you to position the maneuvers directly down wind.  That is true for the eights as well but what a lot of fliers think is that entry to the maneuver should be directly down wind.  The entry to the 8 is half a loop to your left.  It is the intersection that should be directly down wind.  I am pasting a link to Paul Walker's second article on flying in wind below.  If you haven't read it, please do because he explains this 1,000% better than I am capable of.

I hope it has nothing to do with the assembly error, if it is, I will have to ground this plane for quite some time since I'm expecting another baby boy next month.
So any work that requires me to spend some time in the workshop would be impossible to do until everything is settled, or otherwise my license to this hobby will be stripped off completely by my wife  My second daughter caused my license to be revoked for nearly 30 years.  DO NOT let that happen to you!   


Best,
Kafin

See my comments in Red above.  Hope you figure this one out.

http://flyinglines.org/pw.flyinginwind2.html

Ken

[Steve Helmick]

At this point...I'm not even sure which airplane this is. Is it the P-40 profile or the other ARF (from Japan?)?

The 4 grams of tipweight seems very inadequate, unless this is just in addition (fine tuning) to the ARF weight box and/or a bit of iron bar glued in (like the Brodak ARF P-40). The 1/8" raised tank height probably isn't enough for any uniflow tank. More like 5/16"...but I like to overdo a thing like that and back off as needed, rather than spend forever sneaking up on it 1/32" at a time.

We have to rely on your ears to tell us if this is trim related or engine related, I think. Hang in there!  Steve

[Al Ferraro]

   Check your engine offset with the prop to the leading edge of the wing. You should have i/8 to 1/4 inch more on the inboard side.
Al