Author Topic: Magnum Pro 45 (Read 5031 times)

Matt Piatkowski · « **on:** August 09, 2015, 05:07:53 AM »

Hello,
I got the SIG Fazer with Magnum Pro 45 engine with C/L venturi and needle.
The plane and the engine are in excellent shape and I have tried them in the air using the following setup:
1. Prop: 11 x 6 Brodak, wood - wide, rounded blades
2. Fuel 10% nitro Omega, no castor added
3. Launch RPM = 8850 - 8900
4. Lines: 60' eyelet to eyelet

Everything looked and felt fine ( 5.2 s laps and excellent tension overhead ) except the following:

1. When flying level inverted the engine was slowing down a bit but was regaining the RPM when flying level normally (wheels down)
2. The engine stopped in the air with about 1 oz. of fuel still in the tank. I was almost overhead at this moment but landed safely.

This happened during second flight yesterday. During first flight the plane landed after 8 minutes and 45 seconds with empty tank but the behavior 1. above was present.

The uniflow metal tank has the capacity of 7 fl.oz. The tank was initially 3.5 fl. oz but I added another 3.5 to extend the flight time ( it was only 3 min 30 sec. when the plane was flown by the previous owner a week ago ). The tank is box like, with the typical wedged outside face. The fuel pick up tube and the uniflow tube meet in the aft corner of the wedged part. I checked the tank carefully before soldering and flushed it several times before closing. There are no loose solder droplets and no dirt in the tank that is water and air tight.

Changing the volume of fuel did not change the pressure in this volume that is only a function of ram pressure in the uniflow tube. This pressure is the function of the model speed and this speed was almost the same during four flights.

There was no problem to start the engine after priming. It started four times ( two times a week ago, two times yesterday) with the first flip so I believe the glow plug is ok.

By the way: my Evo36 C/L kept stopping in the air with some fuel still in the tank and the cure was the new glow plug but this Evo was hard to start.

Any idea what to check next?

Thanks,
Matt

Steve Helmick · « **Reply #1 on:** August 09, 2015, 07:49:45 PM »

Sounds like your only complaint is that the rpm upright is higher than rpm inverted? Would you say that it's running slower because it's running richer?

Standard fix is to adjust tank height. In this case, assuming that it is running richer inverted, you need to raise the tank when the plane is upright. This will lower the tank when the plane is inverted. Some folks get confused, especially when dealing with a typical inverted installation with access only from the bottom.

I would expect this sort of engine to prefer higher rpm with flatter pitch propellers than a true 11-6...maybe the 12-4 APC or 12.25 x 3.75 APC. But I don't believe I've ever even seen one of these Magnum Pro .45's. It should show "Made in Taiwan" on it, and is sort of an older cousin of the Thunder Tiger engines. Pretty well thought of engines, from what I've read about them.

By the way, the Fazer creates massive vortexes, and will be at risk in calm conditions...if you ever encounter calm conditions. If you have yet to encounter "wake turbulence", it's a lot like flying your stunter into a vacuum. Plane often makes the corner, seemingly no problem, but suddenly pancakes into the ground immediately after. A well-built stunter seldom survives. If it does, it is too heavy. The cure is to learn to back away from the model as you do the maneuvers. Maybe you already know to do this, maybe not. Beware!

Steve

Balsa Butcher · « **Reply #2 on:** August 09, 2015, 10:01:06 PM »

Tank height adjustment is called for as mentioned. Also it is running too slow. That RPM would be OK if it were a ST-46 but it's not. Try an APC 11.5x4 prop at around 9,900 to 10,200 rpm. If you are running the Evo 36 the same way, try high rpm/low pitch also. The APC 10.5x4.5 prop and 10,000 to 10,400 would be a good starting point. The only Evo engine that is tuned for a low RPM run is the 60.

Steve Helmick · « **Reply #3 on:** August 09, 2015, 10:38:01 PM »

I was wondering if there is any evidence that this particular engine had been reworked with cylinder timing and reduced compression ratio. Look for vibro-engraving on the head or lugs. That might allow the low launch rpm and high pitch prop. On the other hand, propeller pitches are often lower than "listed". I wouldn't be wanting to run that low rpm, and would try it with 4" pitch APC's as a preliminary test, as Pete suggests.

Steve

Matt Piatkowski · « **Reply #4 on:** August 10, 2015, 06:56:26 AM »

The previous owner confirmed that the engine has been reworked to lower the compression and it runs beautifully on 11x6 prop with RPM lower than 9,000.

I am staying with my launch RPM ( 8,850 - 8,900) and 11x6 Brodak prop for a while trying to solve the issues I have mentioned before.

Lowering the tank is no problem but, at this moment, the crest of the tank wedged face is exactly at the spray bar level (the engine has customized venturi with OS 20-40 needle NVA, OS PN# 22311000). Having in mind that the engine runs richer when flying inverted, the fuel pick tube may be shifted w/r to the crest of the wedged face of the tank. I have not seen the area of the tank where the uniflow and fuel pick tubes meet while modifying the tank. This corner was covered with small piece of perforated sheet metal that served as support for both tubes. It is possible that the end of the fuel pick up tube is shifted w/r to the crest of the wedged face of the tank but the only way for me to verify it is to open the tank. Perhaps I will do it but for now I will shim the aft of the tank that, at this moment, sits flat on the fuselage.

What about the engine stopping mid-air in the second flight with some fuel still left in the tank? This happened after a very tight loop and sudden, jerk like correction I was forced to apply. Perhaps this jerk caused the remaining 1 fl. oz of fuel to be thrown somewhere and the engine simply sucked air? How to prevent it? Should I subdivide the tank or maybe use a clunker style? I am attaching the photo of double wedged face of my 7 fl.oz. tank.

Turbulence issue: I added two large wing tips that decrease the wing tip vortices. The amount of this decrease is of course unknown but some decrease must be there. The wings area with flaps went up from 700 to 762 sq. in. Otherwise, there is not much that can be done with aerodynamics of this plane and I know I have to be careful flying in no wind conditions.

Thanks,
M

Balsa Butcher · « **Reply #5 on:** August 10, 2015, 11:47:44 AM »

Tank definitely needs to be raised or replaced. As for quitting in a tight loop, what you did is commonly known as a "cut-off loop". It can be practiced and used to advantage at a contest when fuel is low and you need the engine to stop NOW! or risk going overtime. If it is of concern try muffler pressure to the uniflow vent. Cut off loops usually only work when uniflow tanks are vented to the outside and fuel is low. Muffler pressure may introduce some other issues...or it may improve things. Experimentation is the only way to find out as every system is different. This is part of the drill when using IC engines. Some, like me, enjoy the chase, others are switching to electric and glad to be done with this type of troubleshooting.

Matt Piatkowski · « **Reply #6 on:** August 10, 2015, 03:19:08 PM »

Balsa Butcher,
Is"raised" this what I called "shimming of the aft end of the tank" to push this end more to the outside?

Re: Uniflow Tube Inlet: it is on the inside, it is (please see the photo) very short and it is directly behind and only slightly above the engine head.
There must be a lot of turbulence in this area and I started thinking about extending this tube and directing it to the outside and away from the fuselage where the flow is not that chaotic, I guess.

I will probably do it and add the conical funnel to the Uniflow Tube Inlet to scoop more air. If this will not work, I will use the muffler pressure.

I also enjoy experimentation and troubleshooting.
Cheers,
M

Steve Helmick · « **Reply #7 on:** August 10, 2015, 04:01:36 PM »

Tank centerline and venturi centerline or NV centerline are not significantly related, most especially with a uniflow tank. I don't believe anybody has a scientific reason for this deviation. Even upright/inverted lap times being identical is not a guarantee that rpm for insides/outsides will be the same. It is a fact that we have to deal with these facts, and make adjustments to compensate. "Raised" means relative to side-view. Shimmed rear of tank outboard is a completely different adjustment, for a different problem...often related to plane yawing outward due to leadout position being too far aft. If you move the LO's forward, you may be able to cure the early shutoff problem.

Nice work on the tank, however, I would always have the uniflow inlet inboard side of the circle from all of the fuel. You can run a hose over to the inboard side to a remote air inlet and see if it changes the way it works. Do NOT add a funnel or scoop to the uniflow vent. Many restrict the uniflow air inlet to fix various ills. All it needs is enough air coming in to replace the fuel that has been burned off.

I would also shim out the rear end of the tank to get fuel to the rear/outboard consistently. You could have built a wedge shape (top view) into the tank when you modified it. I'd be afraid of fuel coming out of the uniflow vent if outboard like yours, and would always have the uniflow air inlet above tank level. If it does, that may explain why the engine runs out of fuel or stops early/inconsistently. I could be wrong on this, but it's my gut feeling. Here's a link to a thread on the SV-11 tank, which I added a sump onto.

http://stunthanger.com/smf/index.php/topic,21872.msg209505/topicseen.html#msg209505

Steve

Tim Wescott · « **Reply #8 on:** August 10, 2015, 04:06:29 PM »

Quote from: Matt Piatkowski on August 10, 2015, 03:19:08 PM

Balsa Butcher,
Is"raised" this what I called "shimming of the aft end of the tank" to push this end more to the outside?

"Raising" is shimming the bottom end of the tank to push it further from the center of the earth when the plane is on its wheels.

Matt Piatkowski · « **Reply #9 on:** August 10, 2015, 08:01:30 PM »

I will do the following:
1. Shim 0.15" the aft end of the tank. 0.15" is the max I can do without changing the way in which this tank is attached.
2. Move the leadouts forward in 1/16 increments watching the lines tension.
3. Move the inlet of the Uniflow Tube to the inside, away from the fuselage and above the tank level. No scoop it is.

Thanks,
M

Balsa Butcher · « **Reply #10 on:** August 11, 2015, 10:13:51 PM »

Shimming the end of the tank toward the outside of the circle is not a bad idea. It may improve the cut-off characteristics of the engine and improve the fuel pickup. It most likely will not alter the slowing down of the engine in inverted flight. For that the whole tank must be raised, or to put it more eloquently "moved further from the center of the earth when the plane is on its wheels".
The exact distance the tank needs to be raised above the center line of the engine can only be found by experimentation but can be anywhere from 1/16" to 1/4". Don't know if you made your tank mount adjustable but if not you may have to make it so to get the upright/inverted run you want. As an alternative the open end of the uniflow vent tube in the tank can be raised above the fuel feed tube inlet but that requires opening and re-soldering the tank, possible repeatedly until you get it right.

Matt Piatkowski · « **Reply #11 on:** August 12, 2015, 06:33:10 AM »

Hi Balsa Butcher,
You wrote"As an alternative the open end of the uniflow vent tube in the tank can be raised above the fuel feed tube inlet but that requires opening and re-soldering the tank".

I was planning to open the tank anyway and remove a little bracket behind which both tubes ends are hiding.

Should'nt these ends be as close to each other as possible and exactly horizontal when the plane is on the ground?

If I find ( after opening the tank and removing the bracket ) that both tubes ends are exactly horizontal, I will simply resolder the tank, raise it, say, 1/16" and fly the model normal and inverted checking the RPM.

If, after opening the tank and removal of the bracket, I will find the fuel pickup tube end BELOW the Uniflow tube end and SHIFTED DOWN w/r to the tank's crest, I will resolder both tubes in the horizontal configuration, in plane with the tank crest.

Then, I will fly the model normal and inverted to check the RPM. If there still exists the RPM difference, I will keep raising the tank until the RPM are more or less equal. I have found a way to adjust the height of the tank ( its distance from the center of the Earth when the plane is on the ground ) relatively easily within (+)(-) 0.25" w/r to the present position.

Thanks.

Steve Helmick · « **Reply #12 on:** August 12, 2015, 11:16:43 AM »

It's not a good idea to have the (in tank) end of the uniflow tube too close to the fuel pickup, because this can introduce air bubbles into the fuel feed line and cause weirdness. Most have some sort of rule of thumb they use, like 1/2" forward of the fuel pickup, or midway point of the tank's length. Likely related to yaw trim and tank shape, especially top view taper and wedge angle, if any. Some guys use shoebox shaped tanks and are happy with them. Others use puffy LiPos....

It would be interesting to see how moving the uniflow tube up the wedge would affect the engine shutdown. I suspect you'd get a pretty significantly lean blast just before the engine quits. How long that would last is probably not predictable, but a real good warning of shutdown is an excellent safety feature...especially for old deaf machinists like me!

Steve

Matt Piatkowski · « **Reply #13 on:** August 12, 2015, 02:03:07 PM »

Hi Steve,
I have just finished soldering the tank after opening it and flushing four times.
The fuel pick up tube end in the tank is about 1/2" from the Uniflow tube end in the tank. No problem with air bubbles, I suppose.

Both ends are positioned horizontally ( parallel to the ground while the model stands on its wheels) and in-plane with the tank crest so I did not change anything.

The tank (6.6 fl.oz now after minor shape and volume correction) got the bracket allowing to raise it.

The amount of this raise will be decided experimentally watching the RPM in normal and inverted level flight.

More on Monday after flight tests.
Thanks,
M

Steve Helmick · « **Reply #14 on:** August 12, 2015, 11:54:36 PM »

Somebody (not sure who, maybe Dirty Dan) suggested a way to roughly adjust tank height on the ground. As I recall, the plot is to hold the outboard tip down at 45 deg. or so and change it from upright to inverted.

For your setup, with uniflow, I'd jump in there and raise the tank 1/4". If it isn't correct, at least you'll see that it did something. Too much or too little...well, that's what you need to find out.

Steve

Matt Piatkowski · « **Reply #15 on:** August 16, 2015, 06:42:33 PM »

Steve,
Please see the attachment. 1/4" raise of the tank aft end only resulted in normal and inverted RPM to be very close but not identical.
I am ok with that.
Uniflow works well and the engine cuts off very decisively. There is no increase of RPM in the last two or three seconds before cut off and this is very good.

Thanks for your advice.
M

Steve Helmick · « **Reply #16 on:** August 17, 2015, 09:17:08 PM »

Well...if you're happy, I'm happy! I would personally prefer a good strong signal from the engine prior to shutdown. However, since we have 8 minutes vs. your 7 minutes (I assume), it's easier for us to get down within the time allowed. I can't imagine it'll be easy to get a full lap gliding with the Fazer, however.

Steve

Matt Piatkowski · « **Reply #17 on:** August 18, 2015, 06:24:29 AM »

Hi Steve,
"Strong signal from the engine" is another good idea that I am willing to try.
What should I do to get it?

The engine sucks the fuel to the last drop but perhaps I went too far in shaping the tank like shown in the attached photo.
The time of the last flight ~7 min. 20 sec. with wind 10-15 miles/hour + additional thermal turbulence ( it was quite hot and humid last Saturday in Toronto).
The RTF model without fuel weights now 53.44 oz. Wings with flaps area is 762 square inches and this gives loading around 10 oz./square ft.

The model glides easily and I can drag it after the engine stops on 60' long lines (eyelet to eyelet) to any point of landing.

At the same time, the model is quite good in penetrating the wind up to 15 miles/hour.

To sum it all up: looks like I have a good plane to practice the pattern.

Regards,
Matt

Bill Johnson · « **Reply #18 on:** August 18, 2015, 07:23:40 AM »

Prior to shimming the back of the tank on a RingMaster, fuel cut-off was iffy for 4-5 laps. Shimmed, I get about 2 laps notice. So maybe remove or reduce the shimming on yours.

Steve Helmick · « **Reply #19 on:** August 18, 2015, 06:46:37 PM »

I'd agree with that completely. Reduce the "wedge" or move the uniflow tube (inside the tank end) farther forward. Take the easy one of the two in this situation. On an enclosed tank...may need to open up the tank. Even enclosed tanks work better when either tapered (top view, aft bigger) or mounted with the aft end outboard a bit. If your LO's are too far aft, for sure. A lot of laps of burping and such is a strong indicator that you need to move the LO's fwd. With electrons, a lot of yaw will eat a higher % of the charge.

When you start wanting to reduce run time, you can draw out some fuel. Brett says it's most accurate to fill the tank and withdraw a measured amount than it is to just put in a measured amount. The reason is that with a hard tank, you can do a "kill loop" to shut the engine off, leaving a teaspoon or so in the tank. So, you fill it up and draw out some with a 1 oz syringe. Look for a syringe that is all nylon. I found one in the utensils department at the supermarket, intended for injecting seasoning juices into meat.

Steve

It is important to do every flight as you would at a contest. That way, you'll know when you're low on fuel and when to look for the engine's signal...save yourself some airplanes. Especially if you're flying to a 7 minute limit.

Matt Piatkowski · « **Reply #20 on:** August 22, 2015, 06:17:53 PM »

Everybody,
There was no need to reduce the wedge angle. Simple mini-adjustments up and down ( w/r to the Center of the Earth ) of the aft end of the tank did the job.
Normal and inverted flight RPM are now so close that I cannot distinguish by sound if the model is flying wheels down or up.

In the end of the flight ( ~7 minutes ), the engine gives audibly higher RPM that last for about 1/2 lap and then stops.

I consider the issue fully and completely solved.

Thank you all for your valuable input.

Also: I have increased the span of the horizontal stabilizer and elevator 1.5" per side.
Extra surface area helps to support the tail that is not sagging in tight maneuvers like before.

This is the best flying model in my fleet ( see the attachment, please) and I will keep practicing.
Thanks,
M

Steve Helmick · « **Reply #21 on:** August 24, 2015, 02:53:58 PM »

Increasing the TV (tail volume = area x length), you've compensated some for the huge flaps on the Fazer. If you can reduce the flap area, you'll find better corners (smaller radius)...and lower control loads ("hinge moment" per Howard). The stock ailerons are huge, so cutting 1" off the TE would be a good start...maybe 2"!). This is a good reason for making all the hinged surfaces removable!

Good to hear that you've made progress with the engine run!

Steve

Matt Piatkowski · « **Reply #22 on:** August 24, 2015, 06:31:01 PM »

Hi Steve,
Aerodynamics of C/L models is an interesting subject and I have to learn more about it.
Regards,
M