Inverted Flight

[Casey]

When I fly my Half A stunter inverted at around 15 feet, the engine rpm starts to drop. After half a circle, I have to flip it back or it will be an inverted landing with the engine rpm quite low by now and the stunter flying too slow for the wing to generate lift. The moment, I flipped the stunter right side up, the engine will lean out, power is restored and there will be no problems flying right side up. Needless to say, the engine will pull the stunter easily for 3 consecutive loops. Tachometer readings show 20,000 plus rpm before launch.

Anyone experience anything similar?

[Tim Wescott]

Not with 1/2-A, but yes.

First, are you sure it's getting rich and not lean?  Usually on the bigger motors a gradual slowdown means it's leaned out, while a sudden one means rich.  But you can often tell by the sound of the engine -- "blubbery" and four-stroking means rich, "thinning out" means lean.

If you're not sure, try launching a bit richer -- if it slows down less inverted, then it was leaning out.  If it slows down more, or quits, then it richened.

Second, unless it's a Cox Something-Bee, you can probably fix it by adjusting the tank height.  If it's richer inverted then you want to raise the tank (which will make it richer upright and leaner inverted).  If it's leaner inverted then you want to drop the tank.  Part of tuning a full-size stunter is measuring the lap times and shimming the tank up or down, followed by paying attention to speed upright and inverted and doing it again, with smaler shims.

[Brett Buck]

When I fly my Half A stunter inverted at around 15 feet, the engine rpm starts to drop. After half a circle, I have to flip it back or it will be an inverted landing with the engine rpm quite low by now and the stunter flying too slow for the wing to generate lift. The moment, I flipped the stunter right side up, the engine will lean out, power is restored and there will be no problems flying right side up. Needless to say, the engine will pull the stunter easily for 3 consecutive loops. Tachometer readings show 20,000 plus rpm before launch.

Anyone experience anything similar?

      If I ran a conventional "Bee" tank (with the on fill vent on top of the backplate next to the needle valve, and nothing on the bottom, that's what would likely happen. The conventional tank is not intended for inverted flight. There is/was a different tank that had "over/under" vents to permit inverted flight. These vents are in the aluminum part of the tank about halfway between the backplate and the engine.

     The other issue might be where the fuel pickup tube is situated inside the tank. On the conventional Bee tank, it's at about a 45 degree angle, halfway between the bottom and the outside edge. Inverted, this would tend to uncover and suck air if the fuel is low. For stunt, it wants to be right up against the outside edge of the tank.

    If you have s conventional tank with a Medallion, Tee Dee, Norvel, etc, front-intake engine, it sounds like the tank is in the wrong vertical position. From your description, it sounds kind of like it is sagging off lean, which would mean the tank is too high on the fuselage.

      If you could show us a picture, that would be helpful. We may even be able to enlist the aid the factory product engineer for your engine, since he posts here all the time.

     Brett

[Tim Wescott]

      If I ran a conventional "Bee" tank (with the on fill vent on top of the backplate next to the needle valve, and nothing on the bottom, that's what would likely happen. The conventional tank is not intended for inverted flight. There is/was a different tank that had "over/under" vents to permit inverted flight. These vents are in the aluminum part of the tank about halfway between the backplate and the engine.

The "conventional 'Bee'" tank that you describe is the Baby Bee tank.  The "different" tank you describe is the Golden Bee tank.  AFAIK the Black Widow used the same tank in a different color.  The Baby Bee tank is more common, but there's certainly plenty of Golden Bee tanks out there.

[John Park]

I've just completed a Baby Flite Streak with a Cox QRC (the later version of the QZ) to fly on a small rough field I've got access to.  The engine has the 'over/under' vents, and I've relocated the fuel pick-up tube to a 'stunt tank' position, half-way up the tank wall (at 'three o'clock', viewed from the rear).  I'm waiting for my LHS to get me half a litre of 25% nitro/20% castor fuel, and then we shall see how things work out.  I'll report progress.

[Dane Martin]

When I fly my Half A stunter inverted at around 15 feet, the engine rpm starts to drop. After half a circle, I have to flip it back or it will be an inverted landing with the engine rpm quite low by now and the stunter flying too slow for the wing to generate lift. The moment, I flipped the stunter right side up, the engine will lean out, power is restored and there will be no problems flying right side up. Needless to say, the engine will pull the stunter easily for 3 consecutive loops. Tachometer readings show 20,000 plus rpm before launch.

Anyone experience anything similar?

Here's a little video I did for a buddy just to show the differences in tanks. If you need any help, just send me a message.

[Brett Buck]

The "conventional 'Bee'" tank that you describe is the Baby Bee tank.  The "different" tank you describe is the Golden Bee tank.  AFAIK the Black Widow used the same tank in a different color.  The Baby Bee tank is more common, but there's certainly plenty of Golden Bee tanks out there.

  Thank you, I am aware of that,  I just doubted that the OP was.

   However, in fact, many of the later Black Widow and Golden Bees used a blank (no tubes) extended tank, with either  Baby Bee type filler nipples on the backplate, either side of the needle valve, or the PeeWee .020-style backplate with one filler nipple and one "dribble hole" for the overflow. Saying it is a Golden Bee engine, for instance, doesn't tell you all you need to know because it could be the original, the intermediate type, the late Cox type, or the new Cox International type (some of which apparently have the extended stunt tank and others do not).

   As also noted, it might also be the QRC clunk tank, which changes the diagnosis because that should have no problem with inverted flight.

   Brett

[Tim Wescott]

OK, I'm behind the times.  I use the "product" engine backs with a separate slack balloon tank, because that seems to work best.  I save the built-in tanks for RC.

[Casey]

Thanks guys. I learnt a lot from your replies.

Hi Brett

When my stunter was inverted, I would describe the engine sound as a quiet and gradual slowing down. I have attached a picture. The tank feed pipe is aligned with the centre line of the engine.

[pmackenzie]

Thanks guys. I learnt a lot from your replies.

Hi Brett

When my stunter was inverted, I would describe the engine sound as a quiet and gradual slowing down. I have attached a picture. The tank feed pipe is aligned with the centre line of the engine.

Looking at the picture I think the tank is actually a bit below the centre line of the engine 
The top edge of the tank is in line with the motor cut out, but the bottom edge is well below the bottom edge of it.

Perhaps try raising it 1/8" or 1/4" and see how that affects the run?

FWIW, many years ago when I was using a TD on a plane like this I used the timed pressure tap. It always ran perfectly.

Pat MacKenzie

[Tim Wescott]

A quiet and gradual slowing down sure sounds like it's too lean -- but the tank looks low, which would tend to make it go rich inverted.  So, I'm confused.

I'm still thinking that launching a bit rich and seeing what happens would be a good thing to try.  Pat's idear of using pressure may not be a bad one -- I have zero hands-on experience with TD's, but I know they have a reputation as not having much fuel draw.

[Target]

Is that a TD? Didn't look like one to me....

[Steve Helmick]

I'm not current on 1/2a technology, but I've owned and run (and bled by) some TeeDee .049's, and I'm pretty sure that is something "other". Not sure what. The OP didn't say, but conclusions were jumped to, assumptions were made.

My suggestion would be to lower the tank 1/4" and see what happens. If it goes rich, it should go rich by quite a bit, so go back the other way. It's hard to tell whether it goes rich or lean via the internet. Funny how that works, eh?   Steve  

[Target]

Yep. All true.
"My car is making this noise", over the phone, "What do you think it could be?"

The engine on the plane looks like a Norvel to me, just guessing...
I think I'll fly my black widow powered baby flight streak this Friday. Hope to do some of my own inverted flight testing...
Kind regards,
Chris

[Air Ministry .]

USUALLY static , inverted and upright , the engine run mimics the Flight Run .

So holding it up & inverted & upright to see what happens is often usefull .

The Old ' Nose Up, lean out max , open 2-3 clicks ' trip often gives a good setting .

Hammering the tank , up or down . ( or use a srewdriver ) to get even speeds either way up , on the ground
could well get it right, or at least close - for air tests . Most People run 10% Nitro to get tourque , and the needle Non Critical .

[Casey]

Thanks, everyone for replying. The engine is a .061 norvel. Does a plastic clunk tank have any advantages over a metal wedge tank in the sense that there is no need to adjust tank height at all.

[Tim Wescott]

Thanks, everyone for replying. The engine is a .061 norvel. Does a plastic clunk tank have any advantages over a metal wedge tank in the sense that there is no need to adjust tank height at all.

You'll still need to adjust tank height, no matter what.  A slack balloon tank may be best, actually -- no bubbles.

[Target]

I know that one guy that competes successfully with a .061 novel in stunt SWEARS BY a uniflow tank setup...you might try that on the tank you have first.
Might be an easy fix.
Regards,
Chris

[Steve Thornton]

I'm having a similar problem with my Black Widow.  It starts right up and runs fine for 1-2 minutes, then slows the rpm, and here's the odd part, it continues to "diesel"  with no ignition for about 10 seconds before completely quitting.
Anyone see this before?
Steve

[Rich Perry]

Thanks, everyone for replying. The engine is a .061 norvel. Does a plastic clunk tank have any advantages over a metal wedge tank in the sense that there is no need to adjust tank height at all.

 I would not recommend a clunk tank that is this small.  Just too much plumbing inside for the small size.    Using a uniflow vented tank would be a great idea.    I think experimenting with tank position is also the direction you need to go.  On the bigger engines, the top of the tank (upright) should line up with the top of the engine mounting lug.  If you are in deed going lean inverted, then this would not help, but I think I would move the tank up and see what happens.  If it gets worse, then you know you need to go the other way. 

[Motorman]

It could be that your vent tubes are different lengths inside the tank or different airflow over the vents. An old tank should have a filter on it. If you solder the Brodak tank adjusters to the front and back you can easily make up/down adjustments.

MM

[Rich Perry]

Motorman is right, adding the tank adjusters to the ends of the tank would make this easy.  Also, it is amazing how much "castor crap" is inside old tanks.  Pretty much impossible to remove, but for sure the new fuel will loosen some of it.  1/2 A engines are sensitive to rubbish in the fuel. So a fuel filter is a good idea, or even possibly a new tank if you can find one the right size.

[Steve Thornton]

I'm having a similar problem with my Black Widow.  It starts right up and runs fine for 1-2 minutes, then slows the rpm, and here's the odd part, it continues to "diesel"  with no ignition for about 10 seconds before completely quitting.
Anyone see this before?
Steve

Sorry guys...I put this on the wrong thread.
Steve

[Dane Martin]

Sorry guys...I put this on the wrong thread.
Steve

Maybe start a new thread in engine set up, but sounds like you might have the circlip  backwards?

[paw080]

Hi Casey, I like Tim Wescott's suggestion best of all.  Instead of a hard tank; learn how to make a "Baggie"(Baloon) tank.

That will give your engine the best fuel draw possible for a non-pressure set up. Ironically, I first used this kind of

tank in 1952 on my first AJ Firebaby.   Your 1cc Norvel has a rarther large venturi which doesn't help fuel draw

for stunt runs.   I guess my last bit of unsolicited advice is to call your model a "Small A" stunt model not a 1/2A

stunt model.  You should know that engine class 1/2A ends at .050 cu" displacement; not .061cu" displacement.

(So sorry for my pet peeve rant)

Tony

[paw080]

Hi Again Casey, I have to take back what I said about engine class 1/2A.  It turns out that I haven't

paid attention to some AMA rule changes.  For stunt and Combat events, the displacement upper limit

for 1/2A is now .061cu" 

Tony

[dave siegler]

Hi Again Casey, I have to take back what I said about engine class 1/2A.  It turns out that I haven't

paid attention to some AMA rule changes.  For stunt and Combat events, the displacement upper limit

for 1/2A is now .061cu"  

Tony

Uh NO.  AMA combat rules event for event 330 (1/2a combat) has a max engine size of up to 0.0514. read the rules.  That is important as some engines measure out at like .0518 or so.  Show at the nats with and 0.061 and you won't fly.

Although local events usually will allow .061 non ball bearings (sport) engines, as they provide no advantage over the expensive and hard to get combat engines.

And an AMA event for 1/2 stunt well it isn't in the rule book. So this is local rules as well.

____________________________

And judging from my baby flight flight streak with a Norvel 049, I would raise the tank a smidge.  Mine seems to like it with the tank slightly above the needle valve.  It may be going rich inverted.  If you go the wrong way, you will know the effect will be worse.
  
http://www.aeromaniacs.com/norvefsetup.htm

The over under vents gave me fits, so I added a uniflow line, right next to the feed line, about 1/2 way back, then after filling connect the fill and over flow lines with a loop of tubing.

or this works well too
http://www.aeromaniacs.com/busholator.htm

A lot of the solutions proposed will work but introduce new issues.  

Solve one problem at a time.  

This sounds like a tank height or venting problem

You are 99% of the way there, don't introduce a new problem

You are very close resist the urge and the advice you get here to make major changes.