Help wanted with F2b ship!

[Andrew Tinsley]

Hello Everyone,

I have purchased an F2b ship. It is a Northwind 7, a Barry Robinson design from the 1980s. It is approx 700 square inches and weighs 70 Oz's dry. It is powered by an Italian Super Tigre 51, which still needs running in. I have never flown anything bigger than Taurus and I am a little out of my depth with someting like this! I have several questions that I hope people might help me with.

  1/  70 ounces seems very high to me. Will an ST 51 cope with this model? Do I need to do some serious weight reduction? The only other motor that I have is a new Merco 61, would this be a better bet?

  2/  The muffler is a standard Super Tigre Paw type. I understand that this is heavy and could be replaced by a tube type which could save some weight. Reading the literature that came with the engine, it states that the Paw type muffler is a tuned pipe muffler !? If this is really so, what is the rpm required to get resonance?

  3/  If the plane is really over weight and the ST 51 is used, then there seems to be two types of engine run for the ST 51. Some people run them 4-2-4 and others seem to use the low pitch high rpm route. From this, I would expect the low pitch high rpm would give more power for this possibly porky plane? What prop and rpm should I be looking at to get me in the right ball park.

  4/  I understand that the amount of oil is critical in the ST 51 run characteristics, what % should I use? I assume that all castor is the oil of choice, maybe with a small quantity of synthetic, to keep the internals clean?

  5/  The plane has some rudder offset and reportedly on the few flights that it has done, it pulls like a train! I am a bit weak at the best of times, so the rudder offset will go! What else can I do to reduce the line tension to manageable levels? Obviously I don't want to go too much, I can't run fast enough if it comes into the circle!

  I have plenty of time to spare before its first flight, I need to check the control linkages and strip down and clean the gunged up engine. The wings will get a recovering with silk and mylar, the heat shrink film is not giving any real strength to the wing and it could do with some stiffening up and maybe I can save an ounce!

Thanks in advance,

Andrew Tinsley.   

[Alan Hahn]

One question is whether it is already balanced? If so, you may be stuck with the oversized muffler.

[Andrew Tinsley]

Hello Alan,

               The plane is a little nose heavy as it is, so a lighter muffler could be used, plus some lightening at the tail end, which looks possible. Are my initial reactions correct when I assume the plane is way overweight?

Thanks,

Andrew.

[James C. Johnson]

Andrew;

Your questions are probably going to be answered by your own experimentation.. I would imagine the ST 51 would pull the 70 oz just fine.. I know of one Cardinal that is 84 oz with a Big Jim ST 60 that does just fine..

My question to you .. has this engine been modified? It is a worth while investment to have it set up by an Engine Guy that knows this engine. Tom Lay is the first one that comes to mind.. there are others..

My own experience with large stunters is they can pull your arm off in wind.. the first time I experienced "wind up" , it was actually a scary flight.. and that was with a 50-52 oz Model.. I had been flying 35-43oz planes up til then..

Read this article.. and you will be on your way...
http://www.machineconcepts.co.uk/aeromodelling/st51/st51-1.htm
Lead outs are they adjustable?

I have 3 ST 51s... the RC version has a different liner and timing than the CL version.. I also have a couple of Merco's .. try the Merco first as it will run "right out of the box" with no mods.. both are great engines when "set up" right..

I have heard nothing but good things about the Dixon and T&L 51s.. I have also seen great runs with box stock versions.. I have also heard the rings and bearings on the Chinese ST 51.. are not of the same quality as the Italian version..

Windy sells tongue mufflers for this engine..

Some of the most in depth articles on the engine were done by Fred Brigeman in Stunt News .. "Sport Flying" discussions from 1997-2000.. he loved this engine.

I have flown ST.51's on models that weighed as much as 72 ounces with this basic set up:
1) Tube type muffler (Big Art or Scott Dinger type)
2) Hot Plug. I like Glow Devel R/C longs
3) SIG 10% Champion fuel, I/2 Klotz, 1/2 castor for 20% total oil
4) Props have been 12/5 Top Flite, 12/5 BY&O, and redently been using APC 12.25/3.75. Just started working with a Master Airscrew 3 blade 12/6 cut down to 11" and re-pitched to 3.5". So far so good with that but not getting as much practice time with it as I would like.
5) Two to three head shims, depending on the model.
The APC or similar prop would help you wind up problems in the wind. Take off RPM with that prop is in the 10,500 range, and I think this really helps to get the engine up to the heart of it's power band.
I'm going to read you article over when I have the time to really absorb it all. Some interesting ideas in it.
Good luck with it.
Dan McEntee

Improvements to the SuperTigre G51 for Stunt
http://www.clstunt.com/htdocs/dc/dcboard.php?az=show_topic&forum=103&topic_id=310128&mesg_id=310128&listing_type=search

From my own readings.. 22% oil half syn, is a good start for this engine. Overall this has been a pretty versatile engine and with almost two decades of use and experimentation.. I love the sound and the run characteristics this engine makes with a tradition 4-2-4 run..

More guys will chirp in on this post... I suspect you will be faced with some decisions because we all fly and run our engines differently .. that is the beauty of Stunt.. you can play with equipment and engines for years, and still have questions about what is the Holy Grail of Stunt..  the only problem with this question is our abilities.. when they change the questions multiply like rabbits..  wasn't life much simpler when there was the Fox 35 and a Nobler to build?

Jim

[Andrew Tinsley]

Thanks Jim,

The engine is an Italian made version, standard ST venturi and NVA and with the cylinder timed for control line use. It is completely stock ,not been anywhere near an engine tuner! Is the T&l and Dixon reworking aimed at a 4-2-4 or constant speed running? I too have been confused at the varying reports of runs great out of the box, to it really ought to be reworked!
  Somewhere, I read that the ST 60 was effectively a copy of the Merco, in terms of port timing, is this true? If so then the Merco should give a great 4-2-4 run, if set up correctly. Thanks also for the advice on fuel and the lead on props.
  The Northwind is fitted with adjustable leadouts. This is the first time I have seen them for real, so I need to do some archive searching to see how to adjust them for optimum effect. I presume that I can vary the line tension with this device, probably with some unwanted effects if I go for less line tension!
  I too have really only experienced the typical 35 planes like the Thunderbird, something of this size is a little daunting to say the least! I am giving it a go now, as my declining physical state will preclude such things fairly soon!!

Thanks,

Andrew.

[NED-088]

Andrew,

the first thing that comes to mind is: Have you checked with Barry Robinson himself?
I'm shure he'll give you all the advice you'd possibly need...
If you can't reach him, come back to me.

I know that Barry hasn't stopped developing since NW 7 so there might be some good modifications applicable.

[NED-088]

Any results sofar?
What did the doctor prescribe?

[Andrew Tinsley]

Hello Bruno,

[Andrew Tinsley]

Hello Bruno,
                Sorry about the delay in replying, also for the post above, which just says "Hello Bruno". This is the second time this has happened, don't know why!
  Yes I did get in touch with Barry with your contact details. He was extremely helpful towards a fumbling beginner in F2b, a real gentleman!
  As far as weight goes, both his Northwind 7s weighed in at 67 ounces, so mine at 70 was OK. Especially as I can loose an ounce or two.
  Secondly, his comments on the ST 51 were Ahem! "Its a load of rubbish!" He said that it can be made to work well with some extensive mods. Why bother when you can put in a Merco 61 and get excellent runs without touching the motor (Apart from fine tuning with props and a lightweight tube muffler). He even gave me the critical dimensions to make the silencer!
  As far as line tension is concerned, he gave me details on how to get the lateral balance correct and how to check motor offset (1 degree). He also ran through the details of setting up the variable leadouts.
  So the ST 51 has been taken out and I am searching my loft for my Merco 61 Mk1, Barry's engine of choice. If the Mk1 eludes me (you have to see my loft to appreciate the problem!), then it is a Mk2, of which I have two unrun versions in my engine draw. Don't you just hate it when this happens!
  Thanks to everyone who has given me advice. I will leave you with this thought. It takes a  US stunt forum for a Dutch guy to put two Englishmen in touch with each other!

Best wishes,

Andrew.

[James C. Johnson]

Thanks to everyone who has given me advice. I will leave you with this thought. It takes a  US stunt forum for a Dutch guy to put two Englishmen in touch with each other!

 

As a side note here is some more info.. I also love the .49

Merco 61 RC from 1964.

"61" is not. a high revving. engine and seems quite happy starting and running on either straight or moderately nitrated fuel, .with virtually:no vices or peculiarities. It will also start readily at reduced throttle settings. Maximum power appears to be developed in the region of 11,500 to 12,000 r.p.m. with a fairly flat peak and outstanding lower speed torque. Best propeller size would probably be one giving 10,000 to 10,500 r.p.m. static, which means a generous diameter size. A 12 x 6 would probably be right for most R/C applications, although a 13 x 5 or a 14 x 4 might be a proposition on a slower flying or very heavy model. Anything under a 11 x 6 is likely to lead to over-revving in the air, with no advantage. In any case, the Merco is not all that happy trying to push the r.p.m. up past 12,000 with straight fuel."

They sound really nice with a tongue muffler The Merco is very similar to the old Super Tigre but just a bit more user friendly. They like a little more pitch in the prop and may make a tiny bit less power stock but John Wright knows some tricks to up the ponies if necessary. The one I'm currently flying has a .310 venturi with an air filter with the black screen insert and a Rev-Up 12-7 prop. I use the Thunderbolt R/C long plug and fuel with 10% nitro, 20% castor, 4% Klotz synthetic, a dash or two of white gas, and the rest methanol. Like many older engines they like lots of oil. You can run all castor but the ring will get goopy and may stick. Try my "special blend" if you want awesome motor runs If you're wondering about the white gas, it says to add it right in the operating instructions that came from Merco. I tried it and liked it! I don't know why more people don't use the big Mercos. I guess it's just too easy.



Dave Royer

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Dave was running the .49 in his Super Chief until it wore out and he put in a 61. That plane and engine combo was almost perfect.. he said a bit over powered but watching it fly was pure joy. If you want an excellent airplane, this is a great one to build.. it is as simple a plane as you can build and still score as high as your ability. Plus with an up right engine easy to access... I would recommend this plane to anyone wanting stop tinkering and start really flying.. I started one in 2001 and it was banged up in the earthquake we had in Feb of that year.. the bones are still repairable.. top block needs replaced.. one of my projects that got side tracked for one reason or another..

Here info from John Wright...

Yes, I have a lot of experience with Merco's. A .300 venturi with a ST spray bar (.155) is a good starting point. Should take about 6 oz of 10% nitro, 20%oil. Frank Williams cautioned me about using more oil because the Merco runs cool and can "flame out". I had that happen when I used 24%oil. A 13-5 or 6, 2 blade wood is also a good starting point.
The stock Merco will be a nice docile 4-2-4 stunt engine but only modest power. For more power take the engine apart, take the bearings out and "square off" the round intake hole in the case. This gives more intake area without altering the intake timing. I usually square only the bottom of the intake hole where it mates with the shaft. The top is left round to hold the venturi insert. This is a very difficult proceedure that I have done with a hand file.
Notice the construction of the Merco. It has a conventional sleeve but the case is two piece. A lower part holding the crank and bearings, and an upper part which is just alum fins. I have shaved .007 off one set of fins to lower both exhaust and intake timing. Another set of fins I shave .018 but no experience yet on that. And .018 will freeport the piston, so you need to have a new, longer piston made. Not for the faint of heart.
Beyond that I had some of mine bored out to about .63 or .64 cid. The power is definitely improved with this mod. I run a 12.5-5.5 3 blade Mejilik prop on that one.
By the way, I prefer the early (60's) light weight crankcase casting, but if you have the later, heavier case, you can shave some weight off with a hand file if your careful. Or your can interchange shafts, pistons and sleeves on either the light or heavy cases.
Let us know how yours works.

John Wright

Jim