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Magnum 52 FS Speeds Up When The Exhaust Pressure Pipe Is Disconnected.

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David Davis30/03/2019 16:13:28
3751 forum posts
711 photos

I will be entering a model in La Coupe Des Barons competition in September. I have posted on this subject before but for those who want to find out about it and are French scholars, go here: **LINK**

I will be building two models so that if one is unserviceable on the day I can compete with the other. The maximum size fourstroke permitted this year is a 52. I have two 52 fourstrokes, an OS and a Magnum. I ran up the OS on the test stand a couple of weeks ago and it performed faultlessly.

I ran up the Magnum on the test stand this afternoon, it ran well at moderate and high speed but I could not get it to tick over satisfactorily. I was using a 13x6 propeller.

I then fitted a 10x8 propeller. The revs were considerably higher with this prop but then the exhaust pressure pipe, which was rather long, disconnected itself from the silencer and the revs rose higher still.


I am not talking about a subtle increase in rpm, the increase was quite remarkable.

GrahamWh30/03/2019 17:02:11
356 forum posts
53 photos

Hi David - as the fuel is no longer being forced from the tank by exhaust pressure, the mixture in the carb is becoming leaner. The carb must have been set to run a bit rich beforehand.

By the way, how's the BE2e going?.



Jon - Laser Engines30/03/2019 17:21:49
5499 forum posts
268 photos

i agree with graham, it must have been a bit rich. 10x8 is not a great prop though, 12x6 and 13x5 are my sizes for most 50 class 4 strokes.

David Davis31/03/2019 07:04:27
3751 forum posts
711 photos

I was using a 10x8 on the advice of another of the cognoscenti who thought that a 10x8 would be ideal for the speed events in La Coupe while a 13x5 would be better for the Caisse Baguettes and Limbo rounds where accurate flying is more important than sheer speed. I have also run the motor on a 13x6 as I don't have a 13x5. I'm going flying later today, I'll take the test stand and try screwing in the main needle a bit more as well as using a 12x6 prop. If I can't get it to tick over satisfactorily, I'll use one of my OS 48s.

As for the BE2e Graham, the one I bought in an estate sale needs a little fettling but is otherwise in flyable condition. The one I'm in the process of building, I will get round to it after I've finished the second Baron and built a large vintage model which I should have started in January but on 12th January I met the lady who, if not the love of my life, has certainly turned out to be the love of my old age, so I've been distracted! laugh

Don Fry31/03/2019 12:44:20
4557 forum posts
54 photos

Just don't get distracted when you twiddle those needles

David Davis02/04/2019 07:20:30
3751 forum posts
711 photos

I took the test stand to the flying field on Saturday. I got the Magnum going on a 12x6 but the engine was still reluctant to tick over, it also vibrated a fair bit though I had balanced the propeller that morning.

I had brought a pair of OS 48 FSs with me. I bolted one into the test stand and with a slight adjustment to the main running needle, it ran perferctly! Quality will out?

I have not given up on the Magnum. Perhaps the spinner was not centrally aligned and caused the vibration but I am prepared to loose the greater power of the Magnum if the OS offers a smoother and more reliable engine.

Denis Watkins02/04/2019 07:49:20
4430 forum posts
112 photos

Just check under the rocker cover David, that there is a gap at the tappets, that they move up and down and are not sticking, and that a spring is not broken

Also on the Magnum, both the high and the low needle have O rings, so check those

Martin Harris02/04/2019 12:41:48
9333 forum posts
249 photos

What fuel are you using, David? The Magnums seem to be a little more powerful than the other clones and I suspect they may have a slightly higher compression ratio. You might try reducing the nitro content or adding another head shim/gasket to reduce the roughness at tickover - it certainly worked for my SC180FS which always seemed rough on my "standard" 10% fuel.

Alternately, are you using a lightweight wooden prop? A bit more flywheel effect can assist in getting a smooth bottom end...

michael kuss03/04/2019 18:18:09
12 forum posts

Is the nipple blocked a bit ? Cheers

David Davis04/04/2019 11:45:28
3751 forum posts
711 photos

No the nipple is not blocked Chris because I used exactly the same exhaust on the OS 48 and that ran perfectly.

However, I took the time to adjust the valve clearences on the Magnum yesterday and put it onto the test stand this morning. I removed the spinner completely so that was no longer an issue, then I tried to start the engine. The glow plug failed almost immediately so I fitted a new FF7 and it started and ran very well ticking over as well!

I suspect that the problem all along was probably a duff plug. I may still use the OS 48 in my reserve model but if I want to fit the Magnum it's a straight swap.

The prop is a 12x6 Master airscrew.

David Davis07/04/2019 08:07:38
3751 forum posts
711 photos

Thank you for all of your advice gentlemen. It's amazing how frequently a change of glow plug will improve an engine's performance, either that or a change of fuel.

I remember watching a clubmate spending most of a Sunday morning trying to get his engine to run without success. I offered him some of my fresher fuel and his engine ran perfectly!

I hope to fly it in the Baron this afternoon weather permitting.

CARPERFECT08/04/2019 21:18:15
504 forum posts
9 photos

David Davis, What is a FF7 PLUG ? $ strokes take the long reach OS F type plug.

GrahamWh08/04/2019 21:22:17
356 forum posts
53 photos

How did the Baron event go David? Your links elsewhere to previous ones look interesting. Did the engine go okay?

David Davis09/04/2019 09:55:54
3751 forum posts
711 photos

Carperfect, an FF7 is the hottest plug in the Model Technics Firepower range. I have used them with great success in both four-stroke and two-stroke engines for several years. I see that they now make a specialised four-stroke plug. I will be back in the UK next week and may well invest in a few.

Graham, my previous posts about La Coupe Des Barons may have caused some confusion so I hope the following clears it up.

  1. La Coupe Des Barons is an annual event organised by Vol Libre, a club between Chamberey and Grenoble in the south-east of France, for the classic three channel Baron trainer. Last year it was held on Saturday 2nd June. Models have to conform to certain specifications which are summarised here. **LINK**
  2. The competition takes the form of four flying rounds, preceded by a static concours d'elegance in which all of the models are lined up in their "flying groups" on the runway. Pilots fly in groups of up to ten models at the same time so the likelihood of a collision is high as is the attrition rate generally. The flying rounds consist of: "caisse bagguettes," in which you have to knock over 1 metre high balsa wood sticks stuck into the ground; a pylon race between two pylons; "renard" in which a trainer slowly flys a paper streamer behind it in gentle lefthand circuits and you have to try to cut it with your propeller and "limbo" where you have to fly through and sort of goalpost, four metres high and ten metres wide. This is not quite so easy as it sounds as the goalpost is some distance away from the pilots and is not square-on to them. Go here to see a video of last year's event. **LINK**
  3. Last year the maximum sized four-stroke engine allowed in the competition was a 40. Even a Saito 40 would have been uncompetitive against the two-stroke engine of choice, the OS 35AX, so I powered my entry with an electric motor. However, I ran out of electricity with one minute to go in the pylon race while doing well and in the renard, a circlip failed on the rear of the electric motor and I was forced to land and out of the competition. As a result I finished fifty-third out of sixty eight starters but had a great day out, with a four-course French lunch between rounds two and three!
  4. After the event I wrote to the organisers asking them to consider an increase in the size of eligible four-strokes for this year's competition. Maybe other fourstroke enthusiasts made the same request but in any case the maximum size of four-strokes has been increased to that of a 52 for this year's competition which will be held on 7th September. Consequently I will be running a 52 four-stroke in my entry this year. I have re-engined "Boris," my Baron finished in spoof WW1 Russian markings with the Magnum 52 and I test-flew it last Sunday. It flew well enough but it is a bit heavy. I've had to put lead in in the tail to get the cg correct. Picture below.
  5. I have nearly finished building a second lighter Baron with the nose shortened by 2.5 cms which will be powered by an OS52. I plan to put the servos in the rear. I had planned on fitting metal geared micro servos but my experience with Boris leads me to the view I may require the weight of larger servos for it to balance properly. I intend to finish it in RAF inter-war colours and to name it "Percy!" You are not allowed to take a spare model to the event but if I have two Barons, I will have a spare in case I plant one in a practice flight shortly before 7th September!
  6. When I entered last year's event I was the only Englishman in my club, the only representative of my club in the competition and the only English competitor. Everybody else was French (or Corsican!) apart from a German pilot who was married to a French girl who had a property near by and a lad from Switzerland. My trailblazing activity has shamed six of my colleagues into entering this year's competition. At least four new Barons are being built and one or two old ones are being dusted off. I will write a comprehensive preview and summary of the event at the appropriate time.
  7. I have offered to donate a prize, "Le Prix Quatre Temps," (The Four-Stroke Prize,) to the pilot who accumulates most points in the competition while flying a Baron fitted with a four-stroke engine. It will consist of a box of balsa and some glue! In the unlikely event that your humble servant is the most successful four-stroke pilot I will give the prize to the second man!
  8. On 19th May my club is organising a fly-in to which neighbouring clubs have been invited. We will be holding a Mini Coupe competition for our Barons.

I hope that this clears up any misunderstandings.

baron ready for the coupe (2).jpg

GrahamWh19/04/2019 20:55:36
356 forum posts
53 photos

Sounds fantastic David. I look forward to September's account. The four strokes will certainly sound the part more than the 2 strokes and maybe now the permitted size has gone up more people will go that way in the future.

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