Large Model Association Forum

Still think Coronation Street is great, should be on every night then I would have no reason to go in my workshop to play. Used last nights episode to do the programming of the Triple on the mill. The beast will be approx 470 mm long from the prop driver mount to the fire wall, I already have all of the mount plates, couplings etc so only the side & top frame parts to do, which I managed to get done. This one will be inline so that I can use the engines off the twin plus one other which is already run in to the same state. If the water cooling works then I will stick to the inline, but for air cooling the staggered arrangement would be better I would think. The big question is what size prop to spin on it, ideally 3 or 4 blade but 2 blade would do for testing. Does anyone have any very large props I could try, I can make up any prop driver to suit pre-drilled props. I know Karl is using a 37 x 14 2 blade on his which should be in the ball park for size.

Dave

Dave,, theres plenty of paramotor props on ebay,,, the watercooled version of your triple is the way id like to go with my next 3rd scale p51,,,, as you know when I tried the rotax in the cowl it was like chucking a sausage up an alley,,, the rad was a perfect fit in the lower scoop,,, anyway will be up soon,,,,
rob,,,

SEP propellers go up to 42" diameter and 26" of pitch in 2, 3 and 4 blade props

http://shop.strato.de/epages/15366738.sf/de_DE/?ObjectPath=/Shops/15366738/Categories/Luftschrauben

Phil

Look at Fila props, available direct or from Tony Clarke, apologies if there is already a UK importer.
Fine props and very reasonable on price.

Thanks for the info chaps, I think I will try the Moki 400 size prop (40 X 22) as a bench mark. I was surprised to find that the 4 blade Biela I run on the 124 twin is only rated to 3850 rpm on the Moki 250 and the twin spins it at 5000 rpm so I will have to set the max throttle to around 7000 rpm on the engines which is better for them.

I asume you mean 'Fiala' props John.........

Here are some pic's of the basic assembly, I am using the parts from the twin set up for testing so I only had to machine the new side & top plates, all other bits are off the shelf. This will be straight in line with water cooling if the single test engine works out. The couplings need timing for the firing order for when I key way them.

Dave whats the length, ,, rob

Hi Rob it is 490 mm from the fire wall to the front of the drive pulley, then its up to how long you want the prop driver to be, which will depend on the cowl clearance to the first cylinder head, I would say from 50 to 80 mm going by my P-40 set up.

Got it built up yesterday and ran it this afternoon, just like the twin she starts easily, still waiting for the correct test prop so I used the 4 blade biela and watched the revs did not overs peed the prop. Does anyone know if it is OK to lengthen the HT lead on a CDI unit.
cheers Dave

Looks great Dave, had the final inspection on the firefly yesterday so it shouldn't be too long before I get my triple in the air.
I take it you started it by hand, I fortunately used my electric starter, I tried to start it by hand and couldn't move my arm for a week.

Dave ive lengthend HT leads before with no issues,,, back in my motocross days we use to always mess with them,, you could buy a screw in joiner,,,,I few months ago I lengthend one on a da85 with no issues,,,,
rob,,,

David Brown wrote:Got it built up yesterday and ran it this afternoon, just like the twin she starts easily, still waiting for the correct test prop so I used the 4 blade biela and watched the revs did not overs peed the prop. Does anyone know if it is OK to lengthen the HT lead on a CDI unit.
cheers Dave

Thanks Rob I will try it. Karl, I have no trouble starting by hand, the electronic ignition makes a massive change to starting. It actually started first flick which took me by surprise.

Sorry to be a pain but where can you buy the braided HT lead, I have looked on the net but have so far had no joy.

Dave

Dave

The HT lead and the braid are usually sold as separate items. slide the braid over the HT lead and don't forget to earth each end.

John

Thanks for that, no wonder I could not find it.
Dave

Picked up the airframe for the engine today, sods law it is just too long to fit in the van. Tail will have to be removable.

After a mad month with work work I pinched a few hrs to get the tripple re built with a 2-1 ratio drive mounted up front. Two reasons for this, 1: to reduce the prop shaft to engine center line to 75 mm from 90 mm and 2: I only need around 3300 rpm for the 40 X 22 prop I am running (same set up as the Moki 400 radial).
I am pleased to be getting 3150 on the first test run and I still have a little bit of tweeking to do with the carb settings. I had a local welder knock up a stand to fit to the van as the missus was moaning about be screwing the stand to her raised beds in the garden .
It works a treat and I bet it would pull the van along if I let off the hand brake .

Next the water cooling, I have a single nearly ready to test.

I have shelved this project for now because all calculations for the static power show that it will be well over powered for the 1/3 Spitfire, so I will be going with the Twin Zenoah with the reduction drive, air cooled which should be better suited with a more realistic power to weight ratio. Turning a 36 X 16 prop at 3850 rpm will give around 70 lb of static thrust with a projected weight of 88 lb for the model.

The original Mk. IX has a power-to-weight of about 2 kg/hp. Your engine will crank out about 15 hp I guess which then matches a takeoff weight of 30 kg. With your projected weight of about 40 kg I would think that it would be very underpowered with the 124 cc twin.

Detlef Kunkel in Germany have used his homemade geared 124 cc on several 1:4 warbirds, and it seems that it fits the 20-25 kg models very well with regard to power.

Also, for a warbird I would make sure that I´m able to run a very high pitch prop to provide a dynamic flight envelope.
I have been running a 30x16x2 on my King 140 twin, at about 5300 rpm static, and this provides the speed I would expect from a warbird. It´s mounted on a towplane though...:-)

For a 2:1 geared engine I would look at a prop with at least 25-30" pitch, if not more, and then match the diameter and blade number to the available power of the engine.