Earthstar Forums

Which is more desirable a "B" gearbox 2.58 to 1 on a 503 Rotax turning a 3 blade prop


or a "C" gearbox 3 to 1 ratio turning higher pitch blades but the same 3 blade prop just at a slower RPM?
I think there are propeller efficiency losses at the blade speed goes up and considering the Gulls wide speed range compared to other ultralights, I would think a "C" box 3to1 slower turning prop would be more efficient


Am I missing something here????


Also it seems that most use approach speeds around 60 MPH, this seems high??? WHy such a high speed?
If you get too slow does the tail drag on touch down????thus the higher speed????
Inquiring mind whizzing away!!
Mark in Davenport

Hi Mark
We prefer the 2 to 1 C box for lower noise.
And 60 is what I recommend on the Odyssey but 55 is good for the 24 foot Gull 2000 and 60 for the 20 foot wing.
The flaps are powerful so your roll out will be short any way.
Happy Flying
Mark

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Woops I went 3-1 c box !

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Thanks for the reply,
I figured the УCФ box and the 3 to 1 gear ratio was more desirable. Just wanted to make sure. I have 2 Rotax 503s with that configuration.
Only my Ridge Runner has a УBФ box with 2.58 to 1 on that 503.

My eyebrow fairing is made from fiberglass. IS that correct or did someone make it? Should it be made from .0 16 aluminum? I know builders all put their УtouchФ on a plane when they build itЕ..
I noticed the plane I just bought in Houston ,on the ailerons, the hinge is full length piano type hinges on both ailerons, and the flaps too.

On the one I have here in Washington, the aileron has 2 short piano type hinges.

Mark in Davenport, Washington

I approach at 50mph in my light eGull with 28ft wing. Mark B is right: the
flaps make deviations from the ideal landing speed very forgiving.

The brow fairing is indeed fiberglass. I lined the inside with copper foil
to increase the ground plane for my antenna. I would love to go to an
aluminum fairing - compound curves, but large radii - should not be too
difficult to form one.

Martin

A few years ago I decided to make some cowling Blisters for my top spark plugs on my Taylorcraft. The ones I had were vacuformed plastic and no good in the cold Alaska climate. So I went to the local industrial metal place and he gave me a bunch of scrap 3003 industrial grade aluminum but the softness he had was ╝ hard.
I took two 3/8Ф thick steel plates and cut out the vertical view outline of the blister. Then I spent several days rounding the edges of one of the plates and then polishing it smooth.
Next I made a maple male plug that I would push down into the cutouts on the steel plates.(oh the steel plates were bolted together with 3/8Ф bolts on 4 corners. IT literally took me a week to make all this stuff. Finally the day came and I put some .040 thick 3003 ╝ hard aluminum in between the steel plates, lightly grease thealuminum on both sides and tightener the bolts down but not tight just enough to hold the plates together. Then I put this assembly in a 12 ton hydraulic bottle jack press like you see at harbor Freight Tools and started to press. To my amazement, the aluminum started to stretch and form a blister, however it got about ╛ of the way to where it needed to be and thenit got really hard to press. The metal had work hardended at this point and so I kept pressing and with a bang, the plug punched thru the metal and ruined the part. SO I tried again and when it got hard to press, I stopped, took everything apart and heated the aluminum with a rich carburizing flame from a torch, toput sooth all over the blister part and then I used a neutral flame and heated just enough for the soot to burn off. I read this anneals the metal. Then I tried again and I got a little farther but then the part failed. So I was pretty disappointed. I read all the books I could find and nothing new. Finally I called Univair in Colorado and told them what I was trying to do and they said you must have dead soft aluminum. I said will you sell me some? They said NO. They donТt want any competition. I said it is just for my plane and just an experiment to try to learn how to do it. He said I will send you several 1 sq foot pieces of different thickness dead soft aluminum and you can try it but I wont sell it. I ll just give it to you. He said they have to buy a roll from Alcoa for $5000 a roll and it is what they use to form most of the parts they sell. He said, as I already learned, the metal work hardens as it is formed. So he sent me the metal and it was dead easy to press out the blisters. I made 4 of them and they were just about perfect.


I have hand hammered small cowling parts with a hammer and shot bag but you can tell when the part starts to work harden. Maybe if you had a oven that could go to 900(f ) you could anneal the part and continue on.

I have heard of people annealing AD rivets by heating to about 870(f) I think and then putting them in the ice box.
Esp RV guys because it makes it real easy to flush rivet a wing skin and make it real smooth. The danger is you might introduce intergrannular corrosion if you heat treat the rivets wrong. Guys who do it use a dental oven which can be found on Ebay once in a whileЕ

Mark in Davenport




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depends on your prop diameter. A c box at 3:1 allows a bigger prop when the engine is mounted higher like in the Gull 2000. The J series, (and titan tornados), have the engine mounted lower which means a 62” prop that has to turn faster with the 2:58 b box. The 2000 and odyssey have a 68”
prop turning slower. Bigger disc, better climb. IMHO.

I have a 503 and a C box with 3 to 1 ratio. Ivo sent me a ultralight prop with +12 blades, (higher pitch )
Because other wise I would not have enough adjustment to set static RPM. I think they are 62ö diameter, but I can go measure again. Looks like about 2ö clearance to the tail boom.
I remember in A&P school 40 yrs ago, they said around 2000 PRM was good for a prop, faster and you lose efficiency because it takes power to turn the blades thru the air , air friction on the blades and also tip speed, once tip speed gets up to fast you get into compressible flow on the blade tip area and efficiency really falls off fast plus vibration.
So slower turning and higher pitch are more efficient for normal flying
So what is the diameter of your 3 blade? And what gear ratio do you run?????lookslike hyou have a C box.

Mark inDavenport

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Hi Martin, Could you either send me a photo or post one on this website of your windscreen fairing. Mark B. said there are two thin pieces of .016 and the fairing slips into that and is not attached to the wind "D" cell.
The plane in Houston that I bought had the fairing riveted to the Wing so I will have to rework all that. I noted the fairing was fibreglas.


My trailer being built in Oregon will not be ready for at least 6weeks. There was a snag in the personnel and the lady who took my order was fired so my paperwork got lost but it is on trak now...just have to wait longer...


Mark in Davenport.