mark IX

My Feedback: (9)

I have a OS BGX-1 engine and I am wondering who has any experience with this engine and using a 4 blade propeller. More specifically, I am wondering if this engine can turn a 24-12” 4 blade prop at about 6000 rpm or higher.

Thanx, Mark

earlwb

Sorry that is too large of a propeller for the engine. OS suggests a dual bladed prop in the range of 18x8, 18x9, 18x10, 18x11, 18x12, 20x8, 20x9, 20x10. People are generally using 18x8, 18x10, 20x6and 20x8 props on them. When well broken in they ought to turn a APC 20-10 at about 9,000 RPMs. Now then it might be able to turn a 24x12 four bladed prop, but that is very likely out of its power band, so it may not like it at all. But then maybe it would be OK, hard to say though unless someone tries it to be sure.

speedracerntrixie

My Feedback: (29)

It would usually take 70cc to 80cc to spin that size prop.

mark IX

My Feedback: (9)

Speed racer, are you speaking from experience? Have you tried this size prop before?

1QwkSport2.5r

According to a prop thrust calculator I use occasionally, spinning a 24x12 at 6,000rpm requires 5.8hp to spin. IIRC, the BGX engine is about 30-35cc I think? That's a LOT to ask of that size engine.

mark IX

My Feedback: (9)

1Q, where can I get access to prop thrust calc that you use?

Thanx, Mark

1QwkSport2.5r

Actually, I inputted the data wrong; missed the blade count. A 4-blade prop 24x12 at 6,000rpm would require 9.9hp to turn it. That's a pretty large load even if that is a generous estimate from the calculator.

The calculator I used for the above data is from here: http://personal.osi.hu/fuzesisz/strc_eng/
The late Pé Reviers' prop thrust calculator is probably more realistic and can be had here: http://www.fmfk.dk/Prop-power-calculator.xls

mark IX

My Feedback: (9)

Yeah............hmmm, I have been playing with that spread sheet. It's hard to believe it takes that much power to turn that prop, but that's what the calc's say. I guess we need to keep in mind that theses are static conditions. I think the required power is less in the air since the plane is moving.

Thanx, Mark

1QwkSport2.5r

24" diameter at 12" pitch is a LOT of prop in 2-blade form, let alone 4 blades.

speedracerntrixie

My Feedback: (29)

I realize this is the internet and sometimes its easy to come across in a negative manner while not meaning to do so. This reply is one of those cases. I'm going to assume it was not meant to be negative and simply answer that yes, I have run many engines in the 70cc and 80cc displacement range. Enough to know what size props they run well with. I also have run the BGX and know that 18X10 is about it's max prop size with 2 blades.

PS. I just looked up the HP figures for a DA 85. Very close to what the corrected prop calc. estimate that 1Qwk posted.

earlwb

I remembered that my MVVS/Evolution 58cc gas engine turns a Top Flite 24x10 wide propeller at about 5800 RPMs. CH-Ignitions in Florida was getting a good 6,000 RPMs out of the same engine and prop there. It must be they had better gasoline than I did.

But then a while back I was test running a K&B Twister .61 engine and it was turning some amazingly big propellers OK. it didn't seem to upset the engine any to turn a prop as large as 14x6 OK. Granted it only turned the 14x6 at 8,400 RPMs, but it did it without complaining.

So the BGX-1 may turn the 24x12 four blade prop, but you would likely need to use zero or 5% nitro glow fuel (helps retard the timing on glow fuel), and the RPMs won't be all that impressive, probably down around 4,000 RPMs. Now if you had a reduction drive unit for the BGX-1, then it may do better too. But I don't know if those are available anymore. Someone had made some in the past.

mark IX

My Feedback: (9)

Speed racer, it was not intended to be negative. I apologize if I came across that way. I just wanted you to elaborate, which you have, on any experience you may have had with this engine/prop combo.


Thanx, Mark

speedracerntrixie

My Feedback: (29)

Mark, its all good. Having 4 teenagers in the house has tought me to ask before assuming LOL. I do have to ask why you are thinking about such a large prop on this airplane?

Earl, I too have tried to squeeze as much out of a glow engine as possible. I once had a Rossi 61 spinning a 11x11 APC at 12,000. However getting to Marks goal with the BGX would require more then double the power output available. It would be a good experiment though to lower the nitro and run a cooler plug along with a 40cc tuned pipe with a 150% length header to see just how much torque he could get out of the BGX. I'm sure Mark will clue us in but I assume he is wanting to spin a scale prop on a warbird.

earlwb

yes you are correct. But it would be interesting. Currently I have the ASP copy of the BGX engine on a profile 80 inch Extra plane. i am running a 20x6 APC prop on it. it is mainly to let the plane fly slow though It flies really slow and a 18x8 prop would let it go too fast. But it really liked running the 18x8 prop too. The 20x6 feels like it is a little too large for it. The extra large control surfaces might flutter if it goes too fast.

mark IX

My Feedback: (9)

Speed, you're correct. I want to spin the scale prop config for the warbird. I know I can do this by going electric, but I wanted to find what experience an body had with a 4 blade and the BGX. My BGX is brand new, never seen fule, so I am reluctant to use it as a test bed. If I decide to go to electric, I will probably sell it, somewhat reluctantly, however, since I not sure I what I need for the electric power system ( motor, ESC, batteries, etc).

Mark

airraptor

My Feedback: (66)

http://www.apcprop.com/ProductDetail...tCode=LP415512

This will be your best prop for this engine in a four blade prop.

The DA 85cc engine only turned a 24 inch four blade prop at 6,000 and it really didnt like it much.

Mark sometime scale props on our model planes isnt good for max performance. sure they look good on the ground and some can look good in the air if they have yellow tips but not good for flying.

break the engine in with a 18x8 2 blade prop and then you could switch to a 19x8 2 blade for the warbird. I just dont think that engine and a four blade will do well unless on a very light low drag plane.

Earl the twister 60 with the long long heavy heavy tuned muffler was like a old 90 four stroke when it was out. it liked to be in the 9,000-10,000 rpm range. a 13x8 seemed to be a good prop for it.

1QwkSport2.5r

This topic was moved to the tachometer forum?

speedracerntrixie

My Feedback: (29)

New thread, second opinions I suppose.

mark IX

My Feedback: (9)

Looks like there's not a lot of experience out there with this engine / prop combo. I kinda had that feeling. So the DA 85cc turned this prop at 6000 rpm. This engine is rated at 8.5 hp which is close to the numbers I saw in the prop caculators listed above. Looks like thats a valid conclusion.

Hobbsy

My Feedback: (102)

Mark, as a point of reference a SuperTigre 4500 converted to Diesel operation turns a 22x12, (two blade) at 6,000. www.zingerpropeller.com might be something at Zinger that would suit

Hobbsy

My Feedback: (102)

Here's a better one

http://www.zingerpropeller.com/4_bladed_propeller.htm

mark IX

My Feedback: (9)

Yeah, I am planning on using the Zinger 4 BL 24-12 prop. Did a Google search on the internet and found an ESM 50cc Corsair (85" ws, 26 lbs) powered by a 50ccDLE turning a 20-10 4 BL prop. Which by the way is the recommended 4 BL for that engine. The video of the flight showed it to fly quite well with that combo. I am going to look at the DLE 60cc engine. Just need to find the dimesions of the engine to see if it fits my cowl. It must be a new engine since it's website does not have a dwg of it yet.

Mark