No.. could it be..?
02-20-2015, 12:36 PM
#205
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Got the Nelson today, but so far only fondled it at my desk at work. Bit of a distraction I must say..
Eyeballing it, the exhaust timing seems to be in the 170 degree range. It is definitely not 180 or more. What would typical timing be for a Form 1 engine running on lightly lubricated nitromethane? There is a good .100" of liner blocking the top of the exhaust port.
No pinch whatsoever. Carb throat looks like 10mm. I wonder if this will turn out to be one of the sport .40's? Not many were made as I understand.
I'll disembowel it when I get home and see what the combustion chamber looks like.
Eyeballing it, the exhaust timing seems to be in the 170 degree range. It is definitely not 180 or more. What would typical timing be for a Form 1 engine running on lightly lubricated nitromethane? There is a good .100" of liner blocking the top of the exhaust port.
No pinch whatsoever. Carb throat looks like 10mm. I wonder if this will turn out to be one of the sport .40's? Not many were made as I understand.
I'll disembowel it when I get home and see what the combustion chamber looks like.
Last edited by MJD; 02-20-2015 at 01:12 PM.
02-20-2015, 03:43 PM
#206
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Let there be light.. bolting on a prop and shining a flashlight down the plug hole reveals the timing to be more like 180 +- my measuring accuracy. That's a good start.
Combustion chamber is a double bowl - flat in the squish band area. Measured a stroke of 0.712"/18.1mm, bore 0.848"/21.54mm = we know it's a .40. Crude deck height measurement 0.016".
Carb ID 9.5mm/-0.374". That suggests a low-mid 20's powerband does it not? Starting to small like it might be a Form 1 derivative.
Big thing is, the crankcase has forward mounting lugs, and I am pretty darn sure none of the sport variants did, don't see them in pictures I found.
There is a bit of nip at TDC, I was mistaken.
Combustion chamber is a double bowl - flat in the squish band area. Measured a stroke of 0.712"/18.1mm, bore 0.848"/21.54mm = we know it's a .40. Crude deck height measurement 0.016".
Carb ID 9.5mm/-0.374". That suggests a low-mid 20's powerband does it not? Starting to small like it might be a Form 1 derivative.
Big thing is, the crankcase has forward mounting lugs, and I am pretty darn sure none of the sport variants did, don't see them in pictures I found.
There is a bit of nip at TDC, I was mistaken.
02-20-2015, 07:18 PM
#207
You can get an accurate deck clearance by slipping a bit of 1/16" solder through the plug hole towards the squish band, then squishing it flat with the piston and read the results . The solder should probably have a high lead %. I think 50% - 50% is typical with electronics solder.
It's good to have a baseline number that you can match to the fuel and prop size when you start your journey to find the "hot set up".
It's good to have a baseline number that you can match to the fuel and prop size when you start your journey to find the "hot set up".
02-20-2015, 08:41 PM
#208
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Yeah, I will do that and actually make notes for a change. Still want know exactly what this engine is all about, so far it seems to have no actual purpose. Unless it is some practice engine derivative.
02-20-2015, 09:16 PM
#209
It would be nice if you had either separate fuel ingredients or a jug of FAI fuel and a jug of 40 or 50% to custom mix small batches in your wife's nice Pyrex mixing cups.
If you want, you can arbitrarily say what the highest % of nitro is that you want to run...then go from there. What ever you're comfortable with.
If you fail at finding the right tune for 10 or 15% nitro...you'll always have other engines to burn that fuel with.
Very few Nelson engine owners [that I know of] ran them for the same reason that you are running your's. They can give generalized advice that gives you a ball park idea, but Dave Shadel is the guy I'd trust most for prop suggestions once you are able to furnish him with your engine's timing info.
If you want, you can arbitrarily say what the highest % of nitro is that you want to run...then go from there. What ever you're comfortable with.
If you fail at finding the right tune for 10 or 15% nitro...you'll always have other engines to burn that fuel with.
Very few Nelson engine owners [that I know of] ran them for the same reason that you are running your's. They can give generalized advice that gives you a ball park idea, but Dave Shadel is the guy I'd trust most for prop suggestions once you are able to furnish him with your engine's timing info.
02-21-2015, 06:25 AM
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Yeah I should reach out to him - there appears to be little more than guessing until then. However I feel inspired to finally make a degree wheel. To the Bat-CAD! (after morning tea)
I noticed how dumb it is guessing at timing without using light or a prop. I was off by 10+ degrees in terms of gas flow versus "I think I see a crack".
I noticed how dumb it is guessing at timing without using light or a prop. I was off by 10+ degrees in terms of gas flow versus "I think I see a crack".
02-21-2015, 10:32 AM
#211
I just looked at Eliminator's selection of 7 inch props with 5/16" shaft holes. I've got an engine like your's and never took the time to optimize it. I fed it "hand me down props" from the FAI project and also Q-40 APCs. I never fed it much nitro, either. At any rate, it's a great "Delta Engine".
Shadel is mentally geared for racing, so you'll need to be able to take a suggestion [for example 7.75 x 7] then figure out how much that amount of load translates to what you want to do. You might be able to just flip the numbers to 7.2 x 7.5 [or something like that].
Shadel is mentally geared for racing, so you'll need to be able to take a suggestion [for example 7.75 x 7] then figure out how much that amount of load translates to what you want to do. You might be able to just flip the numbers to 7.2 x 7.5 [or something like that].
02-21-2015, 11:33 AM
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I agree, the thing to do is take a good pylon prop candidate and shift the gear ratio up one notch while keeping the same shaft load.
I just finished drawing the Demon mounting plate, gotta open up the nose ring, redesign the radio bay/tank area and put in a pair of Jett pylon tanks lying flat. Or something like that. The RE Ultrathrust muffler does not clear a regular fuel tank installation well at all.
I just finished drawing the Demon mounting plate, gotta open up the nose ring, redesign the radio bay/tank area and put in a pair of Jett pylon tanks lying flat. Or something like that. The RE Ultrathrust muffler does not clear a regular fuel tank installation well at all.
02-25-2015, 08:01 PM
#213
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Here's the K&B 7.5 Fi mount I came up with.
It has the standard 2" spinner ring. It stands off via a piece of 1/4" balsa. That's a long engine!
I think I'll have the short kits all packaged this weekend.
In the meantime find a couple of pieces of 3/16" sq spruce or basswood and set them aside (Rudeboy I have a couple of pieces I can send you, it's an odd size over the pond. The rest is standard). Use those instead of the regular 1/4" sq balsa on the LE, and lap the sheeting over that before sanding to shape. Much better LE.
And I have the Nelson 6-point mount cut too. That is one light engine.. I'll build it a Demon as light as I possibly can but tough. Probably 1/16" sheet to the high point with shear webs. Whee fun.
It has the standard 2" spinner ring. It stands off via a piece of 1/4" balsa. That's a long engine!
I think I'll have the short kits all packaged this weekend.
In the meantime find a couple of pieces of 3/16" sq spruce or basswood and set them aside (Rudeboy I have a couple of pieces I can send you, it's an odd size over the pond. The rest is standard). Use those instead of the regular 1/4" sq balsa on the LE, and lap the sheeting over that before sanding to shape. Much better LE.
And I have the Nelson 6-point mount cut too. That is one light engine.. I'll build it a Demon as light as I possibly can but tough. Probably 1/16" sheet to the high point with shear webs. Whee fun.
02-25-2015, 08:10 PM
#214
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BTW I cut blind nut doubler plates for all the mounting plate configs - you can see them in a couple of these pics - and tossed those in the bag.
The mount is more sturdy than the original and still very light. A 1/8" spruce ply plate interlocked to the ribs, a 1/8" doubler underneath, a 1/16" aircraft ply doubler on top (harder skin for the mounting lugs), and the nut plates.
The K&B will be really easy to cowl in using standard materials. A good tip for blending the lower ring to the fuse is to get a chunk of 2" kraft mailing tube, split a short piece, and trim the U shape section to fit up nice between the 2" OD ply nose ring and the fuse underside, then fill in with ply each side. Once you glue in and finish the paper tube it is tough as nails.
The mount is more sturdy than the original and still very light. A 1/8" spruce ply plate interlocked to the ribs, a 1/8" doubler underneath, a 1/16" aircraft ply doubler on top (harder skin for the mounting lugs), and the nut plates.
The K&B will be really easy to cowl in using standard materials. A good tip for blending the lower ring to the fuse is to get a chunk of 2" kraft mailing tube, split a short piece, and trim the U shape section to fit up nice between the 2" OD ply nose ring and the fuse underside, then fill in with ply each side. Once you glue in and finish the paper tube it is tough as nails.
02-26-2015, 03:42 PM
#218
I still have a pile of ultra light contest balsa from my last pattern plane build. Scratch building a full 2 meter electric pattern plane and come in under weight means buying about twice the balsa you need and weighing each piece. I will use this for cowling in the engine.
03-01-2015, 03:13 PM
#219
I did the first testing today on an electric setup. It swings an APC 8.8x9.25 pylon prop at 20k+ rpm @ < 3100W. The motor, ESC and battery weigh 39 oz. Can a SD handle that much weight? I wasn't thinking of the SD when I put this setup together, but it's got lots of poop, so I figured I'd ask. Anyone care to guess? The testbed is a Sundowner 50. No flights yet, just ground runs for watt-meter readings.
03-01-2015, 04:15 PM
#221
Probably more like 3.75 hp at the shaft, (90% efficiency) but yeah, it should really scoot. The problem (?) is the 2.5 lb. part. I've got some birds with sky-high wing loading, but none of them are that small and they all have wheels.
What's the heaviest SD that's actually flown?
What's the heaviest SD that's actually flown?
03-01-2015, 05:35 PM
#223
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I probably have the most grossly overweight SD in existence. My .67 version is around 4-1/2 pounds dry. The engine package on that is probably, lessee... 25-27 ounces with pipe? Add 11.5 liquid oz fuel and we're up to 35-36 ounces, add three ounces for the tank and we're about the same drive weight. It's not a lot of fun to land or launch, but a lot of that is fear of snagging and breaking $16 props on landing and cartwheeling.
Yeah you could do it, but you will be making some significant mods to the center section to fit batteries etc. What is your battery pack? You can check out the Scr Demon .65 thread to see how I butchered the kit to make room for fuel.
PM me your email address, I'll send a pdf planset you can check out. Honestly, a new version should be designed to hold more battery without extensive builder modifications. But hey if you're a builder & improviser you'll figure it out, but the airplane will be a somewhat white canvas for the mods.
Yeah you could do it, but you will be making some significant mods to the center section to fit batteries etc. What is your battery pack? You can check out the Scr Demon .65 thread to see how I butchered the kit to make room for fuel.
PM me your email address, I'll send a pdf planset you can check out. Honestly, a new version should be designed to hold more battery without extensive builder modifications. But hey if you're a builder & improviser you'll figure it out, but the airplane will be a somewhat white canvas for the mods.
Last edited by MJD; 03-03-2015 at 02:03 PM.
03-01-2015, 05:48 PM
#224
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To all those waiting for short kits - I got the parts all sorted and boxed, just to insert plans and tape them up. Perhaps it might work if each of you PM'ed me your contact info? And remind me the engine config so you have the right bits.