True.
But I was thinking about the "seventh" glow plug all on its own. It would be OK if you had a dummy resistor of the correct value to balance the thing up. But then you have this odd resistor floating about in free air, getting very hot just like a glowplug. JimB
I Believe the heater is Only Required for Starting the Plane.
Not for Running it.
Back when I was YOUNGER, (50 years ago) guys had single Piston Planes, and the battery was Just for Starting
After that, the Ignition of gas, would keep the plugs Glowing.
Sorry, Bad Day Yesterday, Can't Count Correctly and Can't Divide the voltage by Two.
• Glow driver battery (1.2V 6000–9000mAh Ni-MH battery required)
Glow Plug Starting Battery
The starting battery or on-board battery (whichever you prefer) should be a 1.2 V 6000–8000 mAh battery pack. We’ve had success building a pack of (6) 1300–1600 mAh NiCd (preferred) or NiMh (takes longer to cycle to full capacity) 1.2v battery cells wired in parallel so the total capacity is 7800–9600 mAh. The total draw on 7 glow plugs at 2.2–2.7 amps per plug is 15.4–18.9 amps. With a 7800–9600mAh battery pack, you can expect about 30 minutes of ‘on-time’. Once the engine is broken in, you will likely find that the engine idles and runs very well without an on-board battery.
Installing On-Board Glow Drivers Although Evolution Radial engines run just fine without constant glow heat applied, the use of on-board glow drivers allows for easier engine starting and can ensure adequate heat in the glow plugs at all times. This is particularly important on radial engines where oil collects in the lower cylinders. SonicTronics/McDaniel RC on-board glow systems work very well with Evolution radial engines. 7-cylinder applications: MCD477 9-cylinder applications: MCD479 We recommend installing the glow driver socket on the side of the cowl or fuselage and keeping the battery wires as short as possible. Longer wires between the battery pack and the glow drivers will reduce the amount of glow plug heat. Attach the ground wire to one of the engine backplate screws or the crankcase.
6Ah to 9Ah is a wide range; you can define the nominal duration by referring to the discharge graphs in the battery data sheet. The glow plugs require 1.5V at 3A not 1.2V. The OP is not asking about ground starting if that is what you are describing.Glow driver battery (1.2V 6000–9000mAh Ni-MH battery required)
The starting battery and on-board battery are two separate things. Once again, the plugs are 1.5V at 3A, not 1.2V at 2.4A. The former corresponds to only 2.88W instead of 4.5W which would greatly decrease the effectiveness of the plugs, especially when saturated with fuel/oil.The starting battery or on-board battery (whichever you prefer) should be a 1.2 V 6000–8000 mAh battery pack.
All batteries behave differently, but the number of charge discharge cycles to reach absolute full capacity is little more than a very minor inconvenience. Besides which, NiCad batteries have some awkward characteristics of their own including the need to attain full capacity. They are also extremely heavy.We’ve had success building a pack of (6) 1300–1600 mAh NiCd (preferred) or NiMh (takes longer to cycle to full capacity) 1.2v battery cells wired in parallel so the total capacity is 7800–9600 mAh.
This is not correct. The plugs take 3A each as stated by the OP. 7 * 3A= 21AThe total draw on 7 glow plugs at 2.2–2.7 amps per plug is 15.4–18.9 amps.
What specific batteries are you talking about? 7.8 Ah to 9.6Ah is a wide range.With a 7800–9600mAh battery pack, you can expect about 30 minutes of ‘on-time’.
The on board plug power is not required for startingInstalling On-Board Glow Drivers Although Evolution Radial engines run just fine without constant glow heat applied, the use of on-board glow drivers allows for easier engine starting.
SonicTronics/McDaniel RC on-board glow systems work very well with Evolution radial engines. 7-cylinder applications: MCD477 9-cylinder applications: MCD479.
We recommend installing the glow driver socket on the side of the cowl or fuselage and keeping the battery wires as short as possible. Longer wires between the battery pack and the glow drivers will reduce the amount of glow plug heat. Attach the ground wire to one of the engine backplate screws or the crankcase.
This is another Ah range. NiCd does not supply 1.5V. Also six 1.5Ah NiCad batteries (if that is what you are talking about) would be costly, bulky and, worse still, very heavy, bearing in mind that they would be inside the plane. Take an example. The weight of a 3Ah LiIon battery is 48 grams. The weight of a 3Ah NiCad battery is 86 grams, but you would need three NICad batteries to equal the energy of one LiIon battery, giving a total weight of 3* 86 grams= 258 grams ie 5.375 times heavier, and this is not mentioning the bulk which would be greater by a factor of 4.43.We’ve had success building a pack of (6) 1300–1600 mAh NiCd (preferred)
View attachment 99828
As an interested observer .... the plugs seem to have individual wires and must be bought together to the 1.5v supply somewhere (for starting ) in flight would a 7 pole rotary switch ( mechanical or electronic) work? just cycle (step ) through 1-7 connections. just need one 1.5v 3A battery .
Seven plugs will do pairs with dummy plug resistor as stated on previous post. Glow plugs take some time to heat, so too quick a scan won't do. I don't think 48 grams will be a problem.OP said I think possibility of one or more cylinders could stop firing during flight and needed some glow current , Pilot would not know what cylinder ? so a quick cycle through each ( 7 wont do pairs ! ) would do . Weight of batteries etc could be a problem (Would like to see pic of OP aircraft , Sopwith camel ? )
spec , that has answered a mystery I have had for 55 years , ... I built a Cesna 127 balsa and tissue , 36" wig span with a .049 glow , but to make it look like the real thing I mounted engine upside down ! , it was a really good looking model , second flight after some balancing etc in my uncles field , engine running well ( I think they lean out in flight) launched into wind , 2 ch 27mhz working OK , engine slowly lost power, wind took it back down hill , loosing altitude 20 ft > 2 ft , crashed headlong into field 5 barred iron gate....It seems that the bottom plugs are the ones that mainly need the heat due to oiling,
spec , that has answered a mystery I have had for 55 years , ... I built a Cesna 127 balsa and tissue , 36" wig span with a .049 glow , but to make it look like the real thing I mounted engine upside down ! , it was a really good looking model , second flight after some balancing etc in my uncles field , engine running well ( I think they lean out in flight) launched into wind , 2 ch 27mhz working OK , engine slowly lost power, wind took it back down hill , loosing altitude 20 ft > 2 ft , crashed headlong into field 5 barred iron gate....the RC got built into a boat !
sopwith.. sorry to mess your thread..
Seem to remember I had a wet 2v lead acid cell for the glow plug , had to watch the red and black crock clips didn't touchNever did get the engine to work well. It was always a pain to start..
Seem to remember I had a wet 2v lead acid cell for the glow plug , had to watch the red and black crock clips didn't touch, my worst disaster was a large balsa Gypsy Moth powered by about 8 feet of 1/4" rubber , wound up with a hand drill ( egg whisk style) , 100 or so turns great,,,, My kid go chasing after it... "more turns Dad .." at 400+ little peg in tail holding, said elastic, shot from one end to other taking all the spars with it ... we nearly cried ....
Hy Reloadron,
I am having trouble relating your post to the OP's post.
6Ah to 9Ah is a wide range; you can define the nominal duration by referring to the discharge graphs in the battery data sheet. The glow plugs require 1.5V at 3A not 1.2V. The OP is not asking about ground starting if that is what you are describing.
The starting battery and on-board battery are two separate things. Once again, the plugs are 1.5V at 3A, not 1.2V at 2.4A. The former corresponds to only 2.88W instead of 4.5W which would greatly decrease the effectiveness of the plugs, especially when saturated with fuel/oil.
All batteries behave differently, but the number of charge discharge cycles to reach absolute full capacity is little more than a very minor inconvenience. Besides which, NiCad batteries have some awkward characteristics of their own including the need to attain full capacity. They are also extremely heavy.
This is not correct. The plugs take 3A each as stated by the OP. 7 * 3A= 21A
What specific batteries are you talking about? 7.8 Ah to 9.6Ah is a wide range.
The on board plug power is not required for starting
So there is an off the shelf solution. What is the size, weight, and cost?
Agree, but the critical item is the switch to turn the high current on. A relay to switch 12A at 3.6V or 21A at 1.5V in a small size with a reasonable coil drive does not exist, as far as I can tell. The alternative is to use MOSFETs as the switch which will take a bit of sorting. Heavy gauge, high temperature wire (silicon sleeve/silver coated multi strand conductors) will also be required. It would be better to fit the connector away from the prop for obvious reasons.
At the high currents required the connector choice will be critically important to ensure a low voltage drop and long life. The contact material, like any relay contact, will be a challenge, not only because of the high current, but also because of the low voltage. Being DC doesn't help either.
This is another Ah range. NiCd does not supply 1.5V. Also six 1.5Ah NiCad batteries (if that is what you are talking about) would be costly, bulky and, worse still, very heavy, bearing in mind that they would be inside the plane. Take an example. The weight of a 3Ah LiIon battery is 48 grams. The weight of a 3Ah NiCad battery is 86 grams, but you would need three NICad batteries to equal the energy of one LiIon battery, giving a total weight of 3* 86 grams= 258 grams ie 5.375 times heavier, and this is not mentioning the bulk which would be greater by a factor of 4.43.
Thoughout your post you do not say what specific batteries are being described. The battery model make a big difference to the performance and you seem to have missed the point that the OP wants a light weight, short duration (5min) on board system, not 30 minutes. But even so, LiIon would be a much better solution.
In general LiIon batteries are far superior to NiCad- much lighter, much less bulky, and easier to charge (no memory effect or reversal). they also hold their charge better. LiIon is also better for the environment. These are the reasons for the overwhelming move from NiCad to NiMH to LiIon. Although NiCad were better at high currents, the latest generation of LiIon can also source high currents, 35A in the case of one of the Sony LiIon 18650s, for example.
As I have mentioned already, there are a ton of fake batteries around which have a radically poorer performance than the genuine article, especially for high current applications like this. These fake batteries tend to have a sharply falling output voltage as they discharge and they also start with a high internal resistance.
One final point is that it is important to have a good charger with the correct voltage set points. Once again there are a load of rubbish chargers on the market. For good battery life and reasonable capacity it would be best to charge to 4.1V constant current with no topping charge and cutoff at 3.1V on discharge.
spec
PS: I am an aero-modeller too, but mainly sailplane.
The best scale model I ever saw was a from scratch B17 with four glow plug engines. The real thing flew over the sea front, where I live, last year at the annual air show.
That was not me, I quoted the manual.
http://www.evolutionengines.com/ProdInfo/Files/EVO_Radial_Glow-Manual.pdf
Everything I quoted was from the manufacturer but I managed to forget to link it. That is why it shows in my post as a quote.
Ron
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