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Mar 12, 2018, 11:57 PM
Right on the Edge!
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On-board glow ignition on low RPMs: bad idea?


Hi there,

maybe because of the slightly rich settings I keep on the LS needle, or maybe because of the 15% nitro, my ASP .91 fourstroke is quite bumpy at low RPMs (anything below 2800 gets too bumpy to be safely set as idle). I already tried playing with mixture, little success.

I was thinking about something like this:

- an igniter always on
- an electronic switch connected to the Rx
- a regulator set to 1,5 V that goes from the switch to the igniter
- a setting in the Tx that tells the switch to switch on when the throttle is lowered below X% (10%?)

Its only purpose would be to help lowering idle RPMs and diminish vibrations, maybe reducing a little bit fuel consumption as well. When the igniter is on I can indeed go much lower. In this case I should probably be able not to even add a separate battery for it.

Does this sound like a good idea or is there something important I am not thinking that I should?

Thanks
Last edited by Hlaalu11; Mar 13, 2018 at 02:10 AM. Reason: Spelling & grammar fixes
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Mar 13, 2018, 12:42 AM
Registered User
Sounds like a good idea to me.

That said there will be others berating you for not properly adjusting the carb.

If it's a 91 you could probably haul a "D" cell around which should light the plug at idle for quite a while.
Mar 13, 2018, 01:11 AM
most exalted one
There are "smart" onboard glow igniters available for a reasonable price from places like Hobby King. You can use a LIFE 6.6V battery with them or a large enough LIFE for that and your receiver combined. The ones from HK and elsewhere that are cheaper actually operate the opposite of what we want so you insert a reverser in the line or connect them to a separate channel and mix them with the throttle but in reverse.
Sounds complicated but isn't. For about $20 you can get one that can plug into a spare channel and if you have a LIFE battery of at least 1600 mah or so you can use it for both rx and onB glow.
I don't have that setup on all my glow models but on most and on any new one. I may get around to the one or two old ones yet.
The other advantage is you keep your fingers out of harms way. Turn on, throttle low(so glow is on), fire up the engine. No need for attaching an igniter or removing.
Have that mixed channel on a switch so you can turn it off if you want to play with the prop with the model switch on.

https://hobbyking.com/en_us/hobbykin...ow-driver.html
Last edited by 4*60; Mar 13, 2018 at 01:22 AM.
Mar 13, 2018, 01:41 AM
Right on the Edge!
Thanks for the replies.

I have actually always used a regulated Lipo for the Rx, because I want to check the charge status via voltage, and that's not easy with a Life. I already have a Lipo and a BEC installed now.

Tinkering with OpenTX is probably the funniest and easiest part, but the problem is that the updated version of the item you posted the link of (https://hobbyking.com/en_us/hobbykin...driver-v2.html) does not seem to have a wire for the Rx at all. The one you posted has quite a low rate from buyers...

I mean I guess I can physically remove the switch and replace it with an electronic switch, but why they removed the Rx wire in the first place I don't understand...
Last edited by Hlaalu11; Mar 13, 2018 at 01:48 AM.
Mar 13, 2018, 02:36 AM
Registered User
SeismicCWave's Avatar
Quote:
Originally Posted by Hlaalu11
Hi there,

maybe because of the slightly rich settings I keep on the LS needle, or maybe because of the 15% nitro, my ASP .91 fourstroke is quite bumpy at low RPMs (anything below 2800 gets too bumpy to be safely set as idle). I already tried playing with mixture, little success.

I was thinking about something like this:

- an igniter always on
- an electronic switch connected to the Rx
- a regulator set to 1,5 V that goes from the switch to the igniter
- a setting in the Tx that tells the switch to switch on when the throttle is lowered below X% (10%?)

Its only purpose would be to help lowering idle RPMs and diminish vibrations, maybe reducing a little bit fuel consumption as well. When the igniter is on I can indeed go much lower. In this case I should probably be able not to even add a separate battery for it.

Does this sound like a good idea or is there something important I am not thinking that I should?

Thanks
Great idea and fairly easy to do. The glow ignition really helps the low end reliability. You can use a mechanical micro switch and a servo to activate or an electronic switch that simply plugs into a spare channel.

I would add a spare battery just so that you have a peace of mind and not running the airborne receiver pack too low. LiPoly packs and a regulator combo are so light nowadays it is really not an issue.
Mar 13, 2018, 02:45 AM
most exalted one
Some of the ratings are there because there were no instructions at one time. Some are there because some people don't have a clue. Some may be there because HK products are not always 100%. If you go to the UPLOAD FILES tab there are instructions. I was using rcd3001 rcd3004 products but they seem to have quit selling them anywhere so I have a few of these.
The one servo lead is to be plugged into the receiver and will draw approx. .8 amps (.8 not 8 because you convert 4 amps at 1.2v from the 7 or more volts of your pack)when actually on and insignificantly when glow is off.
Remember the language barrier and the poor description of a lot of HK products because the updated V2 version is really a basic version where you push the button and it stays lit for 15 seconds. It is not controlled by a receiver and therefore may be V2 but is not an updated version. They just don't seem to understand what they are selling sometimes.
4-16v input so a lipo would be fine. Really!!! Buy one and try it on the bench. They work well. I have used many different OB glow including simply a switch activated one but these are the easiest to use and very inexpensive.
I finally had a few people abandon the microswitch route and use this style of device. I used to sell the microswitches a D cell Nicads etc to some local guys.
Last edited by 4*60; Mar 13, 2018 at 02:54 AM.
Mar 13, 2018, 02:54 AM
Right on the Edge!
Thanks for the inputs. I think I'm going to tinker with this soon.

As for the setup, yes I've gone Lipo + BEC since my first days with gas and my plans are to stick with that.

The question is rather, as you say, whether to add another battery or not for when I'll try the glow igniter... I've little clue of how much current it would use, if set up in this way. I've the feeling that if I set it up so that it only kicks in in taxing mode, at low RPMs, and not during regular flight idle (which is higher anyway), then it shouldn't impact much on the battery consumption...

Right now I'm using 920 mah packs, which I replace after 5-6 flights, still half charged. I don't mind at all replacing the packs this often, so this wouldn't be a problem per se.
Mar 13, 2018, 03:00 AM
most exalted one
Take a look at the document I uploaded in my previous post. There are ten configurations for this in that document. 920MAH seems a little light to me but if you get 5-6 flights normal then you might be using 80-100mah a flight? If this was on 1/3 of a 10 minute flight that would take approx 30MAH plus the start time or amount of time it is on on the ground.
The only question is the bec good enough to add another 800mah draw at times when this would be on.
That's why the LIFE packs made sense to me and most of us around here use them. They do not require a bec. Not trying to convince you to change just poimting out why they are attractive.
Last edited by 4*60; Mar 13, 2018 at 03:10 AM.
Mar 13, 2018, 03:03 AM
Right on the Edge!
Quote:
Originally Posted by 4*60
The one servo lead is to be plugged into the receiver and will draw approx. .8 amps (.8 not 8 because you convert 4 amps at 1.2v from the 7 or more volts of your pack)when actually on and insignificantly when glow is off.
This is what I was looking for when I was writing the other post! It seems that I won't have to add another battery. Even better this way.

Quote:
Originally Posted by 4*60
Remember the language barrier and the poor description of a lot of HK products because the updated V2 version is really a basic version where you push the button and it stays lit for 15 seconds. It is not controlled by a receiver and therefore may be V2 but is not an updated version. They just don't seem to understand what they are selling sometimes.
I guess that in theory if you physically unsolder the 15sec switch and connect that end to a electronic switch coming from the receiver, you should be fine, in theory... but then you would also have to re-wire a LED to tell you when it's on and when it's off. Could be done but too much hassle... I've read all the comments about the "old" version. You're right, some of them are just because of lack of instruction (back then).

I think I'll go with this and I won't even need a separate switch. Thanks!
Mar 13, 2018, 03:08 AM
Right on the Edge!
Quote:
Originally Posted by 4*60
Take a look at the document I uploaded. There are ten configurations for this in that document. 920MAH seems a little light to me but if you get 5-6 flights normal then you might be using 80-100mah a flight? If this was on 1/3 of a 10 minute flight that would take approx 30MAH plus the start time or amount of time it is on on the ground.
This would definitely mean I won't have to go for a bigger battery. In fact I'd say that the time the igniter would be on would probably be fairly less than 1/3 of a flight: even if I'll decide to make it switch on during regular flight mode (as opposed to landing/taxing, which has a lower RPM), I don't think it'll get to one third... I'd say closer than 1/5 or 1/6, including engine starting time.

EDIT: I was seeing that very file on Hobbyking file section, apparently it has been uploaded for both the "old" and the "v2" versions... but it should not apply to the v2 as far as I can see/tell.
Mar 13, 2018, 05:05 AM
Registered User
Quote:
Originally Posted by Hlaalu11
Hi there,

maybe because of the slightly rich settings I keep on the LS needle, or maybe because of the 15% nitro, my ASP .91 fourstroke is quite bumpy at low RPMs (anything below 2800 gets too bumpy to be safely set as idle). I already tried playing with mixture, little success.

I was thinking about something like this:

- an igniter always on
- an electronic switch connected to the Rx
- a regulator set to 1,5 V that goes from the switch to the igniter
- a setting in the Tx that tells the switch to switch on when the throttle is lowered below X% (10%?)

Its only purpose would be to help lowering idle RPMs and diminish vibrations, maybe reducing a little bit fuel consumption as well. When the igniter is on I can indeed go much lower. In this case I should probably be able not to even add a separate battery for it.

Does this sound like a good idea or is there something important I am not thinking that I should?

Thanks
I don't get this....

I am not berating or trying to advocate against on board glow here.
Normally these engines idle very well, when running on the fuel they are designed for (5~10% Nitro).
A bumpy idle to me indicates that there is a bit too much Nitro (easier igniting fuel) and then you want to fix that by heating the glow plug, making ignition even easier. In my opinion this is about as logical as having a leaking canoe, then drilling a 2nd hole "so the water can flow out again"....

Why don't you just install two headshims? They cost about 1 dollar, and are a 15 minute fix, with a very good chance the bumpiness will be gone as well.

Nothing wrong with onboard glow, but that is usually NOT used to fix a bumpy idle, but to fix the problem of the engine dying below certain RPM.
Mar 13, 2018, 07:04 AM
Simply Reliable
Gary Cee's Avatar
What Bert said!

Please take no offense, you asked the question. On board glow is fine when done right and for the right reasons. Stepan, what you propose is neither.
Mar 13, 2018, 07:31 AM
Right on the Edge!
Quote:
Brutus1967 wrote:
Nothing wrong with onboard glow, but that is usually NOT used to fix a bumpy idle, but to fix the problem of the engine dying below certain RPM.
Do your engines, when RPM is low, die all of a sudden while smoothly idling or do they get bumpy as RPM drops before actually dying? Mine does quite the latter: lower than 2800 gets bumpy AND at higher risk for dying. THIS "mixed" condition is what I thought I could cure with an onboard glow ignition. But judging from what you say it seems that those are to be tackled as separate issues... I guess I have to get this right first. If so, then yes I guess a headshims could cure the bump. It's not that "I don't want to buy some", but that I didn't think of it before you mentioned it...

Quote:
Brutus1967 wrote:
Normally these engines idle very well, when running on the fuel they are designed for (5~10% Nitro).
A bumpy idle to me indicates that there is a bit too much Nitro (easier igniting fuel) and then you want to fix that by heating the glow plug, making ignition even easier. In my opinion this is about as logical as having a leaking canoe, then drilling a 2nd hole "so the water can flow out again"....
If I could find any fuel with less than 15% nitro in Korea, I'd be the first to try lower nitro content fuel. The reality is that even 15% is harder to find compared to higher mixes. Onboard glow ignition was more like a patch, or a workaround, whatever we want to call it. Not meant to address the "source" of the issue, whatever it is. If it were normal, every glow engine would have an onboard glow ignition as default...

Quote:
Originally Posted by Gary Cee
Please take no offense, you asked the question. On board glow is fine when done right and for the right reasons. Stepan, what you propose is neither.
No offense, why would I? That's why I asked after all!
Mar 13, 2018, 07:54 AM
Registered User
Well... if the bumpiness goes away by connectng the glow driver, it certainly is worth a try of course.
But usually, and especially at the RPM you mention, 2800 RPM, if idle gets bumpy lower than that, IMHO there it is an ignition timing issue, which in the case of glow engines always is either a fuel issue, or a plug issue, or a carb adjustment issue.

What I am used to (or better: my personal experience) is that a poorly adjusted carb does not make the engine "bumpy" it just makes the engine slowly fade away (too rich) or slowly speed up then die (too lean).
Bumpy as in "running harsh and shaking the plane", in my experience is a matter of mismatch between plug, compression ratio and Nitro content. Since there is usually not much options in plugs (Enya 3, OS F, some others maybe) and you cannot get any other fuel, I would suggest to lower the compression.

Of course, above all literally depends on MY interpretation of your description of "bumpy".

If actually your engine runs smoother when connecting the glowplug, then I would rather refresh the plug, and try to make an effort to get the carb dialled in properly (and in that case I suspect it is currently too rich)

Don't forget: changes to the adjustment, especially to the LS needle, really take some time before the effect is noticable. Can't really explain that, but it does. Make a small change, and go fly, see how it works out after a few minutes.
Mar 13, 2018, 08:02 AM
Registered User
Cougar429's Avatar
If installing an onboard glow heat there is one recommendation I would make: Depending on control, you should set up some method to TURN IT OFF. Otherwise, any time you have the aircraft at low throttle your plug will be energized, even while inactive, leading to the chance it may start with any rotation of the prop, (say, picking it up or moving it).

It would also reduce the load on the power source.

If you have it mixed into an auxiliary channel, have that on a switch to disable mixing until required.

There are good reasons for installing onboard glow, mostly to increase reliability. I plan to do this with the Seawind amphib so less likely to go for a swim to recover and the P-47 with the inverted Saito to prevent washout at lower RPM. I do not plan to use it to tame a badly running engine.

Hlaalu11, one thing you did not mention in the OP was if installing a new plug made any improvement and what orientation the engine is mounted. Same with mount type. If running an isolation style you will see lots of movement at low throttle when the pulses are more widely spaced. You can get this effect with some airframe structures that lack rigidity.

Even condition of fuel, (age, exposure, etc.) type of prop, or valve lash settings can contribute to idle quality. Have you checked the later recently?

Having said all that, if the engine is new and break in not complete all bets are off.


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