2 Stroke Tickover Speed?

[Roger Dyke]

Hi All,

 

Although reasonably conversant with 2 stroke engines, I am always at a bit of a loss as to what RPM to set the slow running to. 

 

Too quick tends to carry the aircraft down the runway when landing and too slow givies me probiems with throttle pickup when when abruptly opening the throttle (for a possible go-around).

 

I usually aim for about 2300 RPM but feel that probably it's a bit slow and unpredictable on the pickup.

 

Is there a favoured RPM?

 

[Mark Hewett]

23 minutes ago, Roger Dyke said:

Hi All,

 

Although reasonably conversant with 2 stroke engines, I am always at a bit of a loss as to what RPM to set the slow running to. 

 

Too quick tends to carry the aircraft down the runway when landing and too slow givies me probiems with throttle pickup when when abruptly opening the throttle (for a possible go-around).

 

I usually aim for about 2300 RPM but feel that probably it's a bit slow and unpredictable on the pickup.

 

Is there a favoured RPM?

 

The favoured idle RPM will be the slowest you can achieve consistent with the engine idling on the ground for say 20-30 seconds, and still picking up reliably. Accurate tuning of the idle mixture will enable the slowest reliable idle speed. It will be different for different engines, and for a given engine, with different prop sizes.

[john stones 1 - Moderator]

Tachos of no use Roger, your ear and the engines response to tuning is the way, less pitch on prop can assist to slow landing speed also.

[Nigel R]

Never tacho'd an idle for anything other than interest.

 

Just go for the lowest that you can get it reliable.

 

1 hour ago, Roger Dyke said:

Too quick tends to carry the aircraft down the runway when landing

 

Reasonable excuse to add some flaps?

[J D 8 - Moderator]

1 hour ago, Roger Dyke said:

 

 ---- problems with throttle pickup when when abruptly opening the throttle (for a possible go-around).

 

 

 

  There is an issue that many engines including some full size of old just do not like the throttle being opened abruptly and will cut. Take a second or so to move the stick to flat out or if you find you just can not how about a servo slow.

[Roger Dyke]

Thank all for the info.

 

I usually aim for about a minute or so idling time, but no matter how I fine tune the slow needle, I always have to be careful how fast I increase the throttle for the revs to pick up after that time. Otherwises it's touch and go whether they suddenly quit. From what you say, It sounds quite normal.

 

By the way, the two engines in question are a Super Custom 61A with a new carb and a Irvine 61 Mk2 (red one). Both are in very good condition with good compression. The props are 13x6 APC.

[john stones 1 - Moderator]

Props ok, bit of nitro in your fuel ? Model nose heavy by any chance, tweaking c.g may help.

 

[J D 8 - Moderator]

 A minute is a long time for a model glow engine to idle and so cool down. 

[Nigel R]

41 minutes ago, Roger Dyke said:

Thank all for the info.

 

I usually aim for about a minute or so idling time, but no matter how I fine tune the slow needle, I always have to be careful how fast I increase the throttle for the revs to pick up after that time. Otherwises it's touch and go whether they suddenly quit. From what you say, It sounds quite normal.

 

By the way, the two engines in question are a Super Custom 61A with a new carb and a Irvine 61 Mk2 (red one). Both are in very good condition with good compression. The props are 13x6 APC.

 

Sometimes it is difficult to get an acceptable balance between ideal idle setting and ideal pickup setting. Plus engine temperature affects the ignition, as JD8 says a minute is plenty of time for the engine to cool down. And we don't have accelerator pumps so cannot compensate with an extra dollop of fuel when the throttle is gunned...

 

Servo slow is a pretty good feature to take advantage of on modern radios.

 

 

[Roger Dyke]

I do run 5% nitro (newish fuel) and aircraft balance is good.

 

Yes, a minute is a long time for a glow engine isn't it. I hadn't really considered the cooling down making that much difference but you may be right. With the slow idle I'm probably trying to over-egg the pudding, as they say. Thanks for that.

[Roger Dyke]

I don't think my Spektrum DX6 G3 has got the servo slow facility. Shame as that could have been useful.

 

I think that I am having to re-think my idling and throttling as what I am after is probably not possible (ideal world).

[john stones 1 - Moderator]

Throttle up gentler, there's your servo slow, revs better once airborne, so you mave have room to reduce a click or two once up.

[GrumpyGnome]

I'd suggest the biggest problem is that minute of idling.... a minute is an awfully long time....

[Martin Harris - Moderator]

It’s a good test though.
 

Does your radio have flight modes?  You could set a “flight idle” mode and a “landing” mode with reduced idle. Ideally, with most models you should plan for an engine on approach rather than a glide approach - more scale like, with a slower air speed if flown correctly and less chance of a dead stick.  

[Nick Cripps]

1 hour ago, Roger Dyke said:

I don't think my Spektrum DX6 G3 has got the servo slow facility.

 

Yes it has, it's in Servo Setup in the Function List, the same place as you set servo endpoints and reversing, etc.

[Chris Walby]

Start the engine and set the idle on the on the TX with the trim (engine coolish) the idle is slowly increasing to the point before take off then go fly. If the engine is getting a good workout then the tick over will be higher so just before landing I give it a few clicks down on the trim just before landing so I know it will be a low tick over, but I am on the throttle for the landing approach anyway. If I lotter of just fly around for long periods with very little throttle (engine cools) I just land without touching the trim.

 

Not sure I like the idea of a slow throttle response, nice warm engine and a mistake at less than 3 mistakes high, you know and need to give it some wellie and the servo is just plodding along...binbag anyone?

[Roger Dyke]

John and GG: Thanks for your input.

 

Martin: Yes, it does have flight modes. I hadn't really looked at that. I don't really want to make it complicated. I like to keep it simple being old school.

 

Nick: I missed that. I'll have another look. Thanks for that.

 

Chris: Thanks for your thoughts.

[Mark Hewett]

41 minutes ago, Chris Walby said:

 

Not sure I like the idea of a slow throttle response, nice warm engine and a mistake at less than 3 mistakes high, you know and need to give it some wellie and the servo is just plodding along...binbag anyone?

I've used a slow throttle opening a couple of times on petrols to get a reliable pick up from idle. Just 0.7 seconds was enough, and the engine must take that long to reach full power anyway, coz I didn't notice any delay in pick up with it set.

[Paul De Tourtoulon]

I use the throttle trim to give a fast idle, then when flying downwind I trim it back down, then use the throttle stick, that is what I thought it was for.

[RottenRow]

I just use a 3 position switch on the transmitter. On a typical Futaba Tx it's the one second from the right along the top front of the case. It might be in a different position on a Spektrum.

 

Up position = normal (fast) idle

Mid position = slow idle

Down position = engine cut

 

Fine adjustment can be made using the trims but they are usually not touched during a flight.

 

On older style transmitters with slider trims I do use those; trim fully up for fast idle, middle for slow idle and down for cut. That's how it was usually done in the days before radios with pushbutton rather than slider trims. I still have a few old Field Force 7s.

 

Brian.

[Engine Doctor]

An onboard glow will help the pick up when throttle is  opened. Set to only come on at half throttle and lower.

As  engines and glow plugs cool when on low throttle any sudden opening of throttle will send a load of cold fuel mix up to th plug and cool it even more. A fourstroke plug might help provided it doesnt advance timing too much.

Get the idle to a speed where engine is happy . Dont worry what tacho says.

[Simon Lumsdon 1]

I have an SC 61A and had lots of trouble getting a reliable idle (spend time getting the low speed needle right) and it still doesnt like a quick throttle up, i suspect the large intake bore is the reason, lots of power but poor throttle up? Last time out i was contemplating adding some expo to the servo, once at 1/4 throttle its almost full power, very on off. I will have to give this a go since otherwise its a fine engine and once adjusted has been worth the effort

[GrumpyGnome]

@Simon Lumsdon 1 you may find a custom 'curve' better than expo, preferably five points, as you'll have more control over the stick:servo movement..... Peter J put a lovely simple diagram of the typical curves needed for glow, petrol and electric power in the mag a while ago

[Nigel R]

14 hours ago, Chris Walby said:

need to give it some wellie and the servo is just plodding along...binbag anyone?

 

I hazard to suggest that a half second throttle response is the least of your worries if you're that marginal. Anyway, the point of the 'slow' is to get the throttle to follow the fastest pickup your engine can manage after an extended idle. It's a last resort of throttle tuning after getting the needles set as good as you can.

 

Put it another way, what's worse for your bin bag scenario? The 'slow' response (which if set right is as quick as the engine can manage anyhow), or opening the throttle - and getting the sound of silence?

 

11 hours ago, Simon Lumsdon 1 said:

large intake bore is the reason

 

Smaller carbs do seem to be easier to manage. 

 

One of the best glow engines I have owned, in terms of throttle response, is the old OS 40FP, which has a tiny carb compared to most 40 size engines (and it's only a single needle air bleed, too). It's smaller than some 20s even. And the motor will idle and idle and idle and then snap to full throttle quite happily.

 

[Roger Dyke]

My thanks to you all for your wonderful and comprehensive replies.

 

You have certainly give me a lot to go at when I'm next down at the field.