RPM Question???
 

Hi,

When you guys are dialing your engines for a given desired RPM, are you setting it to GROUND RPM? I did that, then installed a telemetry RPM sensor and was pretty alarmed at the readings from the sky. I picked up 1500-2000 RPM in the air. Is this normal for a 60cc engine??

great question. The common thought is that the engines will unload when in the air but by that much? That is roughly a 20% pickup in RPM

Sounds like the reading is off by an order of magnitude. I'd believe 150-200 increase in the air.

I have run Gas engines for 30yrs now and that is about right. I always estimated about 1000 rpm increase. The prop you are using will determine the amount of increased RPM

++1

Hi,

Thanks, guys. I'd be curious to know what those of you who are using telemetry are actually reading in flight.

In my H9 Stang I'm running a DLE55re, APC T6 racing prop. Spek Telemetry. Static 6950 peak in air 8500. All level flight. No full throttle dives.

Hi,

Now I feel better.

Shaun

This is one of the many reasons to NOT set your needle to the highest peak on the ground.
Always leave it a little rich on your ground setting.

A 22x10 APC?

Then why does DA recommend setting the high speed needle to peak RPM?

I do not agree with that statement.

All gasoline (hydrocarbon based) engines will maintain the setting throught the flight envelope we use. Our models do not exceed 1000ft +/_ in altitude , there is no reason to leave a Fat or Rich setting on the ground.

Set your engine to turn the desired RPMs on the ground while keeping in mind the MAX RPM from distributor.

Example : XX engines max is 8000RPMs , when setting it up and use whatever prop you want to achieve say 6800 on the ground. Once in the air it will loose some of the dynamic load on the prop with forward momentum and will increase RPMs,

Hi,

That makes it a little trickier. Should we assume that the manufacturer is always referring to 'unloaded' RPM as max? If so, how would one know if you weren't using telemetry? I always knew there was a little bit of unloading in the sky, but I'd have never guessed it would be that much. Frankly, it was a little alarming when I saw the telemetry reading. I don't have any reason to doubt the reading, either, because it's matching the on-board tach and a handheld tach for the ground readings.

Do what you like. I've never torched an engine on a lean run in flight. Seen plenty of other that have in my more than 30 yrs of playing with these things.
Can't say I've ever seen an engine go rich in the air. When all is working normal, they only get leaner.

Well telemetry is fairly new, it has only been commercially sold in the past couple of years. I do not think any manufacture has collected any data . It was always done by ear for me. You can usually tell if an engine is overreving." A guessing game"

The MAX RPM is what is considered a safe number for continuous running at the highest power level on the curve. I have had engines that were taken beyond the safe number a few times weather it be in a dive or underpropped. I have also overpropped engines but that loss of energy has to go somewhere =(heat).

My philosophy is to stay about 12-1500 under the max while being on the ground.

As Shaun stated early, I too would have never believed 1500-2000 increase in RPM. I always assumed, of course you know what happens when you ass-u-me something, that the max increase would be less than 500 RPM. Learning something new every day.

Have to say that I have been lucky as well. Never burnt one up. I agree with the , they only get leaner , but for that to apply air density would have to change . That occurs at about 2-4000ft intervals.

It depends on the prop being used. Example: a 24x6 prop will unload relatively small amounts while a 20x12 will unload much more. Once some of the static pressure load is removed from the back of the prop it will cut faster at a greater distance.

Hi,

I was with you until 'they only lean out in the air.' When I first started messing with gasoline engines, they'd invariably richen up when I took off, resulting in power loss and emergency landings. My glow engines tended to lean up in flight, but not my sparkies.

Anyway, I'm sure there are a few more guys on here with RPM telemetry?

Shaun: I am glad you posted this info. I have a g 62 that I can only turn 6350 on the ground. If it truly unloads that much I feel much better. Plane flies great as is, plenty of power. I am ordering a rpm sensor now.

Jay