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DX8 Throttle Curve and DLE 30ccCan't get it right....

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DX8 Throttle Curve and DLE 30ccCan't get it right....

Old 08-16-2011, 06:58 AM
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stevehookem
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Default DX8 Throttle Curve and DLE 30ccCan't get it right....

I have the DLE 30cc on an Aeroworks Extra 300. The servo end points are set that when the stick is down, the carb is closed. When the stick is up, the carb is all the way open. Watching it move, the throttle valve seems to open in a proportional manner. That is, as I move the stick slowly upwards is slowly opens more and more as you would expect.

However, when running, the engine is not reacting this way. It slowly advances from idle to full but reaches full throttle at 50% stick. Moving the stick up and down between 50% and 100% doesn't change the speed.

I have tried to set the "curve" in the transmitter but can't get it right. What is "expo" on the throttle too? Do I need a curve and expo?

If I want to advance the thottle slowly and get to full power with the stick all the way up, how should the curve look? I had to clear it out. Mine was not right at all.

Thanks for the help!
Old 08-18-2011, 07:11 AM
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DaddySam
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Default RE: DX8 Throttle Curve and DLE 30ccCan't get it right....

Most of the actual throttle response occurs in the first 50% of carb opening on our gassers. Your curve should be a slowly rising line up to about 80% (maybe 90) then go up to 100.
Old 08-18-2011, 01:03 PM
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Jezmo
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Default RE: DX8 Throttle Curve and DLE 30ccCan't get it right....

Steve, try putting 0-10-22-45-100 for your throttle curve points and see if that helps. That's what I run on my MVVS 26 gasser. It makes it feel a bit more linear but in truth most of the small gassers don't gain much if any after about 60% throttle opening unless you are running a smaller prop so it can rev up a bit and use the extra airflow through the carb. If you have a more 3D style prop it's loaded pretty hard and that keeps the rpm's down. Remember the engine is just an air pump so the faster it spins the more air it needs.
Old 08-18-2011, 02:18 PM
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Capt Cash
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Default RE: DX8 Throttle Curve and DLE 30ccCan't get it right....

I've wondered about this too. When I set up a new engine I run it upto full throttle on the ground and then reduce the transmitter's throttle endpoint until I hear an RPM drop.As you mightexpect the carb butterfly is no where near full open when you first heartheRPM begin to drop. Thisappears to besignificant on both the DLE30 and55 of mine and probably all gassers. The goal I think for everybody is to get an RPM change for every click of the throttle and for those that set up throttle curves, to get an evensmaller change at the pointon the stick position youchoose. Although as stated, prop size can affect RPM change in the upper range of throttle. But I'm wondering that if by backing down the upper endpoint of the throttle servo, if I may be limiting my max RPM of the engine while inflight?
Old 08-18-2011, 05:07 PM
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Default RE: DX8 Throttle Curve and DLE 30ccCan't get it right....

You can achieve a better result mechanicaly by altering your servo arm angles as per the pic below.

I did not create this pic. I saved it from a thread somewhere in the Gas Engines forum here on RCU. All credit is due to the original author. (I'm trying to find the thread).
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Old 08-19-2011, 01:52 PM
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Jezmo
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Default RE: DX8 Throttle Curve and DLE 30ccCan't get it right....

WOW it can be done better mechanically huh. Thanks but I'll stick to the reason I bought the computer radio. It makes life sooo much easier. I started out flying helis many many many years ago, before computer radios were even heard of. We had to set up a throttle curve to match the pitch position mechanically and man what a chore that was. I thank GOD for the new computer radios because I now spend time flying instead of cutting, grinding and adjusting.

Also, I can think of at least one very good reason not to limit the throttle travel to the position gaining speed on the ground. After the engine unloads in flight it will need more air to complement the extra rpm's it is now turning. Remember it is an air pump and the more rpm's it turns, the more air it pumps and the more power it makes.
Old 08-19-2011, 11:58 PM
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Default RE: DX8 Throttle Curve and DLE 30ccCan't get it right....

That's up to you.

The diagram looks complicated, but it's simple. All you need to do is use a servo arm 3/4 the length of the carb throttle arm and have the servo arm pointing at the engine at low throttle. The rest falls into place easily.

I also fly helis and use computer radios. I had a MA Spectra-G gasser heli and we did something similar to this on the throttle and it made a huge difference to governor performance because the governor was not aware of the radio's throttle curve.
Old 08-20-2011, 04:17 AM
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Default RE: DX8 Throttle Curve and DLE 30ccCan't get it right....

ORIGINAL: Jezmo

Remember it is an air pump and the more rpm's it turns, the more air it pumps and the more power it makes.
The pumping of air is at max when engine is at max torque- after that even tho rpm may increase - flow thru the engine decreases.
The example you give is true -up til max torque rpm occurs
Yhe only devices where flow keeps increasing is in positive displacement pumps- like a GMC blower- I used to run one on a Olds -on the street - zippy-
When the model is at full power and not moving - it may be at full (max) flow (power)
as the prop unloads in th air - power (flow) is typically decreasing but rpm is increasing .
In a dive - wide open -the thing may scream- but actual power is down.
The reason the rpm goes way up, is that actual load on the engine is decreasing
setting throttle linkage to power delivered is a moving target -
the old mechanical adj is the most simple as typically gassers have max response at lower end of throttle movement.
Old 08-20-2011, 05:36 AM
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Default RE: DX8 Throttle Curve and DLE 30ccCan't get it right....

You're speaking of "peak" Volumetric Efficiency. Yes it "generally" occurs right around torque peak. Remember torque peak is usually (not always) a fair amount lower than HP peak. Sometimes several thousand thousand rpm's less. In order to make that upper rpm number and the added HP to go with it more fuel and airflow through the engine are necessary. This probably ain't the right place for too much on this as I don't want to hijack the OP's thread but if we want to calculate the CFM (Cubic Feet per Minute) for a 4 cycle motor we can multiply the cubic inch displacement of the engine by the maximum rpm and divide the result by 3456. Then we multiply the results by the volumetric efficiency of the motor. I don't have the formula for a two stroke but this formula gives the information showing that rpm's are part of the airflow requirements of an engine.
Old 08-20-2011, 08:31 AM
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Default RE: DX8 Throttle Curve and DLE 30ccCan't get it right....

I'll stop with the problem with the formula -
The formula give peak possible flow - Once the engine reaches peak flow /max pressure - the additional rpm has LESS flow -per revolution - but more per minute-simply because the air can't flow faster under the existing condition. ports carb - valve size -etc..
When you supercharge or turbo charge or on two strokes - add pipe setup- you increase flow capability andy typically at higher rpm.
Or going back a looong way - I ran a flathead ford with 3 carbs enlarged radiused ports - releived block from valves to piston - headers and a cam which allowed for longer dwell times on n on -
It would blow off th then new performance Chev s - But being no fool - I abandoned the Ford -and went for the small block Chev-
It's all about flow potential
Old 08-20-2011, 03:26 PM
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Default RE: DX8 Throttle Curve and DLE 30ccCan't get it right....

The VE thing is very confusing. Most folks think just because the engine reaches peak volumetric efficiency it can't flow any more air as it spins faster. It does continue to flow more air, just not at the same efficiency level as when at peak. That's why the torque level starts falling. However the engine does still continue to ingest more air/fuel as the rpm's rise and as a byproduct makes more Horse Power at those higher rpm's assuming it is properly setup and tuned for that rpm level. I've been building race engines for about 40 years now and although I've quit driving professionally I did so for just a little over 30 years. The VE thing kicked my butt early on and it took a while for me to understand and believe Volumetric Efficiency greater than 100% was possible on a normally aspirated engine. ICE's are what have been my motivation for getting out of bed now for 50 years. Sorry, I'll stop rattling, I just love this stuff.
Old 08-20-2011, 04:59 PM
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stevehookem
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Default RE: DX8 Throttle Curve and DLE 30ccCan't get it right....

Whoa, way more info than I wanted. I'm setting my curve at: 0 15 40 55 100.
Old 08-20-2011, 06:38 PM
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Default RE: DX8 Throttle Curve and DLE 30ccCan't get it right....

ORIGINAL: Jezmo

The VE thing is very confusing. Most folks think just because the engine reaches peak volumetric efficiency it can't flow any more air as it spins faster. It does continue to flow more air, just not at the same efficiency level as when at peak. That's why the torque level starts falling. However the engine does still continue to ingest more air/fuel as the rpm's rise and as a byproduct makes more Horse Power at those higher rpm's assuming it is properly setup and tuned for that rpm level. I've been building race engines for about 40 years now and although I've quit driving professionally I did so for just a little over 30 years. The VE thing kicked my butt early on and it took a while for me to understand and believe Volumetric Efficiency greater than 100% was possible on a normally aspirated engine. ICE's are what have been my motivation for getting out of bed now for 50 years. Sorry, I'll stop rattling, I just love this stuff.
Yes it ingests more air per minute but actually less per each per revolution
That's the rub-
that's why HP is rpm revs per minute - a time function
and torque is an instantaneous reading
If it could ingest more per cycle - the torque would increase
Glad to see another old hot rodder still going after it - I built my first full blown setup - a flathead in 1955.
My hero is /was Smokey Yunick
Old 08-21-2011, 04:12 AM
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Jezmo
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Default RE: DX8 Throttle Curve and DLE 30ccCan't get it right....

OK I think we are saying the same thing now. My point being here, as the rpm's increase in the air, as opposed to sitting on the ground, it needs more air hence the carb butterfly needs to be open more after it unloads. That's what I was trying to get across in my first couple of posts. Yes, it is a function of time, Revolutions per Minute. That doesn't change the FACT that it needs more air/fuel as the "rpm's increase" after takeoff or said another way, after it "unloads" in the air. More air has to get through the hole in the carb in one minute when the engine spins more Revolutions per Minute after takeoff. That is the sole reason I said not to artificially limit the throttle travel to ground rpm's.

Bottom line - I still stand by my original statement from above and I quote - "After the engine unloads in flight it will need more air to complement the extra rpm's it is now turning. Remember it is an air pump and the more rpm's it turns, the more air it pumps and the more power it makes. " Now it might not generate more torque as the rpm's increase but just as you said in the last post, it does make more power AKA "Horsepower" as that is "work" or "torque" done in "time". Yes, I know even that has it's limits but for purpose of the conversation, as it originally started out, the engine will need more air flow after it gets off the ground due to the increase in rpm's from unloading. For those who might stumble upon this thread, it would be wrong to limit the throttle travel to the amount where no further rpm gain is noticed on the ground unless one is NOT interested in obtaining maximum engine performance in the air.

I also agree on the HERO part. "Best Damm Garage in Town" Smokey was a true hero in many ways. According to very reliable sources at Chevy, he did indeed design the Small Block with much assistance from Ed Cole and others in the engineering staff. (Yes I know Ed gets most of the credit here.) Have a wonderful day and Happy Flying.

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