Pond Skipper

If I had a observer he would be holding my radar gun .
My only field help is video soon the gps logger at best.

Chuck the 10% rule pans out good one to remember.

5x3 / 25.47k static / 28.47k / 1.118%
4.75x4 / 23.58k static / 26.48k /1.123%
4.5x4 / 23.98k static /27.63k / 1.152%
5x5E / 20.43k static / 24.94k / 1.22%
4.75x4.75EC / 22.86k static / 26.64k / 1.165%

Average of 5 props: 11.56%

Pond Skipper

https://www.youtube.com/watch?v=MtdA-Xcv0l0

https://www.youtube.com/watch?v=MtdA-Xcv0l0
APC Power Chart / App Data (peak read passing in front of mic)


5x3 / 25.47k / 183w / 27oz static / 28.47k / 81 mph
4.75x4 / 23.58k / 144w / 18.3oz static / 26.48k / 100.4 mph
4.5x4 / 23.98k / 127w / 16.96oz static /27.63k / 104.7mph
5x5E / 20.43k / 120w/ 16.1oz static / 24.94k / 118.1 mph
4.75x4.75EC / 22.86k / 134w / 16.7oz static / 26.64k / 119.84 mph

Actual speeds unknown, only consistent data methods and video's.
The data provides prop selection for: best speed or rpm or thrust or best mix.

The 4.75x4.5EC should do around 23.4k static / 27.4k / 117 mph.

MJD

My Feedback: (1)

I've simply dropped my iPhone on the runway and launched. No observer needed.

aspeed

https://www.youtube.com/watch?v=V0KtE6EKJKI This one seems to be around 15,000 on the ground and maybe 18,000 in the air. Pretty simple camera I think. No problem with Doppler that way. Won't give airspeed though. I found weight makes little difference in speed for control line, but rc accelerates from the corners slower when heavy, and it makes a bit more of a difference.

Pond Skipper

Easy one to read about 17.7k average and one hit a spot in the course for numerous readings that read 18,007 with best noted peak at 18,187
18,007 for 102.31mph best peak at 103.34mph. Using an MA10x6

The vid stated 180 to 190kph / 111.847 to 118.061mph. I don't know if he is using software that accounts for loss or lap times or radar.


My GPS speed logger has been testing with my car and its spot on with my digital gauge and needle dial seems close too but lags the data by about a second or two. The specs state +/- 1% so should get some real time speed readings leaving little doubt other than the losses due to weight of the device onboard and the drag it produces. I would imagine at 100 its only off by 2-3mph with the added drag and weight. I will run a tanks worth and vid then run a tank worth with it onboard and vid should hope not to see / tell much difference or with the audio tach readings.

Mr Cox

Not quite sure what you are after there, looks like a mix up of ratios and percentages...?
Average rpm increase, including doppler effects, might then be around 15.6%?

So with 10% for unloading i the air, that would leave 5-6% for doppler and an airspeed of around 40mph, sounds a bit low...

An onboard keychain camera together with the app would give you the true rpm and together with doppler data from a stationary head-cam, you could also calculate the speed.

Pond Skipper

Chuck said good rule of thumb 10% (averaged out my list without bothering to carry over to the next number)11.56% rpm increase over static with this engine pipe combo good for referencing on the bench for anticipated performance prior to test
flying a new prop selection.

I checked my app this evening with a 190mph video results with a Jett .50 engine from reading thru a speed trap. My app and pitch speed calc read 190.4mph. Numerous checks various video's types all end the same results or very near to any results that have used radar, speed timed traps, onboard data loggers etc. The app is great for showing change in prop selection, averages and desired progress. Readings really doesn't have to be spot on with Doppler effects for me to make use of the data.

Pond Skipper

What would be nice is a small rpm logger using a sensor. The whole setup would need to be light say less than 15g for use with the small planes. Yes true a small camera would log sound or just a sound logger. The GPS logger is a bit heavy at 40.3g for this size plane but will try it. For sure looking forward to trying it with the V12RR that plane should show less drop in speed with it onboard. Think I will try a 4.5 x 5 est. 26.2k / 124 mph.

Based on known 5x5 results 24.94k / 118.1
APC
4.75x5.5 / 24.9k / 130 mph
5.25x6.25 / 23.6k / 140

I think the engine can hack the props so have some on order.
It had no problem with the 5x5 may need to trim the second
one down to 4.5x6.25 if at 24.3k / 144 mph
Note these props have more beef at the blade to hub than typical

aspeed

The post # 1104 readings are 20% higher from the static ground rpm. That was with a 10 -6 prop. Some higher pitches may be more. RPM is not always relative to speed, but a pretty good indicator. A 12-3 for example may not wind up at all when in the air.

Pond Skipper

Yes very good point made Alan, I noticed that with the 5x5 a 12.2% increase better than the rest.
I have used the wood Top Flite 12x4 on a 4cyl not a lot of unloading but bang on thrust was the need at the time.

combatpigg

My Feedback: (3)

I tried the 5.25 x 6.25 on a Zalp .15.
It was really hard to get the engine to start with such a light prop. Just to prove that point I would throw on a larger prop after flubbing around with the 5.25 x 6.25 and it would fire right up.
It performed very well as probably the most undersquare [oversquare?] prop I've run with good results.
It was so wafer thin, but it held up OK for a $4 prop.
I've got no idea what sort of speed the Electric Racers get from these, but my guess is one of the racers has / had influence with APC's product development to get such a specialized prop out there.

Mr Cox

The calculation doesn't add up to me, with or without carrying over numbers...
5x3 / 25.47k static / 28.47k in air; this would be a ratio of 28.47/25.47=1.118 which is a 11.8% apparent increase in rpm.

Taking the average of the ratios would give an average ratio of 1.1556 which is 15.56% ?

This would in turn contain both an actual increased rpm plus the doppler effect.

If the engine is tuned for a pipe I don't think that the 10% rule of thumb will hold anymore, it sort of works with regular mufflers (and possibly open face too).
With a pipe the engine can either jump onto the pipe (giving a much larger increase) or it could be on the pipe already on the ground (giving a very small or no increase in the air).

aspeed

Ya, pipes are on or off. If on, it is an octave higher (or double the rpm) or lower. Anything in between is lugging the motor down. If you can whip it up, or fly downhill to get it up on the pipe, then you are golden. If not, the you are lengthening pipe, or cutting props, or swearing. When on, the swearing stops.

Pond Skipper

5x3 / 25.47k static / 28.47k / 1.118%
4.75x4 / 23.58k static / 26.48k /1.123%
4.5x4 / 23.98k static /27.63k / 1.152%
5x5E / 20.43k static / 24.94k / 1.22%
4.75x4.75EC / 22.86k static / 26.64k / 1.165%

Average of 5 props: 11.56%

11.18+11.23+11.52+12.20+11.65 (57.78) divided by 5 = 11.56% average from 5 tests

For simplicity originally 28.47 divided by 25.47 = 1.118
I didn't need to add in all the extra zero's

Still stated the proper percentage of 11.56%

Chuck I thought about weight with the 4.75x4.75 carbon very light.
But didn't seem to bother the .07 engine. The electric props thus
far have been worth the effort. The thin blades are allowing props
I would normally not consider. Bought 3 of ea. to test and cut down.

Good chance 130 is about to be busted down wind per my data gathering methods.
I will then use the gps speed logger and compare with live vid review of the data.
Averages from the results could be within 7.849721046%

Mr Cox

Looks like you have mixed up the numbers somehow, I think you are after;

(11.8+12.3+15.2+22.0+16.5)/5=15.56% ?

Pond Skipper

Perhaps we can look at it another way to define the number further:

5x3 / 25.47k static / 28.47k / + 3k
4.75x4 / 23.58k static / 26.48k / +2.9k
4.5x4 / 23.98k static /27.63k / +3,65k
5x5E / 20.43k static / 24.94k / +4.51k
4.75x4.75EC / 22.86k static / 26.64k / +3.78k

Average increase of 5 props: + 3,568 rpm
Percentage increase 13.297551%

Average static of 5 props: 23,264 rpm
Average unloaded of 5 props: 26,832 rpm

3,568 is a 13.30% increase of 23,264 for a total of 26,832

So by final review 11.56% + 1.74% increase

Pond Skipper

Average prop: 4.8x4.15 / 105.45 mph

Mr Cox

Well, I think that first we need to "agree" on how percentages are calculated...

In the metric system 1% = 1/100
Så 3,568/ 23,264 = 0.153 which is equal to 15.3%

Pond Skipper

Percentage increase/decrease 3rd calc. down.
26,832 into 23,264 for 13.297%
23,264 into 26,832 for 15.337%

http://www.percentagecalculator.net/

Agreed, 15.34% looks good dividing the increase into the original static number.

Pond Skipper

Here is my next trick to increase tank pressure as observed in the last vid every time the plane was maneuvered vertically or in a hard turn the G forces was starving the engine. Will leave the original feed line length as is just in case the pressure is too much using the one way valve. Can tap the crank case if need be, the option is already set up when I was modifying the car engine back plate.

combatpigg

My Feedback: (3)

Have you ever seen how much of a Fire Hydrant this can produce by dry cranking the engine with the feed line disconnected..?

Mr Cox

I don't think that more pressure will help much, the key is to have less difference in the fuel level position when plane is horisontal or vertical.

Sounds like the tank is simply too far from the firewall?
Don't know the installation, but try putting as far forward as possible, i.e. right behind the firewall...

You could also try with a uniflow set-up, if you don't already have that.

combatpigg

My Feedback: (3)

High pressure makes the fuel that is traveling in the lines less affected by G forces. The engine can be set on the ground closer to the RPM that you expect to see in the air.
With enough pressure, tank position has less importance...but even with high pressure feed, G forces still affect what happens on the engine side of the needle valve to some degree. Engines with poor draw will exhibit the effects more than engines with better pumping action.

Pond Skipper

The .07 has the fuel draw of a typical .10 size engine, it is rather thirsty at full throttle I can take down a 2oz tank in about 4mins. The 1/2A fuel line from the pipe isnt helping as well as I had hoped. I really
don't want the additional weight of med size line if I can help it. The one way valve weighs very little.
I have about about 15mm of slack in the feed line could get rid of.

Pond Skipper

Gee Wizz - OS 26 Surpass belly lander with a APC 8.75x9.5 NN @ 14k / 126mph / 4in aluminum Tru turn spinner is the idea.