Primary Force ARF

[James_Mynes]

I ran across a Primary Force ARF a couple of months ago, and I've been trying to think through converting the front end to electric power. I'm using RSM's 35-40 equivalent system and got the motor snuggled into place nicely using some 3/4x1/2x1/16 aluminum angle.
Finding a way to install the battery has proven to be a challenge.
I've considered boxing in a small pocket in the front top of the wing to support the rear of the battery, but bellcrank movement would hit the box.
I considered raising it above the wing and positioning the battery as far forward as possible, but the motor is in the way for swapping the battery out.
I considered hanging the battery between the landing gear, which looked promising until I mocked it all up and hung the plane from the leadouts. The outboard wing is noticeably kicked up, which I am sure will cause problems.
Fore and aft balance requires the battery to be very far forward, which surprised me.
At this point I'm left with two options;

1) Cut a 1"x2" square hole in the fuselage, about 1" behind the motor mount, and glue the battery box in crossways, like a canard.
2) Strip some covering off the outboard side of the nose and glue the battery box vertically to the fuselage.

Neither of these options seem like they would be aesthetically pleasing.

Is there another option I haven't considered? Maybe flat against the fuselage diagonally?

Anybody have pictures of an electric PF install?

[John Cralley]

Crist Rigotti did an electric Primary Force some years ago. Check this link post #9 for a photo of how he mounted the battery:

http://stunthanger.com/smf/index.php/topic,10458.0.html

[Crist Rigotti]

Crist Rigotti did an electric Primary Force some years ago. Check this link post #9 for a photo of how he mounted the battery:

http://stunthanger.com/smf/index.php/topic,10458.0.html

You beat me by a couple of minutes!

http://stunthanger.com/smf/index.php/topic,10458.0.html

[James_Mynes]

That is a very clean setup. I like it.
My most recent thought was to mount the battery in the chin, P-40 style, cutting the fuselage to get the battery as high as possible.
I mounted my motor so the prop is just forward of the nose wood. That doesn't leave me enough room for the 3S 3300mah battery. BUT.... And I don't know why I didn't consider this before.
It would be easy enough to move the motor forward, which would give me room for a battery.
I like this idea. I like it alot. Thanks for the link, and the picture.

[Horby]

Here is my set up.

Warren

[James_Mynes]

Another one with the prop well forward of the end of the fuselage. I spent the morning fabricating a new motor mount, moving the motor forward and freeing up space for the battery. Thanks for the inspiration!

[Horby]

I had to, to get it to ballance right. I have a scratch build P Force on the table and it will be interesting to see where the motor ends up.
I am going to use the identical set up. I found by mounting the motor front mounted you don't use up brings in the motor every season.


Warren

[John Kelly]

...(bearings)

[Horby]

Yup, rear mounting motors chew bearings up faster than front mount. I have well over 100 flights on my plane with an E-15 and going on my 3rd season and I am still on my original bearings. Others claim that E Flight motors eat bearings and the only ones saying it are the people who rear mount their motors.

Cheers,
Warren

[MikeyPratt]

Here is my set up.

Warren

Horby,
That should work just fine.  My P Force has Power. 15 with a 4 cell pack (2600TP) which is more than adequate for the pattern with a little extra.  I also front mounted the motor for more battery space.  This is a very smooth power system.  I have lots of flights with no bearing noise.  Still trying different props to see which one I like the best.  But all and all very good flying model with the electric set up.

Later,
Mikey

[Horby]

I found that the APC electric 11x 5.5 works great with both the E Flight E 15 and Turnagy G 15.  I use 4s 2800mah with a 5.5 min run.
with the Arf P FORCE I use no ballast weight, it balances perfect at 2" behind the leading edge. It's now my favorite plane and Flys better than my modified Tutor.


Warren

[James_Mynes]

I had a little setback. After gluing the wing into the fuselage I set the horizontal stab on my workbench. I noticed the stab wasn't sitting flat, so I eyeballed it and it's got a good twist in it. Being the thinker that I am, I thought it would be prudent to look at the wing. Egad! That's about a 4 pitch wing! So, off with the covering, misted with water and braced and weighted to untwist the wing. It's pretty flat now, but no longer ARF. At this point it's getting new tail surfaces and I'm going to strip the covering off the fuselage as well.
I still have high hopes this will be a good flyer, just not as quickly as I thought it would be.

[Horby]

On my ARF I had to re make the fuse 3 times before I could get one without a bad twist or too tail heavy.
I feel your pain, but it is well worth it.

Warren

[john e. holliday]

Even after stripping the covering and recovering it is still classed as an ARF.   A good hot air gun and some extra hands should have taken out the twists.   

[James_Mynes]

Well, it flew. The RSM 35-40 package pulled it along for two 2-minute flights. Outboard wing is slightly up, but I think I can pull that out with the heat gun.

Once I got home and charged the battery I did some math and a 5.5 minute flight is going to pull the 3S 3300 mah battery down 81%. That in itself is probably fine, but I have to speed it up a bit, lap time was 5.6 seconds.

So increasing RPM and running a 5.5 minute flight is likely to be in the 90-95% range.

What would the ramifications be if I went to a 4S 2700 mah battery? I know the ESC can handle 14.8v, but would the motor throw a fit?

Would the higher voltage require RPM adjustment? The system uses a KR timer/governor, set for 9200 RPM. I think the governor determines the RPM, I just don't know if the voltage change would override the governor setting.

[Crist Rigotti]

Well, it flew. The RSM 35-40 package pulled it along for two 2-minute flights. Outboard wing is slightly up, but I think I can pull that out with the heat gun.

Once I got home and charged the battery I did some math and a 5.5 minute flight is going to pull the 3S 3300 mah battery down 81%. That in itself is probably fine, but I have to speed it up a bit, lap time was 5.6 seconds.

So increasing RPM and running a 5.5 minute flight is likely to be in the 90-95% range.

What would the ramifications be if I went to a 4S 2700 mah battery? I know the ESC can handle 14.8v, but would the motor throw a fit?

Would the higher voltage require RPM adjustment? The system uses a KR timer/governor, set for 9200 RPM. I think the governor determines the RPM, I just don't know if the voltage change would override the governor setting.

Going to a 4 cell battery from a 3 cell battery usually calls for a lower Kv motor.  The 8XL has a Kv of 1100 and the 4 cell battery would require about a 930Kv.

[James_Mynes]

Going to a 4 cell battery from a 3 cell battery usually calls for a lower Kv motor.  The 8XL has a Kv of 1100 and the 4 cell battery would require about a 930Kv.

That's kinda what I thought, but didn't know if the governor would throttle it back to the set RPM. This KR governor has the sensor wire attached to a motor lead.

[eric rule]

Jim:

Reset the rpm using the KR Program stick that came with your power system. Turn it up so that you get lap times in the 5-4 to 5.2 second range. If you think that you need a bit more rpm in the maneuvers change the gain setting up to 5 or 6. Your system time was set at 2 minutes so that you could trim the model before you went to a full flight time (5 minutes 30 seconds will do the AMA pattern). Once you are satisfied with the trim increase the flight time.

When using the KR program stick always remember to hit the S1 button once to turn on the program mode. After that you press the S1 button 2 times to reset the rpm, use the < > buttons to increase or decrease the rpm. When you are happy with the rpm hit the S1 button to stop. The red light will go out for 2 seconds then flash twice to confirm the new rpm setting.

Flight time is 3 presses of the S1 button. Gain is five presses. The manual covers this in full so refer to it if you have any questions.

[James_Mynes]

Eric,
Thanks for your reply. Programming the timer is not the issue, I have that part figured out thanks to the good instructions provided with the system.
The problem is the battery capacity. My math tells me I will use more than 80% of the battery's capacity after turning up the power and doing a 5.5 minute flight. My first thought was to go to a 4s battery with roughly 10% more watt capacity, but I'm not sure that's the right approach.
I found some 3s 3600 mAh lipos, a little heavier but roughly the same dimensions, that should do the trick.

[eric rule]

Once I got home and charged the battery I did some math and a 5.5 minute flight is going to pull the 3S 3300 mah battery down 81%. That in itself is probably fine, but I have to speed it up a bit, lap time was 5.6 seconds.

* this is not bad at all and will not stress the battery too much so life expectancy will be good.

So increasing RPM and running a 5.5 minute flight is likely to be in the 90-95% range.

* Give it a try and check the capacity used. We run these motors in the 8900 - 9500 rpm range with no problems. With the higher rpm you can probably drop the flight time down to 5 minutes. This should help a lot with the capacity used.

What would the ramifications be if I went to a 4S 2700 mah battery? I know the ESC can handle 14.8v, but would the motor throw a fit?

* The motor will handle a 4 cell battery with no problems. I agree that with a 4 cell I prefer to use motors with kv rates of 900 - 1000 but I have also run these motors with 4 cell batteries with good results (a bit more weight than I like but flies OK).