Aug 22, 2012, 03:06 AM
Team USA F3F Member
Joined Feb 2011
1,273 Posts
Quote:
 Originally Posted by concreteman I have progressively moved the cg rearwards, thinking this would give me better pitch authority, yet found my controls getting "washier" as I tried harder, and removed more weight, thinking this was the answer. yesterday, I went forwards, or backwards, however you want to see it, and the plane was significantly improved, and the feel of pitch authority has returned, I am going to add a pinch or 2 more, and see how it goes. Will report. WD
WD, so you mean you were adding weight to the nose to bring the CG forward and it was better for you? Do you know where you started? and where you ended?

Have you and cortina standardized on the ballast distribution and how it affects the CG yet?

inquiring Pike owners want to know...
Aug 22, 2012, 03:23 AM
F3B
Warwickshire, England
Joined Sep 2006
5,612 Posts

Multiply the weight of the ballast by the distance from the cg and then do the same thing to ballast on the other side of the cg. Play round with it until you can minus one from the other to get as close to zero as possible.

i.e
b = weight of ballast in g or ounce (doesn't matter)
d = distance from cg (e.g mm) - distance to the middle of the bit/s of ballast

(d*b) - (d*b) = 0
one of the "d" values should be negative obviously.

Therefore you can create certain ballast states like, 1/3rd, 1/2, 2/3rds etc. Sometimes you need a removable nose weight for full ballast. Laminate a small idiot sheet and take it with you. Bear in mind left to right ballast as well.

See attached. You could make it calculate wing loading as well of course. You should also be able to calculate nose weights if needed to get rid of CG changes or how much the CG will change by.

# Files

Last edited by satinet; Aug 22, 2012 at 03:54 AM.
Aug 22, 2012, 04:24 AM
Registered User
Bodø, Norway
Joined May 2006
62 Posts
Quote:
 Originally Posted by David Cortina If the plane is a little too tail heavy it will actually pitch down as it accelerates, seems bassakwards but it's true!
Yeah, I know But my plane doesen't pitch up or down according to increasing or decreasing speed. I'm just a bit confused that I still have downtrim. But it flies just the way I like it so I don't care...
Aug 22, 2012, 06:08 AM
Registered User
France
Joined Aug 2003
1,010 Posts
Quote:
 Originally Posted by william123 Yeah, I know But my plane doesen't pitch up or down according to increasing or decreasing speed. I'm just a bit confused that I still have downtrim. But it flies just the way I like it so I don't care...
Same for me !

I was flying at 102mm at the beginning but moved to 107mm beginning of the summer. I do have some downtrim but the plane doesn't pitch up or down depending of the speed, funny. Even at 107mm the Pike is very gentle.

When flying at 102, I needed lots of snapflap deflection (10mm or more). I noticed that when moving the CoG backward, and reducing at the same time the snapflap I could have more speed in the turn, especially during the first half, because less drag. I have now around 5mm of snapflap (and 6 to 7mm of elevator).

Pierre
Aug 22, 2012, 10:36 AM
Yep it's Phil!
United States, CA, San Diego
Joined Apr 2007
1,279 Posts
That is good feedback!

Phil

Quote:
 Originally Posted by prondel Same for me ! I was flying at 102mm at the beginning but moved to 107mm beginning of the summer. I do have some downtrim but the plane doesn't pitch up or down depending of the speed, funny. Even at 107mm the Pike is very gentle. When flying at 102, I needed lots of snapflap deflection (10mm or more). I noticed that when moving the CoG backward, and reducing at the same time the snapflap I could have more speed in the turn, especially during the first half, because less drag. I have now around 5mm of snapflap (and 6 to 7mm of elevator). Pierre
Aug 22, 2012, 12:40 PM
Registered User
United States, CA, Los Angeles
Joined Sep 2003
3,521 Posts
Ok here is a picture before the maiden toss, and my yellow Brio next to it at point fermin, i didn't put any ballast in it yet but next time i sure will. Ian

# Images

 Aug 22, 2012, 08:24 PM Registered User United States, CA, Torrance Joined Aug 2004 1,977 Posts not exactly sure where I started, around 102-103, and Ive removed pieces. I will see where I was, I flew again today, with another.25 added. All went well. WD
 Aug 23, 2012, 12:38 AM Registered User France Joined Aug 2003 1,010 Posts for information, to move from 102mm to 107mm, I removed only 35gr from the nose. Pierre
Aug 23, 2012, 03:53 AM
Registered User
France
Joined Aug 2003
1,010 Posts

Hi all,

Following the info from Satinet, I made a ballast spreadsheet for the Pike Precision that give the value of CoG moving depending of the ballast.

Can somebody check it to see if there is any error in it ?

You enter:
- Ballast slug weight (of each type)
- empty weight

Then you can play with the repartition between the front joiner compartiment, the rear joiner compartiment and the wing compartiment.

As ouput, it give, the total ballast, the wing loading and the variation of the CoG.

Hope this helps.

Cheers,

Pierre

# Files

Last edited by prondel; Aug 23, 2012 at 04:02 AM.
 Aug 23, 2012, 07:03 AM Registered User France Joined Jan 2006 241 Posts Thanks Pierre for this very useful spread sheet. Regards Nicolas
Aug 23, 2012, 08:55 AM
Registered User
Joined Sep 2007
219 Posts

Based on a spreadsheet from a flybuddy, I prepared this for my Pike Precision.

Maybe not so fancy as the one above, but it is nice to put the sheet on your ballast box, showing how to load your ballast, and also know how your CG behaves in the different configs. Here is also a nice graph showing the wing loading. Hope some can find it useful.

I can not guarantee 100% accuracy, but maybe someone could check the figures.

# Files

 Aug 23, 2012, 02:50 PM Registered User Norway, Rogaland, Tjelta Joined Dec 2004 163 Posts I`m geting a bit confused with all these ballast spreadsheets. Where do you guys start to ballst the Precision? The firt sheet from post #161 starts with 2 slugs in the wingcompartment but krvedaa`s sheet starts with 4 slugs in the rear joinercompartment.
 Aug 23, 2012, 03:43 PM Registered User Joined Sep 2007 219 Posts Sorry for causing confusion. To be safe, follow the one from post #161, which I believe was from Benjamin Rodax, if I got the name right, one of the designers of the Pike Precision. In my case, I had the issue with the down trimmed elevator, and did not want the CG to go back too much when ballasting. So basicly, I worked out a ballast sheet, in a way that CG did not move much back from 101mm which is where my CG is, and also I wanted some to move foreward some in some cases. In the one from Benjamin, I reccon much wen't backwards, so the key is the CG when deciding which ballast configuration to use. So go out and fly, and feel what would be the best, to let CG move backwards, foreward, or maybe the best, to keep CG the same in the mostly ballast configurations. My intention was not to confuse, but I hope this made my approach more clear.
Aug 23, 2012, 11:42 PM
Detail Freak
Harbor City, CA
Joined Oct 2003
22,557 Posts
Quote:
 Originally Posted by william123 Yeah, I know But my plane doesen't pitch up or down according to increasing or decreasing speed. I'm just a bit confused that I still have downtrim. But it flies just the way I like it so I don't care...
One would PROBABLY be safe to assume one of a few things:

1. The stab profiles are not set at the proper angle for the given CG you are flying the plane. (maybe the intended CG is forward of where you are flying it?)

2. The stab profile may not have zero camber when neutralizing the ruddervator? Possibly the slight down trim makes the stab zero lift.

I'm certainly no expert aero guy, but that would be my layman's take on it...

And, as mentioned, if the plane flys just like you want it, then having a little trim is really nothing to worry about in that case.
I had a plane with a bolt-on one-piece v tail, and it had a little down trim. Of course, I shimmed the tail LE up a bit with tape.
If I kept adding tape, the plane really didn't seem to fly any better past a certain pojnt of shimming it up. So, I went back to where it seemed fastest, and called it good. 31.61 is fast enough, for an old design! With down trim, too!

R,
Target
Aug 24, 2012, 03:05 AM
F3B
Warwickshire, England
Joined Sep 2006
5,612 Posts
Quote:
 Originally Posted by prondel Hi all, Following the info from Satinet, I made a ballast spreadsheet for the Pike Precision that give the value of CoG moving depending of the ballast. Can somebody check it to see if there is any error in it ? You enter: - Your CoG location - Ballast slug weight (of each type) - empty weight Then you can play with the repartition between the front joiner compartiment, the rear joiner compartiment and the wing compartiment. As ouput, it give, the total ballast, the wing loading and the variation of the CoG. Hope this helps. Waiting for your feedbacks. Note: This spreadsheet can easily be adapted for any F3X plane. Cheers, Pierre
Hi Pierre,

I like your spreadsheet - it works well. Although I guess you will also want to print out a visual sheet that tells you what ballast to put where to take to the field/slope.
Mine is kind of a combination of both. It is a bit rough, but I just did it quickly for myself at the time. The coloured blocks represent where I should put each piece of ballast or spacer. I think in the heat of battle, mistakes can happen, so the easier the better! (the left to right balance is not correct on my sheet in fact, but seeing as the model suffered a fly away in the 70pc state, it became rather academic.

I like the idea of having a picture of the model on the page. I will add that to my ballast sheets in future. A good aide memoire.

Cheers
Tom
Last edited by satinet; Aug 24, 2012 at 03:14 AM.