F-15 Eagle Park Jet--Part 2 - Page 208 - RC Groups
 Nov 25, 2011, 11:45 AM Registered User Hi aqkhana2002, you can use the CG of the plan without any problems. Your plane looks right, happy maiden. To have a longer live for your plane I wouls suggest you to "laminate" it with Aqua Clou or some other Floor Coating (acrylic lacquer) an silk tissue paper. It is not too heavy and the plane would live longer. I did it with mine and after 30 flights it looks ptretty good. yours Al
 Nov 27, 2011, 08:11 PM Registered User Thanks AL, NORMALLY I USE Fiberglass tape. guys just wanna share this having some problem to find the cg, here what steve suggested. "Yes, if the plans came out a different scale then the CG will be different. However, it's easy to figure out where the new CG should be. Just calculate what scale your drawings are at (the easiest way is to divide the wing span on your plans by the original wing span), and then multiply that scale by the distance shown on the plans for where the CG should go. "
 Nov 28, 2011, 02:54 PM Registered User Hi, I think it´s only mathematics. If your plane is for example 70% of the plan, the former CG was 10 cm behind the leading edge, now is 0,7 x 10cm = 7 cm after the leading edge. Don´t you agree?
 Nov 28, 2011, 04:28 PM Registered User Yes al you are rite but how do i know the plan i printed is 70% ? in my case i download letter and printed on A4 while print option i select fit to printed area , if i wont do that , that will not print correctly. any way i am still waiting good weather, its so much rain or windy outside. hope this saturday or sunday i will do maiden.
Nov 29, 2011, 04:41 AM
Crash-safe
Quote:
 Originally Posted by aqkhana2002 ...my case i download letter and printed on A4 while print option i select fit to printed area ...
Two things influence the size, if you print it this way.
First it will be smaller than the original since Letter is 8.5' x 11' and A4 is 8.27' × 11.69', so the width of A4 comes into play.
Second, usually the pdf appliation takes your printer into consideration to determine the printable area.

What you can do is the following:
Print the first page of the Letter plan (it should be the "Wing strakes/inlet top" page), once with your above stated printing option, and once with "paper scaling" "none".
Then measure the long vertical line of the "Wing strakes/inlet top" piece.
CG: 3.25' x length of scaled / length of none scaled.

From my point of view, this should be fine
 Nov 29, 2011, 04:55 PM Registered User Yes lessram u are rite, being a new in RC, i never know if i reduce size how do i figure out my cg, i have sent message to Steve and he also said this.. see in comments "Yes, if the plans came out a different scale then the CG will be different. However, it's easy to figure out where the new CG should be. Just calculate what scale your drawings are at (the easiest way is to divide the wing span on your plans by the original wing span), and then multiply that scale by the distance shown on the plans for where the CG should go. "
 Dec 02, 2011, 07:10 PM Registered User Some one really help me to under stand this cg issue, well I have flown my plan and it was tail heavy damage but repair and move battery forward till my cg reach to 2inch on 2inch if I put finger on cg which is 2inch plan looks little heavy from nose. But as per formula u guys given to me Example 1 Actual span : 27.9 Mine : 26.7 26.9/27.9 = 0.9 Now. 3.25 cg * 0.9 = 2.9 Now my cg should be 2.9 Example 2 Actual length : 42.3 Mine. : 38.9 38.9/42.3 = 0.9 Now 3.25 cg * 0.9 = 2.9 So formula looks ok in both butttttttt If I check my cg with holding hand on 2.9 plan is heavy from nose tooOOOO much But if I put hand on cg 2 just little heavy on nose but looks ok I m confuse what's my actual cg is plssssssss Some one help speciall Steve Last edited by aqkhana2002; Dec 03, 2011 at 02:36 AM.
 Dec 03, 2011, 05:52 AM Crash-safe Move your battery backward until your plane balances at CG 2.9 ' ! Then everything should work out fine
 Dec 03, 2011, 06:21 AM Registered User lessram, if i move to 2.9 plan is to much havey nose. i hv seen in some thread they said if you hold your hand in cg your plan should be balance
Dec 03, 2011, 03:34 PM
Fidler & twidler
Quote:
 Originally Posted by aqkhana2002 lessram, if i move to 2.9 plan is to much havey nose. i hv seen in some thread they said if you hold your hand in cg your plan should be balance
I think an explanation of Centre of Gravity is needed.

The cg marked on the plan is where the aircraft must balance so as to make it fly correctly, it is found mainly by design, and partly by test flying.

Everyone builds differently, so when the build is finished, each model will balance at a different place due to the differences in the build.

When this happens, then you must move the battery to MAKE the model balance at the cg point printed on the plan ( or at the scaled point if your model is not the same size as the original plan from JS44).

It seems that your model has a heavier nose , so you have to move the battery back until the model balances at the correct cg point.

N.B. a slightly nose heavy model will fly, but will feel heavy and lack agility.
A nose light model will prove too agile - it will feel twitchy, and if the cg is too far back, could well be un flyable (unstable).

Best regards
Mike
Dec 03, 2011, 06:45 PM
Registered User
have a look in this video , may be clear you what exactly i have problem

 F15 Steve 100% CG problem (5 min 21 sec)

i m assuming in this video my cg is 2.1

Quote:
 Originally Posted by empeabee I think an explanation of Centre of Gravity is needed. The cg marked on the plan is where the aircraft must balance so as to make it fly correctly, it is found mainly by design, and partly by test flying. Everyone builds differently, so when the build is finished, each model will balance at a different place due to the differences in the build. When this happens, then you must move the battery to MAKE the model balance at the cg point printed on the plan ( or at the scaled point if your model is not the same size as the original plan from JS44). It seems that your model has a heavier nose , so you have to move the battery back until the model balances at the correct cg point. N.B. a slightly nose heavy model will fly, but will feel heavy and lack agility. A nose light model will prove too agile - it will feel twitchy, and if the cg is too far back, could well be un flyable (unstable). Best regards Mike
Last edited by aqkhana2002; Dec 03, 2011 at 07:10 PM.
 Dec 03, 2011, 07:41 PM Registered User AQ,, If I am seeing it right, it's pretty far away, but it appears to be taking off straight up? If so, I think the cause of this is your elevator. I noticed in the first of the vid before you flew,, it went over center mark when you worked the controls and you had to manually get it back to the correct position.. First, you need to adjust the servo so that it cannot go past center! This can be done with the radio and the servo arm. I think the elevator is being pulled out of control which makes the plane turn up. If I saw correctly, it never did it on lower speed, only on wot. So not only does the servo need adjustment, it could be getting over powered, again, this could be due to adjustment. Try that, let us know how it does. w.
 Dec 03, 2011, 09:40 PM Falcon's rc the plane is nose heave. I think your problem is on your elevator control like WALTJG say it looks like the pushrod from the servo to the elevator rod is flexing, maybe you need to put a sleeve on it and secure it to the fuselage and also I noticed that the elevator flip over this happened because the pushrod is to close to the elevator rod, you need to move the pushrod 1 or 2 more holes far from the elevator rod hope this help Last edited by DanielMadrigal; Dec 03, 2011 at 09:46 PM.
 Dec 04, 2011, 12:12 AM Registered User Thanks guys just one question left so what is my cg? 2 or 2.99 as per calculation it's 2.99 but if u see video it's ok on 2.10
 Dec 04, 2011, 08:04 AM Registered User The cg that is on the plan is good if you built the original size.. fix the elevator problem, then you can adjust your cg if needed.. w.