HobbyKing.com New Products Flash Sale
Reply
Thread Tools
Old Dec 20, 2012, 08:49 PM
Jason KD0ZEQ
Dubjay's Avatar
United States, CO, Snowmass
Joined Nov 2012
229 Posts
Batteries

Finishing up my first Crash Test plane. Am getting ready to put my radio gear in . My question is this.. as far as getting in the ball park for correct CG what size batteries are you guys using? I was thinking two 3 cell 4000mah. Or maybe two 3000mah?
Dubjay is offline Find More Posts by Dubjay
Reply With Quote
Sign up now
to remove ads between posts
Old Dec 20, 2012, 09:03 PM
Jason KD0ZEQ
Dubjay's Avatar
United States, CO, Snowmass
Joined Nov 2012
229 Posts
Wing Tips and fins

I pretty much built my deep reaper from the instructions on the CTH website.
However came across instructions on here also the RCgroups. I noticed there was some instuctions on wing tips that were not in the one on site. I have not put my fins on yet . Is there some cuts that i should have made on tips. I have stock wing tips with no modifications . Will i be o.k just slapping fins on with a little toe in??
Dubjay is offline Find More Posts by Dubjay
Reply With Quote
Old Dec 20, 2012, 10:37 PM
Lee
PERFECT LANDING !!!
Lee's Avatar
USA, UT, Orem
Joined Jul 2004
9,156 Posts
The instructions at the first of this thread are out dated although the basics are still there. Go with the instructions here http://crashtesthobby.com/products/grim-reaper. They are regularly updated.
Lee is online now Find More Posts by Lee
Reply With Quote
Old Dec 20, 2012, 10:40 PM
Lee
PERFECT LANDING !!!
Lee's Avatar
USA, UT, Orem
Joined Jul 2004
9,156 Posts
Quote:
Originally Posted by Dubjay View Post
Finishing up my first Crash Test plane. Am getting ready to put my radio gear in . My question is this.. as far as getting in the ball park for correct CG what size batteries are you guys using? I was thinking two 3 cell 4000mah. Or maybe two 3000mah?
Lighter flies better but you still need to get CG correct and I am a believer in not adding lead when you can add batteries for longer flights. I think either way it will work depending on placement. Difference in weight between 2X 3000s and 2X 4000s will be 8+ oz.

Lee
Lee is online now Find More Posts by Lee
Reply With Quote
Old Dec 21, 2012, 06:55 AM
Registered User
United States, MD, Kensington
Joined Dec 2008
323 Posts
Quote:
Originally Posted by Dubjay View Post
Finishing up my first Crash Test plane. Am getting ready to put my radio gear in . My question is this.. as far as getting in the ball park for correct CG what size batteries are you guys using? I was thinking two 3 cell 4000mah. Or maybe two 3000mah?
To add to what Lee said... It's really about how fast you fly and how long a flight time you want. The Reaper should balance fine with a single 3 cell 3000mah battery up against the forward spars. I use a 2300 mah battery and the flight time is fine for me. But I'm not usually flying full throttle either, and I keep a spare battery in my pocket.

You don't have to get it perfect the first time. It's easy enough to cut a new battery hole, perhaps stuffing the old one with a chunk of scrap EPP.
michaelingp is offline Find More Posts by michaelingp
Reply With Quote
Old Dec 21, 2012, 07:58 AM
UH60 Pilot
E1Allen's Avatar
United States, KY, Fort Campbell
Joined Jan 2010
273 Posts
Quote:
Originally Posted by Lee View Post
Lighter flies better but you still need to get CG correct and I am a believer in not adding lead when you can add batteries for longer flights. I think either way it will work depending on placement. Difference in weight between 2X 3000s and 2X 4000s will be 8+ oz.

Lee
I agree, none of the wings I've built from Lee required lead. Battery always went in last. If I've ever added anything just to make it that much closer it would be tape which just protects. Also I've built a few light and heavy wings. Seems like getting the CG right is the most important thing.
E1Allen is offline Find More Posts by E1Allen
Reply With Quote
Old Dec 21, 2012, 08:32 AM
wheeeeee!
elCapitan's Avatar
United States, UT, Provo
Joined Oct 2011
916 Posts
Indeed, getting CG correct is the real important thing, here, and I think you should be able to accomplish that with either of those battery setups.

The instructions used to include a really good, widely used method to make sure you get the proper CG, but it seems to be gone now. Basically, once everything is laminated, and the elevons attached, you flip over to the bottom of the wing, and measure back from the nose the proper distance for CG. Then use a square to measure out from that, onto either side of the wing, and make symmetrical marks. (A line between the two would then be the CG axis). Place a pushpin in the marks.

Now flip the wing back upright, and lay out all your electronics, including the batteries, where you think you want them. Try to lift the wing from underneath, balancing it on the pushpins with your fingers. If it tips forward, you know you're nose-heavy, and have to move some of the electronics back. Vice versa for tail heavy. Once you get things as close as possible to balancing on those pushpins, mark where all your electronics will go, and then you can actually cut or melt the bays.

The good things about this method are that it's proven (lots of people build this way and accurately attain the proper CG), and versatile. In other words, it doesn't matter what wing you're building, or which electronics you're using. You can always make sure you're on CG by building this way instead of relying on measurements that may not work for your particular setup, or trial and error guessing based off pictures of someone else's build.
elCapitan is offline Find More Posts by elCapitan
Reply With Quote
Old Dec 21, 2012, 08:44 AM
Jason KD0ZEQ
Dubjay's Avatar
United States, CO, Snowmass
Joined Nov 2012
229 Posts
Thanks you guys . That helps a lot. Nice to get feedback so quickly!!
Cant wait to get this bird in the air. Is like no other that ive built thats for sure.
Dubjay is offline Find More Posts by Dubjay
Reply With Quote
Old Dec 21, 2012, 08:53 AM
UH60 Pilot
E1Allen's Avatar
United States, KY, Fort Campbell
Joined Jan 2010
273 Posts
Elcapitan's method is what I usually do as well. I did that to make sure I could keep my batteries within the spars when I added the 2x8000mah batteries at 600g each. Almost 2.7lbs in batteries alone.
E1Allen is offline Find More Posts by E1Allen
Reply With Quote
Old Dec 21, 2012, 10:59 AM
Registered User
United States, MD, Kensington
Joined Dec 2008
323 Posts
Quote:
Originally Posted by E1Allen View Post
make sure I could keep my batteries within the spars .
This is important. Once you've covered the plane it becomes hard to see the white spars, and even the extreme tape. So, it's not like you can just put the electronics and batteries anywhere you want. You can't cut the spars, and I assume you want to minimize cuts into the Extreme tape.

elCapitan, I think the instructions still include the "move the battery to adjust the CG" steps. I know it does for the Grim Reaper, because I just looked. Maybe it's not as explicit as before, but it's still there:

Installing the electronics.
...
b) Set the parts on the top of the plane where shown and see if the CG needs to be adjusted.
...
e) Move the battery forward or back to get the CG 10.5" back from the nose of the plane.
michaelingp is offline Find More Posts by michaelingp
Last edited by michaelingp; Dec 21, 2012 at 10:59 AM. Reason: oops, misspelling
Reply With Quote
Old Dec 21, 2012, 01:40 PM
Lee
PERFECT LANDING !!!
Lee's Avatar
USA, UT, Orem
Joined Jul 2004
9,156 Posts
I see conflicting weather reports for today.

http://www.google.com/imgres?hl=en&s...2&tx=179&ty=82

http://www.google.com/imgres?hl=en&s...9,r:1,s:0,i:95

http://www.google.com/imgres?hl=en&s...r:11,s:0,i:130

Happy End of the World!!!!
Lee is online now Find More Posts by Lee
Reply With Quote
Old Dec 21, 2012, 01:54 PM
Fly Now.
United States, TX, Austin
Joined Aug 2012
53 Posts
This too is how I determined gear placement. Forgive me if this was already mentioned, but be sure to have your winglets installed as this adds a significant weight behind the CG.

As far as batteries, on my DeepReaperXL with a 3536 motor, and lots of camera gear up front, I still needed nose weights with 2x 3300mah3S. I've recently bought some 4400mah, but haven't tried the CG yet.

If you're going with a similar setup as mine but don't plan on a lot of FPV gear, I would think about moving your motor closer to the CG than what is in the instructions. I was really worried about being nose heavy during the build, but the opposite happened.

-Parke

Edit: I just looked at your pict, and your motor looks pretty far forward already. You should be good shape.

Quote:
Originally Posted by elCapitan View Post
Indeed, getting CG correct is the real important thing, here, and I think you should be able to accomplish that with either of those battery setups.

The instructions used to include a really good, widely used method to make sure you get the proper CG, but it seems to be gone now...
Parke_ParkeFlyer is offline Find More Posts by Parke_ParkeFlyer
Last edited by Parke_ParkeFlyer; Dec 21, 2012 at 02:02 PM. Reason: addendum
Reply With Quote
Old Dec 22, 2012, 07:53 PM
Lee
PERFECT LANDING !!!
Lee's Avatar
USA, UT, Orem
Joined Jul 2004
9,156 Posts
We shot this video this afternoon of and with the 63" Herc Pusher.

Herc Pusher 63" with 808 #16D (5 min 20 sec)
Lee is online now Find More Posts by Lee
Reply With Quote
Old Dec 23, 2012, 10:38 AM
Registered User
United States, CT, New Haven
Joined Dec 2011
166 Posts
I fly my Grim Reaper with an NTM 3536 1800KV with and 8X4 prop. Overkill I know but this is what I like, power on tap. I recently experimented and put a 7x6 prop and a 4s battery in her and when I opened her up to full throttle the plane started to I guess you call high speed flutter. Am I going to fast is there a limit or is something wrong It flew fine as long as I didn't go full throttle. I switched back to 3s on 8x4, it's also less noisy. Any thoughts (I know this plane is not designed to be a speed racer)?
cmaynex is offline Find More Posts by cmaynex
Reply With Quote
Old Dec 23, 2012, 10:53 AM
Registered User
United States, MD, Kensington
Joined Dec 2008
323 Posts
Quote:
Originally Posted by cmaynex View Post
I fly my Grim Reaper with an NTM 3536 1800KV with and 8X4 prop. Overkill I know but this is what I like, power on tap. I recently experimented and put a 7x6 prop and a 4s battery in her and when I opened her up to full throttle the plane started to I guess you call high speed flutter. Am I going to fast is there a limit or is something wrong It flew fine as long as I didn't go full throttle. I switched back to 3s on 8x4, it's also less noisy. Any thoughts (I know this plane is not designed to be a speed racer)?
Traditionally there are two causes of flutter. The first is a hinge gap, but most Reapers have continuous hinges. The other cause is play in the control rods or in the servos. You need to beef up the servos and control rods. CTH now recommends standard (40g) servos for the Reaper. If you're not going to fly combat, I'd recommend solid control rods, like dowels. The CTH instructions are optimized for combat survive-ability, and the thin rods and the staple used to minimize play in the rod are probably not adequate for really high speeds.
michaelingp is offline Find More Posts by michaelingp
Reply With Quote
Reply


Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Sold Reaper GR60 Stagger_Wing Aircraft - Electric - Power Systems (FS/W) 0 Jan 13, 2010 01:43 AM
Sold Reaper GR 60 wrpsr1911 Aircraft - Electric - Power Systems (FS/W) 0 Jan 06, 2010 09:28 PM
Build Log House of Balsa "Grim Reaper" P51 Mustang Gun Jam Electric Warbirds 28 Dec 20, 2009 03:25 PM
Discussion Body count... Grim but it's really gotta be done. Bilbobaker Life, The Universe, and Politics 15 Nov 15, 2009 01:09 PM
Gallery Grim reaper Wickett R/C Pumpkin Contest 1 Oct 31, 2005 04:37 PM