180 CFX Payload Question - HeliFreak
Fun, Learning, Friendship and Mutual Respect START  HERE

Go Back   HeliFreak > R/C Helicopters > Aerodynamics, Physics and Engineering

Aerodynamics, Physics and Engineering Aerodynamics, Physics and Engineering Discussions

LinkBack Thread Tools Display Modes
Old 11-28-2016, 09:20 PM   #1 (permalink)
Registered Users

Join Date: Nov 2016
Location: Toronto, Canada
Default 180 CFX Payload Question

I'm kinda interested in using a small cam on my 180 CFX like a RunCam 2 or mobius 2 but preliminary research disagrees with my math. these cameras would add about 50 g to the heli's 200 g but I've seen videos online where a 200 SRX can barely lift the 50 g mobius so what chance does a 180 have?

on the other hand, knowing I draw about 6 A during flight at 50% throttle (5.55 V) and assuming an electrical+drive train efficiency of 80% and a rotor disk efficiency of 70%, I get a max hover thrust of 450 g, which is close to a T2W of 2 for the combined 250 g TOW. If I step that up to the max power from a 20 C 450 mAh lipo with 35 mOhm internal resistance (its much lower than that i'm just assuming the worst) i get 97.2 W and a respectable 3 min of air time but a hover weight of 922 g or T2W of 3.6. These number seem to make sense since without the camera it means the 180 CFX can pull 4.9 Gs which seems like what its doing in full stunt mode.

Coming from a very technical/theoretical background, I'm worried I'm missing something but, on the other hand, there are a lot of incompetent people on the internet.

Thanks for any help
velo24 is offline        Reply With Quote Quick reply to this message
Sponsored Links
Old 11-29-2016, 12:19 PM   #2 (permalink)
HF Support
Posts: 21,971

Join Date: Jun 2008
Location: Wisconsin


Here is a thread I've been following.

There may be information of interest for you also?


TowPilot is offline        Reply With Quote Quick reply to this message
Old 11-30-2016, 12:29 PM   #3 (permalink)
Registered Users

Join Date: Aug 2010
Location: AZ


Generally speaking these machines burn about 80W/lbf thrust. That can vary with headspeed and gearing- and with many other considerations. But that is a fairly typical value. It is consistent with your hover values (assuming the voltage is correct- not sure how you came to that), and so seeing 90W at 450g thrust is plausible. Your rotor is no where near 70% efficient in hover. At the a 200g thrust level, your Ct is at about .0027. For efficient rotors (with some twist, proper airfoils, etc), your figure of merit (which is just ideal power / actual power) is probably closer to about 0.5.

What isn’t clear is if the power system can deliver that output, and if the rotor’s blade loading remains low enough to be useful. The later should not be a problem assuming stock RPM (4200?), where your blade loading is only at about 0.03, and normally stall is not seen in hover until closer to 0.15 for reasonably good rotors. That margin drops when you start adding a lateral flow component, since retreating blade stall becomes more and more a problem etc.

I don’t think you will find much difficulty in a 50g addition to AUW from a thrust perspective. But there are other considerations- especially as regards CG and moments of inertia, where you may find some weird resonance/instability in the control loop, or significant drag in FF, etc.

Is there any reason you have not just tried to fly with an equivalent-mass ballast?

Good luck with the effort-

"The problem with quotes found on the internet is you have no way of confirming their authenticity." - Abraham Lincoln
extrapilot is offline        Reply With Quote Quick reply to this message

Quick Reply

Register Now

In order to be able to post messages on the HeliFreak forums, you must first register.
Please enter your desired user name, your REAL and WORKING email address and other required details in the form below.
User Name:
Please enter a password for your user account. Note that passwords are case-sensitive.
Confirm Password:
Email Address
Please enter a valid email address for yourself. Use a real email address or you will not be granted access to the site. Thank you.
Email Address:
Where do you live? ie: Country, State, City or General Geographic Location please.
Name and Lastname
Enter name and last name here. (This information is not shown to the general public. Optional)
Helicopter #1
Enter Helicopter #1 type and equipment.
Please select your insurance company (Optional)
Helicopter #2
Enter Helicopter #2 type and equipment.
Helicopter #3
Enter Helicopter #3 type and equipment.
Helicopter #4
Enter Helicopter #4 type and equipment.


Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.

Thread Tools
Display Modes

Posting Rules
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

Copyright © VerticalScope Inc. All rights reserved.

SEO by vBSEO 3.6.1