Leaning backwards in flight despite being front heavy? - RC Groups
Shop our Airplanes Products Drone Products Sales
Thread Tools
Mar 25, 2018, 11:17 AM
Registered User
Help!

Leaning backwards in flight despite being front heavy?


Hey guys!

Beginner here trying out his first scratch foam build, I'm at my wits end trying to figure out why I'm getting some weird behavior from my build.

My plane seems to be leaning backwards while its flying despite me making sure the CG is balanced (at this flight it was actually way more front heavy in attempt to correct this stalling behavior)

here is a video link:
Flight_1 (0 min 22 sec)



No clue as to why it keeps doing this, I have broken so many propellers ( Even with prop saver)

I can post better pictures of the plane, or provide any extra information.

I just want this plane to fly T_T

Please let me know if I should be posting this in another category !
Last edited by jawsqb; Mar 25, 2018 at 08:18 PM. Reason: Added Pictures
Sign up now
to remove ads between posts
Mar 25, 2018, 11:47 AM
Scratch building addict
rotagen's Avatar
My first guess, check your wing incidence angle. I found that 1-1.5 degrees incidence is best. The wing incidence is the amount of "up" pointing of your wings relative to the horizontal stab (elevator surface). The hor. stab normally determines your attitude of the plane during flight. It should be parallel to a line that basically goes straight down the fuselage and not at any drastic angle relative to it.

The wing should be pointing slightly upwards (1-1. 5 degrees) in the front, relative to the stab.

The reason for this is that a proper CG is always in front of the center of lift of the wing. This results in a moment force which drives the nose downwards. Therefore when the wing is parallel to the ground, the hor. stab will be counteracting this force and pushing the nose back up slightly.

So I bet one of 2 things is happening

1. The leading edge (front) of your wing is up too high relative to the back.
2. The leading edge of your hor. stab is too low relative to the back of it, it should follow a straight line down the center of the fuselage.

I recently had the exact same problem with a model that had too steep an incidence angle (wings angling up too much), it always wanted to point up and climb and moving the CG forward had no effect.

The only other option I see is your motor is angled upwards but since you have it pointing up at very slow speed during takeoff I doubt that is the problem.
Mar 25, 2018, 11:51 AM
Scratch building addict
rotagen's Avatar
I forgot, since it's pretty hard to measure 1-1.5 degrees after the model is made... from personal experience on a plane that size it usually translates to the wing being a little less than 1 cm up in the front, relative to a line parallel to the horizontal stab.

Also, check the obvious first, make sure your elevator is trimmed properly (flat with the stab) ?
Mar 25, 2018, 12:08 PM
IMO ( In My Opinion ) →
balsa or carbon's Avatar
Quote:
Originally Posted by jawsqb
Hey guys!

Beginner here trying out his first scratch foam build, I'm at my wits end trying to figure out why I'm getting some weird behavior from my build.

My plane seems to be leaning backwards while its flying despite me making sure the CG is balanced (at this flight it was actually way more front heavy in attempt to correct this stalling behavior)

here is a video link: https://www.youtube.com/watch?v=iz5L...ature=youtu.be


No clue as to why it keeps doing this, I have broken so many propellers ( Even with prop saver)

I can post better pictures of the plane, or provide any extra information.

I just want this plane to fly T_T

Please let me know if I should be posting this in another category !
It's clear in the beginning of your video that you have a LOT of up elevator ( see screen shot below ) .

If you're tired of breaking propellers , I recommend building a plane where the prop is NOT on the nose . Here is the plane ( EzFly ) I use to teach first time RC flyers , it has a protected motor/prop :


Copy of EzFly with under-cambered wing (1 min 57 sec)



If you would like to build an EzFly , let me know and I'll be glad to help you .
Last edited by balsa or carbon; Mar 25, 2018 at 06:57 PM.
Mar 25, 2018, 12:14 PM
Kimbers Keeper.
BHOFM's Avatar
Looked like about 10` up elevator when you launched?

Take all the FPV stuff off and get the plane flying properly first!

How much flying experience do you have?
Mar 25, 2018, 03:40 PM
Registered User
PaulB's Avatar
Hi???? (sorry, didn't catch your name),

So where is the C of G?? Tell us what the wing chord (depth at the root) is and how far back from the leading edge the model balances.

Also, do us a favour, take a picture of the model from the side with the horizontal stabiliser parallel to whatever the model is standing on (table, floor) and with the propeller vertical.

Paul
Mar 25, 2018, 07:27 PM
Registered User
Here some pictures of my plane: https://imgur.com/a/URWN3

Its a dihedral, I read online that it will fly a bit more stable if it is.

The horizontal stabilizer seems to be cutting right through the middle

I made the motor angle a bit down as I read online that the thrust angle might cause it to stall they way it has been.

The elevator was up a bit before my friend let it go, however when it was let go i kept it at neutral. I can test it again tomorrow .
Mar 25, 2018, 07:40 PM
Registered User

Pictures of Plane


Hey Guys!

Here are some pictures of my plane!

Thanks so much for the responses, please let me know what I can do to improve my plane.
Last edited by jawsqb; Mar 25, 2018 at 08:37 PM.
Mar 25, 2018, 08:00 PM
Registered User
It appears my horizontal stabilizers are going through the center of the plane.

My incidence angle might be the source of issue here, though its hard to tell with a dihedral.

I made my motor angled down a slight bit in attempt to adjust the thrust angle, please let me know if this isn't the way to go.

I posted some pictures below please let me know what you think!
Mar 25, 2018, 08:22 PM
Kimbers Keeper.
BHOFM's Avatar
The black makes it a bit harder to see, but it really looks close. That may be a bit too much down
thrust. Half that should be about right. And just a bit to the right. I didn't measure the wing,
but the CoG should be in that area. The plane just looks heavy and tail heavy.

Is the trailing edge of the wing turned up? That can really make things funny! Like a spoiler all the time.

Mar 25, 2018, 08:25 PM
Registered User
Quote:
Originally Posted by rotagen
I forgot, since it's pretty hard to measure 1-1.5 degrees after the model is made... from personal experience on a plane that size it usually translates to the wing being a little less than 1 cm up in the front, relative to a line parallel to the horizontal stab.

Also, check the obvious first, make sure your elevator is trimmed properly (flat with the stab) ?


I havent trimmed yet, just because I though that there is a much larger aerodynamic construction issue that trimming cant fix

Horizontal stabilizer is flat, perpendicular to the body
Mar 25, 2018, 08:26 PM
IMO ( In My Opinion ) →
balsa or carbon's Avatar
Quote:
Originally Posted by jawsqb
Hey Guys!

Here are some pictures of my plane!

Thanks so much for the responses, please let me know what I can do to improve my plane.
If you want to try again with your current plane , AFTER you turn on the transmitter and plug in the battery ...... make sure the elevator is centered/neutral before you throw it in the air .

The following is IMO ( In My Opinion ) :
If you are using this plane you made for learning to fly ( without the assistance of an experienced RC flyer ) , I strongly recommend starting over . For an unassisted first time RC flyer , it's best to use a plane that is lightweight and can fly slowly ( light wing loading ) . A slow flying plane gives you time to think , time to react , and time to correct a mistake . And a slow flying lightweight plane is also more crash resistant because : 1) it's easier to fly and less likely to crash , and 2) if it does hit the ground , it does so with less speed/mass/momentum/energy ( than a faster flying heavier plane ) ...... keeping the damage to a minimum ( if any ) . And a plane like the EzFly ( in post #4 ) has a protected motor/prop , so if it crashes nose-first you're only damaging a little foam .




Here's an example of a plane ( similar to yours ) that was built with very light wing loading , be sure to watch the impact to the ground at the end of the video :



Lightweight 40" wingspan FT Old Fogey-ish (2 min 58 sec)
Mar 25, 2018, 08:30 PM
Kimbers Keeper.
BHOFM's Avatar
jawsqb

Check you messages!
Mar 25, 2018, 09:03 PM
Registered User
Quote:
Originally Posted by BHOFM
Looked like about 10` up elevator when you launched?

Take all the FPV stuff off and get the plane flying properly first!

How much flying experience do you have?
I have no FPV Equipment on the Plane as of yet.

I also have zero flying experience and no one in particular around me to show me how. I'm trying to learn from what I found online.
Mar 25, 2018, 09:04 PM
IMO ( In My Opinion ) →
balsa or carbon's Avatar
jawsqb , here's the info for building an EzFly . Do you have access to flat foam sheets ?

For determining how large to build your EzFly , what is the size/weight of your battery ? To keep wing loading light , you may have to build an EzFly airframe sized 110% or 120% .... depending on the weight of your battery .

Here are the plans ( PDF file ) : https://www.rcgroups.com/forums/show...6&d=1334660760
You'll need a computer connected to a printer . Open the file on Adobe Reader , then scale up to the size needed ( 100% , 110% , 120% , etc ) at the top of the page . Then on your printer's set up page , select "poster" , "cut marks" & "labels" . The printer will then print out tiles that can be assembled into one large poster-sized set of plans .


Here ↓ are what the foam pieces should look like before assembly , and assembly instructions .


Quick Reply
Message:

Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Help! APM Tricoper yaws left while in backwards flight. dynam Tricopter Drones 3 Sep 22, 2016 03:19 PM
Discussion US healthcare ranked lowest in developed world, despite being most expensive Tim Green Life, The Universe, and Politics 122 Sep 07, 2016 10:48 PM
Discussion Young voters in 2014 may be less Democrat-leaning Mr Mootsie Life, The Universe, and Politics 58 May 11, 2014 10:46 AM
Discussion Despite Being Careful Accidents Can Happen! Big Foot 48 Life, The Universe, and Politics 8 Apr 07, 2014 08:49 PM
Discussion T-Rex "leaning" front to back 40trainer Mini Helis 3 Feb 27, 2007 06:56 PM