Basic question about aeroplane flight (for science!)

almoststew1990 · 16 Dec 2018 at 14:02

I have a remote control plane. I want to mount the cheapest, naffest and most importantly lightest camera to the top of it. I am not sure where to place it on the plane.

I have play Kerbal Space Programme and counter intuitively have spent a lot of time making aeroplanes so I understand the basics of Centre of Mass, Centre of Lift and Centre of Thrust. But when I cellotaped the camera to the plane in what I thought was the best place, the plane nose dived repeatedly.

Here is my plane. I have marked on where the CoM is by just balancing the plane on my finger. I have estimated CoL by looking at the size of the main and tail wings. The little black thing is the camera in the picture below.

I put the camera on top of the wing in the middle of the CoM and CoL as right over the CoM "felt" too far forward. However even with the camera this far back, the plane nose dived the whole time as soon as it left my hand.

Where would you put the camera? Underneath the plane under COM? Between COM and COL? Do I just need to throw it harder to get past it's "new" higher stall speed because of the additional weight?

The plane weighs 40 grams with battery and the wheels. The camera weighs 14 grams. However I feel the plane has enough power to carry the weight as it is has a very low stall speed and very high top speed (relatively speaking!)

Any ideas appreciated!

I have already tested the plane on a treadmill for science and I can confirm the plane turned inside out.

Hotwired · 16 Dec 2018 at 14:05

I was thinking underneath would make it more stable even if it means getting a somewhat downward view from there.

Dis86 · 16 Dec 2018 at 14:07

It's probably disrupting the airflow over the rear stabilizers. Hence nosedive.

Slam62 · 16 Dec 2018 at 14:09

Needs to be on the CoG as low as possible

Moley · 16 Dec 2018 at 14:10

I am guessing the plane is balanced so that the centre of mass runs along the line running through the centre of the propeller shaft to the tail of the plane. By mounting the camera above that line you are completely unbalancing the plane and putting it's mass too high - there is a reason why commercial liners put freight in the bottom of the fuselage and passengers in the top.

Mount your camera below the cockpit and you will probably have more success.

paradigm · 16 Dec 2018 at 14:10

Dis86 said:
It's probably disrupting the airflow over the rear stabilizers. Hence nosedive.

This. I’d probably put it directly below the CoM under the fuselage.

almoststew1990 · 16 Dec 2018 at 16:10

I had a go with it underneath and it didn't like that at all either (although it was starting to rain and without the wheels on) it ended up flying upside and crashing. I would post the video but it is a blurry mess and you really can't see anything (£8 camera :cool:

)

Slightly crazy idea but what if I cut a hole through (top to bottom) the plane, and slotted the camera in that way, as it is a vertical camera? It would centralise the mass vertically (i.e. on the top or the hanging from the bottom) and would be less of an aerodynamic brick, if that matters at 5mph.

Firestar_3x · 16 Dec 2018 at 16:36

Can the wings even generate enough lift for the added weight?

I'd add 14g distributed internally and see how the plane flys.

LOAM · 16 Dec 2018 at 16:41

you don't happen to have a treadmill do you?

Minusorange · 16 Dec 2018 at 16:52

You need to build an aerodynamic housing if you want to stop it from nose diving or figure out a way of mounting the camera into the body of the plane

Dano · 16 Dec 2018 at 16:55

LOAM said:
you don't happen to have a treadmill do you?

You monster.

Brizzles · 16 Dec 2018 at 16:56

Drink some Red Bull

Bigpops · 16 Dec 2018 at 17:03

Find where the centre if mavity is on the underside of the wing. It's usually around a third back from the leading edge of the wing. Pivot the plane (with battery in it) on your fingertips from underneath the wings. Once you have it where it balances, mark it.

Then mount the camera so it pivots at the same point as before, and flight characteristics will be largely unaffected (assuming the camera isn't too big or heavy).

Resident · 16 Dec 2018 at 17:36

LOAM said:
you don't happen to have a treadmill do you?

Dano said:
You monster.

I was just about to post the exact same

Hades · 16 Dec 2018 at 20:13

Damn you. I came here to post the treadmill comment

ianh · 17 Dec 2018 at 04:30

Your Centre of Lift is way too far back as the tailpane is supposed to be slightly lift negative by design meaning the vast majority of the lift is wing based so your CoL would be around the middle of the wing depending on the wings chord and AoA.

Also, I didn't realise that the camera was meant to be mounted verically so you will always have huge issues with such a slab sided object being placed in nto the airflow which means your idea of cutting a hole in the body and just allowing the lens to show is a much better one than the initial idea of externally mounting it.

Gixer · 17 Dec 2018 at 06:17

Firestar_3x said:
Can the wings even generate enough lift for the added weight?

I'd add 14g distributed internally and see how the plane flys.

The wing loading will be increased however as long as there is enough speed the aircraft will still fly. Think X15 or F104. Tiny wings but they still flew.

I'd mount it on the CoG so as not to affect the aircraft's handling characteristics too much. I imagine it'll be twitchy to fly as it is and you don't want to make it worse. If you do anything mount it slightly forward of the CoG. Making an aircraft tail heavy makes it rather interesting to fly!

Squark · 17 Dec 2018 at 06:59

Bigpops said:
Find where the centre if mavity is on the underside of the wing. It's usually around a third back from the leading edge of the wing. Pivot the plane (with battery in it) on your fingertips from underneath the wings. Once you have it where it balances, mark it.

Then mount the camera so it pivots at the same point as before, and flight characteristics will be largely unaffected (assuming the camera isn't too big or heavy).

That's what I'd do too.

Blinkz · 17 Dec 2018 at 09:37

ianh said:
Your Centre of Lift is way too far back as the tailpane is supposed to be slightly lift negative by design meaning the vast majority of the lift is wing based so your CoL would be around the middle of the wing depending on the wings chord and AoA.

Also, I didn't realise that the camera was meant to be mounted verically so you will always have huge issues with such a slab sided object being placed in nto the airflow which means your idea of cutting a hole in the body and just allowing the lens to show is a much better one than the initial idea of externally mounting it.

This is spot on, your original vectors weren’t correct. I think you are going to struggle as you are trying to increase the weight by 35% and adding a huge amount of drag. I don’t think you’ll be able to get it balanced.

EdButler · 17 Dec 2018 at 13:04

Im an NPPL so know some basics although not being able to see the attitude of the nosedive makes things difficult to diagnose.

The CG must still be forward of the CL if its nosediving which is correct to an extent, but there may simply may be insufficient airspeed for lift. You've increased the weight so you must proportionally increase the airspeed to increase lift to maintain a flyable attitude. If you look at the diagram posted above, you've increased the CG arrow down (a lot), but not increased the CL up arrow.

If your speed is limited (Prop pitch and Motor RPM is maxed out), you'd need to increase the chord of the wings (add Flap)