Angelwing FVT3 v3 beta kit build

[Smoggie]

Just putting the finishing touches to a beta kit build for Andy at Angelwing Designs for his new FVT3 v3. For those who havent seen the FVT3 it's a really interesting and unusual flying wing design with no vertical stabiliser. It used Prandtl/Horton 'bell shape lift distribution' magic to achieve directional stability and pro-verse yaw.

The new version is designed to be more agile, easier to build and lighter. Mine is on target for a rtf weight of 210g, which is a full 100g lighter than the previous version. Obviously getting under the magic 250g limit is a bonus but the new lighter weight should also make it good for even the slightest of breeze on the slope. It's been a really fun build.

You can pre-order a kit at Angelwing now:  fvt3-pre-order

 

[oipigface]

When I built an earlier version of the Prandtl, I covered it with Eze Tissue and Eze Dope. It came out at about 2/3 the weight I expected - around 140g. Since most of the covering was behind the CG, I had to reduce the nose weight substantially.

[Smoggie]

Yeah, reducing weight behind the CG is critical on this design. Anything added much behind the CG is multiplied several times over in noseweight. I know Andy did consider adding some sort of nose extension but decided it would spoil the purity of the flying wing design (I agree with him).
The covered airframe on this version was 100g. I've got a 50g noseweight plug already fitted, 30g battery and two 5g servos and micro Rx.. I'm allowing another 10g of extra noseweight to finally balance.

What was the all up flying weight on your original one?

[MikeE]

Looking very nice.

Using a double or heavier covering on the nose. Adding weight and strength, might be a worthwhile option.

[oipigface]

5 hours ago, Smoggie said:

What was the all up flying weight on your original one?

140g.

[Smoggie]

45 minutes ago, oipigface said:

140g.

For the FVT3, you sure? The original one i built was 320g, the manual says 330g so i thought I was doing quite well. 118g of that was nose weight (as per manual) but given the layout i cant see how it could ever be built without any weight at all in the nose. I recall that the woodwork alone on mine was about 140g and I'm usually a reasonably light builder.

[oipigface]

That was from memory. If the manual says 330g, then I’ve probably misremembered, because I thought at the time I first weighed it that it was about 2/3 of the expected weight.  I’ll check again and let you know. But before I look out some exercises to improve my memory!

[oipigface]

On 14/02/2024 at 09:02, oipigface said:

That was from memory. If the manual says 330g, then I’ve probably misremembered, because I thought at the time I first weighed it that it was about 2/3 of the expected weight.  I’ll check again and let you know. But before I look out some exercises to improve my memory!

226g. 

[Smoggie]

That's a very impressive weight for the previous version of the FVT3. Is it including battery? How does it fly at that weight?

[oipigface]

Battery is a fixture. There’s no gyro in it, which saves some weight. As I said in my original post, I believe that using tissue and water-based dope saved a lot. The area of the plane behind the CG is much bigger than the area in front, so any weight saved in covering also saves nose-weight. It’s a while since I built it, but I remember following the instructions and fitting nose weight before the covering. For me that was really annoying, because reducing the nose weight when I found that the CG was way forward meant taking the nose apart.

Flying? Well, I can’t say it’s my favourite plane. It has an apparently uncurable tendency to Dutch roll, which makes it very hard to steer! Nick Chitty noted this in his build video and suggests that it can be cured by reducing aileron throw. I haven’t managed to cure it myself, and I haven’t yet fully assessed the circumstances which cause it. Life’s too short for that sort of thing!

One thing that occurred to me is that this tendency may be greater in mine because it is so light. Lower weight, less inertia, lower directional stability. 

It’s the first plane I’ve made when the build was more fun than the flying!

 

[Smoggie]

Dutch roll is something that the original version is prone to, it's not just you. I put a cheap gyro in mine which reduces the Dutch roll a lot. You do need to be gentle and smooth on the controls though, just enough to steer the model, it's not a model for 'stick banging'.
 

The new version was designed to greatly reduce or eliminate any Dutch roll (by taking out the dihedral) so I've set up up without a gyro. I'll report back on how it goes.

Here's my original, you can see that the gyro takes out almost all the Dutch roll:

 

[oipigface]

On 16/02/2024 at 18:35, Smoggie said:

The new version was designed to greatly reduce or eliminate any Dutch roll (by taking out the dihedral) so I've set up up without a gyro. I'll report back on how it goes.
 

I’m looking forward to seeing how your new one goes. Maybe I should think of getting the new version as well. Are the elevon leading edges still curved? 

[Smoggie]

Elevons are curved along the hinge line, same as the previous version. The false leading edge has a shallow laser cut line marked on it to give you a guide to sanding the bevel, so it's actually dead easy.

[oipigface]

I did suggest to Angelwings that they cut slots for the hinges, which would have indicated the bevel as well. It’s nice to know that they seem to have taken some notice.

[Smoggie]

It flies:

 

[oipigface]

That looks almost controllable! Well done.

Some questions:

Wind Strength?

Gyro fitted?

AUW?

 

[Smoggie]

Sorry I forgot to measure wing strength, I'm guessing 18-20mph or thereabouts. No gyro. Weight about 220g. The modifications to the design certainly do work as there is less Dutch roll on the new one without gyro than on the original with gyro fitted. It will still get a bit of a 'wobble' if you get aggressive on the controls but not to the point of being problematic.

She's extremely pitch stable so prefers to fly at a certain (leisurely) airspeed. It would be happier in less wind but as you see can cope with a bit more blow. Getting a move on requires a lot of down elevator. Unlike any other wing I've flown it needs more elevator throw than aileron.

As the main aerodynamic change on the new one is taking out the dihedral you could probably modify yours just by chopping the wings at the centre, and gluing back together without the dihedral. I believe Andy at Angelwing used exactly that method to test the modification.

Edited March 8 by Smoggie

[oipigface]

Way down on my list of ideas for my new CNC machine is a double-size version! (I kept all the spare pieces from the laser cut kit for just this reason.) But maybe I should try what you suggest first.