First Balsa Slope Plane Kit

[SDsloper]

Hey All,

New to the forum, but have been flying for a few years. I've been slope flying for the past couple years but have been involved in RC for 20+ years. Mostly RC cars (racing buggies), but have flown 3d helicopters, aerobatic planes, boats, basically anything rc at this point. I recently bought a laser cutter and for my first project I designed a slope glider. I've built guillow models before but have never built an rc balsa plane. So this was my first stab at it. I definitely learned some things in the process but this was a quick build. About 6 days from start to finish. The wings were designed to be removable but in future designs I think I will eliminate it. Would love to have some feedback on improvements that I can make. I have yet to fly it but I did a little cg tuning in my front yard just from tossing it. Like other wings I think the cg will be highly sensitive. The vertical stabilizer could probably be bigger but I want to fly it before making changes. Current AUW is 146g or 5.1oz, wing area is 175.5 sq/in. wing loading = 4.18 oz/sqft. Model is designed with 9gram servos in each wing. Also if anyone is interested in being a beta tester I would be happy to send you a kit. I would just like feedback on areas for improvement.

Thanks,

Nick
San Diego, California

 

[Konrad]

Welcome.

Flying wings (AKA plank) are difficult to design and get to fly well. It can be done and done well. But as a first attempt I don't think they are the best choose.

Now we have a member here on the forums that is real good with these planks and computer generated aircraft (laser or CNC cut). I hope @thenated0g stops by with his insight.

 

[Red]

Nice Job Nick. Make sure you are running a little differential in the ailerons, that may make the wanting a bigger tail feeling go away. Good luck with the flights!

 

[Konrad]

Differential aileron (more up than down motion in the control surface) on a flying wing may require some down elevator mix. This brings up another question, what radio do you have and how comfortable are you manipulating its programing?

 

[SDsloper]

Differential aileron (more up than down motion in the control surface) on a flying wing may require some down elevator mix. This brings up another question, what radio do you have and how comfortable are you manipulating its programing?

Currently I’m using a DX9 and I’ve played around with most of the settings on my models, flaps, reflex, dual rates, etc. the closest plane I have to my model is a dreamflight weasel. I have three modes, 120% travel, 80%, 65%. I’ve never tried differential though. I could easily setup some mixing on the weasel to try it out though. Not sure if the weasel would really need it though.

 

[Konrad]

The Weasel is a good flying ship. No need for advanced mixing. But it will make a great test bed for you to develop the mixes you might need. If these mixes aren't needed you can set them to zero. But it is nice to have the mix option available when you are setting up the values on your test flights.

I have a DX9 and have to admit it pull out a lot of my hair when ever I try to set up advanced mixing. I think there a few good videos out there so dig around if things start to look overwhelming.

 

[Red]

Nick,

Don't put any down elevator mix in with the differential, that will just negate the differential in the first place. Get the CG correct and there will be little to no pitching. You only need 20-30%. The DX9 is a quite easy radio to program, you can simply add diff right in the diff menu.

 

[SDsloper]

Nick,

Don't put any down elevator mix in with the differential, that will just negate the differential in the first place. Get the CG correct and there will be little to no pitching. You only need 20-30%. The DX9 is a quite easy radio to program, you can simply add diff right in the diff menu.

Thanks Red, are you suggesting 20-30% from the leading edge? And would I include the ailerons as wing area?

 

[Konrad]

I think that is a 30% or less value aileron differential on your DX9.

As to CofG % wing chord you will want to use the ailerons as part of that calculation. Aim to start with 15% to 20% of mean aerodynamic chord (MAC) for planks.

 

[Red]

Thanks Red, are you suggesting 20-30% from the leading edge? And would I include the ailerons as wing area?

No, 20-30% total diff. Yes you include the elevons in the “projected area” for MAC calculation. The MFG should have a good starting point for you, but 15-20% is very far forward. It’s flyable there, but you will need more up elevator trim and it will be very speed stable meaning if you dive to go faster it will want to pull up on its own. This also makes adverse yaw even worse. My experience has been a little further aft with reduced elevator throws. Google flying wing CG calculator, and you can put the dimensions in to see what it says. Regardless, flight testing and moving it to your liking is best.

Good luck!

 

[Konrad]

For a low time plank pilot start with a very forward CG. And then move aft. As noted they fly much better as the CG is moved aft. But you need to get past the maiden flight!

 

[Wayne]

You stated you have already performed some CG test flights in your yard. If you got the plane to glide, then GREAT! That is 90%of the challenge with a plank design. The CG on a plank if very small. Smallest of any aircraft design I am aware of. Just a few mm will make the plane dive into the ground.

Make sure everything is mounted solidly, battery can't shift in flight.

Typically you will have very small elevator inputs once the CG is dialed in. The cheap 9 gram servos may have enough play to make this very annoying!

Looking at your photos, it looks like your leading edge does have a bit of rear sweep, I suspect this will tame down some of the Plank character, but pretty sure you still fall into the plank arena. To be clear, a Weasel is a Chevron Flying wing (a different animal) and an Alula is a Plank. The handling and performance are very different.

 

[SDsloper]

Thanks for the advice Wayne! I ordered cheap servos because I didn't know how successful the design would be. If it flies decent I'll build up a second one with more improvements.
With the leading edge having some rear sweep, I was taking some ideas from the weasel, but definitely seems to fall under the plank category.

Separate note: Does Anyone have an airfoil recommendation? I used a s6063 but I am open to changing it, to improve inverted flight. http://airfoiltools.com/airfoil/details?airfoil=s6063-il

 

[SDsloper]

Well… I maidened her. Luckily a new friend and local flyer ‘Chris’ at Dave’s beach gave me some really good advice and provided a ton of help when setting the CG and setting up the servo throw. I started off with about 10grams of weight in the nose and 80% throw for both elevator and aileron. He had me turn the rates way down and and add more weight. We ultimately landed on 25% elevator, 65% aileron, no differential (yet) and about 30grams of weight at the nose. The plane flys great. I will be tuning the cg further when the wind is good and I’m going to re make the hinges from covering. Overall I’m ecstatic with the plane. Really accelerates, it was flying great in about 5mph of wind and was very predictable. First day of testing was a success.

 

[Red]

Congrats!

 

[Doc J]

Thanks for the advice Wayne! I ordered cheap servos because I didn't know how successful the design would be. If it flies decent I'll build up a second one with more improvements.
With the leading edge having some rear sweep, I was taking some ideas from the weasel, but definitely seems to fall under the plank category.

Separate note: Does Anyone have an airfoil recommendation? I used a s6063 but I am open to changing it, to improve inverted flight. http://airfoiltools.com/airfoil/details?airfoil=s6063-il

HI SD - the Selig 6063 is not a really good choice for a plank, as a bit of refelex would help in many ways.

I'd suggest going old skool for the next one and getting back to the Eppler 180 series or maybe one of martin Hepperle's ( E180 or maybe E182 or maybe MH42)

Cheers,

Doc.

 

[Wayne]

Woohoo! Congrats!

 

[thenated0g]

Looks great! Any pics/videos of flight? Hoping to check out daves beach in a couple weeks.
My goto plank airfoil for slope has been the pw51 for many years.

 

[thenated0g]

Randomly had Instagram load up your videos

@goodcleanflying on Instagram: "Stormy winter flying today"

48 likes, 2 comments - goodcleanflying on January 16, 2023: "Stormy winter flying today".

www.instagram.com

 

[SDsloper]

Hey Nate! Thanks for the follow, I just started up the instagram but its getting some traction. Hold tight for my next post on my new twisty design.