FTFC'18 WWII Curtiss-Wright XP-55 Ascender

[HilldaFlyer]

Hey everyone - Thanks for your help.
I'll post photos of the CG and the minimal flight damage along with a complete tear-down of the model following the 5 maiden flights:

Enjoy - 11+ minutes of my life.

 

[F106DeltaDart]

Congrats on the 5 maiden flights man! By flight 5 it was looking like you had it dialed in pretty good, and you proved that your model is pretty dang tough! It shrugged of the impact quite well. That stall looked nasty though and it looked like it really needs some more throttle to push it through high bank turns. Actually seems to handle a lot like an EDF. I do wonder if the stall can be tamed a bit.. Maybe limit the canard throw a bit more and add a bit more vertical stabilizer area. Would be a pretty easy experiment to oversize those wing fences by 15% or so and see what happens. Looking forward to seeing more!

 

[DamoRC]

Great job! That's pretty tough prototype - held up well as you got her figured out.

Congrats on the maiden!

DamoRC

 

[Michael9865]

Congratulations!

 

[LitterBug]

HilldaFlyer,
Absolutely AWESOME! Great build and great flying for such a challenging design!

Cheers!
LitterBug

 

[HilldaFlyer]

Congrats on the 5 maiden flights man! By flight 5 it was looking like you had it dialed in pretty good, and you proved that your model is pretty dang tough! It shrugged off the impact quite well. That stall looked nasty though and it looked like it really needs some more throttle to push it through high bank turns. Actually seems to handle a lot like an EDF. I do wonder if the stall can be tamed a bit.. Maybe limit the canard throw a bit more and add a bit more vertical stabilizer area. Would be a pretty easy experiment to oversize those wing fences by 15% or so and see what happens. Looking forward to seeing more!

Thanks so much for your thoughts on how to deal with stalls. I have never flown an EDF, but I have a Viggen on the bench. I've watched the video several times and stalls happen after really banging the sticks. The motor doesn't have the guts I was hoping for... maybe next build, but you're right, slow calm movements seem to be key.

Would you thing that making the fences thinner or am I just after more surface area? Certainly both are doable.

Currently the model is scale, right down to the rivets! Just kidding - scale is size and placement of everything. I need to make the wing tips more foiled because right now they're kind of blobs on the tips of the wings. Making the fences larger is probably a good thing to do.

Anyone else with ideas...

 

[HilldaFlyer]

Placement of the battery as determined by the CG calculators.

Here is the location of the battery using the simple Flying Wing CG Calculator.

Here is the placement of the battery to balance at the CG determined by Canard Center of Gravity Calculator. You know, I’m really glad I didn’t try flying this with the battery in the back - that would have been a complete tail-in failure.

 

[HilldaFlyer]

​Post Maiden Wrap-up.

Fits nicely into the trunk for the trip to the field.

Grass skid marks post maiden, and a bit of nose separation.

More skid marks on the wing vertical stabilizers.

This is the air scoop that tore off after the last landing.

Every time I hit the ground, the back section of the fuselage would slide back into the prop.

Here is a better view of the carnage.

Here is a view of the cockpit removed. It is held in place with four bamboo skewers through holes and four head to tail magnets. Snaps on pretty good.Probably don’t need the skewers, but it is a trick I’ve used before to hold things in place.

The fuselage was only held onto the plane with a couple wraps of tape. Cut the tape and the fuselage peeled away.

Here is a photo of the battery cradle I made to go with the second CG calculation. Of course the one on the right (rear of the plane) never got used - so I’ll have to add this to the plans.

[h=1]Antenna Placement[/h]

This shows how I ran the receiver antenna. I just use some coffee stir straws. The one nearest has a 90 degree bend and goes into the foam. The hole was made with a bamboo skewer. That puts two antenna with 90 degree between them. The straw was bent by carefully heating it with a lighter.

The ESC was placed on the lower part of the rear fuselage and the battery plug pokes up to the canopy.

I’ve marked the locations of the CG. The rear and most forward ones are calculated. The one in the middle is where the plane flew on flights 2-5. The wing is held on with four screws.

The wing mount saddle has two pieces of plywood that the screws go into.

 

[PsyBorg]

Congrats on a successful run mate. That looks awesome to. Very much like the real ones. The wings came out nice I think. Great job over the whole thing and sticking with it to get it dialed in and flying with the fairly hard pancake landings says a lot for the design. :applause:

 

[F106DeltaDart]

Thanks so much for your thoughts on how to deal with stalls. I have never flown an EDF, but I have a Viggen on the bench. I've watched the video several times and stalls happen after really banging the sticks. The motor doesn't have the guts I was hoping for... maybe next build, but you're right, slow calm movements seem to be key.

Would you thing that making the fences thinner or am I just after more surface area? Certainly both are doable.

Currently the model is scale, right down to the rivets! Just kidding - scale is size and placement of everything. I need to make the wing tips more foiled because right now they're kind of blobs on the tips of the wings. Making the fences larger is probably a good thing to do.

Anyone else with ideas...

Glad to help, seems to me that the large amount of fuselage area in front of the CG just really tends to make it yaw into a spin after the stall. So more vertical area as far back as you can get it should help that tendency. If you are doing some work on the tips, you could try a bit of washout as well, and angle the leading edge of the tip section down ~2 deg-ish. I had a hobbyking Lancaster that had a nasty habit of dropping a wing, and a bit of washout really tamed things out.

 

[HilldaFlyer]

you could try a bit of washout as well, and angle the leading edge of the tip section down ~2 deg-ish. I had a hobbyking Lancaster that had a nasty habit of dropping a wing, and a bit of washout really tamed things out.

Just so I understand, make the wing tips with less angle of attack to prevent stalling. I'll have to think about how to do that since it is one piece of foam.

 

[F106DeltaDart]

Just so I understand, make the wing tips with less angle of attack to prevent stalling. I'll have to think about how to do that since it is one piece of foam.

Yes, lower the AOA at tips so that hopefully the stall starts closer to the root, giving you a forward "mush" stall instead of dropping into a spin. On the Lancaster I did it by making a slice about 1/3 way through the tip, bending the leading edge down, and regluing it there. Then I applied some hobbico filler over it and blended the transition together.

 

[rockyboy]

Hmm... will have to try that trick out for adding a little twist at the tip.

Also, I really need to make some battery cradles like that for a whole lot of my planes! I thought I was being slick drawing a line where the battery end should be, but that foam case is a much easier way to line it up.

 

[FAI-F1D]

Hildaflyer,

You asked for this info on facebook after I referenced it and then found out that the plans I directed you to don't actually list the CG. So here's the skinny: for a free flight model of the XP-55, the CG goes at or slightly ahead of the wing root leading edge. This actually from three different people who have gotten these to fly, including a retired AeroVironment designer, so I reckon it's pretty authoritative advice.

I'd tack onto that the prediction that you'll need about 10 degrees up trim in the canard to maintain level flight, so make sure you have enough travel to accommodate that if you also want to be able to do inverted (if it's stable, it'll do inverted ).

 

[HilldaFlyer]

Hildaflyer,

You asked for this info on facebook after I referenced it and then found out that the plans I directed you to don't actually list the CG. So here's the skinny: for a free flight model of the XP-55, the CG goes at or slightly ahead of the wing root leading edge. This actually from three different people who have gotten these to fly, including a retired AeroVironment designer, so I reckon it's pretty authoritative advice..

Thanks! And I agree that is probably good advice. All I have to say is mine is nowhere close. Mine is aft, more near the trailing edge. Which begs the question why? So, What is the difference between a free flight plane and a powered plane? Nothing, I hope, as far as CG is concerned, right?

I'd tack onto that the prediction that you'll need about 10 degrees up trim in the canard to maintain level flight, so make sure you have enough travel to accommodate that if you also want to be able to do inverted (if it's stable, it'll do inverted ).

Wow, that much? Currently I have 1 to 2 degree up trim on the canard. I did have it a zero until moments before the maiden. I've got lots of throw to play with, probably 40 degrees (I'll take some more photos).

During the first flight, after getting the roll straightened out was full up and it still went into the grass. So I doubt very much that I'll move the CG more forward. My plan was to leave everything as is, do a series of flights and move the battery a bit more forward on each flight and monitor the characteristics. Can't argue with a good flying plane. I'll get it there.

 

[HilldaFlyer]

To follow up the conversation with visuals.
Here are some photos of the CG and Canard movement.

Wing Root is 22 cm.
CG #1 is at the trailing edge (100% from leading edge). Calculated from the flying wing CG calculator taking nothing else in consideration. I built a battery cradle for this CG but it was never used.
CG #2 is 9.3 cm from the trailing edge (57.7% from leading edge). Calculated from the Canard Center of Gravity Calculator. Built another battery cradle for this CG and it was used for Maiden Flight #1. When giving full up, the plane pancaked into the grass.
CG #3 is 7.8 cm from the trailing edge (64.5% from leading edge). This is the CG point used for Maiden Flights #2 - #5.

Trim of canard at level. I think the photo is a bit off center, the angle is about 2 degrees up from level.

Canard angle at full up.

Canard angle at full down.

 

[HilldaFlyer]

While the damage was very minimal for the 5 flights, I did discover more damage while looking at the CG moments ago. Under the clause of full disclosure, the foam in the box fuselage below the battery has been compromised. The paper is not ripped, but the foam underneath the paper feels like it has been squashed - which it was when performing those awesome pancake vertical landings.

I’m gently pushing down on the foam where the battery sits and the foam flexes about 5 mm. If you look close at the hole where the servo wires come up through, you can see the paper has torn away from the foam. This fuselage will get several more flights refining the CG.

 

[FAI-F1D]

Thanks! And I agree that is probably good advice. All I have to say is mine is nowhere close. Mine is aft, more near the trailing edge. Which begs the question why? So, What is the difference between a free flight plane and a powered plane? Nothing, I hope, as far as CG is concerned, right?

I believe the reason would be this: we don't want our stick and tissue models to go into a spin. Ever.

More importantly though, I'd put it in the category of Don Srull knows where the CG should go and given that he's got UAV designs in current military service, I'm disinclined to argue.

 

[HilldaFlyer]

Hello everyone. After hours of pouring over the plans, they are now in a shareable format. They're not perfect so I expect I'll have updates as I build another. But these are a great start for someone who wants to build it.

 

[rockyboy]

Nicely done sir!