Regal Bipe - w/KF Wings (Video, Pictures, Free Plans, and Discussion) - RC Groups
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Dec 18, 2007, 01:39 AM
Heli's don't fly voluntarily
Kaos2's Avatar

Regal Bipe - w/KF Wings (Video, Pictures, Free Plans, and Discussion)

The purpose of this thread is to introduce the next generation in the Regal family, the Regal Bipe. In order for this biplane to be named Regal, it had to posses the flight characteristics that I consider to be definitive of the first Regal. Those characteristics are the following: highly aerobatic, light wing loading, excellent slow flight, positive control even at slow speeds, easy to fly, and generally makes a pilot look good. Having flown this plane, I think the Regal Bipe delivers in all respects.

My son built our prototype and got to fly it today (12/17/07). He made a total of 3 flights. The first was with the CG too far aft creating a plane out of balance, the second was in 8 – 10 mph wind, and the third was in ideal conditions. The video is a selection of clips from these three flights. I won’t go into the specifics about the plane’s handling and flight characteristics because 30V2 will post those details in this thread himself. I know the video is a bit on the large side, but I’d like to think it’s worth the download. I hope you enjoy.


KF Regal Bipe Flight Demo (4 min 35 sec)

Downloadable Flight Video: First flight video of the Regal Bipe

Link to the Original Regal: Regal Monoplane

Last edited by Kaos2; Jan 14, 2008 at 10:09 PM.
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Dec 18, 2007, 01:41 AM
my nCPX is my sim!
30v2's Avatar

Regal Bipe Flight Report

Earlier today the weather was great for a maiden flight so we headed out with the new plane to put some air under the wings. The morning air was very calm, and this Bipe jumped into the sky after rolling about four feet on the pavement. I quickly discovered that the CG was too far aft, so I only flew for a few minutes before landing and heading back to the house to make some adjustments. By the time we got home, made some changes, ate a quick lunch, and got back to the field, the wind had picked up to about 7-9mph. Nonetheless, I flew in the wind for another pack before deciding to wait for calmer air. Fortunately, it calmed down this evening and I was able to get in another quick flight before dark. This last session was by far the best demonstration of what this plane is capable of when properly balanced and flown in the right conditions.

My first impressions are that this plane flies VERY slow, and is able to just float along with a little power. It was somewhat surprising how slow and stable this plane flew, it is definitely still a Regal. There is no mistake that this is a slow flight biplane. That said, it is very nimble and responsive to inputs, and the extremely light wing loading makes it even more forgiving than the original Regal when falling out of maneuvers. Also, when rolled inverted this plane needs practically no down elevator! The first time I rolled inverted I did not even touch the sticks for a couple seconds and it remained flying perfectly straight and level, thus making low inverted flight circuits enjoyable. Snap rolls, barrel rolls, and tailspins were performed nicely, and it performed knife-edge circuits very well with little or no coupling.

Hovering with the motor I installed is only possible at near full throttle, but is easy to maintain despite not having a lot of extra ponies to climb out if I got in trouble. Once I install a larger motor it should be very fun to hover and 3D. (Even though I would personally like a fully capable 3D plane, the 2825-09 motor is fine for normal sport flying, aerobatics and light 3D.) All the control surfaces have good authority resulting in positive control at slow speeds and superb aerobatic potential. The roll rate is respectable, yet relatively slow for a biplane. Also, if you plan on only using one servo for the ailerons be sure to install a high torque servo. The HS-56HB that was originally installed did not hold well at full deflection, but for the second flight I had swapped it for a WOW-RC 17 gram servo that did much better.

Because of the need for more weight fore, the plans have been adapted to enlarge the battery bay to accommodate a larger battery. This will also be beneficial for me since I want to install a more powerful (and heavier) motor. Ideally the added weight from the larger Lipo and motor will give me the CG location I want without having to add any dead weight.

This plane is undoubtedly best flown in less than 5mph winds. In the right weather conditions this is an extraordinarily enjoyable slow flying biplane that is very 3D capable. Additionally, because of how slow and nimble this plane flies, it would be a good choice for smaller flying fields and may even be a good indoor plane with a scaled down version. I am really looking forward to flying this plane again to test its full potential. If you enjoy flying the Regal then I think you will find the Regal Bipe to be a real blast!

AUW (Ready-to-Fly): 25.3oz
Motor: 2825-09
Prop: GWS 1170 (But I think an E-Flight 11 x 4.7 may be better)
ESC: Align 35A ESC
Servos: HS-56HBs (Switched to a WOW-RC 17 gram servo for aileron)
Battery: WOW-RC 1200mah 3S 15C
Receiver: Hi-Tech Electron 6
Last edited by 30v2; Dec 18, 2007 at 12:47 PM. Reason: adding weight info
Dec 18, 2007, 04:37 AM
How do I change this text?
Darth_Elevator's Avatar
Awesome plane. I'm going to have to try this one. Would you mind telling me what the AUW is? Sorry if I missed it.
Dec 18, 2007, 06:59 AM
Postcards From The Purple Edge
tuppertn's Avatar
Crap! Can't access YouTube at work! Nice flight report, though.

It sounds like it flies great as is, but just out of curiousity--what do you think would happen if you flipped the bottom wing into a KFm1?

Dec 18, 2007, 08:57 AM
Registered User
Dickeroo's Avatar

Incredible performance!

You guys have outdone yourselves. That is an amazing bipe. Extremely smooth in the air. And, one of the best videos I seen because you're right up close and can watch this ballet without straining your eyeballs. It all looks so effortless. Congratulations on an outstanding piece of work.
Dec 18, 2007, 09:40 AM
Brit in Bahrain
Nigelp's Avatar
Congratulations on a very sucessful maiden, a great video and the A4 tiled plans ! Flies like a bird !

I'm going to have to build one of these - the lightweight version of course !

Question - what are the outboard cabane struts made of ?

Dec 18, 2007, 11:02 AM
Heli's don't fly voluntarily
Kaos2's Avatar
Darth, sorry we forgot that AUW item here. I'm pretty sure 30V2's plane came in around 25.3 oz. (edit I just weighed it)

Kendall, I'm assuming that you're talking about making the bottom wing a bottom step KF airfoil (sorry, not familiar with KFm1). Eric and I discussed the whole wing arrangement "thing" when I was drawing the plane up. The reason why I chose this arrangement was due to the inverted flight characteristics exhibited by the monoplane Regal. By that I'm referring to how little “down” elevator a Regal requires to fly level while inverted. My hypothesis is that when a top-step wing becomes a bottom-step wing (rolling inverted), there’s a bit of an increase in lift, or the center of lift shifts forward in the wing chord. Either way, the result is a plane that rolls to inverted and requires very little down elevator input to fly level. This particular trait inspires a lot of confidence when performing various maneuvers involving inverted flight since the plane fly’s nearly the same. If I were to orient one wing with the step up, and the other wing with the step down, it’s true that the lift would remain constant whether inverted or upright. That would mean that while upright, lift would be the result of the angle of attack induced by some amount of elevator trim. If the lift/center of lift remained unchanged when rolling inverted, that upright elevator trim would have to be manually eliminated plus some additional down elevator to create an angle of attack for the wings while inverted. I know this is just my hypothesis, but the bottom line is that both the Regal and now the Regal Bipe require very little down elevator when flying inverted, which I consider to be a Regal trait. Sorry for the long answer, but my intent here is to share information about the RC hobby. The short answer to your question about flipping the bottom wing over is I think the plane would require more down elevator input when flying inverted.

Dick, thanks for your kind comments.

Nigel, the struts are made from the same foam used for the rest of the plane. It's actually quite sturdy when both wings get locked together at all three points.
Last edited by Kaos2; Dec 18, 2007 at 06:47 PM. Reason: Corrected weight.
Dec 18, 2007, 12:33 PM
Foam Wannabe
The video is great, another nice job and one to add to the build list.

Did you use a single servo for the ailerons? Is it just mounted to the bottom of the wing?


Dec 18, 2007, 12:42 PM
Heli's don't fly voluntarily
Kaos2's Avatar
Originally Posted by rcallison
The video is great, another nice job and one to add to the build list.

Did you use a single servo for the ailerons? Is it just mounted to the bottom of the wing?


Thanks Ron.

Yes, in the interest of saving as much weight as possible, there is one servo in the center of the wing on the bottom.
Dec 18, 2007, 02:06 PM
my nCPX is my sim!
30v2's Avatar
Thanks for the compliments.

I have updated my previous post with the AUW we ended up with ready to fly after adding weight for balancing (and Kaos2 just posted it as well). Also, here are a few more pictures of the plane:
Dec 18, 2007, 02:53 PM
Postcards From The Purple Edge
tuppertn's Avatar
Just got a chance to watch the vid--OUTSTANDING! Love the antigravity thing. Big and floaty. Just gorgeous!

Dec 18, 2007, 05:31 PM
my nCPX is my sim!
30v2's Avatar


If anyone is interested in seeing some pictures of this plane being assembled, I posted a few in my Blog while building.
Last edited by 30v2; Dec 18, 2007 at 05:37 PM. Reason: inserting hyperlink
Dec 20, 2007, 01:44 AM
Flying for the fun of it
beep684's Avatar

I am amazed at how well this plane flies. It can fly so slow and be so stable. Great design!

I am in a competition where I have to drop 3 golf balls onto a target from a rc plane.
I have been looking at various designs of aircraft that can fly as slow as possible.
This biplane seems to fly very slow and still be very stable. How does it handle wind?

I am thinking about making one of these Regal Bipes at 200% size, and powering it with an E-Flite power 46 Outrunner. I have attached a word document in which I have done some calculations to do with the weights of all the components needed, and to do with wing loading, wingspan, area etc.

From what I have calculated, if I make one of these at twice its original size, it should be able to fly nicely and slowly.

Can some of you more experienced modellers out there, or anyone who knows about wing loadings etc. please tell me if this will work or not?

I am intending on flying it with a high angle of attack like in the video to acheive slow flying.

Here are some figures. They are all estimates though.

Do you think it is possible to make a strong 200% airframe that weighs 1kg (35 oz) or under? I am intending on reinforcing everything with carbon fibre.

AUW (RTF): 2.6kg 91.6 oz 5.7 pounds
Wing Loading: 5.1 oz/sq.foot
Wing Area: 2592
Wingspan: 72 inches (each wing)
Wing root chord: 20 inches
Wing tip chord: 16 inches
Average wing chord: 18 inches

Target Weights: - Airframe: 1kg (35.2 oz) (2.2 pounds)
- Everything else (powerplant, electronics etc.): 1.6kg (56.4 oz) (3.5 pounds)

Motor: E-Flite Power 46 Outrunner - 290g (10 oz)
Prop: APC 13 x 8E - Not Much
ESC: Dualsky 100 amp - 125g (4.4 oz)
Servos: JR ES539 x 4 - 38g (1.35 oz) each - 152g (5.36 oz)
Battery: FlightPower 5S 3700MaH - 380g (13.4 oz)
Receiver: JR RS77S - 20g (0.7 oz)

- Total Weight (Everything above): (967g) (0.967kg) (34.1oz) (2.13 pounds)

Releasable Payload: Golf Ball x 3 Each– 45g ( 1.6oz) - Total – 135g (4.76 oz)
Release Mechanism and avionics - At least 500g
-Weight (Payload, Avionics etc.): 635g (22.4 oz) (1.4 pounds)

Sorry for the long post.

If anyone could tell me if this would work, or offer any suggestions for a slow flying design, it would be greatly appreciated.

Do you think it is worth scaling up this aircraft, or should I look at some ARF .46 3D biplanes, which I could fly around in high-alpha. I like biplanes because they are more compact than monoplanes, and I am not worried about drag.

Last edited by beep684; Dec 20, 2007 at 01:51 AM.
Dec 20, 2007, 02:05 AM
my nCPX is my sim!
30v2's Avatar



This biplane is certainly very capable of flying slowly while also remaining very stable. However, because of the light the wing loading and the amount of surface area, it does tend to get pushed around by the wind. That's why I recommended flying in less than 5mph winds. But because of the large control surfaces it is still extremly controllable when flying in some stronger wind (within reason, ie 5-10mph). I will tell you that if you are wanting to fly in the wind you will do well to make sure you have a good power to weight ratio so that you can make your way back upwind at a respectable pace.

As to looking at larger 3D bipes, most aerobatic biplanes are designed with a heavier wing loading, so you may have trouble finding one that will float as nicely as the Regal Bipe. That said, I'll leave it to the more experienced modelers to advise you on the logistics of scaling up a design.

Either way you decide to go, good luck.
Dec 20, 2007, 02:23 PM
Heli's don't fly voluntarily
Kaos2's Avatar
Ben, I'll give you my best advice concerning your proposed project. Please be aware that I haven't scaled anything up to the size you're suggesting. I’m going to begin with some foundational info that begins with the Regal monoplane, and then extrapolate an estimate for the weight of a 200% Regal Bipe. Many have found that the weight of the Regal monoplane, ready to fly, is in the 18 – 20 oz. range. Also, the airframes for those same planes have run 13 – 15 oz. That would suggest that roughly 5 oz. of the flying weight is electronics of some sort. We know that our Regal Bipe weighs roughly 25 oz. , ready to fly. If we subtract 5 oz for electronics, the bipe airframe is in the neighborhood of 20 oz. If you double everything in size, it’s logical that you’d have a 40 oz. airframe.

However, there are a few additional considerations. Wing halves would have to be built and joined. If the cabane and wing struts are all doubled in size, they may also need to be doubled in thickness (laminated). That means that the glue required for the additional laminations may add up more quickly than expected by simply doubling the weight of the smaller airframe. Since the wingspan would be increased to 6’, doubling the spar to ½” square stock could produce an unexpected increase in weight. CF could possibly be the answer for the wing spar. I’m thinking that it would be tough to build a craft of the proposed size in the 3 lb. range, and more than likely it would be 3.75 – 4 lbs.

Another consideration would be the design of the KF airfoil. The plane is designed to be built out of blue/pink FFF, purchased at Lowes, Home Depot, etc. The KF wing has no structural support aft of the spar and relies on the strength of the foam to retain its shape. The same is true for the control surfaces. They are all a single thickness of FFF. These surfaces must remain proportionally the same size to deliver the positive control at such slow speeds. If you double these unsupported areas in size without doubling their thickness, you may be asking for structural failure. If you double up in both area and thickness, the glue to create the lamination is additional. As you can see, I’d have serious reservations about trying to build a bipe from FFF that is double the size of this one.

Now with that said, this bipe has a “ton” of load carrying ability as it is. If the three golf balls aren’t required to be airborne all at once, setting up a drop installed on the plane’s CG should produce excellent results. If one must scale up this bipe for this task, I think a scale that results in a 48” wingspan instead of the 36” would be feasible.

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