Working on a remake of the Pun Jet

[Lob0426]

I decided to redesign the FT Pun Jet. After reading the comments about it. It seems it had a number of problems. Those most commented was it was more likely to crash rather than fly. The motor torque appeared to be a real problem. It also tended to be hard to fly. Some believed it needed more wing stiffness. I tried to address these issues.

I have been looking for a small plane that I could take on My motorcycle rides. I am contemplating it will have folding wings as the original. The KFm2 will complicate this but it is doable. I will be using manual locks, not a servo, to lock the wings. For right now it is about getting it built, then try to fly it.

I have extended the wing to 18.5" (from 14.5") the chord remains the same, but the sweep angle is less, due to the length. It is not going to fit in the Guinea!
I have built it as a KFm2.
The fuselage has been widened about .28" but is the same length as the original.
I added doublers in the Nose.

It still will be powered by a 250-size motor, and I plan on using a 3S 1806 2280Kv. I will probably use a 5x4.5 prop. The servos remain as original also. I would like to use a 1300Mah 3S. I will probably use either an AR630 RX or a Speedy Bee F405 wing mini.

It is still in the redesign process. No motor mount as yet and a few details that need to be corrected in Lightburn. This was cut out, and redesigned, using Lightburn on a 130W laser cutter. The tip fins were designed for KFm3, but I decided to go with KFm2 instead, forgot to fix it. The front hole through the wing for the vertical stabs does not need to be there, I need to just burn a line to help line up the KFM2 additions. The guidelines burned on the wing are not as wide as the fuselage and need to be adjusted. The CG markers will need to be adjusted as well.

I can tell you that wing is way stiffer as a KFm2. I used a weird method to get the KFm2. I cut the KFm plate to fit about 45% back on the wing, then pulled the paper way back then cut a 45deg bevel. Glued the paper back down with hot glue. The front edge foam is peeled off so the paper can cover the leading edge. The wing itself is left as is. It came out pretty well but the beveling and regluing the paper take a bit of work and would be easy to screw up. It does leave a real clean leading edge. If you know an easier method to get a clean leading edge, please comment. Also, I did not remove the paper on the top of the wing or the bottom of the KFm2 panel. This could reduce weight. It really isn't heavy at all so far. Oh, it still fits on one sheet of DTFB. But it is getting tight! LOL

So far it went together pretty much as the original for fit. This build was really just to see what fit and what needed to be fixed. It went better than I thought it would so this one may get tossed into the air.

I don't know. We will see if these changes can make the Pun Jet into an easier plane to fly.

Edit:
Made the corrections to the Lightburn file I mentioned above.
The wing tips have been corrected to match KFm2
Adjusted the Fuse guide lines out.
Converted the cut of the front stab hole to an etch line (changed color to green)
I left the CG marks alone so far.

For the KFm2 panels to fit you need to go light on the hot glue, or wipe it thin, where the panels run along the fuselage. There is a small gap between the panel and fuse. I will probably fillet those to add strength. The wing is inserted through the body just as in the original. Then the KFm2 panels are added. I am considering changing this to make it just 1 panel full wing width.

Seriously considering changing the vertical stabs for better prop clearance after rereading the comments about the Pun Jet in the Forum.

 

[Lob0426]

Some more pictures with the Stabs in place, not glued, and the updated Lightburn screenshot.
The last picture is the original vs new Pun Jet screenshot from Lightburn for size comparison

 

[Lob0426]

Drew up a firewall to 3D print. A power pod is so close to fitting. I may have to change design for a mini power pod. The width is good, it needs about 2mm in Height. Also using a 3D version of Mini Control Horns I pulled off Thingiverse. So, making headway towards giving this thing a flight.

The Firewall is printing now. Already printed the control horns.

Design changes: Added cooling ports for ESC. Many of the changes will come out on the next cutting. Some I will add, or already have added, by hand to this plane.
Not happy with the design of the canopy /add: installed front tab instead of tape plus some side tabs

Needed to fly:
reinforce the Elevon hinges with hot glue. / done
Install servos / done
make control rods
Glue stabs in place
install Firewall, motor and ESC / done firewall printed motor mounted to it. 2mm bullets soldered. ready for install
Install Receiver
figure out CG
/add: fillet KFm panels to fuse / done

Haven't decided which RX/flight controller to go with as yet. The Speedy Bee has launch control which would help settle the roll of death on launch. The Newest AR630+ appears to now have Launch control (Hand Launch assist) as well but, I only have the older ones. Reprogramming does not add the new features to the older AR630's. I do know that I will have to upgrade my radio to setup the new features. Very familiar with the setup of the AR630, minus the new features. I have played with the Speedy Bees setup on my phone.

 

[Mr Man]

Looks good!

 

[Lob0426]

I would like to put out some pdf plans for this if it flies well. And as long as Flitetest doesn't have a problem with this.

I gave it a chuck in the bedroom onto the bed, and it glided really well. It did not have the vertical stabs on it.

 

[Mr Man]

I would like to put out some pdf plans for this if it flies well. And as long as Flitetest doesn't have a problem with this.

I gave it a chuck in the bedroom onto the bed, and it glided really well. It did not have the vertical stabs on it.

I doubt they would, just post it in the resources section. 👍

 

[AIRFORGE]

I would like to put out some pdf plans for this if it flies well. And as long as Flitetest doesn't have a problem with this.

I gave it a chuck in the bedroom onto the bed, and it glided really well. It did not have the vertical stabs on it.

It's OK for you to post plans for this modded version, brother.

 

[Lob0426]

From what I understand I cannot post the Lightburn file.

 

[AIRFORGE]

It would be best to post a pdf or vector file.

 

[Lob0426]

This what I have so far if you want to follow along. I am sure there are more changes in its future. I will put them in "Resources" when it is flyable.

mini control horns

 

[Mr Man]

This what I have so far if you want to follow along. I am sure there are more changes in its future. I will put them in "Resources" when it is flyable.

mini control horns

Plans look great!!

 

[Lob0426]

I am throwing this out there. I moved the wing position higher (approx .33"). Put a cutout in the wing. Then extended the lower part of the vertical stabs, to keep them about the same place for level on landing. The idea is to be able to get the battery low in the fuselage and to get the weight lower.
I did this in the 40mm EDF version of the Pun Jet I am working on

Getting the weight lower should help stability. It should also help fight the torque roll. It is just short of becoming a high wing in this drawing. This also allows more air around the ESC. A Rx will be able to fit at the back of the canopy on top of the wing. The battery can be placed on the bottom of the fuse and well forward. The wing could potentially be moved up to 3/16" higher.

The whole idea here is to increase stability, an issue commented on. This might make it less twitchy. It will change the look quite a bit. Another potential benefit, i believe, is the thrust line will be slightly under the center of lift. This might make it less sensitive to CG or possibly make it worse! What do you people think?

 

[Lob0426]

Well, mostly done. Still a lot of glue strings all over it.

Went with the E-Max 1806 2280kv and a 5x3R Prop. Also has a 12A ESC. Most was from a power pack I bought in 2017 at Flight Fest West.

It has a Lemon RX in it for now. I think I am going to go with an AR630+. That means I need to order one. I still need to upgrade my DX8E so I can program the new receiver.

I need to trim the Vertical stabs as they are just too close to the propellor blades. I shortened the back of the Stabs in the next version to avoid this already. I may move them out further to accommodate 5" props as another measure. Getting closer to a maiden flight. Probably going to take till next week to get the RX in. I ordered a newer programming cord, and it is supposed to be in tonight.

 

[Mr Man]

Well, mostly done. Still a lot of glue strings all over it.

Went with the E-Max 1806 2280kv and a 5x3R Prop. Also has a 12A ESC. Most was from a power pack I bought in 2017 at Flight Fest West.
View attachment 251838

View attachment 251839
View attachment 251840
It has a Lemon RX in it for now. I think I am going to go with an AR630+. That means I need to order one. I still need to upgrade my DX8E so I can program the new receiver.

I need to trim the Vertical stabs as they are just too close to the propellor blades. I shortened the back of the Stabs in the next version to avoid this already. I may move them out further to accommodate 5" props as another measure. Getting closer to a maiden flight. Probably going to take till next week to get the RX in. I ordered a newer programming cord, and it is supposed to be in tonight.

Looks good! Hope it flies well!

 

[Lob0426]

Looks good! Hope it flies well!

Yeah me too! LOL
I could fly it old school, with no flight controller at all, right now with just some settings. Like a bunch of Expo and Dual rates. Unfortunately, I think that would not be a good idea as yet. The controller will allow me the time to diagnose problems. Crashes 30 feet out do not give you much data to work with. I hope I can make enough changes, so you don't need to have a FC just to fly it. Or at least only needing it for launch as a good second goal post. Only flying it will tell!

 

[Lob0426]

Took it up to the field. It has a Lemon RX and the rest is a FT power pack (1806 and 12A ESC). I used the closest hole on the servo arm. I settled on 60% Expo and 70% dual rates. It has about 4mm reflex. THEN while carrying out a preflight found I had installed the wrong prop. It was blowing the wrong direction. Left my flight box at home which had plenty of props. No one else had a 5x3 prop. Has the right prop on it now. So, no flight.

 

[Piotrsko]

Umm you do know you can install the prop the other way (backward) and swap 2 motor wires from the controller?

 

[Mr Man]

Umm you do know you can install the prop the other way (backward) and swap 2 motor wires from the controller?

Unless they're where he couldn't get at em'

 

[Lob0426]

Umm you do know you can install the prop the other way (backward) and swap 2 motor wires from the controller?

I would have had to cut open the fuselage to reach the wires to swap them. A common commented problem on the Pun Jet. And without my flight box I had nothing to seal it back up afterwards. The motor wires are under the wing inside of the Fuse. Besides the motor is going the proper direction, wrong prop. I had a 5030R and a 5030 on the table. I chose the 5030R and it was the wrong one. I even posted that I chose the wrong one! LOL

I have at least 4 of each in my Flight box. Plus, I have a 3S powered hot glue gun, from Hobby King, my brother Robert bought me and glue sticks.

Remember, take Flight Box to field for maiden flights. LOL

 

[Lob0426]

Some of the references I am using for the changes to the Pun Jet,

Pun Jet- Anyone built one yet?

Well along on the construction of my first Pun Jet from a quick built kit. It is very simple build. I am expecting it to be fun to fly. Does anyone have one in the air yet? Any tips?

forum.flitetest.com

KFm airfoils:
flitetest.com/articles/kfm-wings-a-basic-explanation
rcgroups.com/forums Kline-Fogleman Airfoils-Building-Flying-Discussion

"Copilot" gave me these tips

🧪 Common Issues & Fixes for KFm2 Airfoils​

1. Stall Sensitivity​

• Issue: Sudden stalls during slow turns or climbs.
• Fix: Add slight positive angle of incidence (1–2°) and keep CG slightly forward. Avoid sharp elevator inputs at low speed.

2. Pitch Bobbing in Pushers​

• Issue: Nose oscillates during throttle changes.
• Fix: Increase AS3X pitch gain (80–90%) and reinforce the fuselage to reduce flex. KFm2’s step can amplify pitch instability if not tuned.

3. Control Surface Flutter​

• Issue: Elevons vibrate or chatter at high speed.
• Fix: Use stiffer foam or reinforce with tape/carbon spars. Keep hinge lines clean and tight.

4. Poor Glide Performance​

• Issue: Plane drops quickly when throttle is cut.
• Fix: KFm2 has more drag than traditional airfoils. Add a slight undercamber or extend the trailing edge with a thin strip of foam.

5. Unpredictable Turns​

• Issue: Plane rolls unevenly or yaws unexpectedly.
• Fix: Double-check elevon mixing and symmetry. KFm2’s vortex behind the step can affect control if the step isn’t aligned properly.

🛠️ Build & Setup Tips​

• Step Placement: Keep the step clear of control surfaces—ideally forward of the hinge line to avoid vortex interference.
• Wing Thickness: Stick to 9–12% of chord for best results. Too thick and you’ll get drag; too thin and lift suffers.
• Reinforcement: Use tape or skewers to stiffen the wing—KFm2 benefits from rigidity to maintain airflow over the step.

I was trying to find decent settings for the AR631RX for the Pun Jet. Pretty hard to find any real guides on AS3X gains for small light planes. I decided to try Microsoft "Copilot" and see what it could come up with. It found a table with general guides to AS3X and SAFE settings

✈️ General Gain Recommendations by Aircraft Type​

Aircraft Type	Wingspan Range	Suggested AS3X Gains	SAFE Angle Limits
Micro / Park Flyers	< 30"	High (70–100%)	Roll: 45–60°, Pitch: 30–45°
Sport / Trainer	30–60"	Medium (40–70%)	Roll: 30–45°, Pitch: 20–30°
Large Scale / EDF Jets	> 60"	Low (20–40%)	Roll: 20–30°, Pitch: 15–25°

These are starting points—you’ll want to adjust based on flight behavior. For example, a twitchy micro plane benefits from higher stabilization, while a large jet may feel sluggish if gains are too high.

These are what I found for general settings for AS3X and SAFE.

Then "Copilot" asked me specifics about the model,
To tailor gains correctly, I’ll need a few details:

• Wingspan (in inches)
• Motor type (pusher, tractor, EDF, etc.)
• Control surfaces (Elevons, Rudder, Aileron, Elevator)
• Desired flight characteristics (e.g., stable cruiser, agile aerobat, beginner-friendly)

Feel free to toss me those specs!

I told it 18.5" span and type KFm2, Motor type pusher, Control surfaces elevon, Desired flight characteristics Beginner friendly.

✈️ Custom Tuning Profile: Mini Foam Board Pusher with KFm2​

Parameter	Recommended Setting
AS3X Roll Gain	85–95% (High for wind resistance)
AS3X Pitch Gain	80–90% (Helps manage nose dips on throttle cut)
AS3X Yaw Gain	40–55% (Less critical with elevons, optional)
SAFE Pitch Angle	35–45° (Gentle leveling for beginner control)
SAFE Roll Angle	50–65° (Keeps turns smooth and controlled)

compare this to its answer for an intermediate flyer.

✈️ Custom AR631 Tuning Guide: 18.5" KFm2 Foam Board Pusher (Intermediate)​

Parameter	Recommended Setting
AS3X Roll Gain	80–90%
AS3X Pitch Gain	75–85%
AS3X Yaw Gain	40–50% (optional for elevons)
SAFE Roll Angle	45–55°
SAFE Pitch Angle	30–40°

These values balance responsiveness with stability—ideal for progressing beyond beginner mode while keeping control predictable.

So, I asked it where it got this information from! This was the answer.

Most of the tuning recommendations I shared for your AR631 receiver—especially for AS3X and SAFE setup—come from a mix of official documentation and community-tested insights. Here’s where they’re drawn from:

📘 Official Spektrum Resources​

• The Spektrum AR631 PDF manual includes detailed instructions for AS3X and SAFE setup, Forward Programming, and gain tuning.
• The ManualsLib version of the AR631 guide offers a searchable format with setup steps and troubleshooting tips.
• The Spektrum Wiki AS3X+ Setup Guide explains how to adjust gains, priority, and heading hold using Forward Programming.

🧠 Community Insights​

• RC Groups and Flite Test forums are goldmines for real-world tuning advice—especially for foam board builds and KFm airfoils.
• Builders often share their gain profiles and SAFE angle limits based on wingspan, control type, and flight goals.

I distilled all that into a tailored setup for your 18.5" KFm2 foam board pusher with elevons. If you’d like, I can help you walk through Forward Programming on your transmitter next—or even help you create a reusable tuning checklist for future builds. Want to do that?

I was also able to get settings for Stop Lock and Stop Release as well As Hand Launch Assist which are new settings in the "+" Receivers.

I don't know. What do you people think about this? I think it is a starting point and appears to be along the guidelines from Spektrum, as little as I could find. In fact, I have actually never seen anyone post their gains or settings. I certainly will post AS3X and SAFE for this plane. BUT I hope I can get it to fly for an intermediate pilot with no flight control at all. My "expert" settings turn off all AS3X and SAFE settings.