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Nov 15, 2020, 10:39 PM
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Dirty Dee's Avatar
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Thanks Guys. I gave some of the airfoils a try, but it seems like adding camber completely changes the appearance of the plane and requires a bit of redesign. I'll stick with this symmetrical for now.
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Nov 16, 2020, 11:58 AM
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birdofplay's Avatar
My 1st FW was totally symmetrical and it worked just fine.
Nov 17, 2020, 02:19 AM
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TyberJV44's Avatar
This looks awesome and now I want to build one.
Nov 21, 2020, 01:24 PM
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Dirty Dee's Avatar
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Thanks.

I did another maiden attempt Friday during my lunchbreak. Unfortunately I could not rotate from the dolly. I tried to take off from the runway with the built-in nose wheel and tail skids, but it had a hard tendency to tun right, and it did a similar hop as the original maiden attempt where it temporarily went airborn after hitting a bump in the grass, but then dove into the grass tumbled.

Thankfully damage was minimal so it is all repaired.

I am now on the assumption that the bungee is the way to go, unless I modify the nose to have a steerable nose wheel. I have a nose hook modeled and now installed on the airframe, and I will add some screws for extra peace of mind. I found a pedal trigger system on thingiverse, so I am printing that currently.

I noticed that the designer did a level from the ground start on the bungee. Would this work out ok, or would it be better to have a small launching ramp made from pipes?

https://www.thingiverse.com/thing:2905612

bungee launches1 (0 min 56 sec)
Nov 21, 2020, 02:20 PM
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dionnel's Avatar
I prefer a ramp.
Away from the soggy field and wings are level.
Mine is made from small diameter water pipe tubing.

On landing, I pick up enough dirt and grass in the scoops and streaks.
Dec 02, 2020, 11:16 PM
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Dirty Dee's Avatar
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Assuming weather is ok, I am planning to attempt the bungee/ramp maiden this weekend.

I did make a modification to the design and print a new fuselage. I originally did not use any airfoil, and instead traced over the 3 views to get the shape. I replaced those features with proper airfoils, and chose the Selig S8035 (14%) for the wings and vertical stabilizer. This thinned out the rear noticeably, and even shaved a few grams from the airframe as well.

I hope for success with the original model, but I will be very curious to see if there is a noticeable performance difference between the 2. I do have a spare 50mm powerplant and servos that I can fit into the second model.
Last edited by Dirty Dee; Dec 04, 2020 at 09:48 AM.
Dec 06, 2020, 02:25 PM
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Dirty Dee's Avatar
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It's getting close!

Bungee launcher and ramp worked very well. I had the tension set to ~2.3kg, which may have been a little too light as the plane bounced off the grass during all 4 launch attempts. It needed almost full elevator to maintain level flight, and barely climbed. I suspect it will need a bit of reflex trimmed into the elevons.

This flight was with the Cg set to 25% MAC, but I am going to re-attempt with a 30% MAC CG in a few days. This will be using the new airframe that has the S8035 airfoil.

RC Lippisch P13a - Almost Maiden #2 (0 min 14 sec)
Dec 06, 2020, 03:12 PM
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dionnel's Avatar
Quote:
Originally Posted by Dirty Dee
It's getting close!

Bungee launcher and ramp worked very well. I had the tension set to ~2.3kg, which may have been a little too light as the plane bounced off the grass during all 4 launch attempts. It needed almost full elevator to maintain level flight, and barely climbed. I suspect it will need a bit of reflex trimmed into the elevons.

This flight was with the Cg set to 25% MAC, but I am going to re-attempt with a 30% MAC CG in a few days. This will be using the new airframe that has the S8035 airfoil.

https://youtu.be/FzYReGkwSZg
You are getting there indeed!
Very strange but interesting camera view point.

I think you need a minimum ratio of 5:1 for the bungee tension. I use 7:1 for my planes in the same weight range as yours (250-600g).
A slightly lower angle on the ramp will also result in less forces on the hook as there will be less friction against the ramp.
I have something like 10ft of chirurgical tubing - so, fairly short. So I have a fairly short pull distance.

The straight line of pull through the hook to the CG is forcing a nose up attitude on launch, and therefore an initial climb.
Likely need a good chunk of reflex.
(You do not happen to have a wind tunnel near by for testing?)
Dec 06, 2020, 03:17 PM
You know nothing....
Stuart A's Avatar
A pic of the actual plane at the beginning(with a beak!)plus a short shot of a test glide a few minutes in.

German Jet Aircraft of World War II ( Secret German Jet Aircraft too ) (31 min 46 sec)
Dec 06, 2020, 04:32 PM
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Dirty Dee's Avatar
Thread OP
Quote:
Originally Posted by dionnel
You are getting there indeed!
Very strange but interesting camera view point.
It looks like a flying traffic cone

Quote:
Originally Posted by dionnel
I think you need a minimum ratio of 5:1 for the bungee tension. I use 7:1 for my planes in the same weight range as yours (250-600g).
A slightly lower angle on the ramp will also result in less forces on the hook as there will be less friction against the ramp.
I have something like 10ft of chirurgical tubing - so, fairly short. So I have a fairly short pull distance.
I made a dummy mistake when I was setting up the bungee. With a luggage hook scale I was using lbs instead of kg for the units, so I set it for 5lbs instead of 5kg . I'm sure the 5kg would give it a much cleaner launch since it will be 5.5:1 ratio.

I'll also modify my ramp to be slighter lower incline. Do you think it is ok with the length of the ramp, or should I shorten it a little?


Quote:
Originally Posted by dionnel
The straight line of pull through the hook to the CG is forcing a nose up attitude on launch, and therefore an initial climb.
Likely need a good chunk of reflex.
(You do not happen to have a wind tunnel near by for testing?)
I do have XFLR5 installed, so I can actually do a quick analysis of the plane now that I think about it.


Quote:
Originally Posted by Stuart A
A pic of the actual plane at the beginning(with a beak!)plus a short shot of a test glide a few minutes in.
Yup! I think this was the glider variant DM-1. I think there is another variant of the P13a where it has a twin intake at the nose and keeps the triangular tip like the glider.

I wonder if the triangular nose has improved performance compared to the cylinder nose. Though it may be more prone to damage if it digs into the ground.
Dec 07, 2020, 03:47 AM
You know nothing....
Stuart A's Avatar
Another page from history-Horten had a similar design,the only one of theirs with a vertical fin.
http://www.luft46.com/horten/horten.html
Dec 09, 2020, 04:54 PM
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Dirty Dee's Avatar
Thread OP

It flew!


I managed to sneak out from work over lunch and succeeded in a maiden flight ! I'll be working on uploading the flight video tonight assuming there wasn't a recording issue with the mobius camera.

It is hard to tell what was the biggest contributors with helping the flight, as several changes happened with this new airframe.
  • Selig Airfoil instead of the unknown airfoil
  • Servo arms adjusted to provide additional up elevon travel
  • 7mm of reflex
  • CG at ~28% MAC

Flight was kept a bit short due to the pitching sensitivity as well as the sun being low in the sky. I hope to make it out to the larger field this weekend and get some more proper flights logged as well as testing control throws, CG changes, etc.
Dec 09, 2020, 04:58 PM
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japim's Avatar
Congratulations
Dec 09, 2020, 08:50 PM
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Dirty Dee's Avatar
Thread OP
Thanks!

Here is the video. I think it is time to upgrade to a new Action Cam since the spots i thought were smudges are permanent chips in the lens.

3D Printed Lippisch P13a - Successful Maiden Flight (0 min 56 sec)
Dec 09, 2020, 09:55 PM
Retired CAD guy
birdofplay's Avatar
AMAZING !

Thanx for the Vid.

It seemed to be VERY QUICK versus the last vid where it seemed under powered.

Good Job !

I think I have seen a L13 with a bifurcated Nose intake treatment.
In with some old pix gosh knows exactly where now.

Now it we can just get the Availability UP and the Cost Down for LW-PLA !


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