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Oct 05, 2017, 03:52 PM
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InPuls, my Inside based, Plus Inspired f5j plane

I've recieved some requests for more information about my experimental conversion of an Inside wing to a Twin boom, Inverted V-tail configuration.

InPuls of Paradise (2 min 42 sec)

I'm still working on my first try at making my own website for sharing and updating this,, but that's in my own language and apparently there are more people interested than just a few cheeseheads.

so I'll try to make a usefull thread here too.

My main reason to start this project was being curious about what the difference of such a configuration actually is compared to a conventional tail. I really LOVE Vladimir's Plus and not wanting to spend so much on finding this out I thought "hey.....why not build one myself?"

I really like my Inside F5j and it seemed logical for me to use this one as a base to start with.

So I ordered a new wing kit (I only used the centerpanel) and 2 tapered carbon tailbooms (11-8mm) and spend a couple of nights thinking about how to start.

I buildt the centre panel and a couple of mock-up tailpieces and used my eyes to decide wether it looked good.

"If it looks good, it probably is!" is my modelling philosofy.

It did so ont with the build.

First thing was how to attach the booms to the wing and still being able to remove them for transportation.

My choice was to make half-diameter tubes that I use as a bed.

In the front I used a mix of epoxy and glas where the front of the boom slides in. This also transfers the load of the tailboom to the wingtube.

at the rear I use tape around the bed and the boom to fix for flight.
The bed rests on an plywood strip on top of the wing-end (forgot the correct english name) and is glued with epoxy/cottonflakes

This has 2 reasons: first I can still use the original flaps and second the incidence-difference between wing and tail, wiht the top of the boom level, ended up at exactly 1,5 degrees......which is a guarantee for a flying plane.

For the position of the tailbooms I took the dimensions of the tail of the Climaxx and rounded that to a position close to the ribbs.

Length of the tailboom was decided by the supplier as 90cm was the maximum length for shipping.

For the vertical load this was, to my idea, sufficient but not for horizontal loads that might occur during landing.

So I put 1,5mm sheeting on top of the ribs left and right of the tailbooms.

I strengthend the 'inside' of this box with epoxy/glasfibre again for 2 reasons. Making it strong enough to handle the stress during flight and landing and creating a place where I can installe the flap and tailservo's.

I dicided to put all the linkages on the topside to keep the bottom 'clean'

For the tail I took the rough dimensions of the Climaxx tail and rounded them to nice round centimeters. I used a V-tail angle of 110degrees and used some highschool calculations to get the precise dimensions (whicht I again rounded up to nice figures for ease of measurement)

Control of the tail is with Single-pull form the dlg-scene.
so connecting a hook with a small wire to the servo is all that is needed to get a slop-free connection.

Before starting on a fuselage I used an online CG-calculator to find out were to start with the cg

My first motor of choice was a Schambeck 1025 which I've had on my bench for almost a year without good use.
Much to powerful but at least I'll know for sure it'll get to a decent height in notime.

The first version of the fuse is a very simple balsa fuse, based on the sideview of the original Inside fuse, with rounded edges and enough space to use different sizes of batteries to adjust the cg.

After toying around with leftover Oracover I ended upt with a good looking plane (If I may say so myself)

The maiden flight was during the lunchbreak of one of our F5j competitions

InPuls (9 min 37 sec)

This first flight was already so promising that I just hád to continue with this plane!

Each single function of elevator, ailerons and rudder appeared to not have changed too much.......but when you start to use them simultanously (which is what you do during flight) the plane has become much more eager to turn on a dime without losing a lot af stabillity in a straight line.

During the third flight I made a series of mistakes (I flew it 'trough' te sun and lost visual for a couple of seconds) leading to a almost vertical dive and by the time I realised this and gave a quick 'up' on the controls, the speed was already too high and the tailfeathers broke of.

Before blaming the seemingly light tailbooms for bending.....I am positive I underestimated the power on the tailsurfaces during flight and gluing the tail with only CA was the reason why they came off.

The rest of the plane came down like a feather and without any further damage I rebuild the tailpieces and this time gluid them with epoxy and some glas-fibre. I've already flown at higher speeds than when they first came off and am not worried this might happen again.

In the meantime I've already buildt 2 new fuselage versions with lightweight pusher-configurations.
60grams 1350kV with a 9x4, 19A on 3S

60grams 1100kV with 12x6,5, 21A on 3S

They work wel enough for free flying but lack power for competition. I'n waiting on some parts for a third fuse with more power.......when I have it I'll share it on my site and, if you are interested, here too

I'll try to make a drawing with the dimensions of my tail for reference (one of the questions I've already recieved) this will come later this week.

It's al still in an experimental fase so changes are likely to be made but if you have any questions, remarks or ideas just let me know

Last edited by bjlmoree; Oct 06, 2017 at 10:56 PM.
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Oct 05, 2017, 04:29 PM
Tragic case
davidleitch's Avatar
What wing area and all up weight did you get to?
Oct 05, 2017, 04:36 PM
Registered User
Wing area is of the original Inside F5j, I have no idea what it is. The weight of the InPuls (that's the name I gave my experiment) is 1190 grams, and with the newest fuse I hope to save a little bit.

FYI... My Inside was 1180grams so the difference is hardly noticeable. (the change in handling IS)
Last edited by bjlmoree; Oct 05, 2017 at 04:42 PM.
Oct 05, 2017, 06:20 PM
I can fix that ...
scottsdalejohn's Avatar
This looks like a great alternative for those of us with broken fuselages but perfectly fine wings.

Can you tell us about the drive system you used on your current version?

BTW, the Hollein website lists the Inside F5J wing area at 65dm˛
Last edited by scottsdalejohn; Oct 05, 2017 at 07:26 PM.
Oct 06, 2017, 10:29 AM
Registered User
First motor was the Schambeck 1025 with a 14x8, 230mters in 30 secondes at 60-75% power, but I sold this to someone who needed it for electrifying a Supra.

Second was a Dymond 2828 1350 kV with a 9x4. This struggled to give 3m/s, about 100meters in 30sec.

3rd motor is a HobbyKing 2830 1100kV with a 12x6,5. It takes her to 140 to 150mtrs and gets quite hot after 30seconds.

I built the pusher-fuse around the 28mm motor and thought the battery in the nose would be enough to balance. I thought wrong and had to add almost 100grams of lead to get it right.

After rearranging the motor with a shaft I could remove about 20grams.

If I could place the motor more forward I might be able to balance her without lead but I can't do that in this fuselage. I buildt her to small/narrow to get the batterie and speedregulator far enough forward and the motor would still be too light.

Apart from the tailbooms and the wingkit all was built from stuff lying around but I've dicided the plane is good enough to invest a bit in stuff that I cannot build myself. So there is a glass glider-pod underway (ARThobby High Aspect glider). In that one I will install the Reisenauer-Leopard motor from the Inside, according calculations it should make 300W with a 14x8 and I hope to get her flying at around 1150grams. (wich is a touch lighter than my Inside at 1180)

Some measurements:

Total length of the tailbooms : 90cm (I'll leave the conversion to inches to you)
Wing trailingedge to Tail leadingedge : 57cm
Root-cord of the tail : 20cm (including the rudder)
Tip-cord of the tail :10 cm (including rudder)
drawback of the tip :10cm (so the tip LE is right above the root TE)
rootcord of rudder :5cm
tipcord of the rudder : 4cm
Actual height of the tailfeathers :30cm (projected height should be close to 20cm)
Distance between tailbooms : 44cm
Oct 06, 2017, 10:34 AM
Registered User
Double post......
Oct 06, 2017, 08:02 PM
I can fix that ...
scottsdalejohn's Avatar
Thanks for posting the dimensions for your build - it will be helpful for those who would like to build their version! Did you make the linkage used between the motor and the propeller, or you able to purchase it?
Oct 06, 2017, 09:22 PM
Registered User
Sensoar's Avatar
Beautifully done and very innovative, I am thrilled to see some imagination with sailplane designs. I watched the first postings with the front motor and now with the rear drive it is very impressive to see it with the new drive system and nicely done at that. I am curious about the driveshaft and pusher prop arrangements as well. Great colors btw.
Oct 06, 2017, 10:29 PM
Registered User

The coupling is a standard 3,2 to 4mm from a shop with a lot of car and boat parts. A ballbearing in the rear and a 4mm shaft was all that was needed
Oct 07, 2017, 08:05 AM
Registered User

In the rear the bearing sits in a balsa bulkhead that is glued to a 3mm qualitiyply bulkhead.

I was afraid of bending the shaft due to the pushingpower of the prop. Therefore I filled the small gap between spinner and bearing with a couple of gussets so that the pushingforce of the prop is transferred to the bearing. The inner bulkhead is a touch smaller in diameter so the bearing is on it's turn pushed against this bulkhead wich then transfers the power to the fuselage. Maybe the 4mm shaft is more than strong enough but in this case better safe than sorry

The end was filled up with balsa and sanded to shape
Last edited by bjlmoree; Oct 07, 2017 at 09:01 AM.
Oct 12, 2017, 06:24 AM
Registered User
I've changed some parts on my site (more pics and media), I was surprised to see so many international visits so in due time it will be translated to English
Last edited by bjlmoree; Oct 12, 2017 at 06:31 AM.
Oct 13, 2017, 12:26 AM
I can fix that ...
scottsdalejohn's Avatar

If you build another version using the Inside F5J wing, you might want to consider moving the booms out another 2 bays on each side (see the attached screen shots from an online calculator (probably could still do this with trig functions, but the computer is much faster) This will get you close to the 110 degrees of dihereral you noted in your post, and based on Curtis Suter's sailplane Calc V-tail program it will be a bit more stable.

I will start on my version when I get a few other projects out of the way.
Last edited by scottsdalejohn; Aug 12, 2018 at 10:04 AM.
Oct 13, 2017, 01:22 AM
Registered User
The real thing has them a lot wider too.

If I would make a new one that would be a nice experiment: tail booms a bay wider automatically resulting in larger tailpieces. But then I would reduce the aspect ratio of the tail to have approximately the same area
Oct 13, 2017, 02:10 AM
Registered User
If the improvement suggestions started, I would build the wing classic style, and pass the forward end of the boom tube through the main spar, between the carbon caps, acting as end grain balsa for that small 2 cm section of the spar.
Also, would sandwich between two ribs made from ply.
Oct 13, 2017, 03:27 AM
Registered User
The Inside wing does not have conventional spars (let alone carbon caps) and I was not up for making holes in the wingtube.

In a conventional wing-setup I still would not make a hole in the webbing but make a frame behind the spars, well glued/connected to the mainspar, where the boom-end would fit in.
But that would mean designing a whole new wing and I'm not up for that yet.

In this construction I thought of ply-wood ribs in this one too but asked myself what their function would be. They have nothing else to do but transfer the load of the boom to the main wingtube and the trailingedge. The ribs itself don't have a lot of function here, they are only the 'frame' for the sheeting and the fiberglass re-enforce sheeting diverts the load to the trailingedge.
Last edited by bjlmoree; Oct 13, 2017 at 04:56 AM.

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