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Jun 10, 2019, 05:03 PM
Ken Stuhr
Thread OP
Discussion

Horten 18 Success!!


Reporting on a successful flight today. This model has been at the stage shown here for several years now---about 5 I think, without a real test flight.

A few years ago, I did a glide test off a local knoll and hit the throttle during. It sustained flight but I made a poor landing and had a repair to make. After, other projects took precedence.

I will post more as I get into the finish work and ultimate completion, but this for now. I have a fair number of build pics which may be of interest.

Details:
Span 96 ins
Root chord 23.5 ins
Weight less batteries 32 ozs (!!!!)
EDFs AEO 30mm 80000Kv x 4
Controls Elevon and throttle
No gear--hand launch
Structure Very select balsa sheet skins on balsa ribs with epoxy glass reinforcing, washout built in.
Airfoil symmetrical
Batteries 2 x 2200 mAh Li poly ( needs bigger)

This flight was never a sure thing. The thrust available was low, but I felt the span and weight might compensate. I was right. With a very light headwind and a short run, it flew right away from my hand and commenced a slight climb without a drop. But JEEZ those AEOs are NOISY!!!!

Got up to maybe 50 ft with good control response. Note from the pics I am using cheater fins for now. There was NO pitch oddity whatsoever. I am NOT using the exhaust tubes so many others claim essential!! The one pic shows paper exhaust cones added to the constant-diameter ducts, but no extensions.

The fans are sucking air from a plenum formed by wing ribs on either side of each fan, a pink foam block into whih each fan is set, which completely block each channel from rib to rib and bottom skin to top. The fans retain their bellmouth fittings.
The inlets seem to work OK, but are sharp edged and could be better contoured, but would then get maybe too far from scale.

At that point, the fans began rpm fluctuations. I immediately throttled back and knew it was time to land. I suspect I was drawing the batts down and the ESCs were cutting in and out. Anyway, cut the throttle and glided forever to a soft belly landing. The only odd thing was that, under power, trim was perfect, and gliding, there was a mild nose up tendency which I had to correct to prevent stall, but very mild.

Ok for now--send questions if any!

Ken
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Jun 10, 2019, 08:40 PM
Registered User
Great Work... hortens can be Pretty things.
Did cheat a bit tho ?... XVIIIs' featured 6 inwing engines

I have a couple of the IX things. One over 25yrs old ....a shameful addiction.
IMO Hortens are love / hate contraptions. Seductive of planform certainly .. yet of sketchy Aero.
Bros Horten were Not of Lippisch stature....by any imaginative stretch
Most issues are with IX models though ( the efflux Suppositories) Something to do with the centre sections size / influence .
Refusing to fit suppositories, I fitted thrust vectoring on one of mine.. it helps. Still iffy tho.
IXs' fly fine as low powered floaters Or.... PSS models.
Curiously the IX design (as per the Bentley drawings) features little to None of the infamous Prandtl bell lift distribution curve.. just to annoy the true believers.
However Crank up the speeds... to jet like... and on a hard (often not so hard ) turn... the things simply flutter/fall out of the sky.
Nothing works.. except watching on the way down.
Hopefully your XVIII being of differing centre section may not (?) have the famous fault ??
Or the goofy AEOs simply can't get it it going fast enough to approach let alone enter enter the problem range.
Last edited by Bare; Jun 10, 2019 at 09:02 PM.
Jun 10, 2019, 09:38 PM
Ken Stuhr
Thread OP
I'll cut the other 2 holes for dummy installations soon. Don't need the thrust, so didn't indulge.

I suspect the IX models out there all suffer from some basic design error in the wing sections. I built a very heavy sloper IX years ago and it had no trouble with speed and turns. In fact it was so heavy that's the only way it could fly.....

The Hortens were good enough aerodynamicists, but they also had this religious adherence to the 'no fins' part about nurflugels. The whole bell-shaped lift distribution thing was only to avoid adverse yaw when turning with elevons and without better directional stability. To this end, the whole induced drag picture for their planes was very compromised and had they built a long-range bomber, my bet is that its range performance would have fallen short.
Jun 10, 2019, 10:31 PM
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turbonut's Avatar
Nice work Ken. Again you seem to find the coolest subjects...Hortens tend to be a odd form of religion for some..My self included. Do you plan to reduce the vertical and experiment or just have fun flying as is. Please post build pics..Did you make up your own design or start with some plans?
Latest blog entry: In flight
Jun 10, 2019, 10:38 PM
Ken Stuhr
Thread OP
Plans? Whut plans?

There are several 3 vw dwgs around and i picked the one that seemed right, went from there scratching.

Yes, I'll be nipping the fins down as tests continue but I suspect there will be a need for something left. During this flight today, it seemed to turn OK but I also had a lot of differential in.

Thanks Turbo and Bare.................hey, Bare, was it you who a few years ago spotted this plane in the background in a pic of another plane and wanted more info? Stand by!
Jun 10, 2019, 11:01 PM
Registered User
The thrust from a quad of 30mm AEOs is 'nuff power ? That surprises, In general and especially so in an ahem.. Large.. 8 foot span model. 1;16th?
Dr thrust 40 mm efs produce ~12 /14oz Each and can (imo) be shoehorned into a 1;16th.
Don't you have a few on hand?
Current QX 30mm 7000kv fans run 180 gms .. replicably.. at 8 amps /3S.
I threw out my Aeos.
Horten 'full scale' airfoils don't translate well., to model Hortens.
Full scale Aerofoil section choices being superceded by these, amongst others
s5010 and s5020.
Bit late Now.. though

PSS models do passably well though.
Once significant efflux and genuine Speed is added to the mix, It all changes.. usually dramatically.

Yup I spotted the Hulk sitting patiently on the back bench... a while back. Been a Horten addict since early 90's .
It's an anti social addiction though as successes are not overly common TBH.

Then there is This 2.4 M span Horten also 700gms Neither fins nor Suppository tubes needed for no speed flight.
STUNNING RC LIGHTWEIGHT 700 GRAM HORTEN IX HO-229 SCALE 1:7 MODEL AIRPLANE INDOOR FLIGHT DEMO (2 min 55 sec)
Last edited by Bare; Jun 10, 2019 at 11:23 PM.
Jun 11, 2019, 12:27 AM
Ken Stuhr
Thread OP
The 40mm were not available when I built this. I did consider retrofitting them if the AEOs didn't produce enuf thrust--but they did it seems. BUT they are incredibly loud!!! Mine are 8000Kv. Yeah, I've got many of the 40mm!!

I see no reason to use anything but symmetrical airfoils for these model flying wings. This eliminates one unknown factor, which is the effect of airfoil pitching moment that needs to be balanced for trim. In building a 3 dimensional wing with all the complicated effects on lift distribution, you just can't know what the net pitching moment of your complete wing, not the airfoil, is without testing. With a symmetrical section, you at least know the total wing pitching moment is zero, leaving only the issue of washout to provide the positive total wing pitching moment that needs to be balanced by CG location. Besides, there is not really any advantage to a more complicated airfoil choice, cambered in the front, reflexed in the back, for example, for a model. We can't tell if its more 'efficient' from the ground, flying for 8 or 10 minutes. If we were flying the Atlantic, sure, it makes a difference.

Its a bit ironic, and most people aren't aware of it, but Boeing used fully symmetrical airfoils on the B-17, B-15, and I think B-29. Combined with huge tails, this allowed very large CG ranges, good when dropping huge weights of bombs from all along a bombay.
Jun 11, 2019, 05:51 AM
EB-66C Team Member
J Morgan's Avatar
Cool build Ken!
That guy in the video builds the most amazing aircraft.

J
Latest blog entry: A2D Skyshark at 1/8th scale
Jun 11, 2019, 10:19 AM
Ken Stuhr
Thread OP
Thanks! Yes, he's a talent way beyond me for sure!!! Maybe the Hortens could have learned something..............
Jun 11, 2019, 10:47 AM
Ken Stuhr
Thread OP
Here are some of the shots I took during the build-afraid I took very few. 1/8" balsa ribs and 1/4" balsa for the shear webs. I recall selecting my very finest (lightest) sheet for this job. The skin is also 1/8" edge joined, but block sanded and tapered from 1/8" to 1/16" at the trailing edge. This was very helpful in keeping the structure CG forward.
Jun 11, 2019, 01:21 PM
Pro Hoarder
turbonut's Avatar
Nice...I think Jack Northrop would like the design..Very close to his ...
Latest blog entry: In flight
Jun 11, 2019, 02:44 PM
Ken Stuhr
Thread OP
Turbo-

Somebody else also thot so.......
Jun 11, 2019, 04:26 PM
Pro Hoarder
turbonut's Avatar
Your airfoil choice looks close to jacks also...
Latest blog entry: In flight
Jun 11, 2019, 06:19 PM
Ken Stuhr
Thread OP
He used symmetrical on everything that was a flying wing. My Horten was as well, but with the large variation in chord, a very nicely tapered thickness resulted. It very much looks like it wants to soar when flying!!
Jun 12, 2019, 11:14 AM
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turbonut's Avatar
We need some Vid!
Latest blog entry: In flight


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