Xb 35 ? - Page 3 - RC Groups
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Sep 26, 2012, 05:07 PM
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Stuart A's Avatar
Originally Posted by Blendedwing
By the way for those who asked: here is the Servos layout.
Nice,I have got to get me some of that micro gear!
Regards Stuart
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Sep 26, 2012, 05:26 PM
HerkS's Avatar
Because this is so small and basic, it would be easy to overlook the accomplishment that it represents. This is truly an impressive model.
Sep 26, 2012, 05:36 PM
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Blendedwing's Avatar
Last edited by Blendedwing; Sep 26, 2012 at 05:39 PM. Reason: wrong post edited
Sep 26, 2012, 05:41 PM
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Blendedwing's Avatar
Better picture of control servos layout.
Sep 30, 2012, 04:46 PM
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Blendedwing's Avatar
Hi Stuart,
I am making progress toward flying indoor. So here I am as promised reporting on it.

To fly Indoor, this model needed much more agility than the one she had displayed so far. However, after many hours of trimming and flying, I now think we are very close to be able to do it.

The outdoors lawn where I practice lays between a soccer field and a small country road. This patch of lawn is just about as large as the gym where we fly indoors in the winter. So if I can fly just over the lawn, I am in the gym. If I fly in half the patch, say between the corn field and the soccer goal, then I am flying the half portion of the gym reserved to this type of plane and 3D Shockfliers.

This time the flying style is very aggressive for this type of flying wing architecture, sometimes the response is a bit brutal and yes at times I have flow outside the limits, but overall I think we are almost there. Have a look ...

YB-35 virtually indoor (8 min 49 sec)

Now the model mechanical construction is dramatically simple: one 3 mm Depron sheet, completely flat till 50% of the halfwing, then twisted brutally till 13° at the tips. You can see this very well in the initial picture. The twist is achieved like in paper airplanes, by bending the tips by an appropriate angle. Carbon tube for stiffening the leading edge, another carbon stab to stiffen the rear of the wing, and that is it.

The Silverlit motors plus propellers deliver about 6 g each static trust, time four that give the YB-35 about 24 g static trust for 60 g of weight. I like this ratio. It is more "scale" as many airplane models we see today. However in flight trust falls off with speed.
Matching the trust curve of the airframe and the trust curve of the engines, I estimate that the model flies at speeds comprised between 5 m/s and 10 m/s.

However the work is all in the programming of the transmitter.
I happen to use a Spektrum i7DX, like HerkS, so at least he will understand what I am talking about.

The four control surfaces need to be about in the appropriate position in each one of the nine focal points of the right side stick. Yes, I fly Mode 2, so there I have elevator and ailerons.
Nine times four gives 36 configurations that need to be trimmed and controlled with four servos.

In addition the model is extremely sensitive to center of gravity position, not only in the longitudinal axis, but also on the transversal axis. Finally the motor inclination needs to be appropriate.

When all that is in place, it is actually, pretty much fun to fly it !
Sep 30, 2012, 05:16 PM
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Blendedwing's Avatar
Hi Herks,
I have now looked at your threads and I see with pleasure that we have been thinking along the same lines and making some of the same experiments related to flying wings.

My approach has been to take airplanes that have been flying in the past and try to understand the architectural decisions of their designers.
Indeed the proof of the pudding is in the eating, so after the study comes invariably a model that implements my understanding of those decisions.

A peculiarity we have in common is that we both try to reduce the model to the minimum . This has several advantages: for one it reduces their costs and accelerates the development, but more importantly it removes all those unnecessary details that may be considered critical for a given airplane, but really they are not. Reduction to the essential, I call it. If something that I removed was needed, then the model would not fly, or it would display specific problems in given flight conditions.

Of course, been the models so "basic", I can afford to modify them a number of times. This gives me the chance to learn a lot at an accelerated speed.

So if you want to know which airplanes have been the subject of my experiments, here is the picture in attachments.
I like to think of it as a summary of 50 years of flying wings development.

The airplanes were:
Type Designer First flight
Storch VIII (auch Mini-SNAH) Lippisch 1932
Me163 Lippisch 1941
Ho-IX (auch Go229) Horten 1944
YB-35 (auch XB-35) Northrop 1946
Avro Vulcan Chadwick/Davis 1952
Concorde Aerospatial/BAC 1969

You can see them flying on my YouTube Channel "Blendedwing".

There you will find also a bigger version of the Vulcan and one of the Concorde.

Last but not least a couple of bird like airplanes, I call them the "Owls" (Eule in German), because I think they are steered with the same technique owls use to fly in the forest.
I think I have read in the appropriate Forum terms like "camber flaps".
Well for these "Owls" I use "Camber wings".

Yes, they flap their wings, but not to generate propulsion, only to steer themselves through the air.

I would be delighted by your feedback.
Sep 30, 2012, 05:21 PM
You know nothing....
Stuart A's Avatar
Pretty much fun to watch as well!.A quite remarkable wing.Deceptively simple build,expertly trimmed and flown!
I have every confidence that you'll pull off the indoor flights.
Best regards Stuart.
Oct 01, 2012, 02:15 AM
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Blendedwing's Avatar

Bigger airplanes web site and construction pictures.

Thank you Stuart,
as for the bigger airplanes, I have built them with the help of a friend with experience in this field and a great web site. http://www.fly2air.com/

The pictures and the detailed description and of the build, together with more videos, are included there.

Vulcan scale 36:1 http://www.fly2air.com/a07/index-a07.htm

Concorde scale 48:1 http://www.fly2air.com/j03/index-j03.htm

Best regards
Oct 01, 2012, 07:50 AM
HerkS's Avatar
I will definitely enjoy viewing your projects.

I am sure that there will be much interesting flying there.

Also I will study carefully your owls. I think I would like to build an owl. My friend Joel K Scholz is also building bird models - His work is now on RCGroups.

Thank you for this excellent information.
Oct 15, 2012, 05:50 AM
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Blendedwing's Avatar
Hi Stupot46,
I have promised to keep you updated on the development of the YB-35 tuning for Indoor flight.
As you know, there was a lot of work going on during the last couple of weeks to insure that the sender was programmed in such a way as to cause exactly the desired movement of the control surfaces in every flight condition. The test flight outdoor was satisfactory, but ... would that really work indoor?
Would those ominous walls slam onto the unprotected flying object before it could turn away and avoid them?

Well this week end it was time to test it in real conditions.
The program included: banked turns with 30°, 45° and 85° bank angles, soft and sharp turn inversions, high speed low pass and soft landing in the pilot's hand.

Was it really enabled to fly indoor?
Well, have a look at the video and judge for yourself.

YB-35 Indoor summary (3 min 7 sec)
Oct 15, 2012, 01:52 PM
You know nothing....
Stuart A's Avatar
Excellent! A quite incredible exhibition of a remarkable plane and piloting skills to match.Thanks for posting,I hope we'll be seeing more of your exploits in the near future.
Regards Stuart
Oct 16, 2012, 10:09 AM
HerkS's Avatar
Nice to see it handles well enough to work well indoors.

That is truly a beautiful venue for this sort of flying.

Did you change the CG in order to achieve slower flight???

Is there some other action that you took in order to prepare for the indoor test???
Oct 16, 2012, 10:49 AM
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Blendedwing's Avatar
Hi HerkS,
well I did experiment a lot, also with CG. However my starting point was 7% SSM and I ended up with 7% SSM. I have also gradually tested up to as much as 15% to see the impact of stability and controllability. There is no doubt that with 15% SSM it flies more like a normal pilot would expect: straight and level. However the climbing performance is practically wiped out. It could hardly climb anymore.

Instead, I went back to the 7% SSM and worked on the effectiveness of the control surfaces. That required changes in : material, accuracy and authority.

Material: In the first version, flying gracefully and majestic, they were built with Durofly 0,6 mm. That was way too flexible. So I replaced them with new ones built in Polistyrol 0,5 mm.

Accuracy: the DX7 sender is great, but it was not designed to implement Northrop type Elevons. The actual movements are all depending on the centering of the servos, their throw, the mixes from Elevator and Aileron to the Rudder and Flaps channels. This work was exausting. First of all I was not sure which exact position the surfaces needed to take, then I was not sure how to play with the mix values to achieve them, last but not least I was not sure how to control that these positions were actually achieved.
So I have built a simple rig to measure the surface movements, I have also taken pictures of the surfaces in the 9 key positions (up, level, down)x(left,straight,right).
Then I have built a spreadsheet to record and predict what would happen if.
Sorry that was an understatement, I have built twenty spreadsheets, the last one apparently worked well enough.
When the surfaces started moving symmetrically and with the desired amplitude I moved over to...

Authority: well if I want to steer aggressively the controls must also move aggressively. When the flight tests proved that the servo programming was accurate, I started reducing the length of the surface horns. So from the initial 18 mm, I went down to 12 mm, then 8 mm and finally 4 mm.

That's where I am now and what you have seen flying. I suspect I went may be a little too far, but I plan to introduce some expo, at least on the aileron.

Then may be I would also program the Flaps Switch to introduce three flight modes: landing, cruise and speed. I have done that with the Concorde model and I have found it very helpful.

I will keep you posted on these next evolutions.
Oct 16, 2012, 10:55 AM
HerkS's Avatar
I think that Mr Northrop and his engineers would have a very good understanding of what you have had to work through with this development.
Oct 16, 2012, 11:15 AM
You know nothing....
Stuart A's Avatar

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