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Flying Wing launch dolly

Old 07-25-2016, 11:59 AM
  #1  
severnside
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Default Flying Wing launch dolly

Just finished building an Orion 7 (Horten) electric pusher flying wing 3.2M span.
I had not realized that it is not suitable for hand launching & needs a bungy or dolly launch. Not keen on bungy so am looking at making a dolly. Anyone have experience of this please. Model is rather heavy at 2.68K.
Also posted in flying wings
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Old 07-25-2016, 01:07 PM
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fhhuber
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That will need a WIDE dolly

Typical is a trike dolly with steerable nosewheel. We have found that you can plug the dolly nosewheel servo to the aircraft RX with the servo connector filed down a little to make it slide out of the extension plug reliably with just the weight of the typical "standard" servo.

Main wheels appx 1/3 to 1/2 wingspan track width. The mains will need to be on appx 50% MAC line.

Nose wheel forming an equilateral triangle with the other wheels. You really don't want the oversensitive steering of having it further back. Further forward is fine if desired.
That will most likely put your nose wheel forward of the model's nose.

The frame cradling the wing high enough for decent prop clearance and preventing the wingtips or prop from hitting if you have the 3 wheels on the ground and the wing takes a 30 deg up angle.

simplest release is best. We've used trapping a small dorsal fin in a slot. Appx 1/2 root wing chord X 1/16 inch wide plywood fin with well rounded leading edge and straight vertical trailing edge appx 1.5 inches tall in a 1/8 inch slot 1/4 inch longer than the fin. (excess slot length to the rear)
Fin height chosen for our paved runway... if the model tends to bounce out of the dolly early make the fin taller.

The fin also acts as a landing skid. Make sure it is VERY well attached to the model.

I strongly recommend skid-fins appx 1/2 span and at the tips on that model to reduce damage from landings.

Mount the nosewheel steering plug forward of the dorsal fin

Cradles for the wing sections at the width of the main wheels and centerline should hold the wing at appx +1 to + 3 deg AOA relative to the ground. More than +5 can make the model stall when it lifts itself off.

Don't force it to lift early... your elevons should have authority to pull the nose up long before the plane is ready to fly. When you see the model start to leave the dolly apply gentle up for appx 10 deg climb and if nothing is binding, the dolly should never leave the ground.
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Old 07-25-2016, 02:47 PM
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severnside
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Thanks for reply. Will try to absorb your info & do a drawing.
Never used a bungy or dolly before. Included a pic showing dorsal fin. Velcro can now come off! Could not get anywhere near enough speed with hand launch.
The drawing for this model shows 2 bungy positions on the fin, the second one is under the velcro (close to CG). Why 2?
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Old 07-25-2016, 07:58 PM
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That fin might work to keep the model centered in the dolly... but may be marginal for dragging the dolly

Maybe add verticals to the front of the center wing saddle to catch the leading edge.

Don't put posts out at the side saddles.... they always release one before the other and cause the plane to yaw severely as it comes off the dolly.
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Old 07-25-2016, 08:24 PM
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That's a really nice looking model you have there. The Horten designs are sooo graceful, she will look great in the air I'm sure.

I've no experience of dolly launching anything that big but on the smaller models i've used a dolly on the challenge was having a secure enough attachment to the model so that the dolley stayed secure and aligned while on the ground, yet also 'loose' enough so that it didn't snag and remain attached to the plane when it lifted. A servo operated release is helpful but would be a hard retrofit.

A bungee should also work but i'd imagine that finding the correct attachment point would be very critical on a tailless design. It might be good policy to make a smaller scale 'chuck glider' and experiment with bungee launches on that?

Good luck with however you get it in the air!
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Old 07-26-2016, 06:17 AM
  #6  
severnside
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Much to ponder on. Do not hold your breath.
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Old 07-26-2016, 08:26 AM
  #7  
fhhuber
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You can go to a servo released dolly... but that adds complexity and potential failure points.

If you go to a servo release, you should work to have the CG the same with the dolly attached as without. The model is very likely to be able to fly with the weight if it doesn't alter CG. (been there)
With that option... you could get it flying, then do a low relatively low speed pass over grass and drop the dolly. Landing in high grass at low speed shouldn't break it.

The primary potential failures are:

Failed release... the dolly stays with the plane the whole flight. No big deal.
Partial release... the dolly hangs unevenly on the aircraft. This can cause a crash due to the CG shift.
Uncommanded release... which has the model come off the dolly before its ready to fly.

******************

Looking back a bit you asked about the multiple hook points.

the forward point is typically for high power or high wind launch.
The more rearward would be for a gentle almost kite-like launch.

The basic idea is the towline acts as a weight and the further forward, the more it tends to pull the nose down. The nature of a flying wing is to nose up with increased airspeed. High power launch pulling at the aft location would potentially bend and break the wings. Pulling from the front tends to not launch as high, but with higher airspeed.

Towline/bungee/catapult launch of a wing is a little tricky due to them being unstable until they have some airspeed.
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Old 07-26-2016, 10:03 AM
  #8  
severnside
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Had this response from the person I bought the plan from (Raimund).
`You must start the orion with a little rubber (20 Meters). You can not start the orion with hand launch the speed is to slow.
You begin the test Start with rubber shot and fly 200 Meters with no curves and looking the model.
Make Elevators with high 2mm then the CG is ok and you can testing with elektric Motor and high fly.'
Any thoughts?
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Old 07-26-2016, 10:10 AM
  #9  
JetPlaneFlyer
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Sounds like he has tested with a bungee. See if you can get more details of the attachment point he used and the 'pull' of the elastic.

Generally with a bungee the further back the hook is located the more that the nose pitches up and the faster it climbs. Too far back and it becomes unstable and will spin into the ground. Too far forward and it doesn't climb.. Start forward and work back is the safest approach.
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Old 07-27-2016, 10:17 AM
  #10  
severnside
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Got this back from Raimund,
`The bungee rubberpower middel -> strong, lenght rubber 20 Meters then strain about 15 Meters. Front hook position.'
Does this make sense?
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Old 07-27-2016, 10:54 AM
  #11  
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Yep... more of a catapult launch than a high start. Not a lot of height from it.

Actually, it helps to know the tension at the hook when the rubber is stretched.
Different rubber will have different "spring constant" kg tension per meter of stretch.
Knowing the tension he used will allow you to use a fish scale to prevent applying more power than the aircraft can survive.
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Old 07-27-2016, 11:11 AM
  #12  
severnside
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OK will try again.
He has asked for my build pics so will ask when I send them.
Might take a while. Is this tread the best way to stay in touch?
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Old 05-25-2020, 10:13 PM
  #13  
jacm
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Originally Posted by severnside View Post
Just finished building an Orion 7 (Horten) electric pusher flying wing 3.2M span.
I had not realized that it is not suitable for hand launching & needs a bungy or dolly launch. Not keen on bungy so am looking at making a dolly. Anyone have experience of this please. Model is rather heavy at 2.68K.
Also posted in flying wings
Dear Sir
do you know this Vimeo video ?


Kind Regards
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Old 05-26-2020, 09:13 AM
  #14  
severnside
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Thanks for that jacm. I have not seen it before.
The model has still not flown, I realized some time ago that it was too heavy, I need to replace the motor with a much lighter one, I could then take the huge amount of lead out of the nose.
Have not got around to it yet.
Regards Pete
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Old 05-26-2020, 01:07 PM
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For such a model - I would go for a Bungee to be honest .... its so simple and avoids all that hassle of ground condition etc.

Here's my pal launching his big wing of a bungee he copied from mine :

[youtube}
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Old 05-27-2020, 08:24 AM
  #16  
severnside
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Thanks Solentlife.
Any chance of a sketch & info on the bungee? ie. How long - how much tension etc. I have never used one and have not seen one in use in the flesh.
As I mentioned in my previous answer I need to reduce the weight before attempting another flight so there is no rush for the info.
Many years ago I made a launcher with a foot pedal release also have a bungee from RBC kits never finished the model it was intended for.
Still have it. Pic enclosed.
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Old 05-27-2020, 03:37 PM
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This is my second version - I modified to shorten the 'trigger' line so it would never be close to pusher props. In many years - I only ever had it happen once - but that was enough to change to the split trigger line.

I have two systems ... Red 8mm bungee and Blue 10mm bungee. The red is for my small to mediums sized models ... the blue for the large jobs.

Both systems are designed to have stretched length of 27 paces ... on the red gives about 6kg pull and the blue about 9kg.

OK - the ramp - I see your version - but that I would suggest is good for lightweight stuff but has no forward support ... I recc'd standard 3/4" plastic water pipe ... with front and rear legs.

Trigger is two ply plates hinged with a 2" nail through ... the top plate basically pushes the bungee ring of !





This shows you are well clear of props etc.



The trigger line goes to front of ramp and holds a pivoted 'arm' that then has the bungee release line slipped over...



Note the trigger line is made fast to the 'arm' to stop it jumping up.

Here you see the doubled bungee connection to the thin model line.



The line can be down to good fishing line if you want ... I chose 1mm coloured line so I could see in the grass to find and reset.

Ramp as travels ... (it pushes together using standard plumbers joints)..



Here is the line dividing of from model tow line to release line



Trigger board .. 4 tent pegs ... fishing weighscale for checking tension (I count steps instead of using the scale now !)



Line wound onto board with bungee of course ..



Travel pack :



Trigger in place and ready to 'fire' :



VERY IMPORTANT ... the bungee anchor - I used a dog stake but that pulled out one time .. so I changed to a three tent peg system. I have put 20kgs pull on that and it stayed set. I did have a single peg one day out of laziness and while resetting bungee - it pulled out and hit me in the back ... THAT HURT !! I was lucky I was facing away from it.





Time to setup ? about 5 mins max ... once you have done a few times - it just goes out easy. As I mentioned - I used the weighscale on first setups until I had an average setup for most models. On setting the bungee - I had counted my steps and they were 27. So now I just peg out ... count 27 steps and set the ramp / trigger. Simple.

Here's the ramp :



I tried insulation on it - but it slowed the model 'slide' ... so removed it. I have measured my 50mm T45 exit of the ramp with the 8mm and 27 paces tension - it hit 113kph without any power on the motor in a distance of little over 60cms !

Here's a demo video I made years ago ...



Here's same bungee launching a larger model that really needed the blue setup ... but it did it !!


Here we see me put my Scratchbuilt Concorde on the ramp ...



To give idea of 'hook' position ... about 40% nose back to CoG is good .. too far fwd and she can spin on the line ... too far back and she can pitch up ...



Any help I can give ... I'm always here !!
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Old 05-28-2020, 06:35 PM
  #18  
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???
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Old 05-29-2020, 06:14 AM
  #19  
severnside
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Don't know what happened but I sent a reply to your last post but it ain't here? Must have pressed a wrong button.
You have sent an amazing amount of info, I have printed it out and will try to absorb it, I have been inspired to get off my butt & do what is necessary to get this model in the air.
It will mean replacing the motor for a lighter one to reduce the lead in the nose.
I shudder at the thought of a ground hook flying about. I recall a club I used to belong to banning bungees because of such an incident.
Thanks again, I am sure there will some questions.
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Old 05-29-2020, 10:58 AM
  #20  
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No worries ... always here to help.
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