this is exactly what ive been looking for! ive been trying to figure out how to make a simple foamboard prandtl wing for ages and thought id need to find some way to put a twist in the foam but this is an elegantly simple design! thankyou so much im definitely going to make one of these to slope with
Very clever and simple way to create washout at the wing tips in order to achieve your bell-shaped lift distribution. Have you tried making a straight vs swept back wing? Seems like having both dihedral and sweep is overkill, as they both do about the same thing.
I don't think that stable wing with no sweep is possible with this design. I tried zero dihedral, wing was marginally stable so sweep alone seems a little insufficient.
Thank you for sharing these plans. I built two wings at 2.16 X the dimensions given in this video (to maximize use of my foam board length). The first wing I gave a large dihedral due to cutting mistake. The second I gave about the same dihedral as these plans. Today was the first test flight outside. It was gusty, so my high-dihedral wing flew well; but the flat one porpoised (phugoid) or was blown out of its ability to recover stability. I'll keep working on finding good CG balance. But I'm very pleased with the easy build and the excellent glides.
Thanks! I'm glad the plans are useful. Yes, phugoid mode is a problem with flying wings, as they inherently have worse pitch stability than regular aircraft. I think that moving the CG a little forward might help, the one in plans is definitely tuned for indoor flying in calm air. Also, increasing wing twist (by increasing the crease angle between front/rear wing parts) might help as well.
Forgot to mention that the Twisted wing tips while also adding the necessary satbility Also add significant drag. MORE than the traditional stab /rudder design typically does. Explaining Why Very Few all wing designs exist... 100 years after Prandtl
Not exactly. Twisted wingtips add more drag only when the twist is large enough to produce significant downforce. Otherwise, they actually reduce drag, like winglets. All wing designs have many problems, like overall lower stability, but higher drag is not one of them.
Just one note: wing with BSLD doesn't produce downforce at wingtips. Wing produces upward lift across the whole span if flown at lift coefficient for which BSLD was designed. Trim is achieved by producing more lift in centre in front of CG rather than putting downward force at wingtips. AoA at very tip of the wing is zero and becomes positive as you move from tip inward.
Yes, good point. Generally I tend to set the centre of gravity so that a little downforce is needed at the tips, but I agree, in perfectly balanced wing lift is positive everywhere. I wonder if the need for downforce at tips for stability (at least as far as I observed) has something to do with very low Reynolds number.
@@davidziemkiewicz1350 downforce on wingtips isn't related to pitch stability nor Re numbers. It is related to trimming the model. If we fix model geometry then stability depends on CG position. As you move CG forward there is less and less lift generated in front of CG and more and more behind CG. For this reason you start having need for downforce on wingtips to trim the aircraft. Another option is to use reflex airfoils which produce most of the lift at the front part and hence changes 3D lift distribution of whole - move lift in front of CG to balance nose down pitching moments.
@@High9231Yes, I worded my last response wrong. I meant that all my attempts to set the cg position backward enough that no tip downforce is needed resulted in unstable wing and I suppose that this may be connected to overall weirdness of very low Reynolds number aerodynamics. The geometry of this wing is very similar to NASA Prandtl-d, which probably is far from optimal at this small scale. Also, I should point out that the tips seemed to produce downforce, but I have no good way to verify it. So in the end this is only a very simplified version, where it's easier to intuitively show the balance of forces that is analogous to traditional, tailed designs. So this is a BSLD, just a sub-optimal one :)
I watched everything I could about the Prandtl wing design specifica and why it works, but there were still several gaps in my knowledge that I couldn't figure out. This cleared it right up, in a very intuitive way. Thanks!
Thank you David ... I have lots of cardboard around which is going to find better use now .. and maybe my struggles to come up with something 'uplifting' from it are over . in any case your little clip works fine with a cup of tea :)
Suppose I wanted to add a couple of props for power/differential steering. Where along the wing would be a good place to put them so as not to disrupt the nice lift characteristics of this design?
@@randyhelzerman pusher propellers shouldn't inrerfere. I have seen multiple models of Horten style wings with multiple propellers, seemed to work fine.
id say from my experience with BSLD wings keep them close to the middle and ideally have them counter-rotating. Its also important to have the thrust line / Centre of Thrust align with the centre of gravity / CoM of the wing to eliminate pitch up or down trim change with power increase or decrease. The spinning disk the prop creates acts a bit like an elevator and a rudder, and the Maxims i described keep the adverse effects of that to a minimum. On a sidenote, flying wings REALLY dont like puller props/ props in the front. think its because it messes up homogenous flow over the wing.
Excellent. Question. Foes the wingtip twisted or is just as is? If twisted how many degrees? Is there any article about thus? I know nasa was researching about thus concept.
No, wingtips are not addotionally twisted. All the twist comes from the crease. Yes, nasa studied it as a part of prandl-d project. In fact my wing has very similar proportions and twist to their model.
@@davidziemkiewicz1350 thank you for reply. I just finished one of the videos. Their researcher of this project displayed data that wing from root to tip was twisted 12 degrees which is quite high compared to Cessna 152 which is about 3 degrees.
@@noneNone-mw1px The twist on a Cessna is only "washout" to obviate tip stalls. The twist in this wing as shown on David's flow diagrams is to use the outer 25% (approx) of the wing as a tailplane to keep the wing stable. The effective span of the Prandtl wing is about 75% of the total because of this.
This is exactly what I have been searching for....... a starting point for a foam-board Prandtly Wing..... have you done any further work U could share?
Hi! Glad it could be helpful. I had a topic on rcgroups forum: www.rcgroups.com/forums/showthread.php?2653178-50-cm-super-simple-Horten-wing Some of the important results: -This model works fine when scaled up, even to 2 meter wingspan -Despite its simplicity, the twist is actually very close to ideal wing twist in real Prandtl/Horten wings -Dihedral here is somewhat excessive; the wing is stable with less, and even marginally stable with no dihedral (e.g. dihedral effect coming only from sweep)
I am going to build a prototype..... them move an 40" RC Version for fun. the beauty of your model is its absolute "simplicity" in order to develop the Prandtl twist....... you figured out how to make a very challenging Foamboard problem "simple"! Stay tuned.... Jeff
Built prototype today using 5mm Dollar tree foam board and hot glue. Used plans in RU-vid video where wing root dimension is 2+4=6 cm (is that you most recent design iteration?). Total weight was 11.6 gm (how heavy was yours?) DAMN IT JANET ....IT FLEW !!!!!! It was a little windy, need some fine tuning tomorrow on CG and dihedral (my wing is pretty flat). I am even more excited about your design after today. Congrats David.... very well engineered "Simple Solution to a Complex Problem" !!!
Dihedral shown here is certainly excessive, but in my tests 0 dihedral wing with the same geometry was a little unstable. Bell shaped lift distribution wings, such as NASA Prandtl-D, which I based this on, typically do use a little dihedral.
Sweep and or dihedral both reduce a wings lifting force.. You are trading off lift for stability.. Why use both.. That makes the wing very innefficent at producing lift.. Design a wing for either sweep or dihedral for lateral stability, but not both..
I need sweep for pitch stability so only 0 dihedral option is viable. However, in my tests no dihedral wing needed a lot of sweep for roll stability, which sacrificed a lot of lift. A little sweep and a little dihedral results in best lift/drag ratio, at least in my tests.
