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Aug 09, 2018, 11:23 AM
kellanplanes
Discussion

New STOL design thoughts.


So I have been really into STOL lately and I wanted to make a new design loosely based on the Double Ender bush plane. I quickly drew up an idea on google sketchup and I was wondering what you guys think? I could make plans if anybody is interested. I would love to see some people build this thing. Here is what I have.
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Aug 09, 2018, 04:56 PM
Build straight - Fly twisty
Whiskers's Avatar
That is excellent.
It would also make a very nice FPV plane. For that use I'd not have the wing struts or landing gear.
With that shape it would skid off the grass just fine.
It's very similar to something that has been rattling around in my brain box for a while.

However with the gear on there would be a lot of fun to be had doing the STOL thing.
Aug 09, 2018, 06:26 PM
Registered User
cbalgra's Avatar
Kellan,

I too have been bitten by the "STOL bug". The last couple of planes I have designed were definitely, heavily influenced by the flying characteristics of STOL aircraft. There is something satisfying in trying to fly slowly and land in short distances. Also, In my opinion, most aircraft just look better with large bush tire on them.

In early 2015, I designed and built two Beekers to see if I could possibly replicate the flying characteristics of STOL aircraft. The prototype was built in a matter of a few days and proved that if built lightly, short field performance was well within reach. My second one was built with a little more detail and fully covered with brown paper and WBPU, then painted, and it flew even better than I imagined!

Take a look at the build thread of the Beeker, and you'll see that your "Single Ender" should fly quite nicely. Two things I would recommend would be; 1. keep it light. 2. use a thick airfoil to create tons of lift and keep the speed down.

https://www.rcgroups.com/forums/show...8with-video%29

Good luck with this plane!
Aug 09, 2018, 10:27 PM
Registered User
SNice's Avatar
Your plane looks great and I have no doubt it would be an excellent flyer as designed. However, in order to really get it to execute the unique characteristics of a STOL aircraft, IMHO - it needs a tractor style prop. Without going into too much detail , the prop wash over the wings not only helps to generate downward thrust (with flaps and or slats, etc.) but it also helps you maintain roll control at slow speeds. You will need both in short takeoffs and landings.

Good luck with the plane!!! Glad to see folks are still designing and building. I’ve been away for a while but am starting to get that itch again!
Aug 10, 2018, 10:47 AM
kellanplanes
Thanks everyone for the encouraging words. I really feel like this is going to become a fun model.

Whiskers, I love the idea of using it for FPV. I will have to make some design modification to make it really good for that as an option.

Cbalgra, thank you for the suggestions I will definitely use them for sure! I love the Beeker design you linked. It looks like a very fun plane!

SNice, thank you for your information. I was starting to get that same idea. If you don't mind, I would love to hear more about the subject. I will have to make some design variations to take full advantage of an air frame like this.

Perhaps I will go ahead and start making plans and build one. Thanks again for all the advice and encouragement!
Aug 11, 2018, 05:23 PM
Registered User
SNice's Avatar
I'm gonna try and keep this simple - mostly because it is easy to fall into the rabbit hole of hardcore aerodynamic theory/equations/calculations! I have studied it, but , FOR ME, most of it is not really relevant to my RC hobby. I love designing, building, and modifying RC planes out of foam/balsa/paper - whatever I can find. My largest model was around 52" WS. All of my airframes stay well under 100MPH. I've put lots of time and effort into fancy theory based designs and 9 out of 10 times - I have found that my best performers share 4 common characteristics: A light but sturdy build; light wingloading; properly calculated CG, and adequate power.

That being said, you need to determine what STOL means to you! Short takeoffs and landings can be achieved on a light model with adequate power and a nice headwind. If you build your model to plan with a light wing loading and a strong power system with the proper CG you will be fine. You may want to increase the size of your tail surfaces a bit as they look a little small for an RC model (IMHO). There are certain proportions that if you stay close to will pretty much guarantee a solid flyer. There used to be a wonderful online resource with info and calcs on basic model design but it appears to be gone. It might be worth a quick google search.

As for the tractor vs. pusher thing - STOL aircraft generally have a light wingloading with a very powerful engine. The wings are often equipped with aerodynamic devices to keep air flowing over the wing at slower speeds and high angles of attack (slats, vortex generators, grooves, flaps, slotted flaps, etc.). They lower the stall speed of the wing and allow it to continue flying where a "normal" wing would have already stalled. Think of a traditional tractor setup - you've got a powerful engine producing a lot of thrust. If the flaps are deployed, the thrust is diverted down - helping to push the plane up. This is great for lift, but think about the tail surfaces which are now not receiving clean air because a portion of it is blocked by the flaps. You could increase the size of the tail surfaces to give them more authority or maybe even move them higher to get them out of the way of the wing and into clean air. At slow speeds and high angles of attack, you really need to be able to keep the wings level to prevent a tip stall so ailerons need to be extremely effective. The flipside to this is that the down aileron deflection can not be so great that stalls the high wing - so you need aileron differential to keep things "safe". I like to program the flaps into the aileron channel (very small one-way deflections) to help use the propwash to control roll at slow speeds.

With a pusher setup, you could achieve all of the above too, granted you are flying into a nice headwind. However, if you slowed her down too much going with the wind, your roll control could get a bit mushy. The good thing is that your tail surfaces would always be getting hit with unobstructed propwash and would always have good authority.

So... interestingly enough it seems like the full scale model that you have based your design on is actually the best of both worlds. I had never heard of the plane before and was quite intrigued as I thought it was odd to have a full scale STOL plane with a pusher setup. However - after looking it up, I see that is has both a tractor and a pusher! The best of both worlds for all the issues above. It even handles another one that I did not mention - Torque!!! The torque from the counter rotating props would cancel out so you don't have to worry about the engine/prop torque rolling the plane at low speeds and high power settings! Pretty cool!

All that said (it was a lot) - I think you've got a good looking plane. My advice is to build it as you have planned, get it flying to your satisfaction and then worry about the possibility of adding a tractor powerplant later. Whatever you do, have fun and enjoy doing it! The above is just a peek into my design/thought processes. I hope it helps to inspire you to dig deeper and learn more as many others have helped me to do on this forum over the years! This is a great place and I have missed it!
Happy Building and Flying!
SNice
Aug 11, 2018, 08:17 PM
Going back to balsa
I think that you have a good eye for style and proportion. Nice looking airplane. I hope you build and fly it.

PS - Do you have a name for it?
Aug 12, 2018, 11:18 AM
kellanplanes
SNice, thank you so much for all the information! I really appreciate learning more from people. I have been building and designing airplanes since I was 10 and I still learn everyday. I am making some changes to the design and starting make plans to start a build as soon as I can.

S.Davy, thank you for the kind words! I am for sure going to be building it and ill post a build log as soon as I can. I don't have a name for it yet. I was thinking about calling it the "Single Ender" both because of the full size one its inspired by and because cbalgra called it that. However if I make it so it has both ends for better STOL then perhaps not the best name. What do you think it should be named?
Aug 13, 2018, 12:51 AM
Going back to balsa
Quote:
Originally Posted by kellanair
What do you think it should be named?
How about the "Monty Python"?
Aug 13, 2018, 01:08 AM
Build straight - Fly twisty
Whiskers's Avatar
"Push Up"
Aug 14, 2018, 10:08 AM
kellanplanes
Ha those are fun names! I will have to choose one when I do a build log. Does anyone else have and other improving ideas?
Aug 18, 2018, 11:26 AM
kellanplanes
So design work is well under way! It should prove to be a very versatile platform for sure!
Aug 18, 2018, 04:09 PM
Build straight - Fly twisty
Whiskers's Avatar
Looking good.
I'd tilt the thrust-line a few degrees, with the shaft rising towards the rear.
This will counteract, to a large extent, the tendency for planes like this to go nose down when they accelerate.
Aug 19, 2018, 07:36 PM
Registered User
A 'pod and boom' pusher makes a surprisingly good combination. It can be flown just as well on grass with no undercarriage if required.
It does rather depend on just how much STOL you want but big flaps can help.
Eventually the prop torque becomes a significant factor. Two motors with counter rotating props is one solution.
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It can take off and land it little more than it own length - even in still air
Aug 19, 2018, 08:29 PM
Registered User
cbalgra's Avatar
Quorneng. Nice pusher- puller. Like the flaps!
Last edited by cbalgra; Aug 19, 2018 at 08:30 PM. Reason: msitake


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