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Mar 05, 2010, 08:33 AM
the answer 42 is
Oky doky Project Cancelled for me now back to my SAL foward sweeped wing

EZ
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Mar 05, 2010, 08:40 AM
Herk
HerkS's Avatar
A flying wing sailplane with electric power would probably work better for you if you put the prop on the front.

The main reason to do this from my point of view is that you are able to hand launch the plane with the motor running. Launching with a rear prop running is very dangerous. Some designs with rear props are tossed power off and then the power turned on. Others use a bungee launch to get it to flying speed and then turn the motor on after release.

You also need something to hold on to for launching the model. Some sort of fuselage or keel is almost always necessary - or at least desirable.

Here is one idea - a smaller model, but not so different in layout. This pod is removable and can be replaced with a simple keel to make a pure glider. I like this convertible feature on this model.
Mar 05, 2010, 09:15 AM
Registered User
miniphase's Avatar
Quote:
Originally Posted by HerkS

Here is one idea - a smaller model, but not so different in layout. This pod is removable and can be replaced with a simple keel to make a pure glider. I like this convertible feature on this model.
looks nice Herk, do you get much of a pitch change when you deploy the flaps?

Paul
(with a scar on the back of his hand)
Mar 05, 2010, 09:25 AM
Herk
HerkS's Avatar
Miniphase - There is a pitch change - but it's actually very slight.

There is a compensation that depends on a lot of factors. Putting the flap down increases the nose down pitching moment of that part of the wing. However it also increases the effective twist to create a nose up moment. How they balance depends on flap size, sweep angle and other factors. I had an earlier wing with smaller flaps and there was no change in pitch when they were deployed.

Care to explain the scar ????
Mar 05, 2010, 09:40 AM
Registered User
miniphase's Avatar
Quote:
Originally Posted by HerkS

Care to explain the scar ????
Let's just say I employed neither the bungee, or 'launch first switch on later' method....luckily it was only a shallow cut

I'm a sucker for a pusher prop on a wing, I've heard it's suposed to be more efficient due to a less disturbed air flow over the wing, also it adds stabiliy and looks darn sexy!!
Mar 05, 2010, 10:06 AM
Red Merle ALES
Curtis Suter's Avatar
Quote:
Originally Posted by miniphase
looks nice Herk, do you get much of a pitch change when you deploy the flaps?
http://www.youtube.com/user/cloudyifr#p/u/6/0uMAaJ7c-Xo

Watch Tinamou at 1:25 to see the pitch change, it's negligible, but I have some up elevon mixed in to compensate.

Curtis
Montana
Last edited by Curtis Suter; Mar 05, 2010 at 10:21 AM.
Mar 05, 2010, 10:51 AM
Registered User
cliffo's Avatar
Christian Behrens' Nurflügel DLG (1 min 15 sec)


Drela foils with lots of sweep.

Find a destroyed Supra, for some cheap wings, and give it 45 degress of sweep and winglets. Woo hoo!
Mar 05, 2010, 10:53 AM
internet gadfly
nmasters's Avatar
Hi, Wardo--

Quote:
Originally Posted by wardo78
I could put them on the bottom, but flaps might be the ticket. Also, miniphase's suggestion of using the center portions trailing edge is interesting. I like the simplicity and likely need for only one servo. The major rub I see is conflict with the motor and prop.
A forward split flap produces more drag and less lift than a plain trailing edge flap with a smaller Cm shift. The flap that miniphase showed will cause a pitch up and a lot of vibration in the prop, especially if you use an extension shaft.

Here's another thread with a picture of such a flap/dive break on a full size plank

Quote:
I was thinking of trying to find a longer prop shaft which would allow the motor to be mounted forward, I would then support the shaft at the rear with a bearing arrangement of some sort. I don't have ready access to a machinist, but I am sure I could turn something up.
Maybe a helicopter anti-torque rotor drive shaft would work.
--Norm

OK now I really am leaving for the weekend
Mar 05, 2010, 11:19 AM
Registered User
Quote:
Originally Posted by wardo78
Herks, thanks for the input, I was hoping you would chime in. I'll rethink the spoiler idea, I could put them on the bottom, but flaps might be the ticket. Also, miniphase's suggestion of using the center portions trailing edge is interesting. I like the simplicity and likely need for only one servo. The major rub I see is conflict with the motor and prop. On that subject, I was thinking of trying to find a longer prop shaft which would allow the motor to be mounted forward, I would then support the shaft at the rear with a bearing arrangement of some sort. I don't have ready access to a machinist, but I am sure I could turn something up.
Regards,
Wardo
Here's a link to a site with details of an extension shaft that you might consider. It's for a tractor installation, but you could always point it the other way! Not an English language site, but the photos detail the installation very well. Scroll to lower half of page.

http://nasgul.blogspot.com/2008/01/r...lution-xl.html

Rudderman98 has a great build thread for a Merlyn using an extension shaft in the power system. You might care to read it for the details of his system.

https://www.rcgroups.com/forums/show....php?t=1003150
Mar 05, 2010, 11:31 AM
Registered User
Quote:
Originally Posted by Edwinzea
Oky doky Project Cancelled for me now back to my SAL foward sweeped wing

EZ
A 2 to 2.5 meter Alula could be quite a model!

The Redwing is pretty close to that concept.
Mar 05, 2010, 12:24 PM
Registered User
wardo78's Avatar
Curtis,

Thanks for the explanations. I also reread your RCSD article (http://www.rcsoaringdigest.com/pdfs/...SD-2008-10.pdf). I was an NFO in the Navy for 7 years,so I learned much of this back in the 80's. It's amazing how much I've forgotten, and how little I ever knew about design. So I really do appreciate the information, I do get the lingo....

I downloaded XLR5, but I was having a hell of a time finding the airfoil database. I used to have Profili on my old computer, and I remember it was readily available. What am I missing? I do have a slow, rural internet connection, so I try to avoid big downloads.

So a few questions on your post. Firstly, how far out should the transition from semi-symmetric to symmetric occur? Are the winglets also symmetric? How do I select an airfoil? I am likely to simply do what other, more informed designers have done before me, but I would like to have some sense of the decision process and the results applicability to my specific application.

Thanks,
Wardo
Last edited by wardo78; Mar 05, 2010 at 07:13 PM.
Mar 05, 2010, 12:34 PM
Registered User
wardo78's Avatar
maybe split the flaps either side of the motor, and just accept you'll have to use 2 servos?


Miniphase,
I really struggled with the CG on the MWC 84, and ended up running 4s, just to get balance. I realized that if I could move the motor forward, I would have several benefits. First, the trailing edge wouldn't need to be cut as much, thus allowing for a better spar location. Secondly, I could use lighter components due to not needing to balance the motor out. I could have saved at least 10% of the wings weight by going this route. Finally, challenge is part of the fun, so I'll try to sort it out. I really like your flap idea, but of course there are more coming in as I write this....

Wardo
Mar 05, 2010, 12:40 PM
Registered User
wardo78's Avatar
Quote:
Originally Posted by DT56
Here's a link to a site with details of an extension shaft that you might consider. It's for a tractor installation, but you could always point it the other way! Not an English language site, but the photos detail the installation very well. Scroll to lower half of page.

http://nasgul.blogspot.com/2008/01/r...lution-xl.html

Rudderman98 has a great build thread for a Merlyn using an extension shaft in the power system. You might care to read it for the details of his system.

https://www.rcgroups.com/forums/show....php?t=1003150
DT,
Thanks for contributing, those are GREAT links. The first one is exactly what I had in mind. I had to go to the hardware store to pick some things up, and I bought some aluminum angle to fab mounts out of and brass tubing and rod that is 5mm. I need a 5mm ID coupling and 5mm ID bearing, but those shouldn't be hard to come buy. If that fails I'll visit the machine shop.

Thanks,
Wardo
Mar 05, 2010, 12:45 PM
Red Merle ALES
Curtis Suter's Avatar
Wardo,

Here's about every airfoil imaginable, not all, but most. You can import these into XFLR5.

http://www.ae.illinois.edu/m-selig/a..._database.html

Curtis
Mar 05, 2010, 12:47 PM
Registered User
wardo78's Avatar
Quote:
Originally Posted by HerkS
A flying wing sailplane with electric power would probably work better for you if you put the prop on the front.

The main reason to do this from my point of view is that you are able to hand launch the plane with the motor running. Launching with a rear prop running is very dangerous. Some designs with rear props are tossed power off and then the power turned on. Others use a bungee launch to get it to flying speed and then turn the motor on after release.

You also need something to hold on to for launching the model. Some sort of fuselage or keel is almost always necessary - or at least desirable.

Here is one idea - a smaller model, but not so different in layout. This pod is removable and can be replaced with a simple keel to make a pure glider. I like this convertible feature on this model.
Herks,

That is a nice looking model. Thanks for the input. I understand the safety concern. I initially struggled to launch the MWC 84, but quickly sorted it out. I do admit that at the age of 50, I still race off-road motorcycles, so my risk profile is skewed. Certainly a forward facing prop would solve a lot of issues, so I'll think it over and see how things develop. I do like the look of a pusher, and I can use as large a folder as I care to without wing interference. I am pretty sure that if it is a pusher, I will use a keel to hold onto and make launching more controlled.

Wardo


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