Multimaniac

Hello Boys out there!

Together with a friend I am working, or better still CAD-designing a Tu-95 "Bear". So far, the size will be 3,00 m of wingspan, about 2,8 m of length, and we think we well get it airborne at about 15 kg of weight, powered by 4x 6,5ccm.
Since this is my first scratch built plane with a swept back wing design, I have no experience with this.... so there are my two questions I hope somebody of you can help me:

1) Do I really need washout? (I never used washout on my "normal" twins and never had any problems, but as far as I know a backswept wing provides earlyer tip stalling, unfortunately...)

2) How do I best design the carrying structure of the balsa/plywood-wing??? I need to have a "corner" in the center of the wing, but I have no Idea how to do it best and most stable!?!


Chris

grbaker

My Feedback: (29)

You might want to contact B. B. Weber. He built this one. You can probably contact him thru the website.



http://www.bomberfieldusa.com/bbweber.htm

Multimaniac

WOW!!!! That's gigantic !!!!

I will contact him about this! (even if we will be a little smaller with our project...)

multiflyer

The main problem with a highly swept wing is tip stall with yaw. It doesn’t take much yaw to greatly disturb the flow over the side moving back. Plus effectiveness of the side moving forward is increasing. I think a little washout never hurts, but it is no cure for the main problem. Modern jets with swept wings just about always use yaw dampers (active directional gyro stabilization). I recommend building a quick and dirty sport practice plane with a thin high sweep wing. Perhaps bash some ARF slope soaring glider. Then practice stalls and spins to see how it behaves. I haven't done this yet but have experimented with gyros on the rudder for taming ground looping tail draggers. It is effective. I’m thinking some type of yaw damper for the swept wing is the best answer? The Bear is on my dream list for some day??

Multiflyer

Multimaniac

The jaw damper is in fact another possibility. But, reading lots of local rc-journals, the gyro on the ailerons is commonly used for stabilising and giving the plane a smoother flight, especially in big jets. It may help in most situations when the boundary is not yet dissected, but I think there must be another solution for the real problem, the tip stalling. I will sure use one, mostly for stabilsing the flight.

Most of the sowjet planes of the early jet aera use boundary layer fences, like they are installed on the Tu-95. Therefore, I guess most of that planes had about the same problem??? What do you think, could such a fence in the area of the ailerons also be a part of the solution of the problem??

Multimaniac

multiflyer

Yes, fences do help. They limit spanwise flow during any side slip. Problem is for scale building, if the full size didn't have them then the model shouldn't.

Multiflyer

Multimaniac

Well, the originla Bear does have them, so that should not be a problem... a little washout really does not hurt, and I hope it will help!

Multimaniac

Multimaniac

Well, the first steps are done... it seems to become a GIANT plane...

So far, I have drawn a first version of how I think we would build the wing structure. But, I can not really believe that the structure (see on the picture, yellow field) will stand all the forces in flight!?!? How do you recommend the joining of the two wing halves??

Chris

William Robison

My Feedback: (3)

Chris:

Use full scale construction, build what's called a "Wing Box."

I'd suggest a variation to the point that instead of having the upper and lower spars attached to the sides of the box, build sockets in the box for the spars to plug in.

Bill.

Pneuman

LOL screw these minor problems, I want to see you guys pull off the counter-rotating props.

Cheers,
Lawn Dart

slevin1

My Feedback: (23)

TUPOLEV TU-95 BEAR
Scale 1/12
Power 1.8 to 2.1
Wingspan 202 in. / Length 188 in.
Wing Area 5535 sq. in.
Plans $125.00
Cowls $40.00 ea.

http://www.donsmithplans.com

Hi Multimaniac,
Just wanted to send you a web address that might make your life a little easier. The TU-95 built by B.B. Weber is built from Don Smith Plans. My suggestion would be to by a set of plans, take them to a local printing shop, & have them sized down to what ever scale you would like to build. Hope this helps.
Saul

Multimaniac

Hi Saul,

Many thanks for the hint! That would things make really easier! On the other hand, the construction is quite progressed (Bill: thanks for the idea with the full scale method to attach the spars, I got a very good solution with this!), so that it would be not too much work to finish it - but the real reason is that for me it is the greatest challenge in model aviation to design it by myself !

would be - unfortunately, my friend decided to quit work on this plane. Well, unlike me, he has never designed and built a model aeroplane by himself before, so I can really understand him. Even I sometimes have to fight against the feelings of "will it really fly???" and "it is much too much work and problems"!!! Therefore I stopped construction and postponed the project for later, when all my examinations are done and some other unfinished projects are airborne. Designing and building the whole plane will be a good piece of work, but it is unalterable on my project list!!!!

regards

Chris

Moyo

Hey Chris

I didn't say it's off my Project list.

I think i will build the bear some day. Maybe next winter with the Help of a 3D CAD Program.


Oli

___________________________________

Always happy Landing

Multimaniac

Love to read that from you, Moyo!!!!



Chris

Multimaniac

The project has been sleeping a while, but actually, after CAD-Designing two models (but until now none of them built) during some spare time of my examination session, I am looking for a new (=bigger) challenge. Was thinking about a jet (De Havilland Vampire or FFA P16, a Swiss fighter prototype of the late 1950ies, the wing was 1:1 copied on the early Learjets) or - the Tupolev which is the thing I am working on now.

I blew up our old project to a wingspan of 3500mm, corrected wing shape and stab contour and changed the profile from the Göttingen 796 to the NACA 2415 - I wanted to use the TNT, but the thickness of 18.something % was too much (more than half of the fuselage hightat the wing root)... Now, the profile length at the wingtip is about 200mm which gives a suitable reynolds-number out there on a wing design that anyway is likely to be more critical than a normal wing, my main concern on this project!

By the way - found some very nice videos about the real Tu-95 on the net! ENJOY! ( Spoken in Russian, fortunately almost no problem for me, but I guess most of you guys don't understand - no matter, it is interesting anyway [8D]!)

regards

Chris

http://www.patricksaviation.com/videos/rechfurlan/581/
http://www.patricksaviation.com/videos/rechfurlan/462/

ampbomber

My Feedback: (7)

I'm happy to see that someone else enjoys building from scratch.

I've been working on my Tu-95 for almost four years now and hope to have some answers to your flight questions next summer. Power is going to be electric. You can see some of my progress at :
http://www.rcuvideos.com/
Do a search on Tu-95 and Tu-4.

Also there are some pictures at:
http://www.aviation.ru/contrib/dmaiorana
Items 4, 5 ,6,7,8 and 46.

Thanks for the video links. I had one but not the other.

Best regards,
George

Multimaniac

Hi George!

A really nice project you are working on!! I Really love it! For me the most interesting thing on your Bear are the retracts

I have been thinking about it for months, how to do the characteristic tupolev-movement.... Since I am a simple doc in two month time and therefore not too familiar with mechanics I never got a suitable solution [] ... One year ago I bought second hand pneumatic retracts for 20kg (approx 40 lb)-jets, thought that we may design some mechanics around it to get that movement. But your solution, including the gear-down-lock, looks much better than our ideas!! Very interesting are also the geardoor sequences. How did you do that???

Do you think your retract mechanics can be modified to be used in my 15 to 20kg (approx 30 to 40 lb) Tupolev??? Can I have / buy a set of plans of your tupolev retracts??

regards

Chris

ampbomber

My Feedback: (7)

Chris,

Thanks for the kind words.

I think my gear would work. My Bear will be about 30 lbs. As for drawings of the gear, I'm one of those that builds a wooden prototype to work out the mechanics and then proceeds to measure the prototype and build the final assembly. Here are a couple of pictures of the gear to show you what I have done. When I went to mount the gear in the plane I found that I had made the main leg a half inch too short so I had to remake the leg. My bear is 1:18.5 scale so it is very close to yours. Send me a private email and I can send you all kinds of pictures.

The gear is my second choice for degree of difficulity of the project. My first choice is the contra-rotating gear box with the home made CF props.

I am always joking that a scale modeler at NATO named it the "Bear" because he knew it would be a bear to model.

Best regards,

George

ampbomber

My Feedback: (7)

Things don't always go as planned. Here are the pictures( I hope).

Multimaniac

George,

I have sent you my private email adress. My Tupolev is 1:14,6 scale, wingspan 137,8". The contra-rotating props are far back on my list, maybe they will be realised when all the rest flies successfully! I think it may produce some more problems since I plan to power my Tupolev by four .71 four stroke engines (imagine that sound [8D] ). Also, the gear is easier to build than the gearbox (some sort of differential gear!?) for a "mechanical" rookie like me!

regards

Chris

Multimaniac

BTW: looks like this now...

Multimaniac

Not the very best drawing because you need to tape 32 sheets of paper together, but I think a good one from www.airwar.ru showing the Tu-95MS. This is the drawing on which I base my construction... think it is accurrate enough!

ampbomber

My Feedback: (7)

Yes, I like that drawing myself. It probably has the least amount of mistakes of all that are out there. I sat down last winter and pasted the pieces of one of the pages of that drawing together in Photoshop. See it attached here.

Also, my model is that of a late production Tu-95 MS. The one thing I find that is lacking in all of the three views is that the late models retrofitted/upgraded to the 15000 SHP ( shaft horse power) engines from the 12500 SHP is that the dorsal fin was enlarged at that time to accept larger electrical generators. Depending on which model Tu-95MS you decide to model you have to watch the size of the dorsal fin.

In all I think there were three sizes of the dorsal with the earliest models being smaller than the two shown here. I cut and pasted a similar size part from each photo below it's dorsal to show the size difference.

Multimaniac

Found another one... simply great! Surf that site, full of nice stuff [8D]

Chris

http://www.aviapedia.com/bombers/lon...training-video

RCPilot100

My Feedback: (4)

Chris,

Several friends of mine and myself have been contemplating a build of this plane. My friend Larry was approached by a friend of his who has a business - and who is trying to get noticed for an electic motor system with two counter rotating props - which comes in two sizes. Some of the inital noodling we have done indicated we could go to about 180" wingspan with these powerplants. Even at cost, it won't be cheap for the motors, speed controls and LiPo back, but it does make it very feasible. If you are interested, let me know and I will pass the info back to my friend Larry.

Dan