searching for ideal fitting on aft fuselage

[gubii]

Hello all,

I am researching how to install a vortex Generator with a Profile (like a shark fin) to a pressurised CS25 aircraft on the aft fuselage. I have three ideas in mind. The easiest one would be in my opinion to fit them with the shear tie because then you dont need to do extra holes in the Skin. Just to replace the shear tie with a bigger one and to have two attachement points (one at the beginning and one at the end) at the frame stations. The Forward attachment will be fixed and the aft attachment will have a movable bearing in x-direction. The Fitting with the Skin/shear tie to the Profile will be a T-Profile where two fasteners on each side will be fitted for compression/tension stress. Another idea is the usual one with internal doubler and another one is to glue it on the skin with few chicken rivets for fail safe. But the Problem is how I would prove it in a Simulation that this adhesive sealing can withstand the loads? Thats my other task to simulate it in Ansys.

The dimensions for the vortex generator is (not final as it can be changed due to the Fitting and loads, you can also share your ideas on the dimensions): length varies from 70 cm till 1,5 meters ; height is round about 20cm and the thickness 6mm .

Does anybody have an idea how to fit it? It would be very nice if you can help me and bring further.

Thanks a lot

 

[rb1957]

Sounds like a VHF antenna ... research how we install antennas (and the support structure required)

another day in paradise, or is paradise one day closer ?

 

[gubii]

Hello,

It is a vortex Generator with dimensions of: length varies from 70 cm till 1,5 meters ; height is round about 20cm and the thickness 6mm which has an aerodynamic Profile.
So it can`t be an antenna. It would be very nice if you can give me a hint.

 

[WKTaylor]

Sounds a lot like a ventral fin, such as on an F-16...

These fins require multiple fitting on multiple fuselage frames; and corresponding fittings/spars within the Fin(s). These are complex design features.

See attached.

http://files.engineering.com/getfil...-a073-0cd68d46ecca&file=F-16_Ventral_Fins.jpg

Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion"]
o Learn the rules like a pro, so you can b

 

[rb1957]

with a height of 20cm (8") and a length of about 1m (40"), it's more like a strake ... but anyway you look at it, "vortex generator" is an odd description (given that a vortex generator is usually several very small "stubs", maybe 1" x 1" or 2" x 2" ...)

another day in paradise, or is paradise one day closer ?

 

[berkshire]

Sounds like some kind of delta fin like those used on the back of a Learjet.
B.E.

You are judged not by what you know, but by what you can do.

 

[WKTaylor]

OK OK... my brain SI unit conversion was inop, previous reply.

Sounds more like the vortex control strakes occasionally seen on 'fat fan-engine cowls', thus...

http://files.engineering.com/getfil...-522b04f5a015&file=737_Engine_Cowl_Strake.jpg

http://files.engineering.com/getfil...-fffef79cf85a&file=767_Engine_Cowl_Strake.jpg

And/or like the T-37 nose strakes [on each side] to control oscillating vortex's that formed on the otherwise smooth nose contour. These oscilating vortexes , short aft fuselage and small stabilizers contributed to the loss of the prototype YT-37. Production T-37s had the nose strakes, a longer aft fuselage and enlarged stabilizers to enhance spin stability/recovery.

YT-37

http://files.engineering.com/getfil...le=Cessna_XT-37~prototype_in-flight~c1954.jpg

T-37A [Production acft] with nose strakes

http://files.engineering.com/getfil...ile=Cessna_T-37A~Prdctn~With_Nose_Strakes.png

Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion"]
o Learn the rules like a pro, so you can b

 

[WKTaylor]

Darn It... here is T-37A *.pdf copy for those who can't open the *.png file...

http://files.engineering.com/getfil...akes__&_Extndd_Aft_Fuslg_&_Enlrgd_Stblzrs.pdf

Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion"]
o Learn the rules like a pro, so you can b

 

[gubii]

Thanks for the answers. I am really thankful to you. But to come back on the question....I gave some ideas, whether to glue it on the Skin or to connect it with the shear ties. What do you think? Now it seems like the vortex Generators will be around 2meter length, so that will make it more tough. What do you say? They should be installed on the aft fuselage. They should delay the stall...What do you think how would you install them and why you would do like this?

 

[rb1957]

don't, repeat don't, glue it on.

I would consider an external doubler.

At a minimum you'll need something like "formers" (short frame portions) to beam the vortex generators attmt screw loads to the striners.

A 2m long vortex generator !? I suspect this is more like a strake, straightening the airflow. How high (into the airflow, 8" ??

another day in paradise, or is paradise one day closer ?

 

[gubii]

yes it is for straightening the airflow and to delay the flow detachment...it is 20cm high

 

[rb1957]

yeah, like I thought, 8" = 20cm.

This will straddle several fuselage frames. These provide ideal places to support your strake (let's call it what it is). It's unlikely you can use the airplane fasteners, maybe if they-6 rivets (replace with #10 screws. More likely you'll want 1/4" bolts, which means dedicated tension fittings ... easy enough if the frame flange one way (mount of the other face).

beyond that it's a bunch of work ... detailing loads (from CFD, from abuse loads). shouldn't be the end of the world, but it's also not trivial.

another day in paradise, or is paradise one day closer ?