The Razorback construction thread

Yep, "windmilling" props were also the cause of some BD-5 crashes in the approach / landing phases (connected also with the presence of a "sprague clutch".)

A propeller remaining in a fixed position in the event of an engine stop is way better than a windmilling one, from the drag point of vue - this is generally the case of PSRU drives, when the airflow force is insufficient to rotate the "dead" crankshaft.

 

Very low actuating forces, while they always have a positive gradient (no force reversal).
Extremely simple construction.
Very low internal forces (contrary to normal speed brakes or SH flaps)
Extremely powerful.
No significant change in the spanwise lift distribution.

 

How much lift do they add?

 

Hi,
They don;t add any.

 

About 0.5 give or take, largely dependent on the relative chord and span.

 

Could they be extended to 30% of the chord? 0,5 is pretty much the lift increase of a standard flap. It would make up a very light system. Hard to tell the aerodynamic center of the setup as part is burried in the wing. i am seriously weighting on using this setup in order to simplify my project.

 

Yes. The first 15 degrees or so of deployment you get most of the lift increase and a surprisingly modest increase in drag. After that... be careful with your nose or it might hurt...

 

So they are difficult to pilot as the stall becomes harder to predict? Would you say they suit a semi stol concept? I would cover 70% of the wetted wing and size them at 30%.
The gap looks to be crucial

 

Hi,
How do drag brakes add lift?

 

Its really a flap that presses the air down thru a slot.
Sorry for hijacking but wouldnt the actuation be much more simp`le with a torque tube running all along the flap?

 

By changing camber. Look at it like a deployed plain flap and a spoiler. The flap generates more lift than the spoiler kills.

 

Thanks for the pix Jarno - I had forgotten the Salto used them also. There is no gap (study the photo) but the drag of the above wing and below wing panels are matched so giving little actuation force . More sophisticated versions allow for around 20 degrees of simple flap range before the balanced drag deflection occurs (eg mini nimbus/Ca21 -not aware of any more modern examples )

I don't think there is any net Cl gain from full deflection but didn't stall(Club libelle after repairs ) with full dive brake either --in fact how many pilots have stalled their aircraft with negative flaps for that matter (or full airbrake or 90 degree flaps ? ) -- there is only usually training using zero flap and in clean configuration but the stall/spin problem can arise in other configurations . (and the wake of airbrakes and flaps can affect the recovery and entry behaviour.) Probably X plane could not duplicate such effects either.

 

Hi,
Have just returned for a bit of lunch after gluing together the foam for the rear wing inner section. Just getting the dihedral right, and the airfoil templates glued on the ends of the foam with identical incidence proved to be a difficult job. I am DEFINITELY going to get my wing plugs CNC'd. With Profili Pro designing the wings are a breeze. But actually constructing them accurately would be a nightmare.

The plan is to set the foam plugs on a flat surface, box the individual sections together firmly and make sure everything is true. Then cover with Stretchelon plastic film and vacuum bag the lot. This will give me a perfectly smooth base, as well as automatically releasing film. Then with the little vacuum pump running, I'll lay my glass, 3mm foam sheets and inner glass sandwich plies and vacuum the whole thing, this time using my heavy duty infusion pump. Infusion is definitely the way to go. Within 24 hours I should end up with a perfect one-piece 4mm thick wing skin which should be extremely rigid. I'll bond the graphlite rods in place with a couple of layers of glass tape covering the lot as a secondary process, and leave everything in the mold while I fit the ribs and control lines etc. The bottom skin is a little more complex, because it will need to be recessed to accommodate the split flap, but that's the general plan.

I haven't figured out quite how to do the shear web yet...

Cheers,
Duncan

 

Thoughts on chasing a bit of tail...

Gentlemen, As you may remember, I recently moved the Razorback plug (on its stand) to an adjacent work space, and in the process, the stand broke and the plug dropped onto the tarmac. It sustained some minor damage (small holes neatly puncturing the surface) which have now been repaired.


Unfortunately, I have now discovered that the tail sustained more subtle, (ie less obvious) but more serious damage. There is a crack running diagonally from the base of the LE of the tail backwards. And I fear the tail is no longer perfectly aligned with the airframe. I am now faced with a dilemma:

1. Try to ignore this possible misalignment and proced with building the molds
2. Give in to my fears and chop the tail off and replace it with a new one

The first option is going to be WAAAAY easier. But I'm not sure I'll sleep easy knowing the tail may be off a degree or so. And it is damned difficult to measure accurately, even with plumb-lines and lasers. I just can't tell one way or the other.

The second option is going to be a right royal pain in the arse. I just KNOW that fairing a new tail into the fuselage is going to take a long time. However, I'll sleep easy. Another reason for making and fitting a new tail is that I am no longer sure that the airfoil shape of the tail is as originally designed. I have added many layers of micro in my efforts to fair the tail into the fuse, and think that I'm going to encounter difficulties adding the rudder, and avoiding weird and sudden tapering issues. But, from your experience, how serious is having a tail which doesn't conform to a recognised airfoil shape?

So, at this late stage, I am looking for some feedback from you regarding the shape of a new tail. Currently it is swept backwards quite rakishly. There was some discussion on the forum some time back regarding possible issues of this configuration in spin recovery. However, I really like the aesthetics of this configuration, although now is an opportunity to make a change.

I have attached a sketch showing two possible tail configurations I like. Both are rather appealing to my eye at least. I like the raked back tail a lot. But I am also very keen on the forward raked tail. It is both striking visually, as well as fitting in quite well with the design cue from the forward swept front wing. Both represent about the same amount of work. And before someone asks: I HAVE tried drawing different "more traditional" tails, and don't like them.

Could I get your opinion on which of the following you prefer - both from a flight characteristics point of view, and as far as marketability is concerned.

Regards, Duncan


Or from X-Plane, a bit more realistically...

 

rearward sweep gets you more control leverage.

 

...and looks a **** sight better.

 

Mmmm marginal. But rudder effectiveness isn't an issue. Either configuration has more than sufficient. Probably too much...

The forward swept tail looks a bit "cheeky" though...

 

2-nil. Mmmm Keep 'em comin...

 

Re: Thoughts on chasing a bit of tail...

The swept back tail looks MUCH nicer to my eye. Spin recovery shouldn't be an issue now that you've gone to a tandem wing design.

 

Duncan,, Definitely the swept back version. In the X-plane image the trailing edge of the rudder is forward of the new rear fuselage extension.
As long as you are doing a new tail might as well slide it back to the end of the fuselage.
wizzardworks