B-24 Liberator rudders are angled up

[Pete M.]

And Monogram (Revell) also missed it on their 1:48 scale kits..needs a bit of 'fettling' to get it correct.

 

Pete M.

[Nachtwulf]

On 7/16/2021 at 7:01 AM, JWM said:

I think it was similar also in Consolidated Coronado. 

I have noticed it doing the Mach 2 kit...

Regards

J-W

 

 

 

It appears to me that the horizontal vertical stab is exactly perpendicular to the wing chord line. It does look like it is at an angle compared to the fuselage.

Edit: It looks like the same could be true of the B-24.

[JWM]

2 hours ago, Nachtwulf said:

It appears to me that the horizontal stab is exactly perpendicular to the wing chord line. It does look like it is at an angle compared to the fuselage.

Edit: It looks like the same could be true of the B-24.

This will result that (as someone already wrote before) the B 24 was flying with  nose down like Whitley...

Regrads

J-W

[Graham Boak]

Being perpendicular (i.e. at 90 degrees) to the wing chord?  Odd sort of tailplane.  Do you mean the vertical stabiliser (i,.e. fin and rudder)?  Plus I don't believe you can actually make out the wing chord line anyway.  Tailplanes are usually set at a negative angle to the flightpath.  The whole arrangement seems very odd.  It seems to have worked.

[Nachtwulf]

1 hour ago, Graham Boak said:

Being perpendicular (i.e. at 90 degrees) to the wing chord?  Odd sort of tailplane.  Do you mean the vertical stabiliser (i,.e. fin and rudder)?  Plus I don't believe you can actually make out the wing chord line anyway.  Tailplanes are usually set at a negative angle to the flightpath.  The whole arrangement seems very odd.  It seems to have worked.

 

My very first "red lines" post! be gentle.

[tempestfan]

Does a positive wing incidence automatically result in a nose down flight stance? In the Tiger-powered Whitley that may have been the case, but perhaps only because of the Tigers... The late-mark Marauders IIRC had some fairly substantial incidence added (3.5°?), but I don't think they look different in flight than, say, B's. Doesn't the engine thrust line mainly determine where an aircraft is going?

[Graham Boak]

For the Whitley, the high incidence was needed to shorten the take-off run, blame that on the engines if you like but it was probably, like the Stirling, more a matter of being overweight.  The same reason did apply to to the later Marauders, but bear in mind that this is only a few degrees and this would be barely noticeable in flight.  However I'm pretty sure that, at the same weight, the later ones would be more nose down - difficult to imagine how anything else would work.

 

Yes, the engine thrust line is the main determiner, but in that case the later Marauder must have flown more nose down as they didn't change the engine mountings.

[corsaircorp]

Ooooh Cousin !!

I'm a bit envious, nice pics @Corsairfoxfouruncle !!

Thanks...

CC

[Corsairfoxfouruncle]

1 minute ago, corsaircorp said:

Ooooh Cousin !!

I'm a bit envious, nice pics @Corsairfoxfouruncle !!

Thanks...

CC

Hello Cousin there are some more photo’s you might like here. 
 

https://www.britmodeller.com/forums/index.php?/topic/235096612-louis-university-airshow-romeoville-illinois-071721/&tab=comments#comment-4142285

 

[Nachtwulf]

On 7/19/2021 at 9:13 AM, Graham Boak said:

Being perpendicular (i.e. at 90 degrees) to the wing chord?  Odd sort of tailplane.  Do you mean the vertical stabiliser (i,.e. fin and rudder)?  Plus I don't believe you can actually make out the wing chord line anyway.  Tailplanes are usually set at a negative angle to the flightpath.  The whole arrangement seems very odd.  It seems to have worked.

Yeah,  I meant the Vertical stab not horizontal...

[Jamie @ Sovereign Hobbies]

On 7/19/2021 at 6:59 PM, tempestfan said:

Does a positive wing incidence automatically result in a nose down flight stance? In the Tiger-powered Whitley that may have been the case, but perhaps only because of the Tigers... The late-mark Marauders IIRC had some fairly substantial incidence added (3.5°?), but I don't think they look different in flight than, say, B's. Doesn't the engine thrust line mainly determine where an aircraft is going?

 

At the risk of muddying the waters, there isn't a straight forward answer to this. The characteristics of different aerofoil sections are all different and what may appear to be a geometric chord line isn't necessarily the aerodynamic one, and by that I mean there are numerous aerofoil sections which still provide positive lift with the geometric angle of incidence negative by a couple of degrees. Add in to this the fact that to make stall characteristics of the whole aircraft better, many straight wings will have either geometric washout (i.e. a physical twist along the span placing the tips at a lower geometric incidence than the roots so the root will tend to begin to stall first), or aerodynamic washout - that is a deliberate choice of aerofoil section change from root to tip with the tip sections having characteristics of keeping upper surface flow attached at higher angles of attack than the root sections, again so the roots begin to stall first, or a combination of both.

 

Geometric washout illustrated nicely here:

 

For that reason it's tricky to draw a red line through most illustrations of aircraft and determine much that's definitive - you need the real datum lines the designers worked to which they write down in the engineering manuals for the maintenance engineers to work to.

[Flankerman]

As an aside.... check out photos of Spitfires in level flight......

 

The elevator is always a few degrees down ......

 

This pic shows it well   https://cdn.airplane-pictures.net/images/uploaded-images/2017/8/28/954733.jpg

 

A simple Google of 'Spitfire' will turn up more showing the slight down elevator.

 

Ken

[Black Knight]

Does the B-25 also have a tilted-tail?

Or is it

1. an optical illusion

2. the way I'm looking at it

 

https://64.media.tumblr.com/6a2128269ec206e2807999dda13d7c77/tumblr_inline_p5jyo3iTZw1t9qtgy_1280.jpg

[Nachtwulf]

8 hours ago, Jamie @ Sovereign Hobbies said:

 

At the risk of muddying the waters, there isn't a straight forward answer to this. The characteristics of different aerofoil sections are all different and what may appear to be a geometric chord line isn't necessarily the aerodynamic one, and by that I mean there are numerous aerofoil sections which still provide positive lift with the geometric angle of incidence negative by a couple of degrees. Add in to this the fact that to make stall characteristics of the whole aircraft better, many straight wings will have either geometric washout (i.e. a physical twist along the span placing the tips at a lower geometric incidence than the roots so the root will ten..............For that reason it's tricky to draw a red line through most illustrations of aircraft and determine much that's definitive - you need the real datum lines the designers worked to which they write down in the engineering manuals for the maintenance engineers to work to.

Agreed- though off the top of my head I can't remember whether there are any four engine WWII birds that did have washout. I always assumed it was more suited to fighters since they are doing much more extreme maneuvers and the purpose of the washout was to delay airflow from separating from the control surface portion of the wing last. Two of the most obvious fighters with washout are the P-47 and the Ta152. In the end everything I've stated here is factual only in my head and is not backed up by anything more than my own suppositions and faulty observations. Don't provoke me though, as I may resort to posting a picture of a P-40 with as many red lines..........oh who am I kidding? It took me almost half an hour to draw two fat red lines on a four engine patrol plane. I'll  get my coat  

 

After reading more on washout (Hat tip to the guy that invented reading. It actually works! Who knew?) I have come to the conclusion that I don't know near as much as my ego says I do. Is there an Ego removal kit available? I'll take the cheap one.......

[Graham Boak]

There's a little known design called the Spitfire that had washout.  Although this almost certainly was an early example, it surely wasn't the first.  I recall a German poster trying to argue that the HP slots on the Bf.109 was a superior solution, but I think history (of aircraft design overall) had proven him wrong before he began.  I entirely agree that washout would be unlikely on heavy bombers, wing twisting under g loading not being a design concern.  Methinks they'd fall apart first.

[Jamie @ Sovereign Hobbies]

I'd like to find out a bit more actually as I hadn't previously considered that larger aircraft might not do it. It appears at a glance that the Lancaster's wing does have a degree or two of washout along the tapered span of the wing

 

https://image.shutterstock.com/shutterstock/photos/205481764/display_1500/stock-photo-england-uk-circa-an-unamed-pilot-flies-the-avro-lancaster-pa-bomber-at-a-vintage-air-205481764.jpg

[Graham Boak]

Thinking a bit more about the angle of the tailplane to provide that tilt.  I said above "Tailplanes are usually set at a negative angle to the flightpath."  This isn't so.  What I was thinking was that the purpose of the tailplane was to provide negative lift, which you would indeed get from a negative angle.  However this is usually provided by an inverted aerofoil, so mounting the tailplane at a positive incidence would reduce this effect.  The precise angle would depend upon the trim required.

 

So the thought then occurred that the longer nose on all but the earliest variants would require a change of trim, but surely this means more negative lift not less?  Or has the movement forward of the cg eased what otherwise had been an excessive requirement, allowing a reduction in the inverted lift required.  (Sink? Drop?)  Either way, the question is: did the earlier B-24s not show this inclined tail?  or were they the same?

 

Baffled of Lancashire.

[Jamie @ Sovereign Hobbies]

Surely that would lead to generally sloppy control with a defacto aft-CofG?

 

I am wondering if the combination of high mounted, highly cambered upper surface wing and tailplane mounted at the same level results in the tail being washed by slipstream with a downward vector. The negative incidence on the tailplane may be geometric but not aerodynamic, I mean. Had they used a big T-tail to place the tailplane up out of the wing's wake the incidence requirement may have gone away.

[Jamie @ Sovereign Hobbies]

A bit more digging on this reveals that the Davis wing's main attraction for Consolidated was its low drag at lower speeds and its high lift at low angles of attack, the latter being desirable for their flying boats in particular since ability to pitch a flying boat to break the surface suction and get airborne is limited. They've liked the drag results on the flying boat and carried that wing (aerofoil sections, not literally the physical wing design) forward onto the B-24, no party involved fully understanding why the wing worked so well drag-wise*. That will imply a strong nose-up trim tendency as speed increases towards the B-24's cruising speed and for me that probably explains the tail incidence at 0.5 degrees less than the wing incidence - a fairly modest negative bias.

 

 

*What Davis had designed by accident was an early laminar flow section but ultimately it was an evolutionary dead-end as its high speed drag was a brick wall as aircraft performance rapidly increased.

[Graham Boak]

39 minutes ago, Jamie @ Sovereign Hobbies said:

Surely that would lead to generally sloppy control with a defacto aft-CofG?

 

I am wondering if the combination of high mounted, highly cambered upper surface wing and tailplane mounted at the same level results in the tail being washed by slipstream with a downward vector. The negative incidence on the tailplane may be geometric but not aerodynamic, I mean. Had they used a big T-tail to place the tailplane up out of the wing's wake the incidence requirement may have gone away.

Longer nose moves the cg forward, usually not a problem as long as there's enough elevator power to lift the nose.

 

The tailplane is always washed or close to the downwash from the wing, as a natural result of the creation of lift.  It is desirable to keep it out of the direct downwash so that there are no major trim changes with changes in lift/speed.  (The Harrier had a problem here, that's why you see extended tips to the tailplanes on the production machines - to get some of the tailplane into clean air.)  This is usually done by not placing it below the wing, or a small amount above.  This would normally be fine at all except very high incidences or sink rates.  Neither is really a B-24 problem.  As can be seen by the final development of the tall fin to solve long-standing directional stability problems, but the tailplane stayed low.

 

Placing the tailplane on top of the fin would have considerably increased the structural mass (and is a bit difficult with twin fins).  If fiddling with the tailplane incidence solved the matter, why do anything more?