Morane Type P for rubber power

[Pete Fardell]

I thought I’d start a proper build thread for my Morane Type P. I find it keeps me going.
It’ll be about 29” span (1/15 scale) and mainly for indoor rubber.
I had a nice drawing to start with (makes a change for me!) which is by Ian Stair and is in the May/June ‘93 edition of Windsock International. I blew it up to the size I wanted and will use it as a build plan.
The model will represent this RFC example, of which there are quite a few photos on the internet. The RFC modified the fuselage to take a camera which is helpfully shown on the Stair drawings. It’s actually asymmetrical, with a bulge on the starboard side, so this time if my fuselage isn’t straight then that will be completely deliberate and 100% scale!
 
Progress so far: formers threaded on a knitting needle and removed after the stringers were added…

[Pete Fardell]

I made the cowl from sanded balsa. I’ve also made the dummy le Rhone engine with a glue stick lid for its hollow centre.
This is where I’m up to at the moment. You can see I’ve also put in some internal sheeting to stiffen up the forward fuselage where the motor will be. Tailplane will be enlarged a bit as it is tiny.
It might conceivably be built for the indoor Nats in April, but if not then certainly for Nijmegen in November.

[Squirrelnet]

Great to see the build on here Pete. Another one I'll be avidly following

[billdennis747]

Great scope for weathering Pete. Do Extracolor do 'linen soaked in burnt castor oil'?

[Pete Fardell]

Great scope for weathering Pete. Do Extracolor do 'linen soaked in burnt castor oil'?

I am really looking forward to ‘dirtying this one up’!

 One thing I’d like thoughts on is the nature of the vertical line that comes down from the rear edge of the rear cockpit. It’s not there on French Type Ps. Also, which sections of the forward fuselage are doped fabric and which are metal plated and is this the same for both sides? What about the section with the camera box: fabric or something harder?

[billdennis747]

Pete, I just googled images for Morane Saulnier Parasol P and there are two pictures of what looks like a new Russian aircraft and I'd say the front end is definitely panelled, albeit thin material that seems to follow the line of the stringer. Maybe the vertical line is a fabric join which were sometimes painted, but it's not on the Russian one.

[Squirrelnet]

My first thought was maybe it's a removable fabric panel ahead of the cockpit and its the join line, the same sort of thing that is used on the AVRO Tutor

Looking at images they do all seem different between the different air forces.

I did find a rear image of A'6607 and that does look like the front end is panelled to me too so the line is the end of the panelling ?

[Pete Fardell]

Thanks both. I have that rear view shot and agree it does look like the panelling keeps going right to the mystery line. The RFC definitely modified their Type Ps as it says so in the Windsock article. The cockpits are different to the openings on the French gun-carrying ones too. Perhaps I'll just tissue cover the whole fuselage then add paper panels.
This front view is, I think, the only other I've found of A'6607 so far. Could do with non-watermarked copy really but it'll do for now. Together, the four shots show the whole aircraft quite well.

[Pete Fardell]

Any thoughts, anyone*, on how much I should enlarge the tailplane to get it into a nice easy flying zone?
Here's the drawing...


*Doesn't have to be Jon W but I'm kind of hoping!

[Prosper]

The vertical line in pic 2 of reply No.4 reminds me mightily of the white or black lines painted on American warplanes (I'm thinking F4U Corsair but probably F4F and others too). these were to indicate the recessed spring hatches for handholds and footsteps, needed to clamber aboard. The line looks to me to be between a step and a hold.

As for tailplane size I'd say bigger but not nearly so much as most modellers would suggest, and I wouldn't waste time with tail-volume calculators as these are just playthings at this size of aeroplane, especially if it's a scale model (just my opinion, etc). Ask Bill747 because he made a model years ago - I think it was a Morane, and I think it had a scale tailplane - I've always wondered whether it could/did fly. It might be possible to build your model initially incorporating a sheet-balsa throwaway tailplane which could be cut off and replaced, to establish what size you can get away with, then add the proper finished one.

Stephen.

[Slowmatch]

Morning Pete,

Using Hepcat's calculator the scale tail volume is 0.275.
This is pretty tiny as you can see.

I tend to think in terms of:
Vh 0.3 = marginal
Vh 0.4 = possible
Vh 0.5 = reasonable
Vh 0.6 = comfortable

A 10% linear increase gives you 0.33
20% gives you 0.4
30% gives you 0.47
You might want to go bigger still for 'the really 'easy' zone.

The CG would be very far forward like 15-20% moving back to maybe 25-30% as you increase area. At the smaller size the tailplane will need to provide a strong downforce in order to balance, and being small in area it has to achieve this by a large angle of attack. This high aoa puts it close to stalling, especially a flate plate airfoil and low Reynolds numbers, and if you do overload it then you'll find the model punts in nose down. You certainly wouldn't be able to use the indoor method of pushing the CG forward more and more for more stability, the tail would just give up.

The other consideration is if you use a strongly cambered wing section, the wing will have a stronger nose down pitching moment which further adds to the tail load.

I would suggest having some scope to introduce a fair bit of tail incidence. it's unfortunate that it had an all flying tail - using a degree or two of up elevator introduces camber to a flat plate tail and can give it that bit extra scope for downwards lift before it reaches the tail stall angle.

The good news is that the tail moment arm is reasonable (2.8 x the mean chord) so it shouldn't have any particular issues with dynamic longitudinal stability such as phugoids.

Prop size makes a difference too. Props are destabilising in pitch so if the tail volume is marginal but flyable with a small prop, then a bigger rubber prop might just push it over the edge.

Looking forward to your progress, it's a perfect subject for 'Fardell scale'



Jon

[billdennis747]

sk Bill747 because he made a model years ago - I think it was a Morane, and I think it had a scale tailplane - I've always wondered whether it could/did fly. It might be possible to build your model initially incorporating a sheet-balsa throwaway tailplane which could be cut off and replaced, to establish what size you can get away with, then add the proper finished one.

Andrew Hewitt has built many models of similar layout, including a big diesel Morane similar to the P. Andrew never alters anything so it had no dihedral and a tail you could hardly see. It did fly, occasionally, but it wasn't reliable. I never saw it unstable fore and aft - more often it would just slide in sideways. Same goes for his Eindekkers. The model most similar that I have built was a Halberstadt which most certainly needed enlarging. I went too far but it did fly well.Just as important is a reliable way of fixing its incidence.

[Pete Fardell]

Thanks all. Plenty to get my teeth into there!  I’m inclined to go quite big, in line with what Jon has said, and I was already thinking about Bill’s Halberstadt when I asked the question. Mind you, I think I’m right in saying that Andrew Hewitt actually shrunk the tail surfaces on his latest Morane, which is a much improved version of the Dennis Rattle AM plan I believe. (When I say shrunk I just mean he reduced them to scale size of course; he’s not completely mad!)

Stephen; good thoughts too on the fuselage line. As this aircraft was modified to take a camera, I suspect that section of the fuselage was made easily accessible.

[Slowmatch]

For what it's worth I'm not saying go bigger or not, just hopefully quantifying what you might reasonably expect at each size.

One thing I don't like to see is unneccesary non-scale enlargement because 'that just what you have to do'. I've seen plenty of scale plans where the tail has been enlarged by rote and yet the scale size is perfectly adequate. I'd much rather put an accurate metric on it than guess. Tail Volume, done properly, is accurate at model sizes (and far more meaningful than actual areas or percentages of the wing area) but it is just another tool or measurement. The key is to understand what it means and what it doesn't. There are plenty of things at model scale that are hard to predict accurately and an aircraft at any size is an incredibly complex series of interactions.

...and I wouldn't waste time with tail-volume calculators as these are just playthings at this size of aeroplane...

Thankfully Pete hasn't had to waste any of his time 

(I jest: I enjoy this stuff and appreciate that not everyone is in to it. But I do think trying to understand what's happening in model flight is worthwhile. The purpose of calculating any metric is to give further insight, not a firm conclusion or prediction.)

[Pete Fardell]

Jon- understood. I just meant that your calculations were, as ever,  very helpful in giving me ball park figures with a view to making trimming easier in that particular regard.

[Slowmatch]

Thanks Pete, we are on the same page always happy to help... As long as it's helpful and not tedious.

[Prosper]

Bill, are you sure you don't make so many models that you forget one or two? Y'see that Halberstadt tail doesn't look small to me. . . but I'm sure you posted a picture of a [? Morane?] on HPA which had a tailplane size that was scarily small. Oh well - just a false memory perhaps.

Fair enough, Jon. I tend to think that formulae where one just plugs in numbers are expressly designed so that people don't have to think. P'raps there are calculators now that take account of propwash, aerofoil section, plan outline, wing downwash, wing wake, fuselage shape, and more. . .these are the things that I bring to mind regarding tail size. I think I've said this before on the MIA part of the forums so I'll shut up now .

Thanks for the thread Pete. I look forward to another model oozing with character!

Stephen.

[billdennis747]

Stephen, I admit that I've got to the stage where I decide to go and do something and forget what it is by the time I'm out the door. But I've never done a Morane.
I had built a previous Halb with a scale tail and it was the only model I've built where it really was untrimmable. The tail   would have been just as effective if I'd left it at home. I don't fear small tails, or low dihedral for that matter. That Halb I showed here I enlarged far too much and could come down 30% I'm sure. But it did fly well.
Rotten video:
https://studio.youtube.com/video/usIO1ylK324/edit

[Slowmatch]

Fair enough, Jon.

With apologies to Pete for the further hijack, I'll answer this Stephen because I think we are still in the realms of good faith/useful discussion and what you just said helped me understand where you are coming from. (Although I have to be honest your dismissive comment made me feel rather glum initially.)

I tend to think that formulae where one just plugs in numbers are expressly designed so that people don't have to think.

Perhaps my use of the word calculator has obfuscated things. I'm not talking about the kind of 'design it for you' tools you can find online. Tail volume is a physical measurement or a metric just like wing aspect ratio or wing loading. It's objective. It describes the area and disposition of the tail in relation to the wing. That's it. The 'calculator' is one of John Barker's files that allows me to quickly work it out from model dimensions.

The interpretation of the metric is where things get more subjective. My explanation of those numbers is based on experience, understanding the metric and relating it to models I have flown and with adjustment and consideration for the other factors you mention.

If you take wing loading as a different example: If I post to say my peanut model has a 0.8g/in2 loading you understand what that means in practice and would likely raise a red flag for me. In actual fact wing loading is completely arbitrary and fuzzy when you get into it. Do you include the area within the fuselage? What about LEX's? The lift distribution isn't equally distributed anyway so the assumption is fundamentally flawed. However we make an agreed convention and come up with a number that is approximate but still very helpful. You don't refuse to weigh your model because you can't be totally accurate.

P'raps there are calculators now that take account of propwash, aerofoil section, plan outline, wing downwash, wing wake, fuselage shape, and more. . .these are the things that I bring to mind regarding tail size....

A metric like Tail Volume or Wing Loading is a baseline, it doesn't attempt to factor in all the things you mention but it is meaningful in context. But you are absolutely right to keep those other factors in mind, and providing you're well informed, you realise how the un-calculatable* stuff might swing in your favour for free flight or not. For example a T-tail will be more effecient due to being out of the wing wake and so a lower tail volume might be ok.

I understand that not everyone is interested in putting the brain work into this stuff and I do really try to limit what I post these days. However I do think some of these concepts are useful when considered in the practical context that makes them meaningful.


* I say un-calculatable: all of those things CAN be calculated if you are prepared to go into degree level flight dynamics (!) with the possible exception of fuselage interactions which even full size designers tend to need tunnel and flight testing to perfect. Do you need to? No.

... I'll shut up now .

Me too, off to build something... 

[Richard Hewitt]

Where do these formulae for "tail volume" etc come from please? All too often, they refer to the distance from some arbitrary percentage of the wing chord, which pre-supposes the CG sited at that point. The tail moment varies with the distance of the tailplane FROM THE CG, not from the wing (necessarily).

[Prosper]

Me too, off to build something... 

Cheers, Jon.

I had built a previous Halb with a scale tail and it was the only model I've built where it really was untrimmable. . .

Yesss! So I'm not going mad after all. A Halberstadt not a Morane though. I'm sorry but unsurprised to hear it couldn't be trimmed.  I couldn't see the video you link to in your post - dunno if it's the link or my PC. Can others see it?

Stephen.

[Slowmatch]

Where do these formulae for "tail volume" etc come from please?

For reference the Horizontal Tail Volume formula is:

Vh = (Sh * lh) / (S * c)

meaning: Tail Volume = (Tailplane Area x Tail Moment Arm)/(Wing Area x Wing Chord)

This formula just describes the relationship we already understand from experience: increasing the tail area and moment arm (the terms of the numerator on the left) increases the relative tail effectiveness, while increasing the wing area and chord (the denominator on the right) decreases the tails effectiveness. What it does give us however is the ability to quantify the effect of these changes to the tailplane.

Ref:
https://ocw.mit.edu/courses/16-01-unified-engineering-i-ii-iii-iv-fall-2005-spring-2006/resources/spl8/

...All too often, they refer to the distance from some arbitrary percentage of the wing chord, which pre-supposes the CG sited at that point. The tail moment varies with the distance of the tailplane FROM THE CG, not from the wing (necessarily).

Richard, you are correct and I do regularly make this point. The tail moment arm (lh) should be measured from the CG to the aerodynamic centre of the tailplane. This is assumed to be at 0.25 of the tail mean chord. This is accurate in the sense that in real-life flight, the 'pivot point' for all forces is the CG in three dimensions.

Obviously, this then means that you need to have a reasonable estimate of CG position at an early design stage. Hepcat's calulator is one of the few that does this the correct way with a full Neutral Point calculation, giving you the CG, Static Margin and Tail Volume.

Many online Vh calculators use the aero center of the wing as an analog for the CG, assuming that the CG will be at 25% of the mean wing chord. This approach is actually advocated in some full size design literature because the CG most full size aircraft of conventional layout will end up very close to 25%. So it's another fudge, but one that is probably good enough for conventional scale models.

However, this approach gets you into trouble where the tail plane is considerably bigger or smaller. An example would be duration power models where the tail volume is Vh1.0 or even 1.2 and the CG way back at 80-90% of the chord. In that case you do have much shorter moment than the CG 25% fudge assumes.

The McCombs version (not a fan!) uses the wing leading edge to tail leading edge which introduces a fair bit more error and comes up with some whacky numbers. https://www.flyingacesclub.com/PFFT/TailVolumeCalculation.pdf


Tail Volume itself is not a difficult formula to use - what is difficult, or at least time consuming, is working out the Mean Chords for swept or multipanel wings and tails and getting the CG. This is where Hepcat's calculator is so helpful: you put in the basic aircraft geometry and it does the tedius bit for you.

Unfortunately John B never published his file online but there is an excellent detailed calculator by an aerodynamicist named Dan Prosser here: https://www.rcgroups.com/forums/showthread.php?1106300-Yet-another-CG-Calculator It has a slightly steeper learning curve but is detailed and accurate, and handles multi-panel wings and biplanes.

I suppose all of these methods have some value and being consistent is more important that excessive pursuit of accuracy. I personally wouldn't use McCombs. I might occaisionally use the 0.25 wing chord for a quick check on a conventional lay out to see if a scale model will 'work' but for everything I've built I use Hepcat's or Dan Prosser's and I've never yet had a model that was far off their predictions. None of them are perfect but used in conjunction with practical experience they can tell you a lot more than simply eyeballing or guessing alone. Eyeballing can work too but does require you to have vast experience like Bill!

[Richard Hewitt]

OK, thanks Slowmatch for the explanation. I'm surprised to see wing chord appearing to the power of two in the denominator - do lower-aspect ratio wings produce more downwash?

I wonder if there is any "magic formula" explaining how the demand for tail volume reduces as the CG is moved away from the centre-of-lift of the wing? Because, this is why parasol-wing types such as the Morane (the Westland Widgeon is another example) can fly safely with apparently under-sized tailplanes; with their wings raised well away from the CG, the downwash is less effective in producing a nose-down pitching moment, hence, less need for tail volume.

[Slowmatch]

OK, thanks Slowmatch for the explanation. I'm surprised to see wing chord appearing to the power of two in the denominator - do lower-aspect ratio wings produce more downwash?

Yeah, you could rearrange it to give

Vh = (Sh * lh) / (b * c²)

Yes, low aspect ratio means more downwash, but I'm not sure that's the only mechanism behind the change in tail effectiveness. If you keep wing area, tail area and moment arm constant but increase span (b) to give greater aspect ratio and shorter chord, the the 'same' tail becomes more effective. High aspect wings have a greater aoa sensitivity (steeper lift slope) and you are also making the tail arm longer in relation to the chord (significant for dynamic stability) so there's a few things going on.

I use lh/c as another helpful metric. I look for a tail moment arm that is from 2.5 to 3.5 times the chord. When it gets lower than 2 I'd be wary of dynamic longitudinal stability issues. This was evident on my Bostonian BD5 which had a large tail volume but on a very short tail moment arm and lots of inertia in a long nose. It had some real phugoid problems.

I wonder if there is any "magic formula" explaining how the demand for tail volume reduces as the CG is moved away from the centre-of-lift of the wing? Because, this is why parasol-wing types such as the Morane (the Westland Widgeon is another example) can fly safely with apparently under-sized tailplanes; with their wings raised well away from the CG, the downwash is less effective in producing a nose-down pitching moment, hence, less need for tail volume.

I presume you mean moving the vertical CG? As I understand it, the wing pitching contribution is a moment independent of the reference point (the CG) rather than a force acting at a distance. The parasol effect you describe is real but I think it's attributable to the drag of the wing acting above the CG to provide a nose up pitching moment rather than the Cm of the wing. This effect is not accounted for in Tail Volume, it's one of the extra factors that you need to be aware of and make allowances for.

The moments to trim equation is shown in the attachment from Perkins and Hage p215 http://wpage.unina.it/fabrnico/DIDATTICA/PGV/Appunti_Teoria/PERKINS.pdf (red text mine.) It includes the moment arising from wing drag acting in the vertical Z axis. Wing Pitching Moment C_mac is there but does not need adjusting for the distance of the wing to the CG. I think downwash and wake effects would be dealt with in the the tail efficiency term n_t.


Sorry Pete, way down the rabbit hole now... but one tenously on topic point: Richard is right in mentioning that parasol's high wings bring a slight benefit to tail effectiveness and so you may have that nuance in your favour for a smaller tailplane on the Morane P.

[Richard Hewitt]

Thanks Slowmatch. It seems that the deeper we try and dig into these issues the more complex they get. I think we should let Pete have his thread back now, or he will have finished his model without us...