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Dealing with Tailsitters

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smeg1959
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Dealing with Tailsitters

#1

Post by smeg1959 »

A query following a recent completion, the F-Toys' P-39Q. With such a pronounced "nose up" attitude thanks to its very high nosewheel leg, the Airacobra is always going to be a strong candidate for "tail sitting", so much so that F-Toys include a little clear plastic support to hold the tail up. Well, having always had success with chopped-up pieces of lead sinker, I stacked the nose to the point where I had to modify the supplied instrument panel to maximise the volume available. Almost all in vain, I'm afraid. Yes, the P-39Q will sit with its nosewheel in contact with the ground but the balance is so tenuous that the slightest movement sends its tail hurtling downwards! :(

With other F-Toys' P-39's and a recently acquired ARII P-63 kit sitting awaiting construction, are there any other suggestions for combatting the tailsitter syndrome? Mercury would be the go if it wasn't a liquid and extremely toxic to boot! :shock:
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Jonathan
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Re: Dealing with Tailsitters

#2

Post by Jonathan »

Lead is the heaviest ballast commonly available. There is Tungsten, but the malleable paste form is actually less dense than lead.
Taken logically, :geek: the other options are to cant the main gear backward or move the mounting holes aft, a tiny bit might not be noticeable, and it probobly wont take much...
Lastly, look at how you can remove weight from the tail- not always possible, but sometimes there are some very thick or even solid sections that can be scarfed or drilled.

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MerlinJones
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Re: Dealing with Tailsitters

#3

Post by MerlinJones »

Where you actually have a space to fill, no matter how small, I cannot recommend Liquid Gravity highly enough;

http://www.deluxematerials.com/newitems.html

Essentially, this is tiny balls of a lead-like substance, that fills up every nook and cranny you pour it into. You then add liquid superglue to set it in place.

Failing that, I'd suggest Tacky Wax;

http://www.deluxematerials.com/products ... urist.html

It is as it sounds it is. A tiny blob will hold most nose wheels down.

Before I doscovered these products, I was resorting to short lengths of clear acrylic, or clear sprue.

Regards,
Bruce
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spejic
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Re: Dealing with Tailsitters

#4

Post by spejic »

There is a "cuttable" tungsten weight that can be sometimes be found where pine-car derby stuff is sold. That one is more dense than lead. Saw off slices with a fine saw and then chop that up into pieces that can fit in the model. I use some form of epoxy to glue it in.

Use any space in front of the center of gravity to add weight, such as engine booms or inside wings. Thin down the sides and internal parts, and cut out structural things like pins to make more space for weight. I've even put weight in the propeller nose cone. If it's hollow, make it more hollow and put in weight. You can also thin out some parts in the rear of the aircraft to help.
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MerlinJones
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Re: Dealing with Tailsitters

#5

Post by MerlinJones »

Another thing that I've done is to use thin lead sheet for nose gear doors.

...And then there's always lead paint! :mrgreen:
It's my madness that keeps me sane.
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smeg1959
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Re: Dealing with Tailsitters

#6

Post by smeg1959 »

Many thanks for the feedback, everyone! :D

I hadn't thought of thinning down the back end of the model, so well worth consideration. Not that there's a helluva lot to prune from the P-39Q anyway. Bruce, I checked out the YouTube presentation on Liquid Gravity and will order a bottle from evilBay, as no-one here in Oz appears to stock it. And spejic, you are right about tungsten - it is more than 50% denser than lead. I will try and find the cuttable variety you mentioned.

Not having glued the canopy (it is a really secure push-fit), and depending upon the exact centre of gravity of the P-39Q, I may yet be able to fashion a pilot figure out of this cuttable tungsten or Liquid Gravity (!) and stick him in the cockpit of my completed Airacobra. Or simply stick some Liquid Gravity balls on the floor of the cockpit.
OTB ...
GB13 - Late 298 (Aeronavale), Bf109E-3a Strela (Bulgarian AF), ČKD LT vz.38 Praga (Slovakian Army)

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spejic
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Re: Dealing with Tailsitters

#7

Post by spejic »

smeg1959 wrote:And spejic, you are right about tungsten - it is more than 50% denser than lead. I will try and find the cuttable variety you mentioned.
Here is the product I mentioned:
http://pinecar.woodlandscenics.com/show ... 923/page/1

It's tungsten mixed with something, so it isn't as heavy as pure tungsten, but it's pretty dense. And you can't even buy lead here in California - the regular pine car and fishing weights here are zinc alloy, which aren't really close to lead in density.
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smeg1959
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Re: Dealing with Tailsitters

#8

Post by smeg1959 »

Thanks for the link, spejic. It is worth considering as I have found the Algernon Product Catalina is an even worse tailsitter than the Airacobra! I should add that there is a ready-made white metal conversion for the Minicraft kit of the PBY-5A that would solve the problem, at least as far as the Catalina goes.

In terms of other alternatives, some bright spark on the Fine Scale Modeler forum suggested osmium, the densest metal in the entire Periodic Table. Only problem is that it is also the scarcest metal on the planet, so costs a packet. One evilBay outlet has osmium pellets advertised at $US55 for 1 gram. Would certainly add to your bottom line for a $US10 model! :twisted:
OTB ...
GB13 - Late 298 (Aeronavale), Bf109E-3a Strela (Bulgarian AF), ČKD LT vz.38 Praga (Slovakian Army)

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glehn
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Re: Dealing with Tailsitters

#9

Post by glehn »

I had similar problems with my Amodel An-72. I did not put enough weight on its nose and it would sit ok on all wheels but the slightest breeze would take it off balance. I just noticed it after the model was ready, so I chose to just glue it to its base.

Regards,
Luis

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erix700
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Re: Dealing with Tailsitters

#10

Post by erix700 »

Thin solder wire works great for last minute fixes: just drill a small hole at an inconspicuous place in the front fuselage and insert enough solder wire to restore balance, then use a sharp knife blade to cut off the wire flush with the surface (should leave a smooth surface) and touch up any paint.

HTH,
-- Eric.

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