Heavier or bigger for a breezy day trainer|?

[Chuck Plains]

I'm enjoying building my own ideas in insulation foam and art board at the moment. And trying to learn to fly in a field (with BMFA cover).

Now, my 30" foamy has not completely destroyed itself yet, just partly, and a bunch of hot glue has sorted it several times. But it is tricky during these windy days we've been having recently. Yeah, it's March. Even so, "I will fly if it's dry", has become my motto, believing that stick time will eventually bring about the cure.

So is bigger better? Or heavier, or both at once? I'm guessing that scale planes fly in far stronger than scale winds, but even so, a 500gm sort of Cub copy is really a light wind affair. So can I add weight and improve flyability in 15mph+, or do I need to move up the scale and rely on the extra size bringing weight with it anyway.

I realise that just adding weight will increase landing speeds. And I don't really do much 'landing' yet.

But if size and weight will enhance flyability, I shall take that route, just to keep me out there.

[riverlandgirl.]

Hi Chuck. The way I see it..... higher wing loading, 25 oz plus, good power loading, 1.5 to 1, low drag and yes bigger, its going to fly faster, be harder to see, use up a lot more sky, and run way!

[Biggles' Elder Brother - Moderator]

You can go different ways here Chuck to end up in the same place.

The key to stability in the wind is momentum! The more momentum your model has the less it will be blown about by the wind. So how do you get some of this magic stuff? Well an object's momentum is equal to its mass times its velocity - the more you can maximise that the better the model will fly in the wind.

So, let's consider a 4Kg model flying at 20m/s - its momentum would be 80 Kgm/s - quite a lot, it would hardly even notice a 15mph wind!

But a 0.5kg model travelling at 160m/s would also have a momentum of 80Kgm/s and so would fair just as well! But 160m/s is about 300mph!

And there we have our problem! While in principle its possible to generate sufficient momentum to overcome wind buffeting of a light model via speed - it isn't really practical - we'd end up having to go far too fast!

But if we just go for extra weight to get our additional momentum then we have to lift that weight and if you're going to do that with reasonable flying speeds - you need wing area to keep the wing loading reasonable. So the "solution" is a large heavy model. I'm afraid that for coping with wind - there is no real substitute for size and weight! So simply adding weight to a small model will not benefit you that much. I suppose its an example of "a good big un will always beat a good little un"!

Of course flying skill can considerably extend the wind range in which a model can fly. But there is still no question that a small light model will reach its limits - no matter how good the pilot - before a big heavier one will.

BEB

Edited By Biggles' Elder Brother - Moderator on 08/04/2013 11:26:26

Edited By Biggles' Elder Brother - Moderator on 08/04/2013 15:33:16

[Myron Beaumont]

Is it I wonder a question of whether the wind is apparently "gustier" or less predictable when stronger & that a heavier model will not perhaps be tossed around so much ?.Depends on the flying site partially of course. The amount of drag on certain types comes into it as well .A sleek powerful design certainly will plough through gusts better than say an ultra lightweight glider .

Weather is what we learn to fly in isn't it ---The most unpredictable variable parameter which is what it's all about .Of course ,if you're into sloap soaring then you add ballast around or below the C of G for penetration . Just my thoughts !

[Seraph]

BEB,

you meant Momentum is MassxVelocity, of course.

However, I would argue that an aircraft will resist disturbing forces by virtue of its INERTIA. Ie. it's MASS. The effect of the disturbing influence will be to change its Velocity. (Pt=mV-mU)

Hence the heavier a model, the less it will be disturbed by gusts - so just add weight.

That brings us back to the point you rightly made that the heavier model will need to fly faster to develop the necessary lift.

[crispin church]

in very windy + 25mph for get foamy

4 foot plus wing span 2.5kg plus

low wing or biplane

[The Wright Stuff]

Hi Seraph,

Agreed that inertia is the thing that governs how much the absolute velocity will change from a given force, but I think BEB has a point that it's momentum that will govern the apparent 'stability' from the R/C pilot's perspective (i.e. to blow it off course by a fixed angle will require a larger force if the plane is travelling faster). In other words, we are considering velocity changes as a proportion of the model's existing forward velocity.

However the end conclusion is the same: heavier model = faster model!

One final point, another important factor is the fuselage shape and size. I learnt on a old Precedent T180 trainer. Big and heavy, maybe, but it was also a handful in the wind because the side of the fuselage was huge, so any given crosswind pressure could exert a lot of force!

[David Davis]

Nice big eight-foot 10 lb Senior Telemaster. 6S LiPo like the battery in a diesel truck. 450 KV motor. 20 inch prop.

Fly in anything!

[John Muir]

As I think everybody who has responded knows, but maybe not said (except Myron) it's not the windspeed that's the issue, it's the turbulence, and stability through turbulence. My Wild Thing weighs 27oz and flies quite happily in winds of over 30 mph, so long as I can get it off the hillside in the first place. So the answer might be an electric EPP wing. Chuck it up and get it out of the rough air near the ground ASAP and it'll fly fine higher up so long as the windspeed doesn't exceed the maximum airspeed of the model, in which case you'll have a long walk to find it. Land with plenty of speed on and don't try to be elegant, just plonk it down. EPP bounces.

Or go slope soaring of course.

BTW my Wild Thing has a wing loading around 7 oz/sq ft and it certainly gets bounced around in turbulence near the edge a lot, so everything said earlier I'd have to agree with, but the point is it doesn't matter.

John.

[Biggles' Elder Brother - Moderator]

Seraph - thanks yes I did indeed of course mean "mass times velocity" and I've edited accordingly.

You are correct in that inertia is key - hence why mass is in there at all. But in terms of stability it is really momentum. You see a very light model travelling very fast will exhibit greater stability than a light model travelling slowly - its got the same inertia, but different momentum. That's why you can fly say a Stryker in a quite a strong wind and it seems OK, but you can't fly say an Extra of the same weight in the same wind so easily.

Myron's comment is spot on in that a steady wind - even if quite strong - is a lot easy to deal with of course than a gusty wind - especially if its a cross wind!

BEB

[Chuck Plains]

HEHE! Now I get it. Look at myself in a mirror and model the plane on that! 70" span and 230lbs!! Now, what fuel to use? Baked beans!!

Hmm, the wind is forecast to drop to 8mph tomorrow, so I'll give it another go after work with my beater foamy. All I have is foam actually, and my secodary prob is the field has an odd surface that breaks as soon as you touch it. Sort of dusty down to at least 1 inch.

I will talk to my LMS, as he always has some used wings available, and this weather isn't going to let up for some time. Of course if I sort out a heavier machine and spend some wonga, the weather is bound to improve. And vice versa! Captain Murphy will likely be my pilot.

[Chuck Plains]

Posted by Biggles' Elder Brother - Moderator on 08/04/2013 15:39:21:

Seraph - thanks yes I did indeed of course mean "mass times velocity" and I've edited accordingly.

You are correct in that inertia is key - hence why mass is in there at all. But in terms of stability it is really momentum. You see a very light model travelling very fast will exhibit greater stability than a light model travelling slowly - its got the same inertia, but different momentum. That's why you can fly say a Stryker in a quite a strong wind and it seems OK, but you can't fly say an Extra of the same weight in the same wind so easily.

Myron's comment is spot on in that a steady wind - even if quite strong - is a lot easy to deal with of course than a gusty wind - especially if its a cross wind!

BEB

A steady wind BEB? Hmm, this is 8 miles inland in a field in the River Exe valley I'm talking about.

As it happens, I've flown kites all over the south during the last 20 years, and have never found steady wind apart from at various beaches when it's direct onshore. Camber Sands for instance! But now that I've just checked our area's forecast again, the wind is veering round to NW on Tues PM. And although it's lighter, it's not a good direction for that spot. Nearby trees and adjacent hills etc. Oh well, I am working my way through 10 cheapie props from ebay. You know, those orange ones.

Anyway, no matter the weight or materials of the plane, I will make a pusher next.

[PatMc]

Posted by The Wright Stuff on 08/04/2013 14:14:49:

One final point, another important factor is the fuselage shape and size. I learnt on a old Precedent T180 trainer. Big and heavy, maybe, but it was also a handful in the wind because the side of the fuselage was huge, so any given crosswind pressure could exert a lot of force!

The amount of side area isn't a factor in a crosswind.

[Ian Skeldon 1]

Something that doesn't seem to have been covered here is that a bigger model appears to fly slower, it isn't of course but because it's size allows better orintation you can fly it in more space and thus it gives you more time to nail that final approach and just add small corrections until roundout.

I teach new flyers at our club and always get them to start with something of at least 50inch wing span and a good 40 - 50 size engine, my personal preference is the seagull arising star, it flies well in gusty conditions and can take a bit of extra weight on really bad days. Also it will fly on just rudder really well if you are currently using 3 channel set up. There are probably lots of other artfs out there but this is the one I have got several newbies away with.

HTH

Ian

[Biggles' Elder Brother - Moderator]

I totally agree Ian. Lately quite a few learners are turning up with very small foamies - 20-30" span. They buy them because (not unreasonably) they think a smaller model will be easier for them to learn with. But of course as we all know - it isn't the case! They would be far better off with 50-60" span trainer that would be steadier and easier for them to see at distance.

BEB

Edited By Biggles' Elder Brother - Moderator on 09/04/2013 22:13:04

[The Wright Stuff]

Posted by PatMc on 09/04/2013 21:23:28:

Posted by The Wright Stuff on 08/04/2013 14:14:49:

One final point, another important factor is the fuselage shape and size. I learnt on a old Precedent T180 trainer. Big and heavy, maybe, but it was also a handful in the wind because the side of the fuselage was huge, so any given crosswind pressure could exert a lot of force!

The amount of side area isn't a factor in a crosswind.

Hi Pat,

Interesting point - I guess almost a topic in it's own right - but I'm interested to understand further. I agree that in a steady state crosswind, the plane is moving sideways at the same rate as the wind, so you are correct - there is no resultant pressure. However, talking about stability turning in and out of the wind, or in blustery conditions, it would matter, surely, because a slim fuselage would act to 'damp out' sudden changes in sideways pressure in exactly the same way that the inertia from a heavier plane would do!

If this is off-topic, I apologise! I'm not being argumentative - just interested to understand.

Cheers

[Chuck Plains]

Thanks for all your interest and comments guys.

I already have a Max Thrust Riot, (xmas pressy to self) and flew it at the club patch, with another member doing the take off and landing duties. And, of course she was excellent. But my current pactice location is a bit too rough and loose for me to want to risk a £130 plane that relies on landing gear. So I have retired my 30" DIY trainer and purchased the new 1.5mtr span Bixler 2. I know it's probably only goint to weigh around 2lbs, but all the video evidence points to good stability in various conditions.

And, taking into consideration what PatMc said, I reckon the Bixler's slippery fuselage shape may help to resist some of that sideways shove. Anyhow, I would have bought one last year if they had been available. But I bought the Riot so that my buddies at the club could feel more comfortable training me wihtout having to worry about the vagaries of a home made thingamabob. Even though it clearly contains sparks of genius.

I will be bash proofing the Bixler in relavent areas with plenty of that reinforced strapping tape, wing skids etc, and I have some 4000mah 3s packs that could help with the weight if necessary. Hmm, probably fly for an hour with one of those jobbies!