Blohm and Voss BV215 build blog

[Grasshopper]

Jozef,

 

I had 160 Watts or so per lb which is crazy for something like this on its maiden. Also the control throws were more than double those I now have set - ready for the 'next' maiden. I have gone down to a 2S and set the maximum power at 85 Watts.

 

I don't think you can test glide something like this. A glider or motor glider - yes, I do it every time but normally flying wings need a bit of speed or they simply plough into the turf.

Erflog - yes you are correct about thrust lines but with this model there was a plan error (on the rear/prop end) and as I had built mine before this came too light I more or less had to accept what I had in my hand so to speak!

 

I hope to test mine at the end of the week and will post the results.

 

Peter

[Grasshopper]

Jozef - can you help please with the C of G.

 

If you look at my post to Glenno (20.6.11) I asked him to measure on the underside of the wing along the line of the fuselage from the rear of the wing to the CofG. You have completed your 215 now - can you do this measurement please and let me know the result?

 

Thanks

 

Peter

[Ernesto]

Hi,

 

I'm nearly finished as well, just got the canopy and receiver left to fit. Haven't had a chance to weigh it yet or adjust the C of G.

I'm concerned about the talk of power systems as I had originally decided to fit a 2212-6T 2200 Kv (230W) Brushless Outrunner Motor with a 4.7x4.7 prop (ideal for flying wings). After the issues Grasshopper had I'm seriously considering a reduction in power.

Glenn - you fitted a GWS P38 lightning canopy to yours, is this canopy available from a website anywhere to purchase as I'm no expert at cutting down bottles.

[Grasshopper]

Ernesto,

looks great - especially with the yellow tips to the wings!

 

With any 'plane you need only 60 -80 Watts / lb for initial test flights. My BV probably had over 130 Watts/lb which is much too much for initial testing. I now have a 2S fitted and a smaller prop which gives me 80 W/lb

 

I have your motor in an Easy Star - plus a box of props so tell me if you are on 2S or 3S and I will do a test for you. Then you just weigh the model (should be 1lb 4 oz or so) and you can work out the Watts/lb.

Can you help me please by measuring the marked position of the CofG? I need the distance measured under the wing along the fuselage side from the rear of the wing to the CofG.

 

Peter

[Jozef M]

Grasshopper!

what i can do is to measure CoG on the plan. i haven't done any marking on my depron parts. i am not sure if this is any help, but i can't do anything else. so the distance from trailing edge (the end of the wing) to the CoG on my plan is 11.7 cm .

 

Ernesto!

i really like your plane, i hope it will fly well. i took a picture for you showing my unfinished canopy. i use a piece of paper to draw lines which i simply cut with scissors.

the canopy will be assembled from 3 pieces, and i want to overlap the connection with thin 2mm piece which will imitate the canopy frame.

Edited By Jozef M on 23/06/2011 12:16:24

[Jozef M]

Ernesto, can you tell me what type of paint did you use on your model? i covered my model with tissue paper and glued it with PVA and than i applied a sanding sealer. i am not sure if this is very clever way of doing things, but humbrol spray cans tended to eat the depron out.

[Ernesto]

Jozef, I used RC Styro spray paint directly onto the foam for the base grey. It's a foam friendly paint manufactured by ghiant.

The rest of the paint was applied by brush, Revell Aqua (small square pot) which is water based so doesn't eat the foam.

Grasshopper, I didn't mark the c of g point on my plane but I will work out from the plan this evening where it should be and measure the distance.

I have a 3s lipo for the model, I haven't run the setup with my wattmeter attached yet but will probably do so this weekend.

 

Edited By Tim Mackey - Administrator on 23/06/2011 14:25:49

[Tim Mackey]

Ernesto, please read this ta.

[Grasshopper]

Thanks for the CofG measurements chaps. Yes it is 11.7cm on the plan - but for some reason on my build I had marked it forward of this which would have made it tail heavy - and very difficult to control - perhaps impossible to control!

 

I have it set at 11.7 forward from the rear edge of the wing. That is the

'flat' part of the rear edge of the wing before the angled edge which leads into the end of the elevon.

No wind here tomorrow or Saturday so this is it. I am running 2S for the test and am getting abut 85 Watts which should be fine for testing.

 

I will report back!

 

Ernesto - I will be interested to hear what you get on your Wattmeter.

 

Peter

[Grasshopper]

CofG again - and two possible values for the distance between the rear wing edge and the CofG - measured on the underside of the wing.

 

The 11.7 cm measurement - rear of wing edge to CofG is taken on the side elevation.

The wing plan measurement shows the same dimension is 12.2 cm.

 

The difference is 5mm which makes a huge difference to the weight distribution.

I am more inclined to think that 12.2 cm is the correct dimension as due to an error in the drawing of the plan the placement of bulkheads F and G is incorrect.

 

Can someone who has successfully flown the model tell us what the distance is ON THEIR MODEL on the underside of the wing between the rear wing edge and the CofG?

 

Peter

[Jozef M]

yes please if anybody had successfully flown the plane please let us know your C of G

 

Grasshopper if you will dare to fly it would it be possible to get somebody and to shoot a video and share it with us?

[Grasshopper]

Flew my B&V yesterday after a saga or two.

It was quite windy, 15-20 Kph. Opposite the flying site there is an area of grass nearly 1 metre long. Decided to use the wind to give me some added air speed and the grass as a nice cushion. I had initially rejected test glides as my previous of flying wings has shown they need good speed to glide (if at all!)

First couple of tries gave big dives to the left so I trimmed out the reflex on that elevon until it glided flat. It took 6 or 8 attempts before a somewhat soggy glide was achieved.

The long grass did its bit and saved any damage and the nice steady breeze did its bit by augmenting the air speed my launcher was able to provide with his overarm throws.

Now to the strip. I had the power limited to 110 Watts with a 2S 1800 and an APC-E 6x4 prop. The first launch resulted in a very soggy and short flight which showed it was tail heavy. I taped a 50centime coin to the nose and tried again and off she went. Even on 2/3 power it was quick and later when I opened up to the 110 Watts I had allowed, it was plenty fast enough for the first flight.

I did 3 or 4 circuits without any dramas and then went up to 80 metres or so and decided to do a loop.

This was all OK except that on exit it went into a spin and no amount of stick jiggling would get it out. Result - pancake onto the grass which broke the prop and cracked both the tip pieces.

 

All in all I was content having at last got it into the air and flying reasonably in control.

 

Now - where was the CofG during this flight? Back in the workshop I carefully checked by inserting a 1mm carbon rod through the fuselage and doing balance tests. It turned out to be at 124 mm forward from the rear edge of the wing measured along the fuselage on the underside of the wing. In this position the model will settle either nose up or down but the tendency is nose down if you get me.

 

OK - over to the folk who are waiting to test fly their models - and please let us know how you get on.

 

Peter.

 

 

 

 

 

 

 

 

 

[Ernesto]

Excellent news, glad you managed to fly it. The CofG information will be very usefull as a starting point for eveyone else. Hope the damage isn't to bad and you will be up and flying again.

 

I decided to change my motor for a 10T instead of a 6T. All up weight of my plane (minus the canopy) with a 3S 2200 battery is 529g.

 

I did a wattmeter test using an APC 7x5 prop and this gave 203W. I'm undecided as to change to a 2S pack or a 6x4 prop or just bite the bullet and let rip for the first flight.

[Grasshopper]

Ernesto,

 

with these figures you are running about 380 Watts/Kg or 175 Watts/lb. These are extremely high figures for any model and when I first flew mine on just 160 Watts/lb it was uncontrollable.

 

Basic fact is that any model will fly on 70 - 90 W/lb = 150 - 195 W/Kg. Thus for a maiden where you do not know the CofG is exactly correct or the throws on idle are perfect - if you use more than double this power you are throwing another BIG risk factor into the mix.

 

My B&V flew nicely on about 2/3 throttle - 80 Watts or so and was fast enough for me on full power of 110 Watts. Remember also that my model weighs 615g and yours just 529g so your power need is lower than mine!

 

Hope that has helped,

 

Peter

[Grasshopper]

and . . .

 

to round off my last post - it's simple.

 

Drop down to a 2S and a 6x4 and I think you will greatly increase your chances of a successful maiden.

 

Peter

[Glenno]

Hi Guys.

Sorry for not answering for a bit but I have been away recuperating.

The C of G is as follows

11.5 cm from the trailing edge where it meets the fuz.

12.8 cm for the first test flight.(forward C of G point).

There is plenty of room in the fuz to move the battery about-use a 1500mAh 3s battery. It will fly with a 2200mAh 3s battery but it is a bit heavy for it

the back plate(motor mount) is at 90 degrees to the wing- I.E- zero down/up or side thrust .

The wing tips are also set at zero degrees angle of attack. .

Throw at 3/4 throttle and open up to full throttle if needed.

Honestly the plane fly`s very well indeed. If built right there should be no dramas!! It even fly's inverted 2 feet of the deck!!

Best of luck

Glenn

 

[Patt]

Finaly flew mine last saturday. The all up weight is 600g with a 1:1 power to weight ratio and C of G at 12cm. 3mm reflex.

Launched on three quarter throttle and it went vertical once released. With full down trim on the elevator at half throttle it was still climbing and when full throttle was added in climbed at a very steep angle. This is going to need some down thrust on the motor to sort out.

Went into the first turn on the recommended low rates. Not a chance. Switched to high rates which I had some expo dialed in and this was more like what I usally fly on low rates.

The plane flew very well. Loops and rolls were nice. It even flew well on a quarter throttle and kept its altitude well. The shape can be a little disorientating at times and my colour scheme didn't help.

After 7 min I went high to try the stall out before landing. Disaster, I went out of radio range.

 

So the moral of this story is if you are thinking of buying one of the cheep orange receivers for your spektrum radio, don;t. They are not copies of AR6100. The range is on were as good. They are only any use for indoor flying.

[Grasshopper]

Flew mine today again.

10 minutes or so of reasonable flight but a little too fast for my liking. I found I had to keep the speed up or in tight turns it would drop the inside wing. This finally caught me out when the battery was getting low and I was turning into final approach.

Speed was dropping away and as I turned it just snapped into a stall - and into the ground.

 

Bin liner job - but some good fun along the way which is what counts.

 

Peter

[PlaneMike]

Greetings from Australia. Can confirm we do some flying down here. Also magazines

take a while to get here. Just completed the BV 215 from Glenn Block plans.

About a month to build, a few hours a night. Used the foam from 5mm art board,

after soaking off the cardboard. Found it difficult to bend with heat, but achieved

the desired curve with patience.

 

Flew it in gusty wind today, with C of G at 120mm from TE was OK. Just need

to let it hang slightly nose down. Elevons set at neutral, but made the wing with a

little wash out and reflex. (5mm under TE tip when gluing balsa skin). Used mainly

PVA , with 5 min epoxy to join wings together.

 

A $6 Tower-Pro motor (100w) from Hobby King, 1300 3s lipo and 7.5 x 4 prop.

Easily out-performs anything else using same motor. The AUW is 580 grams,

and it still goes vertical. Power off, it pitches down just right. Can be flown slowly,

but wallows somewhat.

 

A messy landing will wipe off a wing-tip. But easy to fix. Many thanks to Glenn for

an easy build, the measurement problems translate OK for 'about right' once

the pieces are glued, using the side view reference to how it is supposed to look.

 

The only negative comment I have is the orientation at distance. The bottom is

white mainly, glad I did that. Should have had the yellow at only one end though!

 

Thanks again Glenn for this unusual subject.

[Glenno]

Great looking BV215 Mike. Glad sombody made one that flys. I was starting to think I designed a dog!
love the paint job and the nose looks great too. I made a Sukhio SU37 with a paint job the same. Kept losing it in the turns.

finnished my new WW11 experimental twin-Mcdonnel XP 67 Moonbat.

Glenn

 

 

Edited By Tim Mackey on 06/01/2012 17:54:17

[Tim Mackey]

Glenno...that was a duff link, and wrongly inserted too mate

Have a look here please.

[Glenno]

Sorry about that Tim

finnished my WW11 experimental twin-Mcdonnel XP 67 Moonbat.

Glenn

[Erfolg]

PlaneMark

 

Your version looks really good, well done.

 

Another on my what to make list

 

As for the MacDonald, gain outstanding, particularly the use of white foam.

[PlaneMike]

Thanks for the positive comments. Was happy not to have just a wall hanging. As someone once told me, the more you practice the luckier you'll get! ...Better go out and fly again.

[Biggles' Elder Brother - Moderator]

Nice, and original, model that Glenno - looks great in the air. Glad you sorted the motor cooling problems

 

BEB