Bleriot XI

[Jon H]

Yes exactly, although an APC 20x8 will match the master in terms of rpm but will thrash it in terms of performance. And a graupner Gsonic will go even faster but still pull well, although it will be noisy.

Props really can be a minefield

[Don Fry]

My tuppence worth, this is a one speed airframe, slow, and would not a 4 inch pitch suit it, possibly a 10x4, or a 9x4 spinning freely. And no one has clarified what constitutes a soft grass field. Poor moter may not have a chance, what else works OK off this surface.

[Jon H]

11x4 might work. 9 or 10x4 the engine would be revving its bits off. if I remember rightly I got about 10k on the master 10x5 and it didn't really want to be any faster than that

[Birgir]

Thank you all for this discussion, it is very informative for me at least.

The props I have been using are all robbe, dynamic, I have now tested five different props. 9*4, 9*5, 9*6 and this morning 10*4 and 10*5. Using my primitive rubber band, stationary, bench testing the 9*5 and 10*4 give the best result. The 9*4 went up to 12.000 rpm and is probably indicating that it is not delivering the power transmission intended. The 10*5 did 9,500 rpm and the 10*4 just over 10,000 rpm, stretching the rubber band a little more than the 9*5 did at 11,000.

I now have a „on board tachometer“ and look forward to be able to have some max rev reading after the first flights so I can compare stationary and in flight rpm.

Although I find these experiments and testing quite fun and at the same time helping me to understand the complex matter of prop sizes and pitch I think that probably Donald Fry is right. The main problem is the airfield. We have been cutting it very close and not putting any fertilizer in, so now we have the problem of soft moss taking over the grass. I believe that from a proper airfield I could get the model up to suitable take off speed without a problem.

B.

[Jon H]

Don't forget the performance of all of your props will change once you get in the air

[Birgir]

Exactly, - and that is the reason for onboard tachometer ☺

[Jon H]

you are confusing rpm with thrust. They are totally different things. The tacho will tell you which prop unloads the most in flight but not how well it pulls your model. Only your feeling of performance will do that.

At Laser we have no idea what rpm our engines do in the air as its really not at all important

[Birgir]

Posted by David Germany on 28/06/2016 21:10:06:

We have our club Model Of The Year competition this coming Sunday and I was hoping to enter the Bleriot, only problem is that a condition of entry is that the model has flown previously or flies on the day. We'll have to wait and see.

David

How is the outlook – will you be able to enter the competition on Sunday?

B

[Birgir]

Dear friends

I agree that wooden prop will be more scale like on a Bleriot so I tried to order the Zinger props that Jon pointed out to me. But Brian at Elite Models tells me that the production has stopped and they are out of stock.

So I‘ve ordered a Turnigy Type A Beech Wood Propeller from Hobby King. **LINK**

They look similar to me. Do you think that those props are suitable?

I‘ve ordered 9x5 and 10x4.

B.

[Jon H]

Those type A props run really fast. you will need probably an 11x5. I use a 13x5 on my saito 45 because they run so fast. That's a good inch more than the saito can normally handle

I have even run the type A 15x5 on an enya 53 4 stroke and still got 8500rpm. They really do run fast as they are super thin so add at least an inch in diameter compared to what you would normally use.

Edited By Jon Harper - Laser Engines on 02/07/2016 15:48:55

[Birgir]

Thanks Jon I´ll bear that in mind.

The good news is that the municipality has just finished building a cycle-path next to our airfield and it looks good enough to be used as extra runway for us.

I might try that on the next calm day 

B.

Edited By Birgir on 02/07/2016 17:58:10

[Jon H]

You should paint some threshold markings on it

[Birgir]

Just for your amusement I put together a 5 min video of my first, failed flight attempt - enjoy!

[Phil 9]

nice video. not exactly a no fuss set up

[J D 8]

Aircraft of this era do very much need to take off directly into wind, [and land into wind] anything else is difficult as they want to naturaly turn into it.

The fact there is no fin and the rudder is rather small does not help. Watch full size a Bleriot and you will see the rudder moving a lot [flapping all over the place] as the pilot try's to keep control. The later Vickers version has much larger rudder.

The drag of a tail skid [my version has one] may help keep it going in the right direction.

Short grass and directly into wind would help a lot. Good luck on the next attempt.

[Jon H]

you looked about 90% of the way there! but yes, more into wind will be better for you. Also the engine really was thrashing itself mad without really giving the power it needed. Prop change as discussed will help.

I don't know if I missed it, but how heavy is the model?

[Birgir]

Well, to be on the safe side for the CoG I added extra 200 gr of lead up front making it total of 800 gr. That included the total weight of the model is 2,950 gr.

With the right prop and a hard surface, I'm still pretty convinced that I can get it airborne.

B.

[Jon H]

6.5lbs is a bit porky for a model of this type with that size engine but it will go. It will just be very scale in its climb performance. I suggest the longest takeoff run you can manage and then ease it up, once in the air it should accelerate better

[Keith Evans 3]

Just looking at the video(very nice ) would more air in the tyres be of any help .They looked quite flat in the rigging stage .

Best of luck with it .

[David Germany]

Good news & bad news Birgir, Picked up 2 prizes for the Bleriot on Sunday, and then pranged it just after take-off. Took a very long run straight into wind but did not lift off on it's own. With a bit more power and some up it did lift off but felt alarmingly unstable, like it was seriously tail heavy. I elected to try and stall into a narrow band of long meadow grass just over the fence, which it did without too much forward speed. On reaching the scene we found that the 4 spruce rear longerons had cracked allowing the tail end to collapse. Looked a mess but no other damage, everything else intact.

Unfortunately didn't get any video to analyse, but I think a better pilot than me would probably have a) saved it, or b) not flown it.

Anyway, damage is done, need to move forward.Have decided that the rebuild will be much lighter.

By the way, I spoke to Mick Reeves of Mick Reeves Models today as they supply plans for various sizes of the Bleriot, he says that the c of g needs to be at the very least 30% back, probably quite a bit more, and use delicate elevator to control pitching. The model should lift off reasonably quickly, not too fast. Keeping the c of g back helps keep the overall weight down. Should have spoken to him before !

David

[Birgir]

Congratulations on the prizes David. You say 2 prizes, in which categories where those prizes?

Sorry about your mishap but remember Luis didn’t succeed in his first try either. Thanks for the detailed descriptions it helps me a lot to prepare for the first take-off – and the first setback probably too. As you say it seem to have no major damage and I’m sure you can find a way to put the longerons together again without too much gain in weight.

Am I understanding you correctly when you say “at least 30% back” you mean 30% of the cord of the wing, i.e. 30% of 34 cm that is 10 cm, or more. More being more tail heavy?. (Bear with me, English is not my first language)

As you can read in my earlier posts here, I’ve added 200 gr extra to the front to get the CoG point from about 11 cm to about 10 cm back from the leading edge of the wing making the model 2950gr (A bit porky ) Maybe that is not wise after all.

After looking at the pictures in you album it looks to me as the ballast is at the top of the “engine room”. Could it be better to lower it as much as you can to make the model more stable left-right? Did you have any time to experience if the wing warping system is doing its job?

PS.
Thanks Keith, but the wheels are made from foam band and are not really inflated. But probably a little too soft. The making of the spoked wheels is explained (in Icelandic) at : **LINK**

PPS:
„An expert is a person who has made all the mistakes that can be made“ - Niels Bohr

B.

[David Germany]

Best Electric Model and second in Scale (beaten by a dastardly Eindecker).

I had the wing warping disabled and was flying normal rudder / elevator, so I don't know about the effectiveness, but it looks really cool waggling the wings on the ground.

According to Mick Reeves the C og G "will be a lot further back than you expect", the model will be sensitive to elevator, its more a case of trimming the elevator to achieve level flight and leaving it at that, just minor changes to elevator and throttle in flight. Yes at least 30% of chord back from leading edge (102mm), 35% would be 120mm.

By the way Birgir I've used solid neoprene cord for the tyres, it's very flexible but quite dense, even at my 3.1 Kg they don't deform.

I've given the matter some thought today and have decided that the model must lose some serious weight so I'm considering the following:-

• Move C of G back 120mm from leading edge
• Remove wing warping mechanism (at least initially).
• Replace full size servos with 15 - 20 gm units.
• Move servos forward into the next bay.
• Move the ESC forward into the engine bay.
• Move motor forward by about 20mm and construct dummy aluminium cowl as per some original variants. (I'll do this after checking the results of the previous mods).

Unfortunately the strengthening to the repaired rear fuselage will add some weight in the wrong place but I'll try to keep it to a minimum.

Extract from the Wikipedia entry for the Bleriot IX " The Blériot IX was exhibited at the Paris Motor Show in December 1908, but the design proved overweight and could not be made to leave the ground.".

[Birgir]

David, I think you have come up with a very solid plan and I look forward to hear about the result.

I will try to learn from you and have decided to do the following

1. Skip the extra 200 gr leaving the CoG at 33%

2. Skip the on-board tachometer

3. Leave Luis on the ground for the initial flight.

This will probably loose about 250 gr of weight.

By the way, in what kind of stores can you expect to find neoprene cord, what is it used for normally?

I will leave for Glasgow tomorrow morning so more tests must wait until next week.

B.

[David Germany]

Birgir, I usually get mine on eBay, look for someone who will sell by the meter. I've used 12.7mm on the Bleriot. You may want to use Nitrile if your exhaust is ahead of the wheels as this is oil resistant.

David

[David Germany]

Birgir, The Bleriot is now repaired and the ready to fly weight with 2 x 2200 4S lipo's is now 2500g. (5.5 lb), that works out at 16 oz/sq.ft. Much more realistic I think. By the way how have you set up your transmitter with respect of the rudder control ? i.e. rudder and elevator on the same stick, or on separate sticks.

David