SR71 Blackbird first public show Duxford 2010

[JohnPearson]

Hi all

Just back from the LMA show at Duxford held over the weekend. Ian robb rolled out his new SR71 Blackbird turbine jet and taxied the model along the runway in front of the large crowd. The model is not allowed to fly until the test flights are completed and a CAA cert approved, which hopefully will be within the next few weeks. Ian and the team were kept very busy answering questions on the model and even met two US Air force staff who worked on the real SR71 which the model was based on.

Here are a few photos from the weekend :

http://picasaweb.google.co.uk/nijets/LMAShowDuxford201002#slideshow/5498224775483114162


Johnp

[Happy Days]

You call that a “Few” photos………….Phew!

Some very good models there, but I didn’t notice your B52 John.

Just as an aside topic.
I’ve never flown a twin or multi prop plane before but I’d always thought that the props on one wing were supposed to rotate in the opposite direction to the props on the other wing. However, looking at the models at Duxford this didn’t seem to be the case. All the propellers were pitched to rotate in the same direction.
Is it an ‘old wives tale’ I’ve been believing all these years?

Thanks for posting the pictures anyway John.

Keith

[gerryb]

hi keith,
my tuppence worth on twins...
i've flown a few twins but no 3 or 4 eng models. the sound of 2 eng's 'on song' is, i have to say, a most beautiful sound indeed. nothing at all like a single 2-stroke screaming it's head off.
twins need the same care and attention when setting up the eng's as any model, and can be just as straight forward to fly. standard eng's and prop's are used. when running, the eng's must be tuned to produce a similar exhaust note, a musical ear is a big advantage here! because both prop's are turning anti-clock when viewed from the front, thrust lines are set up differently to counter torque and drag. the left hand eng could have 0-3 deg's right thrust, while the right hand eng could have 3-6 deg's right thrust.
the fun really starts when one eng quits, as often happens. if the l eng quits, the r eng has to counter its own torque+drag of fuse + l wing, hence large r thrust. if the r eng gives up, then l eng torque tends to cancel fuse drag+r wing drag, therefore less r thrust required on l eng.
i just realised keith, all you asked about were contra- rotating prop's and you end up with a mini lecture on twin eng thrust lines.

[Happy Days]

Very interesting non-the-less Ger. I always like to hear from people who know what they’re talking about!

Must be very hard to tune both engines to the same note.
I’m thinking: If one engine is producing a certain note, then when the second engine starts up there will be the frequencies of each engine, plus the heterodyne frequency of the two engines together, plus the harmonic frequencies. Changing the speed of one engine will change all the frequencies except that of the other engine. How on earth do you know what you’re listening to?

Presumably this “tuning” problem evaporates with twin electric motors and one just measures’ the rotation speed of each prop?

I’ve heard of a couple of pilots who’ve lost their models when one engine cuts. Why is it that full size plane don’t crash with such regularity when one engine cuts out. Surly they have to face the same problems??

K.

[JohnPearson]

Hi Keith

Twins are a pain in the pocket, any twin which I had never recovered after one engine cuts, black bin bag job, However i did fly a mates catalina flying boat which even with one engine down, flew great ( engines close together). Any twins which I come across on the show circuit, are electric or big petrol engines.

[Happy Days]

Interesting to hear that John.

The reason I was asking about twin prop planes is because I was thinking of getting one.

I find the concept interesting, and I’m looking for a new challenge. (Don’t think flying powered twins/multi propped planes will overtake my love of flying gliders though.)

The problem I face is one of cost. I’d almost certainly buy ARTF and not having any spare outrunners/esc’s, they would have to be purchased as well. So I’d probably be looking in the region of 500 quid.
If the project then went tits up on first flight I’d be pretty miffed!

Something to think about though…………HHHHmmmmm………………

K.

[gerryb]

john is right about getting the eng's as close to centre line as possible. the cat is basically a pylon mounted wing, so it's very easy to get the eng's in there. i resurrected an old 'twintub', (yea, that's what it was called), a few years ago. 7ft span, parasol wing. took off on 2x 25 2-strokes, would fly around on one eng without a bother. the key was keeping the eng's close to c/l. i then bought a hobbico 'twinstar' from tower hobbies, flew very well, i'd certainly recommed it. it was designed for 2x25's but with a few mod's, i'm sure it could be converted to el. check out t. h. website for video.
i had a few eng out's with the twinstar. the chances of saving it depend on several things...
1 total concentration on the model all the time.
2 identify which eng has died as quickly as possible (that means immediately!)
3 throttle back and get the rudder into the live eng . this will yaw the dead eng wing forward and (hopefully) prevent the live eng wing from banking so steeply that a crash is inevitable.
4 when flying twins, always bring a black bag with you!

[gerryb]

keith,
re tuning both eng's...
you're way beyond me on the tech's of freq's, harmonics etc. i just tune each eng to peak rev's then back off a notch or two on the main needle. then i stand over the c/l of the model and listen to the sound of each eng. a little tweaking is usually all that is required to get both eng's 'on song'. a bit of practise and you will know when things are right. patience and time spent on those eng's will reward you with a satisfying flight and a big grin on your face.
i have no knowledge or experience at all on el twins.[/quote]

[Happy Days]

Well, thank you for all that info Ger. (Clearly you are a very adept typist as well as a skilled rc pilot!)

It seems that flying twins is a risky affair. I saw a vid on You Tube the other day of a twin taking off. I’m not sure exactly what happened (I suspect it was your number 3 Ger.) but immediately the plane lifted off the ground the right wing rose, rolling the plane onto it’s left side and crashing before the thing had passed the end of the runway. Pretty sickening stuff!

In my case I’d definitely go electric, I have no experience, starting equipment, or desire to use ic. It does seem like a good challenge. I shall have to think long and hard about this matter.

Thank you both for taking the time to input on this topic.

Keith

[JohnPearson]

Hi Guys

Quick post today, the SR71 completed it's first test flight, all went well with the model and it flew great.

Well done Ian Robb