Thrust from Suby 2.5

[asra]

Is there someone out there who can maybe help us out with an interesting puzzle.

[Tim]

Static thrust from the 2.5 should be somewhere in the region of 400 to 450kg. This is hard to test as it is hard to safely hold a gyro back at these readings.Possible problems:-Slipping GearboxFaulty tachoOverloaded prop depitching itselfProp Pitch or RPM to high and cavitating (stalling)Inconsistant thrust readings

[Des Garvin]

Hi Gyrofan,

[asra]

Hello Guys.I do have to ask just what is being used to measure the static thrust in all these situations, and if has it been checked against some kind of standard.Static thrust seems to be a very important part of initial preflight checks for a new machine or when thrust source is modified, It would seem that some kind of a standard is needed. I may be able to help a little here with suggesting or scraping together a load cell suitable for the test.CheersGG

[asra]

Back againHave a quick look at http://www.pra.org/index.php?view=ar...emid=55Perhaps it could be a regular club type event to have a sort of drag race on the scalesthe figures quoted by the yanks for their thrust tests certainly dont match Tims impressive figures.Perhaps tim could

[NiqueNaque]

Hmmm,Does it have a donut / taper and key connection?? - has it sheared off and is now being driven by friction?Is the gearbox oil clean or does it have those lovely metallic flakes in it?Have you got a strobe light which you can tune to 38 ~ 39 pulses per second to see if the prop appears still at this speed?Tip speed is about 207 m/s which is 207/330 = 62% of sonic speed - is it unusually noisy??What is the tip path like - is the prop travelling in a flat plane?Have you changed the entry or exit conditions to the prop - eg, new fairings / cowls?The prop discharge conditions should be such that the "jet" of air off the blast of the prop should be fairly closely defined immediately after the prop if it is not cavitating - is it tight around two metres back from the prop itself? If it is untidy it points to a problem of over pitching as air will tend to be centrifuged outward rather than properly going to a vena contracta [slight narrowing] about 1/2 a diameter behind the prop. Try streaming some smoke into the prop and see what it does - be careful of the fire hazard associated with the fuel though - know any apiarists? [bee keepers]Take care doing this!!! Try this and see what happens.Nic.

[Tim]

Perhaps tim could

[asra]

Ok Tima brief response. I have heard of vw"s getting 600 lbs static off a 103 inch prop too, and these are all plausible claims. I still have to ask how it is being measured. In years gone buy I have seen a set of bathroom scales pinned by a gyro against a tree. It looked quite dangerous probably cause it was.So can anyone reveal the tequnique or is there a bit of embarrasment about how its done in the country.I have a very good idea how it should be done, but how about telling it like it is.GG

[asra]

By the way Timwhat sort of weight are you clocking for the SUBIGG

[birdy]

In years gone buy I have seen a set of bathroom scales pinned by a gyro against a tree.Now why didnt i think o that. Lot cleaner n easier n my idea. :-Was do"n a bore run a coupla years back wen i seen a cow bogged on the muddy edge of a dam.See"n as it was 60 miles from home and freezn cold, i thought id better get er out before she froze to death.I landed in the flat of the silt trap and walked over, but could see i was never guna be able to heave this ol mum out by meself.So i thought " i got 100 horses straped on that gyro, why not?"After pushn the machine close enuff to the water so"s the ol seat belt, that id just taken off the machine, could reach from the tail boom to her back legs, i tyed um together.Jumped in the gyro and fired it up, checked over me shoulder to see everythn was rite to go, and give it all it had.To me proud amazment, the little gyro slowly snigged the old girl out and across the silt trap like a tracter.Figuren she weighed bout 400KGs, i thought i musta had atleast 400kg of thrust. [ if you allow for the friction between the cow n the boggy silt, the prop blastn the hair off her........ .

[asra]

Talk about make me laugh.are you sure it was a COW?????????it sure sounds like a load of BULL!!!!!!!!!!!!!I guess I realy asked for thatGG

[Tim]

So can anyone reveal the tequnique or is there a bit of embarrasment about how its done in the country.G"day GG.Normally our thrust tests were done with the gyro tail boom tied back to an immovable object through a high reading scale, hydraulic cylinder with a pressure read out or graduated electronic pressure transducer. The readings are taken with zero wind and the gyro on level ground and the pilot in the seat.If you feel that you need to test the maximum thrust of the higher horsepower engines then you have a problem, because they tend to roll over sidways, bend the keel and bend the mast, engine mount and/or nose wheel. You will need to make some sort of "bridle" set up to attach as close to the thrust line as possible (which is a bit risky bearing in mind prop clearance). Another way is to secure the gyro firmly to a light trailer with good "dolly" wheels or such under the front of the trailer and fasten the scales to the rear of the trailer. You will still need to secure the mast or engine mount back to the sides of the trailer to take some of the load off the rest of the airframe. (The gyro on the trailer will push a car along the ground with the handbrake on and the back wheels locked).

[asra]

Thanks Tim,I havn"t got the hang of this quote function going yet, but I am glad to hear how things were done quite well in the bush.Is there an ASRA trust test kit or do any clubs have this sort of gear. With the advent of ebay there are some realy great

[NiqueNaque]

Gyrofan,Is the prop rated for the input power??Here"s a way to confirm that the scales you"re using are about right.You can use a set of bathroom scales to do it - refer the figure attached.You have to chock or chain the machine up so it cannot move forward or bounce backwards, or sideways under full load. I used 2 x 2500 kg load binder straps [$25.00 each] on mine to lock it down using the main wheels onto the trailer. This does not prevent it from rotating around the mains in the pitching direction. Get a strong beam and clamp it onto the keel and then block the end of

[asra]

Dear Nicit sounds like your tree is laying sideways.GG