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Gents,Information only purposes:I received a new Warp Drive 72" 3 Bladed Prop via direct purchase from the Hoverhawk Corporation. The prop blades are the standard plan form, they are not a wide chord prop.It is powered by an EA 81 with a Gyrobits [Ric Douglas] Toothed belt redrive - ratio is 2.2 to 1. I"ve bolted it onto the redrive and was attempting to tune it for max power / revs - here are the results of the revs as a product of the pitch of the blades:Pitch / Static Output RevsDegrees / Engine RPM / Prop RPM / Tip Speed[m/s] / %sonic23.5 / 3800 / 1727 / 165 / 49.8%20 / 4000 / 1818 / 174 / 52.5%17 / 4400 / 2000 / 191 / 57.7%15 / 4800 / 2181 / 208 / 62.8%13.5 / 4900 / 2227 / 213 / 64%As to how much static thrust this is producing I have no idea - I"ll be able to test that when I get up to the the club and can put it on the scales to see how good it is.Off Wikipedia here are the torque and horsepower specs for the subi engine:http://en.wikipedia.org/wiki/Subaru_...nufacturerFuji Heavy IndustriesType:Flat-4Bore:3.622 in (92 mm)Stroke:2.638 in (67 mm)Displacement:108.7 in³ (1781 cm³)Dry weight:171 lb (78 kg)Block alloy:AluminumHead alloy:AluminumValvetrain:OHVCooling system:WatercooledPower output:73 hp (54 kW) @ 4800 RPMSpecific power:0.67 hp/in³ (30.30 kW/L)Torque output:94 ft·lbf (127 N·m) @ 2400 rpm Compression ratio:8.7:1With 4900 max revs on the clock I think it suitable to leave it at this setting, as it is +100 RPM on the max theoretical horsepower on the engine and I see little point in asking it to rev any faster, as I discovered prior it only leads to damage, not only to the engine but also to the gyro when you have to do an out-landing. I expect the revs may go up marginally when in flight, if so and it is less than 5000 RPM I will probably pitch it up to keep the revs to 4800~4850.Can anyone see any fault in this logic?Cheers,Nic.
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yeah nick dump the dinasour, get rid of a ton of weight ,put on a 582 you only lose a few horsies in the exchange and get back to flying ,stop farting around. bob
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i have a subi, but different every thing else. i have absolutly no extra increase in rpm when flying to static testing.engine builder said i would pick up 100rpm , but its never happened.
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Bob,Can"t help farting around, it is a question of affordability, with tax men, w*nk managers, wives and children to house, feed and clothe I have little choice in the matter... might be a different story in a few years time though..Tony,Thanks for the observation.Cheers,Nic.
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Sounds all right to me Nic.
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Dewie,Thanks, it does seem to be a good engine - but let me compare how I"ve pitched it compared to how you have:As per the instructions, as I understand them, the way to measure the pitch of a WD prop is:*Not included in their instructions
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(Do you agree with the idea of setting the prop pitch to allow the engine to only rev up to or just past the peak power engine RPM?)Yes, I agree. But your final adjustment will be done after you test fly the gyro. How you work out your pitch is irrelevant provided you use the same method each time when fine tuning it.Bear in mind that most open frame gyros don’t fly fast enough to have much RPM increase over the static test.
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Dewie,Thanks.After checking:The crankshaft and prop spindle are in alignment with the keel, so the pitch of 15ø for 4800 is relevant. Phil Wright said it flew fast so it would appear to confirm the engine is a good one, you can certainly feel it in the compression if you try to stroke the prop through a revolution.Protractor accuracy is not bad, but it did have a tendency to favour one end of the vial, so it is accurate but not that accurate.Hope this helps others.Cheers,Nick.
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G"day Nick,I use one of those spirit levels with the laser in the end. I do it in the shed. I set one blade up with the protractor (to give me the angle) Then clamp the spirit level to the flat of the blade using a carpenters square at a point measured from the centre of the prop hub. Then I set up a stop (like a jig) so that each blade stops in exactly the same spot for checking. I mark the spot on the wall where the laser points on the first blade, and set the others up on that mark. The further from the wall the blade, the greater the accuracy. Makes the setting on each blade exactly the same. Using the protractor, It doesn"t matter how carefull the setting of the blades was, I found variations when checking with the laser level.You probably knew all this anyway.CheersFred
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Des,No confusion, but I must note the method is an estimate.Users of this method must make themselves aware that the 1/60 applies to **radial measurements**, if you want it to be more accurate you must mark out your 1"s on an arc of 60, not at a right angle to the line of interest to you. If you have a look at the attached sketch you"ll see that if you don"t mark out on an arc 25ø turns into 22ø, the measurement over estimates by 3ø, which might not be vitally important in blade pitching but is important in navigation.Cheers,Nic
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