MikeGazdik
Senior Airman
Does the prop design change or alter the torque affect? Such as if a plane was switched from a 3 blade to a 4 blade propeller.
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Yes I had to look closer my books and cutaway drawings. And still there are no evidence of separate aileron trim tab. So I would imagine that the whole aileron is working as a trim.Look closely - there is no possible way the Spit could remotely run straight with foot off rudder pedals...
It probably will as not only do you have another lifting surface, but that extra blade adds weight increasing torque inertia.Does the prop design change or alter the torque affect? Such as if a plane was switched from a 3 blade to a 4 blade propeller.
Does the prop design change or alter the torque affect? Such as if a plane was switched from a 3 blade to a 4 blade propeller.
Ok, but I could tell you this much - you could feel the difference between a 2 bladed and 3 bladed Bonanza with the same engine intalled - I've always felt it was partially due to the weight of that third blade (which could add up to another 50 pounds).Joe - I need to ponder on prop inertial effects to the above but believe that is only a factor wrt torque in the acceleration/deceleration of the rotational speed to and from zero to the selected rpm. The max torque of the engine should be the limiting and design factor
Ok, but I could tell you this much - you could feel the difference between a 2 bladed and 3 bladed Bonanza with the same engine intalled - I've always felt it was partially due to the weight of that third blade (which could add up to another 50 pounds).
Two V-35s. I worked with a few folks who had STCs that put 3 blade props on them. During the take off roll you were really honking on the right rudder with the 3 blade conversion from what I remember.I'm scratching my head now. I've flown the V-35 and owned an A-36 and trying to remember the differences. IIRC the V-35 was both lighter and lighter on the controls than the A-36, and the V-35 had distinct dutch roll in cruise but seemed more responsive overall. I cannot remember whether the V-35 I flew had two blades or not. The A-36 was definitely three blades.
The extra weight would increase the prop rotational inertia but I can't figure out why that would affect the 'torque' response of engine/airframe and prop system to each other unless we look at interim throttle settings. Maybe we get a slighly lower rpm for same throttle because of the increased inertia of the heavier prop and for the same rpm/different throttle setting the torque supplied (and absorbed) is higher for the heavier prop.
If we ignore an airframe attached to the engine mounts and view it as a test stand anchored, then at max torque (i.e take off) that the engine is capable of - will be applied to the mounts as compression on one side and tension on the other - trying to rotate the stand opposite of the prop rotation.
The amount of propeller 'in-plane drag' is equal to and opposite of the torque supplied by the engine/shaft combination..so, as the rotational moment of the prop system increases it should show up as lower rpm for same torque applied?? I am wandering a little bit here in what should be simple engineering but the only time I fooled with 'props' of any kind in my industry experience was at Bell and that was more in the structural analysis side - not blade performance.
Joe - are you comparing a three blade A-36 to a two blade V-35 or within same model type like V-35 with two different props?
http://www.free-online-private-pilot-ground-school.com/images/trim_tabs.gif
I just found this pic and the description says that
"Figure 16: The movement of the elevator is opposite to the direction of movement of the elevator trim tab."
Does the both aileron and rudder works in the same way?
Two V-35s. I worked with a few folks who had STCs that put 3 blade props on them. During the take off roll you were really honking on the right rudder with the 3 blade conversion from what I remember.
Makes sense - I do know that one of these guys had the Feds nix a field approval when he wanted to put an IO-470 (I don't remember which model) in with a 3 bladed prop. The PMI we were dealing with was worried about torque and the effects on the engine mounts. He wanted to have a bunch of engineering analysis and flight testing done prior to approval. In the end the guy with this aircraft stayed with the IO-470 and a two bladed prop. The FAA hard at work!OK. The reason I didn't fully get this is that I didn't really see very much difference transitioning from the V-35 to the A-36 but I suppose there was a difference that I attributed more to the different weight and tail config than the torque. Had I flown one then the other in succession I probably would have noticed.
The explanation seems then to be the engine applies more torque to overcome the higher prop intertia at same rpm and that it takes a slightly higher throttle setting for same rpm.
Makes sense - I do know that one of these guys had the Feds nix a field approval when he wanted to put an IO-470 (I don't remember which model) in with a 3 bladed prop. The PMI we were dealing with was worried about torque and the effects on the engine mounts. He wanted to have a bunch of engineering analysis and flight testing done prior to approval. In the end the guy with this aircraft stayed with the IO-470 and a two bladed prop. The FAA hard at work!
Yep - I think the aircraft owner was on that line of thinking. It's funny though, McCauley wanted to help us only if they could retain all the flight test data - we figured they were going to get "free data" and then apply for the STC - this pissed off the Feds as well.My 'guess' is that the engine mounts were designed to 2x ultimate for the two blade and should be adequate for the higher torque engine/prop config - but I would err on the side of caution and get an 'official opinion' from Beech, particularly if it was my ass!
Yep - I think the aircraft owner was on that line of thinking. It's funny though, McCauley wanted to help us only if they could retain all the flight test data - we figured they were going to get "free data" and then apply for the STC - this pissed off the Feds as well.
Funny thing about torque on another aircraft - We take care of the twin otters operated by USAFA - recently we upgraded the PT6s to -34s and the aircraft are continually flown to their max. allowable torque. The STC that installed these engines said nothing about engine mounts - we've we noticed that although they have no specified time life, the engine mounts are lasting about 1/3 of what we've seen before. The mount mfg. told us no one ever contacted them about analysis on their mounts with a -34 engine.
On condition - no splits or tears on the rubber - this came from DeHavilland.Joe - what standards are applied during inspections to determine 'near end of life' for engine mounts in an Otter?
It's all in the rubber - the structure is perfect and we have done NDI around the area - the folks from the mount mfg looked at some of the failed mounts - they felt the mouts were being operated to their limits - there is also a bushing in the middle of the rubber - never had any deformation or problems there and they and the bolts are changed every time we change a mount - it seems the rubber it taking al the load.From a structural perspective I sure would want both visual and penetrant inspections of the bolts but what about the engine and airframe mounts?
Are they degrading at attach points/engine and Mount or mount to fuselage or ??
On condition - no splits or tears on the rubber - this came from DeHavilland.
It's all in the rubber - the structure is perfect and we have done NDI around the area - the folks from the mount mfg looked at some of the failed mounts - they felt the mouts were being operated to their limits - there is also a bushing in the middle of the rubber - never had any deformation or problems there and they and the bolts are changed every time we change a mount - it seems the rubber it taking al the load.
At least two implications (or three actually). One is material related if the rubber/elastomeric mounts have changed say in manufacturing process rendering it more susceptible to 'fatigue' due to the vibration.
Two, is the frequency input of the new engines is somehow applying 'more' compression cycles on the rubber (i.e 'fatigue' due to more repeat loads per engine hour).
Third and last is appreciable increase in the load applied to the rubber - but this one would also suggest to me that more Shear is somehow being applied to the rubber instead of compression type loads...
Does the bushing lay slightly below the surface of the rubber mount (seems like it should to allow the rubber mount to compress slightly and create a preload tension on the mount bolts).
I would suspect something related to increased shear loads on the mounts - which theoretically would occur only if the new engine also had significantly more thrust?