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Delivery delay and delivery problems


manuco

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I think these are hair splits.  You might adjust a prop a little coarser or finer to achieve your intended results.  These adjustments are going to be in a very narrow range of efficient operation for any given prop.  Get outside of that range on either side and your performance will wither.

 

There's probably also thrust/drag charts and other aspects that affect all of this.  But I think CT has simplified it a bit too much.  If best efficency for climb and cruise was hit on the same point, there would be no need at all for CS props.

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I agree Andy, that is why there are CS props, but along with manual in flight adjustable pitch, not allowed on a LSA. Pipistrel wanted to enter the US LSA market but to do so they had to have a final assembly across the border in Italy and had to tap down the performance of their sailplane inspired Virus SW. They have an excellent cockpit controlled pitch prop set up that along with in flight pitch adjustment will also feather the prop for engine off soaring. Their airframe and wing is so efficient that 80 hp is good for 143 kt, a tad faster than LSA's limit of 120 kt. So to be LSA compliant, needed a fixed pitch prop (or ground adjustable) at a fine enough pitch to limit speed to 120 kt. The wisdom of the FAA is to limit the SP's work load, but on this plane the Sport Pilot needs to reduce throttle during leveling out after climb so as to not over rev the Rotax. The FAA gave Icon A5 a waiver on weight because of the spin resistant design, I would like them to grant the two time CAFE winner Pipistrel an allowance to keep their cockpit controlled prop. It is rather sad that such a green, efficient aircraft needs to be less efficient to satisfy LSA regs. My argument is the added work load is the same, because with the fixed pitch climb prop you have to reduce throttle setting as you transition to level flight, with the variable pitch prop you would just increase the pitch as you level out, then reduce throttle for a very economical 120 kt cruise with the Rotax at a cruise rpm that is quite a bit less than a fixed pitch. Less rpm for the same cruise speed increases both engine life and fuel efficiency while the lower noise reduces pilot fatigue and angry airport neighbors. A win-win-win.   

 

Why punish both the company and owner of a truly green aircraft? On the Pipistrel forum one of the owners flys with a friend whose plane (CH-701) is only able to manage a 85 kt cruise, so he throttles back his Virus SW to that speed and sips 1.4 gph, while his friend is near 5 gph. 

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You might adjust a prop a little coarser or finer to achieve your intended results.  These adjustments are going to be in a very narrow range of efficient operation for any given prop.  Get outside of that range on either side and your performance will wither.

 

I think that's correct and it brings us back to the initial question - can you limit the speed of the Virus SW sufficiently by just changing the prop pitch.  I think it would put things outside that narrow range of efficient operation.

 

Overpitching would achieve the required result but I think you'd have to overpitch so much that performance would be seriously 'withered', and the engine would be constantly running under a lot of strain.

 

But if you flattened it to keep max S&L below 120kts at full throttle then you'd be overspeeding the engine by a large margin.  The only way I could see this working would be to put a physical limiter on the throttle and use a more sensible pitch.

 

A third option would be to put a less efficient prop on so you could use all the available power (ie run in the optiimal rev range)  but without producing as much thrust as normal.

 

So that begs the question - how does Pipistrel meet the LSA speed requirements?

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...  If best efficency for climb and cruise was hit on the same point, there would be no need at all for CS props.

 

CS props allow you to fine tune for economy cruise, that is different than best climb performance and best cruise speed performance

 

Best climb performance and best cruise speed performance result from a flat pitch where best economy cruise results from a coarse pitch and only an inflight adjustable prop can give you both.

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Or a simple placard.

 

 

Like the 180 hp LSA Carbon Cub SS? I think they are able to pull this off because the Titan engine is built to their specs and as such they are considered the manufacturer and could placard engine ops. I get a kick out of that placard, 180 hp for 5 minutes, 80 hp continuous, with rpm settings for given altitudes, some as low as 2000 rpm. This is why it is such a strong (pun intended) selling LSA, over 2000 fpm climb, and pilot is suppose to follow that placard. He might as well follow the placard because the airframe is so dirty, increased power doesn't add much speed, just sucks fuel at 8 gph.  

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I've seen a few mentions of the Carbon Cub limiting rpm, but this has nothing to do with limiting speed. The purpose of limiting rpm is to limit hp. Because of the high empty weight they had to limit hp to meet ASTM standards.

Its not quite limiting RPM, it is on the honor system. The pilot checks his altimeter and OAT, references the placard and sets his RPM. The Carbon Cub SS doesn't have a chance of exceeding 120 kt even with 180 hp as its Vne is about 120 kt. Too dirty to go fast.

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Its not quite limiting RPM, it is on the honor system. The pilot checks his altimeter and OAT, references the placard and sets his RPM. The Carbon Cub SS doesn't have a chance of exceeding 120 kt even with 180 hp as its Vne is about 120 kt. Too dirty to go fast.

 

Of course it is on the honor system. I was simply stating the purpose for the rpm reduction. They had to limit the max continuous power to 80hp to meet ASTM standards. The formula used to be (empty weight, plus 190 for each passenger, plus 1/2 pound of fuel for each max continuous HP). They limit power to 80HP max, so it is 80x.5 for 40 pounds of fuel. In the case of the Carbon Cub it is 900 pounds empty, two 190 pound people, and 40 pounds of fuel = 1320.

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I believe Toms reasoning is correct on the Carbon Cub placard limit of 5 minutes.

As others have said it really makes no difference because the only advantage of the extra horsepower is climb rate. A 180 horsepower cub strait and level using all 180 horsepower will never be even close to 120 knots.

A 100 horsepower cub would only be a few knots behind in cruise and likely burning half the fuel.

 

As far as a constant speed prop on the 912,  it makes more difference than you might expect. At least it made more difference than I thought it would. I had the chance to try it on a Tecnam. I flew the same aircraft before and after the constant speed prop was installed. it went from 700fpm climb to 1100 and cruise was up about 4-5 knots from 116 to 121.

 

What was really cool was watching the engine RPM go right to 5800 on takeoff roll and stay right there till we hit max cruise where we backed off to 5450 just by adding pitch and it held the same speed.

 

I believe there is a proposal to ASTM for the constant speed prop in LSA. I am not sure if it is making progress or stalled out somewhere. Is anyone here on the ASTM committee?

The argument is that although simpler, a non adjustable prop is not necessarily safer.

 

1. An in flight adjustable prop allows the engine to run correct RPM at all times, thus the engine will not be unduly strained during takeoff and over revved in cruise. This leads to lower inflight engine failures.

2. Pilots will have better takeoff performance during high density altitude and summer/winter temperature changes for obstacle clearance. 

3. Pilots who fly between differing altitudes in mountainous areas are either overpitched or under pitched. There have been several accidents attempting to climb over obstacles in these areas. 

4. Obvious reduction in fuel economy.

5. New technology can eliminate or minimize pilot interface and can give the above advantages without penalty. 

 

Mark Gregor

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I would definitely consider a constant speed or flight adjustable prop for my Sky Arrow were it legal.

 

A fixed pitch prop correlates well with a car with a single forward gear (albeit with a fluid "clutch") - usually "geared" too high or too low, but rarely just right.

 

I have a lot of hours in planes with constant speed props and the benefits are manifold. Fixed pitch seems crude by comparison.

 

Two nits to pick on that list:

 

#1) It would have to be demonstrated that varying the prop pitch increases reliability or longevity. A ROTAX with a fixed pitch prop, operating within limits, should not be under any undue strain.

 

#4) I think you meant an increase, rather than a reduction, in fuel economy.

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I have made many adjustments to the ground-adjustable propeller on my CTsw (E-LSA).  In my opinion, Mark and Eddie are correct, there is a definite compromise between climb and cruise when pitching a fixed-pitch propeller.  if you are below 5500 RPM during a Vx climb, then you are failing to get full horsepower from the engine (look at the HP versus RPM graph to see how much).  The airplane will use more runway to take-off and climb more slowly than a propeller pitched for 5500 RPM at Vx.  If you are getting 5500 RPM at Vx, then you are pulling the throttle way back in level flight and not getting maximum cruise.

 

Yes, it is a compromise.  I suspect that is why in-flight variable pitch propellers are available for Rotax equipped aircraft that do not need to be LSA-compliant.

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I totally agree.  Optimizing for climb vs speed is a choice between fine and very fine.  Optimizing for speed/climb vs economy cruise is a choice between fine and coarse.

 

From the beginning I chose 5,500 @ 10,000' level WOT thereby optimizing for speed over economy as well as speed over climb.  A CT climbs pretty well when optimized for speed.

 

My CT was delivered with a coarse pitch optimized for neither climb or speed but for economy cruise.

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My CT was delivered with a coarse pitch optimized for neither climb or speed but for economy cruise.

My Sky Arrow specified 13.5° at a certain station on its Warp Drive prop.

 

That delivered not even 5,000 rpm on takeoff, and I felt I was leaving a lot of performance untapped.

 

As an aside, I did not feel free to experiment until I was Experimental. At that point I took 1° out and now get 5,200 rpm on takeoff and initial climb, which seems a better compromise.

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My argument for the FAA is since they granted a higher MTOW for the Icon A5 for its spin resistant design, the standard propitiatory prop pitch/feathering panel mounted control should be allowed for both the safety and efficiency for the Pipistrel Virus SW in their LSA version. The pitch range is factory adjusted so that at the finest pitch for take off and climb the engine reaches peak hp without over revving and for cruise the pitch to coarse is limited so as to not labor the engine, rather fool proof. The feathering feature can only be engaged by pulling the trim knob out with the engine stopped, also fool proof. Engine off for soaring is a pilot decision, but in the case of engine failure, the 17 to 1 glide with the prop feathered is quite a safety feature.  

 

Doesn't it seem in-congruent that US taxpayer funded NASA has awarded a foreign manufacturer over a million dollars for their efficient design yet the LSA version for the US market is denied this efficiency and safety?  

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Why do you think there is a 13.5° spec? It seems intended to limit top speed but the airframe isn't that fast.  It prevents you from accessing a lot of power.

 

No idea.

 

Working assumption was they thought it was a good compromise, and established their performance charts on that one setting. I still hold that as an S-LSA I was not free to play around with it.

 

But I take it CT's are delivered with a similar effective pitch? I say "effective" because its measured at one particular station that I do not believe is uniform across various makes and models.

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Depending on how it is written, I would ask warpdrive about it. Often, pitches on ground adjustables are considered a starting point, and not an end-all-be-all.

First, I had a brain fart. Don't know where I got 13.5° from.

 

Here's what the AMM says:

 

23856504730_9d4259646e_c.jpg

 

My take was that as an S-LSA, with no range given that was kinda set in stone.

 

Bear in mind that going even 1° in either direction would invalidate virtually every performance chart in the POH.

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Agree to disagree.

 

I think any owner or mechanic modifying the design and/or specifications of an S-LSA outside of what's called for in the AMM, without an LOA specifically allowing it, could be in legal trouble if an accident were to result from said modification.

 

And that's not so hard to imagine. A CT with a degree more or less prop pitch will not have the range or endurance or takeoff performance or climb performance of one with a stock setting. A pilot would really be guessing as to the effect of modifications on these parameters, without a complete set of tests.

 

I know my Sky Arrow takes off and climbs better now, and has less range and endurance, but it's very hard to quantify the effects. But being Experimental, I'm in the envious position of being able to experiment!

 

Anyway I think I've made my case as clearly as I can. Owners and mechanics can do as they please.

 

Carry on!

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Bad news from FD side regarding the back payment of my order.

In 7th April 2015 I canceled the contract, after almost two years, and they pay nothing, according with the contract.

I made two notifications, at 30 and 60 days, and the third was made by the lawyers after 90 days from the first notification.

Nothing happen, no payment or a mail/call from the FD for an explanation.

We made a claim to the court and the lawyers have had a long negotiation and made an settlement for a back payment in installments, with first payment on 30 December 2015 but they didn't pay, as usual.

We started the procedures to garnishment of the bank accounts and for taking a sworn statement of assets or for seizure of real property.

These are the facts, your comments are welcome but not about air speed, constant speed propeller, MTOW etc., please.

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I'm sad to say that I'm not surprised things have come to this.   The writing has been on the wall for some time.

 

However, I suggest that all is not lost.  The company does have valuable assets and the potential for really substantial future growth, so there's a fair chance (in my opinion) that they won't unethically dump their debt through a bankruptcy and a re-commencement of trading under a different identity.

 

Having said that, this opinion is not based on anything substantial.

 

Please keep us posted on developments.

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IrishAl - that is pure speculation - I wonder if the Germans have an equivalent to our Companies House where you can look up company information and order previous accounts etc? Unfortunately my german language skills aren't up to much .......

 

The disturbing aspect of this to me is the company's apparent refusal to communicate with its customers - that speaks volumes.

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Ian: granted - it is speculation, but it's important to make a distinction between wild and reasonable speculation.  

 

There's a great deal of evidence in the recent trading record of the company and in their recent behaviour to support the speculation.

 

It's very difficult to draw a more positive conclusion, much as I'd like to.

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