Hartzell prop overhaul: metal or composite prop?

[Chris B]

I have read about the case of not taking the aft CG issues too seriously (ignoring the law for a moment, no pun intended) driven by 50g tank spin certification issues. If I am not thinking clearly about this, please let me know!

Hi Arpad -

Since you asked, I'd recommend being careful about this. As you know, getting too far aft is potentially extremely challenging and flirting with unrecoverable. Much worse than modestly over-gross. The fact that the 40g models extend the CG further aft gives me high confidence to run right up to the limit, but in a spin presumably some fuel will get thrown into the outer tanks. I'd prefer not to be a test pilot.

...I scratch my head at why the composite is valued at 2x metal...

IMO, if the composite prop was Hartzell's only option, it would undoubtedly be much lower cost. But with two models, they are just segmenting the market. Besides, don't underestimate the value of sex appeal.

Chris

[Don]

Wow! I didn't realize I had the very first XL made--40.696. Aluminum prop has served me well with no complaints.

Steve, I think yours, use to be mine, was the 2nd XL. At least there was some type of prototype-demo prior to 40.696. Here is a photo of the prototype that factory sent me when they were building 40.696. Not sure what serial number this craft is. Damn...I wish they would have kept the winglets. They are so cool looking.

[ihfanjv]

Wow! I didn't realize I had the very first XL made--40.696. Aluminum prop has served me well with no complaints.

Damn...I wish they would have kept the winglets. They are so cool looking.

It really is a shame they couldn't find a work around to make the winglets work with the 50 gallon tanks. With the shorter wingspan, the Avgas DA40 with winglets would easily fit in a lot more hangars!

[rwtucker]

Were the Aux tanks the only issue with the winglets? It has been awhile but I thought my sales rep said there was a spin recovery issue and a lift issue. They are beautiful and would take five minutes off of my in and out hangar time.

[CFIDave]

Were the Aux tanks the only issue with the winglets? It has been awhile but I thought my sales rep said there was a spin recovery issue and a lift issue.

With the winglets, DA40 spin recovery took too many turns -- due to the higher polar moment of inertia with extended range fuel tanks located out in the wings. But IIRC, winglets also reduced cruise speed a few knots compared to the "standard" DA40 more-horizontal wingtips. The purpose of the winglets was to increase the clearance of DA40 wings inside hangar door openings.

It's interesting to note Diamond's use of winglets on the DA42 vs. the upcoming DA62 (which share the same engine nacelles and wings outboard of the nacelles). For the newer DA62, Diamond replaced the vertical winglets of the DA42 with more-horizontal wingtips, somewhat analogous to the wingtips of the standard DA40. Presumably the more-horizontal DA62 wingtips provide better performance, despite increasing the width of the aircraft to a hangar/tie-down-unfriendly 48 feet.

All of this is to suggest that DA40 owners should be happy with their better-performance existing wingtips. :-D

[Steve]

I'm happy! I have a 44 foot wide hangar...

[agmolnar]

I have read about the case of not taking the aft CG issues too seriously (ignoring the law for a moment, no pun intended) driven by 50g tank spin certification issues. If I am not thinking clearly about this, please let me know!

Hi Arpad -

Since you asked, I'd recommend being careful about this. As you know, getting too far aft is potentially extremely challenging and flirting with unrecoverable. Much worse than modestly over-gross. The fact that the 40g models extend the CG further aft gives me high confidence to run right up to the limit, but in a spin presumably some fuel will get thrown into the outer tanks. I'd prefer not to be a test pilot. Chris

Chris, thanks, that's helpful input. I have about 3-5 years before those pre-teens get considerably bigger and therefore in the meantime can stay well under the 100.4, but at some point I am looking at aft CGs in the range of between 100.4 and 101.0 (still comfortably below the 102.0 threshold). When you say "up to the limit", do you mean the 100.4 limit or the 102.0 limit? I assume you mean the 102.0 limit is when the test piloting begins..

One strategy I am considering is to add front ballast only when I need it -- i.e. in a few years. The irony being that I would need that front ballast on only 5% of the missions even at that time... (and in the meantime can enjoy 920lbs useful load...not too shabby).

Thanks,
Arpad

PS. I guess based on the thread that i have the last non-XL built!

[Chris B]

When you say "up to the limit", do you mean the 100.4 limit or the 102.0 limit? I assume you mean the 102.0 limit is when the test piloting begins...

Hi Arpad -

No. I adhere to the 50g limit, because my aircraft has the extended tanks. Per the discussion about winglets, small changes near the wingtips have a *significant* impact.

I just don't think that a 50g DA40 with 40g on-board is equivalent to a 40g aircraft. At a minimum we don't know, so that is where test piloting begins.

But IMO, you have a pretty high-class "problem" !

Chris

[trepine]

I wonder how much LED strobes and landing/taxi lights impact the spin recovery with the extended range tanks. These LED strobes in particular removes some significant weight from the very tip of the wing, substantially further out from where the end of the long range tank is. It would be nice if diamond could/would retest and provide an updated envelope for these conversions as it is an easy upgrade and having an expanded envelope in the XL/S/T series would be huge. Although I could also see it having negligible effect since the fuel and migrate to the end of the wings providing many pounds of weight at the tip in a spin.

[Antoine]

Good thinking Gilman! Another good reason for buying these beautiful things "Darling they are safer!"

I once talked to a very knowledgeable person about the matter of spin recovery. He said that a simple solution would be to install one-way valves between the aux tanks and mains. This way, fuel cannot flow outboard. Simple, inexpensive fix.
Until this is done, we have to fly within the "50 USG" aft CG limit. Unless we are willing to becomeillegal and risk a loss of insurance coverage among other unpleasant consequences.