Hoffman prop overhaul?

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Dakkman
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Re: Hoffman prop overhaul?

Post by Dakkman »

Due to the Hoffman issues and previous good experience with MT propellers I installed an MTV-21 propeller on one of our flying school DA20-A1 aircraft. There are EASA STCs for it but I don't know about the FAA. Pilots report that the aircraft performance is better than with the Hoffman. Lead time for the MT propeller was about six months.
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Re: Hoffman prop overhaul?

Post by JohnE »

Hi Dakkman,

Good to know. Did you have to replace anything else or was it just the prop? (governor, etc). Also, any idea of the performance increase? Finally.. the difficult question. How much did it cost?

thanks.

john
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Re: Hoffman prop overhaul?

Post by Dakkman »

Hi John,

It is a straightforward swap, nothing else to replace. I've not flown the aircraft myself but the instructors tell me that for normal cruise power settings they are getting at least an extra 5kts airspeed, probably a bit more. Climb performance is also better but I can't quantify that. They say that the aeroplane just feels "nicer".

The new MT propeller was 7000 euros including the spinner ordered directly from the factory so not a great deal more than a Hoffman overhaul. You have to send in your used Hoffman in exchange after you receive the new prop. Price February 2022.
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Re: Hoffman prop overhaul & experimental airworthiness

Post by S2000airforce »

Help!

My Hoffmann prop on my 20A1-100 has excess play according to the mechanic. Time for overall is 6-10 months and about $8000.

MT can get me a field approval and new prop & spinner for $10K, but again, October 2024 at the earliest to get it completed and then shipped from Germany.

Anyone have any other ideas? I was thinking a temporary experimental testing airworthiness certificate for a fixed pitch, ground adjustable, three blade prop that many Kitfox owners have gone to on their Rotax 912s. They are twelve pounds vs. 22lbs for Hoffmann, so balance would be skewed aft. Cost is $2700, so 1/3 to a 1/4 less.

Anyone have any experimental testing airworthiness certificate experience?
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Re: Hoffman prop overhaul & experimental airworthiness

Post by Rich »

S2000airforce wrote: Sat Feb 03, 2024 10:48 pm Anyone have any experimental testing airworthiness certificate experience?
You might check out this multi-year saga: viewtopic.php?t=3451&start=180
2002 DA40-180: MT, PowerFlow, 530W/430W, KAP140, ext. baggage, 1090 ES out, 2646 MTOW, 40gal., Surefly, Flightstream 210, Orion 600 LED, XeVision, Aspen E5
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Re: Hoffman prop overhaul & experimental airworthiness

Post by krellis »

S2000airforce wrote: Sat Feb 03, 2024 10:48 pm Help!

My Hoffmann prop on my 20A1-100 has excess play according to the mechanic. Time for overall is 6-10 months and about $8000.

MT can get me a field approval and new prop & spinner for $10K, but again, October 2024 at the earliest to get it completed and then shipped from Germany.

Anyone have any other ideas? I was thinking a temporary experimental testing airworthiness certificate for a fixed pitch, ground adjustable, three blade prop that many Kitfox owners have gone to on their Rotax 912s. They are twelve pounds vs. 22lbs for Hoffmann, so balance would be skewed aft. Cost is $2700, so 1/3 to a 1/4 less.

Anyone have any experimental testing airworthiness certificate experience?
Not sure I would recommend the experimental route. Do you really want to be a test pilot and flight test engineer? It's probably easy to get the experimental certificate, but not so easy to get a DER/DAR to issue a standard airworthiness once you are done. Can't imagine an "experimental" DA20 would have much resale value.

Quite a few years ago, we had Opa Locka Propellers rework our Hoffmann prop. At the time, they also had an overhauled prop in stock for the DA20. Doubtful it's still there and I don't know if they even work on Hoffmann props any more. Also don't know if they still do decent work. I would contact every authorized prop shop and see what they say.
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Re: Hoffman prop overhaul?

Post by S2000airforce »

Opa Locka doesn’t have any spare Hoffmanns in stock. I would think an experimental DA20 wouldn’t lose too much value. Makes getting parts significantly easier.
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Re: Hoffman prop overhaul?

Post by JohnE »

How easy is it to convert (even temporarily) to experimental? Not sure this is an easy task. If you go this route, I'd recommend sticking with a constant speed prop. I would expect a significant performance decrease without it.
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Re: Hoffman prop overhaul?

Post by krellis »

S2000airforce wrote: Thu Feb 08, 2024 7:24 pm Opa Locka doesn’t have any spare Hoffmanns in stock. I would think an experimental DA20 wouldn’t lose too much value. Makes getting parts significantly easier.
What parts would be easier to get? Owned a DA20 for many years, bought parts for the engine from Lockwood and many other components from various suppliers. Only ordered parts from Diamond a few times.

I've built two experimentals and yes, sometimes the parts are cheaper.

Just my opinion, but again - I think moving a DA20 to the experimental category for the reasons you stated is a big mistake.
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Re: Hoffman prop overhaul?

Post by S2000airforce »

Experimental for R&D is temporary anyway. Example would be the nose gear tire on the DA20 is $700...not including the tube. Due to the rarity of the parts, they are all pricing quite expensive as the planes age. Insurance cost for experimental certificate was only $200 extra per year. Can't think of any downsides to test out more available parts. Grass and gravel performance is not great either, some larger tires would be beneficial. The Hoffmann prop sucks up gravel nicks as bad as a Caravan.
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