Topic: Chipmunk Props

[DGH]

What props do you have fitted to your Chippies? Fairey Reed or Hoffman?

What do you good folks out there who have flown aircraft fitted with each think of them? What would you prefer?

Questions, questions, questions  

[Dean Cross]

Both WP857/ WD305 currently sporting Fairey Reed props. I have never sat behind a Hoffman so cannot comment. I gather there is no difference in performance stated however have heard that one has a tendancy to stop entirely if power is lost during a stall turn and people who have sat behind both favour the metal type    

[Neil Bordessa]

"SL" ( WG474 ) has had a Hoffman prop for quite a few years. The one fitted is only a couple of years old as the last was screwed into the hangar door at Barton    never seen so many flying splinters!!! I have flown a friends Chippie with a Fairy Reed prop and found no real difference though it may be  keep going in a stall turn longer due to more inertia i.e. being heavier.

[Dick Gower]

What props do you have fitted to your Chippies? Fairey Reed or Hoffman?

What do you good folks out there who have flown aircraft fitted with each think of them? What would you prefer?

Questions, questions, questions  :D

Reply:
I had a cracked spacer block in DCZ so had to fit a Hoffman.

They produce much less vibration but are slightly slower in the cruise and not much different in the climb; yes, they do tend to stop in a stall turn due to less momentum.

When you compare the weight of the two and the distribution of the weight along the radius, the Hoffman must be a lot kinder to the ageing GM crankshaft during aerobatics.

Being wood, the Hoffman has the usual issues of prop. bolt torque checkinh with changes in season.

On a cautionary note, the quality of the Hoffman has caused some of the owners some concern.  One had a lot of difficulty convincing Hoffman to accept warranty on a delamination problem.  On mine the paint finish will not adhere to the brass leading edges for more than a couple of flights.

[Vince Chadwick]

On mine the paint finish will not adhere to the brass leading edges for more than a couple of flights.

I fly the same Chippy as Neil (G-BCSL). She' shad a Hoffman prop all the time since I've flown her (starting 1979!), and the paint has never adhered to the leading edge.

I used to fly G-BARS out of Hawarden years ago and she had the metal prop. If anything, I'd say the metal prop is smoother 'cause it has a better flywheel effect. But there's not much in it.

Vince

[Dick Gower]

Both WP857/ WD305 currently sporting Fairey Reed props. I have never sat behind a Hoffman so cannot comment. I gather there is no difference in performance stated however have heard that one has a tendancy to stop entirely if power is lost during a stall turn and people who have sat behind both favour the metal type    

I had a Hoffman prop stop at the top of a stall turn last year with a student who tried to bunt out of it at the last moment and the carby did not like it .  One of those dreadful moments when it goes backwards and you try to brace the controls so that everything does not go into one corner.

Another big plus with the Hoffman is that it comes with its own spinner and back plate so you can dispense with the original and all of its problems.

In 1959 a Chipmunk (VH-RVG) belonging to the local aero club (RVAC) lost the entire engine when one half of the Fairey Reed was shed due to a fatigue crack.  The 2 POBs survived but it wasn't good.  With fewer engineers experienced in overhauling the F-R prop, particularly the fit of the blocks to the blade sheet, the Hoffman looks better and better to me!

Dick

[Dean Cross]

Dick,
I will stick with the FRP for the minute, although I am thinking that way in the future.

Declan

[Rod Blievers]

To my shame, I’ve only just discovered the “Hoffmann prop” thread on the Forum. As I’ve had first-hand experience of both, may I add some comments?

When I purchased my Chipmunk “box of bits” in 1996 it was without a propellor, spinner or backplate. All the pundits recommended the Hoffmann because:

a)   it was more efficient,
b)   it was smoother
and      c) it was “unlifed”.

Initially all went well with this installation until after about 2 years’ use I noted on one blade a white line about 3” long, close to the hub and abort 2” in from, and parallel to, the leading edge. My local engineer was sufficiently concerned with this to remove the prop and send it to the nearest Hoffmann agent in Sydney. Here it was deemed to be de-laminating, and would have to be returned to the factory (in Germany) for repair. Hoffman then stated that since the prop had been purchased 6 years’ earlier it was out of warranty.

As you can well imagine, a series of emails ensued, with me vigorously pointing out that the prop had only flown 85 hours, that prior to installation the prop had been stored in a controlled environment, that my aircraft was always hangared and had spent a mere 4 nights outside overnight in that period. Hoffmann then decided that, “in the interests of customer relations”, they would carry the costs of shipping and repair. I always received a prompt and courteous response from them – overall I was very impressed with their attitude. My prop was "away" for 10 weeks total.

In the interim, I borrowed my brother-in-law’s Fairey Reed prop, which he had previously had coarsened off to the limit. What an interesting comparison! Yes, it was distinctly rougher, but faster! At 2100 rpm, my Chipmunk with the Hoffmann gives a TAS of 93-97 knots, with the F-R prop I had 98-104 knots and a distinctly lower nose attitude. The climb rate and take-off run seemed identical. So much then for the “efficiency” argument!

My other reservation about the Hoffmann is that it seems very vulnerable to leading-edge paint chipping and damage. I mainly operate from grass (actually grass over gravel) and I’m very careful about where I conduct a run-up, yet after 65 hours the prop looked so unsightly that I had the leading edges re-painted (though some would say I’m obsessed about my Chippie’s appearance!). I was also warned, though I’ve never experienced this problem, that flying in moderate/heavy rain would erode the paintwork very quickly.

The downside of the F-R is obviously the fatigue cracking issue. I guess you have to live with the prospect of your prop becoming a useless heap of tin if cracks are detected during maintenance or the required inspections. I agree that given the greater disc mass it would transmit higher loadings than the Hoffmann top the crankshaft, but wasn’t the engine designed for this in the first place?

In my humble opinion, if I had a perfectly good F-R I can see no compelling reason to fit a Hoffmann.

Regards,

Rod

[David Copse]

After the first trip following a lengthy bare-metal re-spray, it was noticed that four of the eight spinner screws were missing and corresponding damage was identified along the back of one propellor blade. It is therefore with interest that I read this forum, but ask if the discussion regarding propeller options is rather academic.
As the preferred alternative, does anyone know if a Fairy Reed propeller can be sourced and if so, from where? If not, is the Hoffmann composite propeller the only other approved option or is there another metal alternative?
Can anybody provide any information regarding the costs incurred with the installation of the Hoffmann prop?

Thanks for any help.

[ACL]

My experience is limited but recent - conversion training on a Chipmunk with F-R prop which cruised at 90kt and climbed at 700fpm, and subsequently a few hours on G-HDAE with Hoffman prop. G-HDAE cruises at 85kts indicated (but just discovered that the rear ASI shows 80kts and I suspect that one is correct) but climbs at 1,200fpm and 2,300rpm. Finding it difficult to set up for cruise as a slight climb or descent has immediate effect on rpm and hence airspeed, with further effect on rpm. Haven't tried aeros yet, but I reckon it's going to be a case of keeping one and a half eyes on the rev counter to avoid overspeeding. I'm not sure what age the prop it, but it's showing signs of wear and tear. Personally I found the F-R nicer to fly, but I think my Hoffman must be a very fine pitch one.

James

[Dick Gower]

After the first trip following a lengthy bare-metal re-spray, it was noticed that four of the eight spinner screws were missing and corresponding damage was identified along the back of one propellor blade. It is therefore with interest that I read this forum, but ask if the discussion regarding propeller options is rather academic.
As the preferred alternative, does anyone know if a Fairy Reed propeller can be sourced and if so, from where? If not, is the Hoffmann composite propeller the only other approved option or is there another metal alternative?
Can anybody provide any information regarding the costs incurred with the installation of the Hoffmann prop?

Thanks for any help.

My FR did that before I fitted the Hoffman.  Gouged teh back of the blade.

The FR (and spinner) look very nice on the wall of my workshop.

[Rob Merrylees]

After the first trip following a lengthy bare-metal re-spray, it was noticed that four of the eight spinner screws were missing and corresponding damage was identified along the back of one propellor blade. It is therefore with interest that I read this forum, but ask if the discussion regarding propeller options is rather academic.
As the preferred alternative, does anyone know if a Fairy Reed propeller can be sourced and if so, from where? If not, is the Hoffmann composite propeller the only other approved option or is there another metal alternative?
Can anybody provide any information regarding the costs incurred with the installation of the Hoffmann prop?

Thanks for any help.

When I required a Fairy Reed propeller back in the 1970's I advertised in an Aviation magazine and got no response!  Eventually I did obtain a damaged propellor that was able to be straightened.  It is hard to imagine that Fairy Reed props are in any greater supply today, so I would agree that the discussion of propeller options is somewhat academic.

When I purchased Chipmunk VH-AFG in 1965 it was fitted with a wooden "Adams" propeller manufactured in Australia.  This was combined with a light aluminium sheet metal "sandwich" type backplate.  

I suspect that during the 1960's several Australian Chipmunks may have been running wooden propellers as Yoeman Aircraft designed and manufactured fiber glass spinners for use with either Fairy Reed Propellors or  a slightly different type for use with wooden propellers.

The Adams propellor had a couple of disadvantages as compared to the Hoffman set up.  Unlike the Hoffman propeller it was not mated to a spinner and backplate assembly, and as explained above, used the original lightweight backplate.

Hoffman on the other hand uses a heavy machined steel backplate weighing from memory, seven pounds.  The mass of the backplate I feel would provide some flywheel effect and help retain the centre of gravity closer to the original position.  Dick Gower reports that with the Hoffman propeller the engine is inclined to stop during a stall turn.  Having flown with both the Hoffman composite and the Adams I can say the "stopping"
occurance was much much worse with the Adams propellor.  As for the original backplate perhaps a picture will suffice to explain why the Hoffman backplate is better:-


 

 


In this case no spinner had been attached to the backplate.  I have been told that this type of backplate in even more prone to cracking when operated without a spinner.  At the time there was an ANO requiring that the spinner be removed to facilitate daily checking of the propeller bolts.  Incidently the cracking was on the engine side of the backplate and not readily appearant until the prop was removed.

I would like to mention that it was Australian engineer Glen Caple who led the way in the developement of the Hoffman propellor/backplate/ spinner combination.  After discussions with Hoffmann, Glen machined up his own backplate and manufactured a spinner.  Keen observers may have noticed the more pointed look of Glen's spinner.

Regarding the cost of the Hoffmann combination I have no current information, however keep in mind that the propellor bolts will have to be exchanged for longer bolts.