"Lippsing" a Q-tip propeller
MP
to our propeller.
We have a Hartzell Q-tip prop on our Glasair. That's the fancy bent over tip
that gets all the jokes about the FAA Inspector who grounded a Cheyenne when
the propellor first came out. (Looks like the prop had a ground strike.)
When we got it, the Q-tip was a hot thing, and we were coming off a Prince
P-tip, which also had a turned under "winglet."
Then Paul Lipps came along and wrote that putting a big hunk of metal out
there on the prop tip is about the stupidest thing one could do, since the
prop tip is where velocity - and therefore, drag - is highest. He wrote
about cutting the tips off a Prince wood prop and getting a phenomenal
improvement in propeller efficiency.
I'm not going to cut off the Q-tip entirely. But I thought I would try a
compromise solution, and cut part of it off. I should link a photo to show
you my markups on the tip, but the plan is to cut the front of the winglet
to put a 60 degree shear on the front, like you see on the Katana wingtips
and on Paul Lipps' Lancair. I will be careful, will sand out the stress
risers, etc. I have a good gram scale to weigh the cutoffs to match, and a
dynamic prop balancer to rebalance after the operation.
It's a homebuilt, so I'm deep into "experimental" mode on this one. Anyone
want to warn me about how I might kill myself doing this? Has anyone done
this before?
Thanks,
Mike Palmer <><
Sea Hawk @seemysig.com Capt. Geoffrey Thorpe
news:gs6jn3$5hq$1...@news.motzarella.org...
> Thought I'd ask for comments before doing something stupid and
> irreparable
> to our propeller.
>
> It's a homebuilt, so I'm deep into "experimental" mode on this one.
> Anyone
> want to warn me about how I might kill myself doing this? Has anyone done
> this before?
Sure, I'd be happy to warn you.
Has anyone killed themselves after cutting down a prop?
Yup.
Cut down props were popular on the early T-18's - at least until the first
few fatal accidents. When the blade broke due to resonance / fatigue the
engine would part company with the aircraft and the result was typically a
dead pilot / passenger.
Changing the length of the prop changes the resonant frequencies with
unpredictable results.
http://www.t18.net/technical_info.htm#Cutdown
--
Geoff
The Sea Hawk at Wow Way d0t Com
remove spaces and make the obvious substitutions to reply by mail
When immigration is outlawed, only outlaws will immigrate.
MP
to our propeller.
We have a Hartzell Q-tip prop on our Glasair. That's the fancy bent over tip
that gets all the jokes about the FAA Inspector who grounded a Cheyenne when
the propellor first came out. (Looks like the prop had a ground strike.)
When we got it, the Q-tip was a hot thing, and we were coming off a Prince
P-tip, which also had a turned under "winglet."
Then Paul Lipps came along and wrote that putting a big hunk of metal out
there on the prop tip is about the stupidest thing one could do, since the
prop tip is where velocity - and therefore, drag - is highest. He wrote
about cutting the tips off a Prince wood prop and getting a phenomenal
improvement in propeller efficiency.
I'm not going to cut off the Q-tip entirely. But I thought I would try a
compromise solution, and cut part of it off. I should link a photo to show
you my markups on the tip, but the plan is to cut the front of the winglet
to put a 60 degree shear on the front, like you see on the Katana wingtips
and on Paul Lipps' Lancair. I will be careful, will sand out the stress
risers, etc. I have a good gram scale to weigh the cutoffs to match, and a
dynamic prop balancer to rebalance after the operation.
It's a homebuilt, so I'm deep into "experimental" mode on this one. Anyone
want to warn me about how I might kill myself doing this? Has anyone done
this before?
Thanks,
Mike Palmer <><
MP
This photo shows the Q-tip as it is now.
http://img13.imageshack.us/img13/6228/qtipbefore.jpg
This photo shows what I'd like to do.
http://img17.imageshack.us/img17/9960/qtipafter.jpg
Naturally, I'd radius the tip better... this was just a quick "photo-shop"
Again, the idea is to "shear" the blade tip much like a sheared wing tip.
Anyone seeing anything horribly wrong with trying this?
Thanks,
Mike Palmer <><
Sea Hawk @seemysig.com Capt. Geoffrey Thorpe
Removing weight from the tip will change the blades natural resonant
frequencies.
The less metal you remove, the less you are going to change them, but do
you know how much room you have between the engine firing order frequencies
and the current resonant frequencies of the prop?
I see a fair amount of risk for not much (if any) gain.
Sea Hawk @seemysig.com Capt. Geoffrey Thorpe
news:C46Gl.55843$ua7....@newsfe17.iad...
> "MP" <som...@microsoft.com> wrote in message
> news:JN4Gl.15864$gC1....@newsfe19.iad...
>> To clarify, I'm not shortening the blade. Here's the plan in pictures.
>>
>> This photo shows the Q-tip as it is now.
>>
>> http://img13.imageshack.us/img13/6228/qtipbefore.jpg
>>
>> This photo shows what I'd like to do.
>>
>> http://img17.imageshack.us/img17/9960/qtipafter.jpg
>>
>> Naturally, I'd radius the tip better... this was just a quick
>> "photo-shop"
>>
>> Again, the idea is to "shear" the blade tip much like a sheared wing
>> tip.
>>
>> Anyone seeing anything horribly wrong with trying this?
>>
>
> Removing weight from the tip will change the blades natural resonant
> frequencies.
>
> The less metal you remove, the less you are going to change them, but do
> you know how much room you have between the engine firing order
> frequencies and the current resonant frequencies of the prop?
>
> I see a fair amount of risk for not much (if any) gain.
>
Oh - forgot to mention - if you do decide to hack at the prop, it would be
a good idea to install a "chicken strap" between the engine and airframe
just in case things do go wrong and you break the motor mount. Eh?
Charlie
> On Thu, 16 Apr 2009 21:14:38 -0400, "Capt. Geoffrey Thorpe"
> <The Sea Hawk @See My Sig.com> wrote:
>
>> "MP" <som...@microsoft.com> wrote in message
>> news:gs6jn3$5hq$1...@news.motzarella.org...
>>> Thought I'd ask for comments before doing something stupid and
>>> irreparable
>>> to our propeller.
>>>
>> <...>
>>> It's a homebuilt, so I'm deep into "experimental" mode on this one.
>>> Anyone
>>> want to warn me about how I might kill myself doing this? Has anyone done
>>> this before?
>> Sure, I'd be happy to warn you.
>>
>> Has anyone killed themselves after cutting down a prop?
>>
>> Yup.
>>
>> Cut down props were popular on the early T-18's - at least until the first
>> few fatal accidents. When the blade broke due to resonance / fatigue the
>> engine would part company with the aircraft and the result was typically a
>> dead pilot / passenger.
>>
>> Changing the length of the prop changes the resonant frequencies with
>> unpredictable results.
>>
>> http://www.t18.net/technical_info.htm#Cutdown
>
>
> it off with a harbor freight angle grinder, make sure the
> prop gets a heavy coat of 3m rubberized undercoating. It
> dampens out those nasty vibs before they have a chance to
> rattle their way through the prop and cause a catastrophic
> failure. Good luck, make sure you wear eye protection using
> those power tools....regards, Joe.
Are we making a test club with no thrust requirements, or are you just
trolling?
Dan_Thom...@yahoo.com
Sig.com> wrote:
> Removing weight from the tip will change the blades natural resonant
> frequencies.
>
> The less metal you remove, the less you are going to change them, but do
> you know how much room you have between the engine firing order frequencies
> and the current resonant frequencies of the prop?
>
> I see a fair amount of risk for not much (if any) gain.
Every certified prop has a Type Certificate Data Sheet, and that sheet
will specify maximum and minimum diameters for particular engines. The
info is there so it's not necessary to go kill oneself learning it all
over again. Here's the TCDS, for example, for the McCauley 1C160 prop
used on many 172s:
http://www.airweb.faa.gov/Regulatory_and_Guidance_Library%5CrgMakeModel.nsf/0/A2153BC309BE73C0862571A800643E15/$FILE/P-910.pdf
For instance, it says that for a Lyc O-320, 150 hp @ 2700 RPM, the max
is 75" and the min is 74".
So you would go here: http://www.airweb.faa.gov/Regulatory_and_Guidance_Library/rgMakeModel.nsf/MainFrame?OpenFrameSet
and look up your Hartzell model and see for yourself.
Dan
