Squealing sound, firewall forward

Jr.CubBuilder · Post by **Jr.CubBuilder** » Fri Sep 17, 2004 12:01 am

Well after 30+ years of dreaming, 4 years of driving 40 miles to fly rental planes, and 1 1/2 years teasing myself with a scratchbuilt SuperCub project I finally bit the bullet and borrowed money from the bank to buy my 170B. I already love it like no other plane I've flown. It's funny how dreams seem to work out if you keep grinding away at them. It's also funny how reality that you dreamt of is always so much more complicated, delightfull, inspiring, and at the same time a pain in the ass. Hmmmm.......sounds like my first girlfriend, but this relationship has already lasted longer.
After the ten hours of dual with an instructor that insurance mandated (which I really needed in hindsight) I was much relieved to get the plane to myself last week. I woke up early this morning at 4:30 and noticed that the wind wasn't blowing. Being as how that's a rather rare occurence in this valley I decided that I would go for a quick morning flight before work. What a treat, I get sort of euphoric looking down at stuff and the flat light of morning or evening makes it even better. I turned the heater off just to make sure I wasn't getting carbon monoxcide poisoning.
Taxing back to my tie-down with my cold feet working the rudder pedals I suddenly heard something that soured the blissfull experience somewhat. Normally I can hear a lot more engine noise in the 170 than I could in the rental planes, but it doesn't sound wrong just mechanical sounds of a big aircooled motor coming through the meager firewall insulation. Suddenly though I discerned a definate squealing sound (faint through the headset but definately not my imagination when I uncovered an ear) kind of like a loose fan belt. It was definately something tied to engine RPM, and my first thought was a bushing in the generator. Not that anybody can tell by that description, but has anyone experienced anything similiar with the generator or accessory case?

N1478D · Post by **N1478D** » Fri Sep 17, 2004 12:59 am

Tie her down good - the airplane, not your first girlfriend. Start her up and carefully walk up to the cowling behind the prop on each side. If the sound is louder on the side with the horn to scare the deer away, that might be what it is.

That venturi tube can sometimes make a sound like you are describing.

doug8082a · Post by **doug8082a** » Fri Sep 17, 2004 1:32 am

Hey Joe, you still remember that deer horn line, eh?

I'll second that. My deer horn whistles quite a bit at low rpm - enough so that some one can hang their arm out the window, place their hand over the back end of it and play a tune.

Hey, why does that deer horn have a small tube inside the big tube? Well, that's because the National Park Service did some research and discovered that different animals respond to different sound frequencies. The small tube is for deer, the big tube is for moose

russfarris · Post by **russfarris** » Fri Sep 17, 2004 4:03 am

I'd wager dollars to donuts (whatever that means) it's the venturi. Mine does it at about 800 RPM and below. More of a squeal than a whistle, at least on my A/C. Russ Farris

Jr.CubBuilder · Post by **Jr.CubBuilder** » Fri Sep 17, 2004 3:05 pm

I'd gladly buy you all a whole pile of doughnuts if that could be the case, and I tried to convice myself that was where the sound was coming from. If I can make it go away by covering the deer horns (I've got one on each side) I'd be exstatic. I'm going to run it up after work tonight, it was raining to much yesterday.

Post by **GAHorn** » Fri Sep 17, 2004 5:56 pm

I sent one of my early flight students out for his private pilot check ride with an FAA examiner in a venturi-equipped C-150. They'd been gone from the chocks about 10 minutes when they taxied back and the applicant came back in with a puzzled look on his face and told me the examiner refused to fly in an airplane with a loud engine squeal!
The applicant didn't hear it (because he was used to the venturi and kept trying to hear engine squeal), so they came back. My laughter at the examiner came back to visit when he busted the applicant on S-turns across the road (which were no longer in the Practical Flight Test guide and the student should never have been required to demonstrate.)
I had to re-instruct the applicant for an hour and fill out another test authorization before the examiner would give him the license.

jmbrwn · Post by **jmbrwn** » Fri Sep 17, 2004 8:18 pm

Was it 'what's his face' up in SHV?

N1478D · Post by **N1478D** » Sat Sep 18, 2004 1:07 am

doug8082a wrote:Hey Joe, you still remember that deer horn line, eh?

I'll second that. My deer horn whistles quite a bit at low rpm - enough so that some one can hang their arm out the window, place their hand over the back end of it and play a tune.

Hey, why does that deer horn have a small tube inside the big tube? Well, that's because the National Park Service did some research and discovered that different animals respond to different sound frequencies. The small tube is for deer, the big tube is for moose

Doug, I sure have enjoyed borrowering that from you. Have had a lot of fun with it, although every once in a while someone seems a little affended that someone would believe that they would believe that. Now, might have to add that the little horn inside is for squirrels, etc!:lol:

doug8082a · Post by **doug8082a** » Sat Sep 18, 2004 2:19 am

N1478D wrote:
doug8082a wrote:Hey Joe, you still remember that deer horn line, eh?

I'll second that. My deer horn whistles quite a bit at low rpm - enough so that some one can hang their arm out the window, place their hand over the back end of it and play a tune.

Hey, why does that deer horn have a small tube inside the big tube? Well, that's because the National Park Service did some research and discovered that different animals respond to different sound frequencies. The small tube is for deer, the big tube is for moose
Doug, I sure have enjoyed borrowering that from you. Have had a lot of fun with it, although every once in a while someone seems a little affended that someone would believe that they would believe that. Now, might have to add that the little horn inside is for squirrels, etc!:lol:

Squirrels! You're right! I agree - a modification of the deer horn functionality statement is in order. I hate those little buggers. They always wait until the last possible second before running out onto the runway and becoming speed bumps.

Perhaps we should develop regional definitions. Up here turkeys and deer are the two principal culprits (also seagulls and Canada geese). Hey, watch out for that turkey on the runway...

N1478D · Post by **N1478D** » Sat Sep 18, 2004 2:40 am

doug8082a wrote:
N1478D wrote:
doug8082a wrote:Hey Joe, you still remember that deer horn line, eh?

I'll second that. My deer horn whistles quite a bit at low rpm - enough so that some one can hang their arm out the window, place their hand over the back end of it and play a tune.

Hey, why does that deer horn have a small tube inside the big tube? Well, that's because the National Park Service did some research and discovered that different animals respond to different sound frequencies. The small tube is for deer, the big tube is for moose
Doug, I sure have enjoyed borrowering that from you. Have had a lot of fun with it, although every once in a while someone seems a little affended that someone would believe that they would believe that. Now, might have to add that the little horn inside is for squirrels, etc!:lol:
Squirrels! You're right! I agree - a modification of the deer horn functionality statement is in order. I hate those little buggers. They always wait until the last possible second before running out onto the runway and becoming speed bumps.

Perhaps we should develop regional definitions. Up here turkeys and deer are the two principal culprits (also seagulls and Canada geese). Hey, watch out for that turkey on the runway...

Haven't had any troubles with Canada geese or seagulls here in N Texas, but there are turkeys everywhere!

Going to order the first venturi that when parents allow their children to use a 170 for a jungle gym at a flyin and just before the kid grabs the pito tube, the venturi flies off the airplane and right up the parents ___, really hard and blowing really loud!

doug8082a · Post by **doug8082a** » Sun Sep 19, 2004 2:35 am

N1478D wrote:
doug8082a wrote:
N1478D wrote: Doug, I sure have enjoyed borrowering that from you. Have had a lot of fun with it, although every once in a while someone seems a little affended that someone would believe that they would believe that. Now, might have to add that the little horn inside is for squirrels, etc!:lol:
Squirrels! You're right! I agree - a modification of the deer horn functionality statement is in order. I hate those little buggers. They always wait until the last possible second before running out onto the runway and becoming speed bumps.

Perhaps we should develop regional definitions. Up here turkeys and deer are the two principal culprits (also seagulls and Canada geese). Hey, watch out for that turkey on the runway...
Haven't had any troubles with Canada geese or seagulls here in N Texas, but there are turkeys everywhere! Going to order the first venturi that when parents allow their children to use a 170 for a jungle gym at a flyin and just before the kid grabs the pito tube, the venturi flies off the airplane and right up the parents ___, really hard and blowing really loud!

I could sure use one of those! Keep us posted on your development efforts. I for one would be willing to pony up some $$$ for the STC

Jr.CubBuilder · Post by **Jr.CubBuilder** » Mon Sep 20, 2004 11:50 pm

Ok doughnuts for all and forget them dammed deer horns, I'm 99.9999% sure it's the tach cable, definately not the horns though.

zero.one.victor · Post by **zero.one.victor** » Sat Sep 25, 2004 5:32 am

Chris, didja get the squealing diagnosed & fixed? Was it in fact the tach cable?

Eric

Jr.CubBuilder · Post by **Jr.CubBuilder** » Mon Sep 27, 2004 4:19 pm

It's still there, but it's kind of transient and not as loud as the first time I noticed it taxiing. I'm going to pull the cable and see if I can lube it/replace it.

Post by **GAHorn** » Tue Sep 28, 2004 12:16 am

Have you tried simply disconnecting it from the tach? I've heard failing tachs scream pretty loudly.