Thorp Air Command - T18.net

After my return from OSH the AD prop needed a re-torque . Today I was looking at the spinner and noticed a small hair line crack on the inside radius of the prop cut out . It is about 1/8-3/16" in length . I stopped drilled it with a #52 drill . Can it be welded ? Just watch the crack ? Or ? No BOOM , just CRACK !

RB

RB I would say that would depend on the placement and length of the crack. I'm not real keen on leaving a cracked spinner on the airplane.
Cubes

Rich,
I have spinner for an AD prop sitting on a shelf. If you decide to replace your spinner, PM me...

File it out (both Sides). You really don't want cracks in the spinner. We have had members of this forum lose spinners in flight. It is an emergency procedure.

_________________
Bob Highley
N711SH
SN 835
KLAL

Rich, do you have a forward bulkhead? With the large size of a T18 spinner I think its a must to prevent a crack. Also the screws that secure the spinner need washers under the heads, be it nylon or metal. I use nylon on my metal spinner, have a forward bulkhead and 1300 hours.

Rich: Spinners can be repaired. There are some manufacturers such as (McCAULEY) that do not recommend their spinners to be repaired. However, there are prop repair shops that advertise spinner repairs for other types of spinners. (Aircraft Spruce and ASEI)

In general most spinners should have 2 bulkheads as Bill has said. Without the fwd bulkhead all the stress is focused on the aft bulkhead and attachment points. http://members.eaa.org/home/homebuilder ... afety.html

My spinner had a small crack on one of the last attachment holes where it attaches on the aft bulkhead. (suspect over tightening). I had a RCAF ACS friend weld the crack and then grind down the weld. I have a few friends in my EAA chapter that have done the same repair with no issues.

The above reference provides additional spinner inspection criteria and possible vibration sources that you may wish to investigate.

_________________
Victor J Thompson
C-GIRQ
In memory of Dad

Here is pic of the crack . It is 3/16" long and I traced the crack with Sharpie . You can also see the #56 stop drill hole . Bill...yes I do have a forward bulkhead , in fact the BN-3 Spinner kit came from Spruce . From the research I've done there are repair shops that can weld spinner cracks , but the cost is almost double what I paid for the entire kit from Spruce . I would not fly with the crack and the stop drilled hole unless it was an emergency . I'll try and find a repair facility in San Diego and see what they say about the Spinner ? Right now I am leaning toward driving to Corona and picking up a new BN-3 spinner ($120.00) . Scott thanks for the offer on your spinner , but going with the BN-3 I can use my current front and rear bulkheads .

BTW...are there any restrictions on flying the T-18 w/o the Spinner ?

Hi Rich,

My BN-3 cracked in the same spot. Found the crack at OSH. I have tried stop drilling cracks on three different spinners (on three different planes) and it shortly will continue cracking. Flys fine without the spinner. Just note cht's to make sure no cooling problems.

I would not fly with a crack. As mentioned, you make think you lost a prop blade when the spinner fails and will probably cause cowl damage as it goes. I put a patch on the outside of the spinner that conformed to the blade cutout. Sort of an L shaped patch about 1 1/2 inch wide that covered the crack. I had to put it on the outside as the patch would have hit the front bulkhead if on the inside. I would also put JB weld under patch to stiffen and deaden (behave Fraze) the movement on either side of the crack. I put a patch of same size on opposite side for balance. Did this at the emergency repair shed at OSH while I missed the F22 debut (couple years back). I flew it that way for a few months and worked fine. If you can put it on the inside and have enough metal thickness to countersink the rivet it would barely be noticeable. Pretty sure it won't work on the inside tho.

I replaced it with a new spinner. The new one was spun from thicker material and was noticeably heavier. The old spinner was very thin in the prop cutout areas and aft of that. The new one is much thicker (almost twice) so I doubt it will crack in the cut outs.

Bernie
N18XS

Rich,

If it matters, I have the entire assembly, including both bulkheads, and it is the standard Thorp spinner.

I think the plans say the spinner is optional on dwg T18-J-548(A)

I have seen this area reinforced with a doubler on some spinners, the complete cutout was reinforced with a .060 or better doubler, also Rich, does the front bulkhead have screws through the spinner into the bulkhead? My spinner is way thin, but I have had no troubles out of it yet....Dan

By the way Rich, that Spinner looks well made, what is it, about .040 thick or maybe a little better....Dan

Dan : The spinner is made from .080 6061 . I measured the area in the crack area and it is .078-.079 . I will not fly with the crack . Tuesday morning I will contact ACS (not Aircraft Spruce) Products located in Lake Havasu as they make the BN spinners for Spruce and see what they have to say about the crack as Bernie had the same problem . Thanks for the info Bernie ! One solution might be to increase the radius in that area . A doubler in that area might be possible , but I hate to add more stress locations with more hole and more rivets . I will ask ACS how they feel about doublers ? The AD prop will eventually have to be replaced and I'll probably go composite with a composite spinner ?

Right now I'll probably go with another BN-3 and increase the radius in that area and take the old spinner to be repaired as a back up ? For $120.00 it seems to be the most cost effective way to fix the problem . To answer your other question Dan , no I do not have screws in the forward bulkhead . I installed the spinner according to "Firewall Forward" and the Tony Bingelis instructions that state screws are not necessary , in fact when the BN-3 spinner arrived the instructions to install it were copies made from Tony's book !

RB

I will have to agree Rich, I have an extra Thorp Spinner and bulkheads in the back Bedroom, they haven't been touched, just in case parts. My Spinner started out as .040 but was reduced in the spin process to about .025 where it attaches to the aft bulkhead, this is typical if the guy in controller of the machine gets in a hurry, too much stretch. Spinners that have been spun and then annealed will not crack as easy as one that has just been spun, they are stress relieved. If you like you can bring your cracked one to KVIS and I will see what I can do with it, might fix it and have a backup? Dan

Thanks Dan . I'll see if I can fit the beast in my small baggage compt. along with Johns Kerr's roll along suit case , six pair of shoes and his personal make up kit ! Your offer is very kind to try and fix the spinner . If it doesn't work we can raffle it off at the Fly In ! BTW...what else do you have in that back room for sale or trade ?

RB