Hail dimples - serious or not?

[New_PIC]

Sorry if this is a dumb question but I was looking at a plane recently and noticed a number of little dimples all over the metal skin. I'm guessing that was hail damage. The little dents weren't densely packed but sparsely scattered over the upper surfaces of the plane. How serious an issue is that?

Does light hail damage need to be fixed? Does it create much drag or affect anything else besides aesthetics? It occurs to me now that maybe I should have looked closer to see if the paint was broken anywhere but I didn't notice anything like that. How much affect would hail dimpling have on the value of a plane?

[burhead1]

I wouldn't fix it, your going to burn more gas.

http://www.physicsforums.com/showthread.php?t=417914

[crazy_aviator]

cosmetic,,,,but TC may differ

[Colonel Sanders]

I would leave it, but plenty of people just bondo
them over (shrug).

[black hole]

My personal experience: The small dimples will make the plane faster (golf ball technology) check out (turbulator tape).If you could get mother nature on you side you could have your plane hailed on just on the surfaces aft of the leading edges. Just a thought:)

BH

[Shiny Side Up]

[DHC2eater]

Hey Pic......

I also am looking at purchasing....

The type I'm considering seem to have been hailed on at one time or another since they spend most of their time on floats outside.

To re skin a Cessna is about 50k or so depending on variables....

The insurance company's offer a cash payout rather than a repair at about 50% or so of the repair estimate..

Lots of owners take the cash and sometime later try selling the aircraft at the going rate ....not the hailed rate if you will....

Hail on a high wing isn't really as noticeable as a low wing of course and less offensive IMHO..

Filling the dents with bondo or whatever is looking for long term problems again IMHO

Some that I've looked at have been absolutely peppered with hail and fly just fine.....this damage should reduce the price but most often does not...

The above are my observations .......

Eater

[CpnCrunch]

Mythbusters found that dimples gave an 11% improvement in fuel economy, which is pretty amazing:

http://dsc.discovery.com/tv-shows/mythb ... nimyth.htm

[GA MX Trainer Dude]

Back in the day when TC inspectors would actually give you some advice - I had a hail damaged C-185 that the owner wanted to fly. It was fairly well dented up and when I approached our TC inspector he said 4 things.

1. - Structural Repair Manual/Section

2. - Dent limitations as per location

3. - Make a skin map for proof that the dents are within limits

4. - Repair if/as required and go flying.

We only found 2 dents that were beyond the limits allowed - fixed them - signed it out and away he went. When he sold the aircraft we got a call from the prospective buyer wanting information on why we had done this. Simple explanation and he was fine with it. I don't know if the selling price was dropped because of the hail damage.

I have repaired shallow dents with aerodynamic filler - epoxy based - NOT BONDO!! Bondo contains fiber elements and usually talc that will allow the moisture to wick into contact with the skin delivering a worse problem in the long run. Epoxy with micro-balloons is more expensive but a much better way of doing things. Micro-balloons being hollow weigh less - and are fully encapsulated by the epoxy resin mix so there is no moisture pathway to the underlying skin.

Once again make sure you can do this in the area that you want to smooth - some aircraft will not allow this at all - others may limit you to specific areas. Use your SRM and if not listed as acceptable / gray area - contact the manufacturer and get approval. Strange how sometimes just a quick request to the manufacturer gets you the information.

Hope this helps,

Mx

[Colonel Sanders]

I see on lots of airplanes - without hail damage -
people are using filler to smooth over the rivets.

I guess it looks good at first, but give it a couple
of years, it always cracks and looks like hell. Worse
than if they hadn't put the stupid filler on.

Reminds me of clear coat. Short term gain for
long term pain.

[black hole]

found that after 20 years or so; the dimples seem to work themselves out, almost. I repainted an AC recently and had to scape the filler off a few of the smaller dents that were filled and amazed --- no dent at all. Must be mother natures--- heating and cooling over the years relieving the stress.


BH

[PilotDAR]

The affect upon airworthiness of hail damage varies by degree and aircraft type. Cessnas will generally provide you with a definition for "negligible damage", which could include some hail damage. If the damage is within the limits it's going to work out okay.

However, I have had to do a repair design approval on a PA28-161 Warrior, which included my flight testing it to prove no effect. (It was fine). However, this was a big approval job. Piper did no provide ANY definition for negligible damage for this type, or many others. There is a service letter which covers a model of the Arrow and the Seminole, but these could not be applied to the Warrior until I did the approval.

While vetting a manufacturer's symposium presentation in 1995, I picked up on the presenter's reference to the need to repair a dent (by reskinning) which was 0.019" deep near a baggage door. I said that the audience would shreek in horror. The presenter changed the reference dent to 0.190" deep, and the audience of owners of the type still shreeked. I don't think that the presenter ever had seen the general condition of the average example of this Canadian bushplane type. Manufacturers tend to be conservative about these things - once the plane is sold, what's in it for them to allow continued service with "damage" - however minor?

Cessna obviously wrote their structural repair manual section to respond to client demands for reasonable repair allowance . Piper would not appear to have been similarly driven - except perhaps by a fleet owner of Arrows and Seminoles, who had widespread fleet hail damage, and the corporate clout to demand a Service Letter repair scheme. Just my speculation there......

I cannot speak to other types. However, if considering purchasing a hail damaged aircraft, particularly if an import will be involved, be very sure you know what will be involved before you commit. For the most part, it will not be worth the cost of skin replacement, unless the plane is the deal of the century. (The Warrior did have to have new flap, aileron and stabilator skins installed to conform to the Piper Service letter for Arrow hail damage, which I eventually did apply). Cessna will probably be a much easier (and cheaper) path to flying. Very simply, what does the maintenance manual say about it. If nothing, you cannot assume that the damage is negligible - a repair is going to be required. This is simply because the hail damaged aircraft no longer conforms to it's type design, and you have no specified data to apply to allow continued operation in that condition.

Sorry, but you asked....

[photofly]

I'm having difficulty imagining a TC inspector going to check service limits and ground a private aircraft because of hail damage. I'm having even more difficulty imagining anyone else giving a toss.

What a lousy imagination I must have.

[PilotDAR]

Well, if you're asking a qualified person to sign that the aircraft is airworthy, as is required at regular intervals, that person can take whatever measure they see fit to confirm that airworthiness. Reference to manufacturer's data, where it exists, is the best start. Note that some skins are zero damage tolerance. If a qualified person is willing to sign for the airworthiness of an aircraft with damage, that's between them and TC. It's not just a TC inspector who might be asked to sign, it could be an AME or AMO.

If you don't plan to ask them to sign, that's a whole different thing...... Perhaps it's an OM aircraft, and you're going to take responsibility yourself....

[photofly]

I'm just curious: approved data aside, do you personally think that hail damage as described (little dents, sparsely scattered) is likely to affect the flight characteristics? Would you refuse to fly?

[PilotDAR]

From a "safe to fly" standpoint, I personally have no aerodynamic concerns flying a hail damaged aircraft. There is a miniscule concern that the hail damage has affected the strength of secondary structure. (like internally a flight control).

But, for a certified aircraft, "safe for flight" and "conforming to its type design" may not be the same, and you're asking for the "conforming to type design" signoff, ("airworthy" = C of A) not just safe for flight (= flight permit)....

Let's look at it a little differently: If, as a pilot, you knew that the previous pilot had flown an aircraft beyond speed or G limits, would you get in and fly it without an inspection? It no longer conforms. If an aircraft has exceeded a limitation, or otherwise does not conform to its type design, you, as the next pilot, expect to be assured that it is safe for flight and conforms to its type design.

The fact that an aircraft manufacturer has not provided data on what damage can be accepted as is (negligible), means you've got nothing to go on to sign it out - if that's what you're being asked to do. It has not necessarily been said that aircraft is unsafe, but remember, that the definition of "airworthy" includes "safe and fit for flight" and "conforms to it's type design". "Airworthy" is required for a C of A to be in effect.

[acidgambit]

Meh.

No biggy I would say. One of our 737s in the fleet have a crap load of light hail damage on the spoilers, ailerons, trailing edge of the flap. Structures guys took a look at it and shrugged it off. But if the dent is deep.....you gotta fill it.

[New_PIC]

... If a qualified person is willing to sign for the airworthiness of an aircraft with damage, that's between them and TC. It's not just a TC inspector who might be asked to sign, it could be an AME or AMO.

If you don't plan to ask them to sign, that's a whole different thing...... Perhaps it's an OM aircraft, and you're going to take responsibility yourself....

In this particular case it's a certified aircraft and, for me, would have to remain certified. So this reinforces the advice I've seen on the forum before, to have the people who will be doing the annual check out the plane before purchasing. Even then, there's a gamble that any future buyer's AME would also agree that the damage is negligible.

Thanks everyone for all the informative replies.